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Über dieses Buch

This the sixth volume of six from the Annual Conference of the Society for Experimental Mechanics, 2010, brings together 128 chapters on Experimental and Applied Mechanics. It presents early findings from experimental and computational investigations including High Accuracy Optical Measurements of Surface Topography, Elastic Properties of Living Cells, Standards for Validating Stress Analyses by Integrating Simulation and Experimentation, Efficiency Enhancement of Dye-sensitized Solar Cell, and Blast Performance of Sandwich Composites With Functionally Graded Core.

Inhaltsverzeichnis

Frontmatter

High Accuracy Optical Measurements of Surface Topography

Surface characterization is a very important aspect of industrial manufacturing. All engineering parts are strongly affected in their performance by properties depending on surface topography. For this reason methodologies able to provide a functional representation of surface topography are of paramount importance. Among the many techniques available to get surface topography optical techniques play a fundamental role. A digital moiré contouring technique recently proposed by the authors provides a new approach to the study of surface topography. This paper presents further developments in surface topography analysis particularly with respect to the resolution that can be currently obtained. The validity of the proposed approach is checked by analyzing existing standards for surface roughness determination. Optical results are compared with NIST certified standard specimen.

C. A. Sciammarella, L. Lamberti, F. M. Sciammarella

Industrial Finishes of Ceramic Surfaces at the Micro-level and its Influence on Strength

The mechanical properties of ceramic materials are influenced by surface finishing procedures. This paper presents a brief introduction to an advanced methodology of digital moiré contouring utilized to get surface information in the micro-range that is a generalization of a method developed for metallic surfaces [1]. Five types of surface treatments are considered. Two of the finishes utilize diamond grinding with a rough grit (100) and a smoother grit (800). The third type is laser assisted machining of the ceramic. The fourth type is simply applying the laser without machining. The final type is the as received ceramic resulting from the process of fabrication. A total of 63 specimens, nine of each kind were tested in four-point-bending. The strength of the specimens was statistically analyzed using the Gaussian and the Weibull distributions. The statistical strength values are correlated with the statistical distributions of surface properties obtained using this advanced digital moiré contouring method. The paper illustrates the practical application of this method that was developed to analyze surfaces at micro level and beyond.

F. M. Sciammarella, C. A. Sciammarella, L. Lamberti, V. Burra

Elastic Properties of Living Cells

Constitutive behavior of living cells is in deep relationship with their biological properties. For that reason gathering the most detailed information on cell mechanical behavior as it is feasible becomes extremely useful in assessing therapeutic protocols. However, investigation of elastic properties of living cells is a fairly complicated process that requires the use of advanced sensing devices. For example, Atomic Force Microscopy (AFM) is a research tool largely used by biomedical engineers and biophysicists for studying cell mechanics. Experimental data can be given in input to finite element models to predict cell behavior and to simulate the tissue response to biophysical, chemical or pharmacological stimuli of different nature. The paper analyzes different aspects involved in the numerical simulation of AFM measurements on living cells focusing in particular on the effect of constitutive behavior.

M. C. Frassanito, L. Lamberti, C. Pappalettere

Standards for Validating Stress Analyses by Integrating Simulation and Experimentation

A reference material and a series of standardized tests have already been developed for respectively calibrating and evaluating optical systems employed for measuring in-plane static strain (for draft standard see: www.twa26.org). New work has commenced on the design of a reference material (RM) for use with instruments or systems capable of measuring three-dimensional displacements and strains during dynamic events. The rational decision-making process is being utilized and the initial stages have been completed, i.e. the identification and weighting of attributes for the design, brain-storming candidate designs and evaluation of candidate designs against the attributes. Twenty-five attributes have been identified and seven selected as being essential in any successful design, namely: the boundary conditions must be reproducible; a range of in-plane and out-of-plane displacement values must be present inside the field of view; the RM must be robust and portable; there is a means of verifying the performance in situ; and for cyclic loading it must be possible to extract data throughout the cycle. More than thirty candidate designs were generated and have been reduced to nine viable designs for further evaluation. In parallel with this effort to design a reference material, work is also in progress to optimize methodologies for conducting analyses via both simulations and experiments. Image decomposition methods are being explored as a means to making quantitative comparisons full-field data maps from simulations and experiments in order to provide a comprehensive validation procedure.

Erwin Hack, George Lampeas, John Mottershead, Eann Patterson, Thorsten Siebert, Maurice Whelan

Avalanche Behavior of Minute Deformation Around Yield Point of Polycrystalline Pure Ti

The aim of present study is to investigate the avalanche behavior of minute deformation around yield point of polycrystalline pure Ti. Firstly, we prepare commercial polycrystalline pure Ti (99.5%) thin plate, and investigate the pole figures and inverse pole figure distribution for rolling direction on the surface of specimen, which is obtained from Electron Backscatter Diffraction Patterns (EBSD). Secondarily, tensile specimens are cut out from 0° 30° 45° and 90° relative to rolling direction of thin plate. Then, we attempt to measure macroscopic stress-strain curve, local strain distribution and minute deformation arising in specimens under tensile loading. In this time, the in-house measurement system integrated with tensile machine control system, local strain distribution measurement system and minute deformation measurement system is constructed suited on a LabVIEW platform. Local strain distribution is measured by in-house system on the basis of Digital Image Correlation (DIC). Also, minute deformation behavior is measured by in-house other one on the basis of acoustic emission (AE). Finally, we discuss about the mechanism of avalanche behavior of minute deformation around yield point of polycrystalline pure Ti on the basis of results in present study.

G. Murasawa, T. Morimoto, S. Yoneyama, A. Nishioka, K. Miyata, T. Koda

The Effect of Noise on Capacitive Measurements of MEMS Geometries

Small variations in the geometry of Micro Electro Mechanical Systems (MEMS) can yield very large variations in performance. Variations in geometry are a consequence of the MEMS fabrication process, and are unavoidable with current fabrication technology. To achieve quick, accurate, and precise measurements of MEMS geometry, we have previously reported on our pioneering use of capacitance to measure MEMS geometry. The ability to capacitively probe MEMS geometries has the potential to more precisely obtain geometric uncertainties, and to realize autonomous on-chip measurements in-the-field. The precision of measurement method depends on the precision of the capacitance meter, which is subject to various sources of noise. In this paper, we examine the effect of this noise using our off-chip capacitive measurement method. In our present approach, we consider four sources of noise and analyze how they individually contribute to the uncertainty in the extraction of MEMS geometry. The four sources of noise are: noise from the voltage source, internal noise of the capacitance meter, noise from external electromagnetic fields, and thermal noise. We verify our analytical results with simulation and validate our results with experiment. With off-chip capacitive probing, we find that the uncertainty in geometric extraction is most strongly affected by external electromagnetic fields, moderately affected by noise from the measurement equipment and thermal noise, and least affect by the applied voltage. We measure the uncertainty in geometry due to shielded and unshielded conditions, and we predict the uncertainty in geometry due to the voltage source and thermal noises.

Joo Lien Chee, Jason V. Clark

Effects of Clearance on Thick, Single-Lap Bolted Joints Using Through-the-Thickness Measuring Techniques

Composite materials have increasingly become more common in ground transportation. As this occured thicker panels, as compared to composite panels used in aviation, become necessary in order to withstand high impact loads and day to day degradation. The effectiveness of these panels was often limited by the strength of the joint in which the panel was attached to the frame of the vehicle. Investigating methods of reducing strain concentrations within these joints would increase the effectiveness in using composite materials in ground transportation applications by increasing the load necessary for joint failure to occur. In this study, fiber optic strain gages were embedded in a composite panel along the bearing plane of a thick, single-lap, bolted joint. The gages allow for the strain profile above the hole to be determined experimentally. Several clearance values were then implemented in the bolt to determine their effect on the strain concentrations. Strain increased at every gage, by nearly the same proportion, when clearance was increased from zero to three percent. When clearance was further increased to five percent strain only continued to increase at gages three and four, with one and two remaining similar in value to what was seen at three percent clearance. Ultimately, like in thin composite panels, the zero percent clearance condition was the stiffest.

John Woodruff, Giuseppe Marannano, Gaetano Restivo

Deformation and Performance Measurements of MAV Flapping Wings

If bumblebees and hummingbirds could speak to us, could they tell us how they fly? Probably not. “How they fly” has been a fascinating question to biologists and aerodynamicists. Recently, attention is directed to micro air vehicle (MAV) research, which is aimed to develop sub 150 mm wingspan aircraft for reconnaissance and surveillance. The hummingbird poses as a perfect emulation target: they can dash like a jet fighter, hover like a helicopter, and they are on the MAV length scale. Warrick et al.

1

examined the aerodynamics of hummingbird hovering with digital particle image correlation to capture the airflow structure. The authors found that the hummingbird’s upstroke and downstroke are not symmetrical in producing lift (thrust): the downstroke responsible for about 75% of the body weight and the upstroke about 25%. This is very different from insects, which have a more symmetrical load distribution. The differences are results of wing kinematics and structure. If a robotic hummingbird or insect is to be developed, understanding the causal relationship between kinematics, deformation and aerodynamics is essential. On the other hand, Tobalske et al.

2

documented the kinematics of hummingbirds in forward flight at different speeds. The authors used a few parameters to described wing trajectories and angles. However such description may be considered insufficient for reconstructing the same kinematics. Therefore, in order to facilitate the research of flapping wing MAVs, an experimental method that can describe the complete wing kinematics and deformation, and correlate with aerodynamic loads, is called for. This paper presents an experimental technique for studying hummingbird-size flapping wings in MAV research. A sophisticated experimental setup featuring a customized digital image correlation system is described; several anisotropic flexible membranous wings are tested and post processed results are presented.

Wu Pin

Dynamic Constitutive Behavior of Aluminum Alloys: Experimental & Numerical Studies

Split Hopkinson pressure bar (SHPB) setup was used to investigate dynamic constitutive behavior of aerospace Aluminum alloys both experimentally and numerically. The study was conducted in the strain rate regime of 500/s -10000/s. Both regular solid and modified hollow transmission bars were employed in realizing this strain rate regime. Four different Aluminum alloys namely 7075-T4, 2024-T3, 6061-T6 and 5182-O were considered for investigation. Copper-110 alloy pulse shaper was used to obtain better force equilibrium conditions at the barspecimen interfaces. Plastic kinematic model was used to model rate dependent behavior of Aluminum alloys using commercially available LS-DYNA software. It was identified from the final results that experimentally determined dynamic constitutive behavior matches very well with that of numerical in the strain rate regime of 2000/s- 5000/s.

Sandeep Abotula

Estimating surface coverage of gold nanoparticles deposited on MEMS

Commercialization of a whole spectrum of useful MEMS is still hindered by surface phenomena that dominate at the micron scale. Altering the roughness and surface chemistry of MEMS surfaces by depositing nanoparticles on them is being considered by the MEMS community as a useful strategy to address tribological issues. Although, gold nanoparticle monolayer is reported to reduce adhesion in MEMS, determining its surface coverage still remains a challenge [1]. A technique to determine the surface coverage of deposited gold nanoparticles is needed, so that its effect on the tribology of MEMS surfaces can be studied.

N. Ansari, K. M. Hurst, W. R. Ashurst

Functionally Graded Metallic Structure for Bone Replacement

Processes for the creation and characterization of functionally graded metallic structures for use as artificial bone tissue were investigated. The metallic structure consists of a solid surface layer, a graded porosity layer and a homogeneous porous core. Porous compacts with varied densities were created using traditional powder metallurgy techniques. The surfaces of the compacts were subjected to a densification process with the use of a specially designed indentation tool. Investigations on the effect of the initial density of the compact and the depth of indentation during the deification process on the densified layer and graded porosity region were studied. Compacts with an initial density of 86 % of the true density were indented to depths of approximately 1.8, 1.25, 1, and 0.65 mm. Compacts with initial densities of 67, 70, and 73% were indented to a depth of 1 mm. Optical microscopy and scanning electron microscopy (SEM) were implemented to characterize the morphology of the porous structure. Results show that deeper indentation during the densification process yielded a larger densified layer. The variation of Young’s modulus along the porosity gradation is investigated using micro-indentation. The graded structures are also investigated for fracture parameters and crack growth behavior using digital image correlation techniques.

S. Bender

Dissipative energy as an indicator of material microstructural evolution

Rapid fatigue limit estimation methods are of strong interest to industry. Some authors proposed rapid experimental methods to estimate the fatigue limit based on the material temperature increase under cyclic loading [1,2]. Yet, heat dissipation phenomena need to be more thoroughly studied in order to give better physical grounds to such methods.

N. Connesson, F. Maquin, F. Pierron

Temporal Phase Stepping Photoelasticity by Load or Wavelength

Phase-stepping techniques in photoelasticity own the isoclinic-isochromatic interaction problem, which causes phase ambiguity zone on the photoelastic phase map and bothers engineers of this field very much. Temporal phase unwrapping is an effective method for circumventing the above problem. In this work, the load stepping and wavelength stepping approaches are applied both but individually on photoelastic samples to compare the different characteristics of them including in accuracy of results, ease of applied technologies, and automation of stepping etc. Load stepping approach is not applicable for stress frozen sample while wavelength stepping is. The constant increment of loading percentage is not easy to be controlled under complex loading conditions. The control of wavelength stepping if integrated with electro-optic components is very flexible and versatile. However, the birefringence error of optical wave plate for different wavelength should be carefully calibrated to minimize the errors. Experimental works are studied to practically verify the differences and limitation of these two approaches.

M. J. Huang, H. L. An

Determination of the isoclinic map for complex photoelastic fringe patterns

Most of the existing algorithms used for processing phase-shifted photoelastic data attempt to compute the unambiguous or demodulated isoclinic map in order to obtain the unambiguous or continuous isochromatic map. However, in some cases experiments on engineering components yield isoclinic maps that are severely corrupted due to the interaction between isoclinics and isochromatic. The result is that some of these algorithms fail in the direct demodulation of isoclinic maps from phase-shifted photoelastic data. An indirect way to obtain the isoclinic map by computing first the unambiguous isochromatic map is presented. The employed approach is based on a regularisation process that, by minimising a cost function, selects the appropriate value of the relative retardation angle at each pixel. In this way, an unambiguous map can be straightforwardly unwrapped and calibrated to generate an isochromatic map. The unambiguous isoclinic angle map is then calculated using the regularized isochromatic map. The process has been demonstrated to be robust and reasonably quick for crack tip fringe patterns.

Philip Siegmann, Chiara Colombo, Francisco Díaz-Garrido, Eann Patterson

A Study on the Behaviors and Stresses of O-ring under Uniform Squeeze Rates and Internal Pressure by Transparent Type Photoelastic Experiment

Rubber O-rings have been used as packing elements for high pressure vessels, oil pressure parts, air-plane parts and nuclear generator parts. The design criterion of an O-ring can be determined through analysis of stresses and deformation behavior of O-ring for various loading conditions, which are dependant on the internal pressure and the fitting conditions of the O-ring. The shape of the O-ring under uniform squeeze rates and internal pressures is changed with squeeze rates, internal pressures and time. Therefore the stresses of O-ring under the uniform squeeze rates and internal pressures should be studied with real time. To achieve this, a loading device for transparent type photoelastic experiment through which various squeeze rates and internal pressures are applied was developed in this research. The validity of the loading device was verified. It was established through this research that the lower corner space of O-ring was filled with the changes of O-ring after the forcing out of O-ring was produced. The stresses of O-ring under uniform squeeze rates and internal pressures were analyzed with the forcing out procedures of O-ring.

Jai-Sug Hawong, Dong-Chul Shin, Jeong Hwan Nam

Strength Physics at Nano-scale and Application of Optical Interferometry

The theoretical basis of the physical mesomechanical approach of strength physics is described. Based on a fundamental principle of physics known as local symmetry, this approach is capable of describing deformation and fracture comprehensively, and applicable to any scale level. It is thus useful to describe strength physics at the nano/microscopic without relying on phenomenology. An optical interferometric technique capable of resolving displacement at sub-nanometer level is introduced. Being capable of quantitative measurement, this technique is useful for characterization of material strength at the nano/microscopic level.

Sanichiro Yoshida

Light Generation at the Nano Scale, Key to Interferometry at the Nano Scale

The feasibility of recording optical information at the nanometric level was considered for a long time restricted by the wavelength of light. The concept of wavelength of light in classical optics is a direct consequence of the standard solution of the Maxwell equations for purely harmonic functions. Propagating harmonic light waves in vacuum or air satisfy the required mathematical conditions imposed by the Maxwell equations. Hence, in classical optics, the concept of wavelength of light was associated with that type of waves. Mathematically speaking, one can derive solutions of the Maxwell equations utilizing Fourier integrals and show that light generated in a volume with dimensions much smaller than the wavelength of light will have periods in the sub-wavelength region. Every oscillator, whether a mass on a spring, a violin string, or a Fabry–Perot cavity, share common properties deriving from the mathematics of vibrating systems and the solutions of the differential equations that govern vibratory motions. In this paper, some common properties of vibrating systems are utilized to analyze the process of light generation in nano-domains. Although simple, the present model illustrates the process of light generation without getting into the very complex subject of the solution of quantum resonators.

C. A. Sciammarella, L. Lamberti, F. M. Sciammarella

Mechanical Characterization of Nanowires Using a Customized Atomic Force Microscope

A new experimental method is introduced in order to characterize the mechanical properties of mettalic nanowires. An accurate mechanical characterization of nanowires requires the imaging with scanning electron microscope (SEM) and the bending of nanowires with an atomic force microscope (AFM). In this study, an AFM is located inside an SEM in order to establish the visibility of the nanowires. The tip of the AFM cantilever is utilized to bend and break the nanowires. Nanowire specimens are prepared by electroplating of metal ions into the nanoscale pores of the alumina memberanes. The mechanical properties are extracted by using analytical formulation along with the experimental force versus bending displacement response. Preliminary results revealed that copper nanowires have unique mechanical properties such as high flexibility in addition to high strength compared to their bulk counterparts.

Emrah Celik, Ibrahim Guven, Erdogan Madenci

Blast Performance of Sandwich Composites with Functionally Graded Core

Sandwich structures have important applications in the naval and aerospace industry, especially when they are subjected to high-intensity impulse loadings such as air blasts. During this event, the core materials play a vital role in the dynamic behavior of the sandwich structure. Since the material properties of a functionally graded/layered core can be designed and controlled, they show great potential to be an effective core design for absorbing the blast energy and improving the overall blast response of the sandwich structure. In this paper, an experimental investigation focuses on the blast resistance of sandwich composites with a functionally graded foam core subjected to shock wave loading. Four types of sandwich composites with a foam core graded/layered based on monotonically increasing the core layer wave impedance, while varying the number of core layers, have been studied. The experimental results show that monotonically increasing the core layer wave impedance while increasing the number of core layers, greatly reduces the wave impedance mismatch between consecutive layers and improves the overall blast resistance of the structure.

Nate Gardner, Arun Shukla

Thermal Softening of an UFG Aluminum Alloy at High Rates

In recent years there has been increased interest in ultra-fine grained (UFG) and nanocrystalline aluminum alloys do to their low density (1/3 that of steel). Failure of these materials often initiates at areas of localized deformation. It cannot be assumed that global temperature and strain rate conditions apply at these locations. In order to understand how reduced grain size and these localized conditions lead to failure we have tested UFG Al- 5083 at both high strain rates (4000s

-1

) and high temperatures (298K – 573K). Experiments were performed using a compression Kolsky bar modified for high temperature testing. It was found that while the microstructure of this UFG material is thermally stable, thermal softening has a significant effect on dislocation mobility.

Emily L. Huskins, K. T. Ramesh

Blast Loading Response of Glass Panels

Accidental explosions or bomb blast cause extreme loading on glass structures. This results in the shattering of glass panels. The shattered glass pieces have sharp edges and are moving at very high velocities. Most of the damage to humans is caused by these high velocity glass fragments. Apart from this, the blast pressure entering the building through the shattered window panels can also cause additional injuries to the occupants. Thus a controlled study has been performed to understand the physics behind the fracture and damage mechanisms in glass panels. This will enable us to reduce the shattering of the panels which in turn minimizes the injuries to the occupants.

Puneet Kumar, Arun Shukla

Novel Approach to 3D Imaging Based on Fringe Projection Technique

In recent years, three-dimensional (3D) imaging system based on Fringe Projection Profilometry (FPP) has been developed tremendously fast [1]. However, all current systems can provide either fast speed [2] or high accuracy measurement, but not both. In addition, very few of them can deal with multiple complex-shaped and separated 3D objects at real-time speed. This proposed paper presents a novel approach to a real-time FPP-based 3D imaging system that is able to handle multiple 3D objects at super high-speed, high-accuracy, and full-field measurement for practical applications, such as object detection, digital model generation, reverse engineering, rapid prototyping, product inspection, quality control, etc. The approach takes advantage of a special design for FPP-based 3D system that utilizes the color wheel mechanism of single chip projector to achieve real-time speed. Furthermore, multiple-frequency technique is fully developed to cope with multiple objects as well as to significantly increase the accuracy. The system with this approach is capable of imaging at 30 3D-views per second with an accuracy of 1/2,000 or 10 3D-views per second with a very high accuracy of 1/12,000.

Dung A. Nguyen

Measuring Shear Stress in Microfluidics using Traction Force Microscopy

Traction force microscopy is a previously-developed method to measure shear forces exerted by biological cells on substrates to which they are adhered (Dembo, 1999). The technique determines the shear stress applied on the surface of a soft polymeric substrate with known mechanical properties by measuring the displacement of micron-scale beads or pattered markers embedded in the surface. Marker displacement is monitored by capturing images of the embedded beads in the substrate when a load is applied. The surface shear stresses can then be calculated from the measured displacement and known elastic properties of the substrate.

Bryant Mueller

Efficiency Enhancement of Dye-Sensitized Solar Cell

Thin nanoporous TiO

2

film with a metal-based light reflective layer was investigated in dye sensitized solar cell (DSSC). In cost-effective DSSC module, the thickness reduction of the nanoporous TiO

2

film was used to reduce the photoactive dye loading. However, the thin nanoporous TiO

2

film has poor light scattering ability so that the film is generally optical transparency, which means many transmitted light would be lost in the electrolyte solution. In order to improve the light scattering issue, we proposed a metal-based light reflective layer which was used on the thin nanoporous TiO

2

film to reflect the transmitted light readdressing in the film. The results show that the photovoltaic performance of DSSC was enhanced when using the metal-based light reflective layer.

Chi-Hui Chien, Ming-Lang Tsai, Ting-Hsuan Su, Chi-Chang Hsieh, Yan-Huei Li, Li-Chong Chen, Hua-De Gau

Integration of Solar Cell with TN-LC Cell for Enhancing Power Characteristics

This study improves the output power and brightness characteristics of a translucent hydrogenated amorphous silicon (a-Si:H) solar cell by integrating the solar cell with a novel twist nematic (TN) liquid crystal (LC) cell incorporating a sub-wavelength metal grating (SWMG) polarization beam splitter (PBS). In this study, a SWMG-PBS is used to replace not only the sheet polarizers in the conventional TN-LC cell, but also the upper and lower alignment layers and transparent electrodes. Therefore, a translucent a-Si:H solar cell integrating with the novel TN-LC cell with the SWMG-PBS could improve power efficiency and durability in UV ray environment. The experimental results show that the transmittance gap between the “on” and “off” states of the enhanced translucent a-Si:H solar cell / novel TN-LC cell is of the order of 26.6% on 800 nm, 6.3% on 400 nm and 2.7% on 510 nm. Moreover, it is shown that the novel TN-LC cell increases the maximum electrical power developed by the translucent a-Si:H solar cell and improves its power conversion efficiency by 0.209% in the “off” state and 0.417% in the “on” state. In other words, the gain factors, the power efficiency of the novel TN-LC cell with translucent a-Si:H solar cell divided by the power efficiency of the standalone translucent solar cell, are determined to be 1.101 (or 110.1 %) in the “off” state and 1.201 (or 120.1 %) in the “on” state. As a result, the proposed device represents an ideal solution for building integrated photovoltaic (BIPV) systems, automobile industry applications, and many other adjustable brightness photovoltaic applications.

Chin-Yu Chen, Yu-Lung Lo

Full-field Measuring System for the Surface of Solar Cell

In this paper, we propose a scheme to measure the difference of the surface of the solar cell during manufacturing and packaging. The measurement in the full-field of the solar cell based on the Imaging Ellipsometry has been developed in this study. By using a complex programmable logic device (CPLD) and a charge-coupled device (CCD), integrating buckets with multiple frames are achieved. The sequentially measuring scheme and the algorithm are designed to achieve full-field range measurement. Also, we can figure out the condition of the surface of the solar cell by using the 2-D distributions of (ψ,Δ ). Based on the optical model, we can obtain the defect of the solar cell more precisely. Hence, the proposing system has the ability to tell the difference form the surface of the solar cell. In addition, the intensity noises induced by environmental disturbance can be reduced by the elimination of the DC component of the output light intensity in the algorithm.

Shiou-An Tsai, Yu-Lung Lo

Photographic Diagnosis of Crystalline Silicon Solar Cells by Electroluminescence

Crystalline Si solar cells emit infrared light under the forward bias as so called “Electroluminescence, EL”. The photographic imaging of EL intensity gives spatial information of solar cell performance with high resolution in less than one second. The EL intensity is proportional to the total number of minority carriers in Si substrates determined by the minority carrier lifetime. The quantitative analysis under various injection conditions can reveal cell performances such as the open circuit voltage. Photographic imaging represents the spatial distribution of minority carrier number at a glance. Intrinsic recombination centers such as crystal defects and grain boundaries which reduce the minority carrier density can be clearly detected as dark parts (spots, lines and areas) due to decreased EL intensity. Extrinsic deficiencies such as substrate breakage and hidden mechanical cracks can also be found easily since they are strong drains of minority carriers. In addition, electrode breakdown and inferior contacts also become visible due to less injection carriers. The EL technique is a versatile diagnosis tool to get the improved performance and high reliability of solar cells.

Takashi Fuyuki, Ayumi Tani

Novel Interfacial Adhesion Experiments with Individual Carbon Nanofibers

A novel experimental method for the interfacial mechanics of nanofibers embedded in polymeric matrices was developed. The debond force was determined by MEMS devices whose motion was precisely measured from optical images by digital image correlation. This method is based on a novel approach to embed nanofiber and nanotubes in a thermoplastic or thermosetting polymer with submicron control of the embedded length and orientation of the nanofiber. The cross-head displacement resolution of this optical method is ~20 nm and the force resolution is of the order of nanonewtons. A traceable force calibration technique was integrated to calibrate the MEMS force sensors. Experiments were conducted for the first time with vapor grown carbon nanofibers embedded in EPON epoxy to reveal the role of nanofiber surface roughness and functionalization in the interfacial shear strength. It was established that the nanoscale surface roughness of nanofibers strongly promotes interfacial strength while surface functionalization can increase the interfacial adhesion strength by more than a factor of three. The present experiments are the first of their kind both in their fidelity and accuracy of the applied experimental method and the data scatter is dramatically reduced compared to prior experimental attempts.

Tanil Ozkan, Ioannis Chasiotis

Dynamic Constitutive Behavior of Reinforced Hydrogels inside Liquid Environment

Dynamic compressive behavior of three different types of hydrogels used for soft tissue applications are tested using a modified split Hopkinson pressure bar. Three kinds of hydrogels: (a) plain epoxy hydrogels, (b) epoxy hydrogels reinforced with three-dimensional polyurethane fibers and (c) fumed silica nano particles reinforced hydrogels with different cross linking densities are considered in this study. The three dimensional pattern of the fibers are generated by a rapid robo-casting technique. A pulse shaping technique is used to increase the rising time of the incident pulse to obtain dynamic stress equilibrium. A novel liquid environment technique was implemented to observe the dynamic behavior of hydrogels when immersed in water. Experiments are carried out for different strain rates with and without water environment. Preliminary results show that the yield strength of these hydrogels decreases when they are immersed in water.

Sashank Padamati

Osteon Size Effect on the Dynamic Fracture Toughness of Bone

Bone is a highly studied material due to its complex microstructure and its ability to withstand fracture. It is a strong and lightweight material that has strengthening mechanisms that would be ideal if replicated in composite materials. At quasi-static loading it has been shown to have several strengthening mechanisms. One of the main proponents against fracture in the transverse direction (perpendicular to the loading axis) is crack deflection

[1]

. Cortical bone, which is comprised of tube-like structures called osteons, is able to deflect a propagating crack up to 90°

[4]

which can reduce the driving force for crack advance up to 50% when compared to the undeflected crack

[3]

. It does this by rerouting the crack along the weaker cement lines that are present along the outside of osteons. It has also been shown that the size and orientation of osteons have an influence on mechanical properties

[1]

. Smaller osteons increase the tensile fracture toughness

[2]

but due to bone’s anisotropic nature, it is unclear if this relation holds true under dynamic loading. Bone loaded at strain rates greater than 1s

-1

will yield different results when compared to static loading

[5]

. This study aims to determine which size and density of osteons will yield the greatest resistance to fracture at dynamic loading.

Michelle Raetz

Radial Inertia in Non-cylindrical Specimens in a Kolsky Bar

For high-strain rate testing of non-cylindrical specimens using a Split Hopkinson Pressure Bar(Kolsky Bar), a correction for radial interia has been developed, based on a first order approximation of stress-variation in the specimen's cross-section. The motivation for such work is the difficulty in machining fragile specimens to an exact cylindrical shape, as is typicallu required in a Split Hopkinson Pressure Bar Experminent. The correction term has been shown to be dependant on the geometry of the specimen's cross-section, the Poission's Ratio and the length of the sample chosen, and hasbeen compared to a similar correction factor, previously developed for a Cylindrical specimen. The latter has been found to be a special case of the formula developed here.

Oishik Sen

Core Deformation of Sandwich Composites under Blast Loading

During blast loading, the core of a sandwich composite demonstrates complicated stress/strain behavior. The shear stress/strain in the core is the primary consideration. Though the shear strain profile is non-linear, the transverse strain in the core is generally modeled with a linear or constant profile in numerical simulation. However, recent numerical studies have found that the transverse strain in the core also has a highly non-linear profile through the thickness. This is important in understanding the mechanism of pulse mitigation in sandwich composites. To date, no experimental investigations have been done to visualize the strain profile in the core of sandwich composites subjected to blast loading. In this paper, the high-speed 3-D Digital Image Correlation (DIC) technique was utilized to characterize such strain profiles. The real-time deformation images of the core material in a sandwich panel were captured by a high-speed photography system. The strain profiles and histories were calculated from these real-time images using DIC technique. These results were carefully analyzed and discussed.

Erheng Wang, Arun Shukla

Influence of Friction-Stir-Welding Parameters on Texture and Mechanical Behavior

During friction stir welding (FSW), a cylindrical threaded tool pin rotates and plunges into the workpieces and produces a stirring action that joins the workpieces together, while the shoulder part of the tool forges down the workpiece providing frictional heating. The joining is accomplished by running the rotating tool along the weld line. Significant heat is generated mainly from the friction between the tool shoulder and workpiece, while a severe plastic deformation occurs in the softened material by the stirring pin. As a result, a severely-deformed ‘stir zone’ with fine grains is produced through dynamic recrystallization (DRX). To date, the challenge remains in the fundamental understanding of the governing mechanisms for the grain refinement, texture formation, and the resulting mechanical behavior after FSW of Mg alloys. It is noted that, for hcp crystalline structure, deformation condition dominates the active deformation modes (slip vs. twinning), and, hence, the development of texture

[1]

. In this study, the objective was to investigate the influence of thermo-mechanical input during FSW on texture development and the corresponding mechanical behavior after FSW of AZ31B Mg alloy. A series of FSW experiments were designed to cover a wide range of deformation conditions by varying the rotation and travel speeds of the tool. Subsequently, the changes in texture of the stir zone were investigated using neutron diffraction technique. The tensile behavior of the FSW plates was also examined. Finally, the relationship among the processing parameters, texture evolution, and the mechanical behavior of the FWP Mg alloy plate is discussed.

Zhenzhen Yu, Hahn Choo, Wei Zhang, Zhili Feng, Sven Vogel

Measurement of Stresses in Pipelines Using Hole Drilling Rosettes

On-shore buried pipelines are loaded by internal pressure, by longitudinal displacement restrictions caused by support or soil interaction, and by temperature differential. If a referential initial state of stress can be established by some means, conventional strain gage techniques can be used to determine the existing loads relative to the reference state. If a reference cannot be established, residual stress measurement techniques are strong candidates for use in the measurements because they measure the absolute state of stress present at the assessed point of the pipeline. This paper aims to provide laboratory test results to show how uncertain measurements using conventional strain gage or residual stress techniques can be when used in determining existing loads. The tests utilized a special device designed and built for applying combined states of stress. The device had a U-shaped format. The horizontal part of the U-shaped device consisted of the specimen to be tested: a segment of an API 5L X60 steel pipe with length, diameter and thickness equal to 910mm, 323.3mm and 9.7mm, respectively. The pipe segment was capped at both ends by welding two reinforced plates that formed the two vertical legs or arms of the U-shaped device. A pressurized water inlet was introduced into one of the caps to provide for the internal pressure loading of the test specimen. Besides capping the pipe, the vertical leg-plates were connected by two threaded spindles. The spindles and the long plate arms made it possible to apply axial forces and intrinsically coupled bending moments to the pipe segment. The spindles were instrumented with four electrical resistance strain gages in a full bridge arrangement to measure the applied forces. The resulting applied stress states in the pipe walls caused by normal force, bending moment and internal pressure were measured using several rosettes of electrical resistance strain gages that were appropriate for applying the blind-holedrilling technique. Three sets of data points were collected during the tests. The first set consisted of measurements of strains caused by applying simple or complex load combinations. The second set consisted of strain measurements made after the blind holes were drilled in order to determine the residual stresses caused in the fabrication of the steel pipe. The third set of data consisted of measurements of strain variations caused by unloading the device. All the data of the experiment were analyzed and compared with strains calculated by means of analytic (Strength of Materials) and numeric (Finite Elements) methods. These comparisons helped to reach the conclusion that the use of a residual stress measurement technique such as the blind-hole drilling method to determine pressure induced and soil movement loading in operating pipeline will furnish inaccurate results even if a reasonable number of measurement points are used to describe the stress states of points along the analyzed cross sections. The reason for this is the possibility of a large variation in the residual fabrication stresses not only along the outer perimeter of one cross section of the pipe, but also the large variation in the distributions that occur along neighboring sections of a short pipe segment. For the case of predicting strains generated by the complex loading applied to the pipe test specimen, the comparison of experimentally and analytically determined strains allowed for the evaluation of an overall strain prediction uncertainty of 50µε. Furthermore, an uncertainty value of 26µε for the hole drilling method was also determined by comparing the initially imposed combined strain states with those measured after drilling the blind holes and unloading the test specimen.

G. R. Delgadillo, F. Fiorentini, L. D. Rodrigues, J. L. F. Freire, R. D. Vieira

Incremental Computation Technique for Residual Stress Calculations Using the Integral Method

The Integral Method for determining residual stresses involves making surface deformation measurements after a sequence of small increments of material removal depth. Typically, the associated matrix equation for solving the residual stresses within each depth increment is ill-conditioned. The resulting error sensitivity of the residual stress evaluation makes it essential that data measurement errors are minimized and that the residual stress solution method be as stable as possible. These two issues are addressed in this paper. The proposed method involves using incremental deformation data instead of the total deformation data that are conventionally used. The technique is illustrated using an example ESPI hole-drilling measurement.

Gary S. Schajer, Theo J. Rickert

Experimental Investigation of Residual Stresses in Water and Air Quenched Aluminum Alloy Castings

Cast aluminum alloys are usually subject to heat treatment including quenching for improved mechanical properties. A significant amount of residual stresses can be developed in aluminum castings during heat treatment. This paper investigates experimentally residual stress differences between water quenched aluminum castings and air quenched ones. The residual stresses in aluminum castings were measured mainly using resistance strain rosettes hole-drilling method. Other measured methods such as Interferometric Strain/Slope Rosette (ISSR), X-ray diffraction method and neutron diffraction method were also applied in this investigation. In comparison with water quenching, air quenching significantly reduces the residual stresses.

Bowang Xiao, Yiming Rong, Keyu Li

Residual Stress on Aisi 300 Sintered Materials

Selective Laser Melting (SLM) is one of t he most interesting technologies in the rapid prototyping processes because it allows to build complex 3D geometries. Moreover, full density can be reached and mechanical properties are comparable to those of bulk materials. However, the most important drawback is related to the thermal transient encountered during solidification which generates highly variable residual thermal stresses. Parameters such as laser scanner strategy, laser velocity and power should be optimized also in order to minimize residual stresses that are strictly dependent on the manufacturing process and cannot be completely avoided. Geometry of parts should be optimized in order to keep residual stresses and distortions low. This paper presents a study on residual stress distribution on SLM rectangular plates built by means of a new scanning strategy, implemented by dividing the fused zone in very small square sectors. Residual stresses measurement on SLM samples are performed by means of the hole drilling technique. Specimens made of AISI Maraging 300 steel are investigated and the residual stress profiles are compared with those related to previous measurements on SLM disks coming from the same process parameters.

C. Casavola, C. Pappalettere, F. Tursi

Practical Experiences in Hole Drilling Measurements of Residual Stresses

Strain gauge hole drilling is one of the most widely used destructive methods for measuring residual stresses. This paper describes hole drilling from 1987 to the present day at Stresscraft. Early procedures consisted of simple installations at readily accessible sites. In subsequent years, demands increased for hole drilling on more diverse component shapes and materials. Critical details of the methodology required for credible and reliable measurements are identified and discussed. These include strain measurements, the hole forming process and strain-to-stress calculation procedures. Developments were made to improve the reproducibility and reliability of the method and accessibility at difficult target sites. Significant developments have included implementation of the Integral Method in 1989 (after G. S. Schajer) and the introduction of PC-controlled miniature 3-axis drilling machines for orbital drilling in 1999. Two machines have been used over a 10-year period to drill approximately 15,000 gauges. While the fundamental elements of the method remain unchanged, in extreme cases, gauges can now be installed and drilled at sites that can only be viewed using miniature cameras. A number of examples of installations and results are presented and discussed to demonstrate the development of the method.

Philip S. Whitehead

Destructive Methods for Measuring Residual Stresses: Techniques and Opportunities

Destructive methods are commonly used to evaluate residual stresses in a wide range of engineering components. While seemingly less attractive than non-destructive methods because of the specimen damage they cause, the non-destructive methods are very frequently the preferred choice because of their versatility and reliability. Many different methods and variations of methods have been developed to suit various specimen geometries and measurement objectives. Previously, only specimens with simple geometries could be handled, now the availability of sophisticated computational tools and of high-precision machining and measurement processes have greatly expanded the scope of the destructive methods for residual stress evaluation. This paper reviews several prominent destructive measurement methods, describes recent advances, and indicates some promising directions for future developments.

Gary S. Schajer

The Contour Method Cutting Assumption: Error Minimization and Correction

The recently developed contour method can measure 2-D, cross-sectional residual-stress map. A part is cut in two using a precise and low-stress cutting technique such as electric discharge machining. The contours of the new surfaces created by the cut, which will not be flat if residual stresses are relaxed by the cutting, are then measured and used to calculate the original residual stresses. The precise nature of the assumption about the cut is presented theoretically and is evaluated experimentally. Simply assuming a flat cut is overly restrictive and misleading. The critical assumption is that the width of the cut, when measured in the original, undeformed configuration of the body is constant. Stresses at the cut tip during cutting cause the material to deform, which causes errors. The effect of such cutting errors on the measured stresses is presented. The important parameters are quantified. Experimental procedures for minimizing these errors are presented. An iterative finite element procedure to correct for the errors is also presented. The correction procedure is demonstrated on experimental data from a steel beam that was plastically bent to put in a known profile of residual stresses.

Michael B. Prime, Alan L. Kastengren

Measurements of Residual Stress in Fracture Mechanics Coupons

This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of the measurements is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.

Michael R. Hill, John E. VanDalen, Michael B. Prime

Analysis of Large Scale Composite Components Using TSA at Low Cyclic Frequencies

Thermoelastic stress analysis (TSA) has been applied to large scale honeycomb core sandwich structure with carbon fibre face sheets. The sandwich panel was subjected to a pressure load using a custom designed test rig that could only achieve low cycle frequencies of 1 Hz. Two calibration approaches have been discussed and investigated to allow the use of the thermoelastic response as a validation tool for the stress distribution predicted by an FE model. The TSA data was calibrated using thermoelastic constants derived experimentally using tensile strips of the face sheet material. It has been shown that by using constants obtained from the tensile strips manufactured with the same lay-up as the face sheet of the sandwich panel it was possible to achieve a good correspondence between the predicted stress distribution and the measured TSA response.

J. M. Dulieu-Barton, D. A. Crump

Determining Stresses Thermoelastically around Neighboring Holes whose Associated Stresses Interact

Since stresses at a geometric discontinuity can be influenced by the neighboring structural compliance, this paper emphasizes determining the individual components of stress in a finite tensile plate containing two different-size neighboring holes. Stresses associated with the respective holes interact. Relatively little information is available for such cases, purely analytical solutions are extremely difficult for finite geometries, and numerical approaches are challenging if the external loading is not well known. An effective method for determining stresses in perforated finite plane-problems is to synergize measured temperature information with a series representation of an Airy stress function. A separate stress function is employed here with each hole. The coefficients of the stress functions are evaluated from the recorded temperatures, imposing the traction-free conditions analytically at the edge of the holes, as well as satisfying stress compatibility between the holes. The number of Airy coefficients utilized is substantiated experimentally. TSA results agree with those from FEM and commercial strain gages. The technology has implications relative to reducing stress concentration factors.

A. A Khaja, R. E. Rowlands

Crack tip stress fields under biaxial loads using TSA

The aerospace industry is striving to design less conservative and hence more efficient structures in order to meet weight reduction targets, and consequently give improvements in fossil fuel use. With this focus comes the need for the development of more accurate techniques for the assessment of the structural integrity of complex, lightweight, safety-critical components. Examples of such components are wing skin panels, which, with their array of stiffeners and holes, present a complex mixed-mode loading problem where cracks can change their growth direction. This paper focuses on the exploration of experimental mechanics methods which can be used to understand such mixed-mode fatigue failure problems.

R. A Tomlinson

Extending TSA with a Polar Stress Function to Non-Circular Cutouts

This paper extends ability to thermoelastically stress analyze components containing other than circular discontinuities. Combining recorded temperatures with a stress function for stress analysis (i.e., TSA) has proven to be effective. Previous publications applied TSA to members having various shaped cutouts by employing a stress function in complex variables [1]. A shortcoming of such an approach is that one can typically evaluate the stresses only incrementally around the entire edge of a hole or notch. Real variables are also easier to use than complex variables and a general series-form of the Airy stress function exists in (real) polar coordinates which enables the stresses be determined simultaneously around an entire cutout. The TSA approach using polar coordinates is illustrated here for the case of an elliptical hole in a finite tensile plate. Little information is available for such finite situations, purely analytical solutions are extremely difficult for finite geometries, and both theoretical and numerical approaches are challenging if the external loading is not well known. The number of Airy coefficients to retain is evaluated experimentally, and the TSA results are substantiated independently.

A. A Khaja, R. E. Rowlands

Novel Synthetic Material Mimicking Mechanisms from Natural Nacre

The biomimetics field has become very popular as Mother Nature creates materials with superior strength and toughness out of relatively weak material constituents. This concept is attractive because current synthetic materials have yet to achieve this level of performance from the same weak material constituents. Nacre, from Red Abalone shells, is among the natural materials exhibiting outstanding toughness, while being comprised of a brick and mortar structure of 95% brittle ceramic tablets and 5% soft organic biopolymer mortar. During loading, that tablets slide relative to each other. This generates progressive interlocking which constitutes nacre’s primary toughening mechanism [1, 2]. We have translated this concept of tablet sliding and interlocking to create a novel composite material. Fabrication of the material will be discussed as well as design parameters. Results from tensile tests will be presented as well as comparison of the synthetic material to natural nacre. Implications to the synthetic materials community will be presented.

Allison Juster, Felix Latourte, Horacio D. Espinosa

Mechanical Characterization of Synthetic Vascular Materials

Biological materials in living organisms are furnished with a vascular system for the transportation and supply of necessary biochemical components. Many critical functions are supported by these vascular systems, including the maintenance of homeostasis, growth, autoimmune responses, regeneration, and repair. Synthetic materials with vascular systems have been created via a number of fabrication techniques in order to mimic some of these functionalities. The direct ink writing technique has been used to create polymer matrix, vascularized materials with micron-scale channels capable of autonomic repair. Liquid healing agents are delivered via the vascular system to sites of damage, where they polymerize in the crack plane, forming an adhesive bond with the surrounding material and recovering the mechanical integrity of the material. Characterizing the mechanical integrity of these materials is critical to optimizing their strength and toughness. The spacing between vascular conduits and the presence of locally-placed particle reinforcement have been shown to affect the local strain concentrations measured in these materials. In this work we study the effect of vascular geometry and local microchannel reinforcement on the bulk properties of the vascular material. Dynamic mechanical analysis is conducted to evaluate the stiffness of various vascular designs, and single edge notch beam (SENB) fracture samples are used to quantify the effect on fracture toughness.

AR Hamilton, C Fourastie, AC Karony, SC Olugebefola, SR White, NR Sottos

MgO nanoparticles affect on the osteoblast cell function and adhesion strength of engineered tissue constructs

The objective of this research was to evaluate the influence of magnesium oxide (MgO) on the adhesion strength between hard tissue and soft tissue constructs. The scope of works for this research were: (1) to determine the viability of osteoblast cells in hydrogel and hydrogel with 22 nm MgO particles, (2) to design and construct a test setup for the measurement of adhesion strength of engineered tissue constructs, and (3) to determine if MgO nanoparticles affect on the adhesion strength of the engineered tissue constructs. Mouse osteoblast cells (MT3T3E1) were cultured on polycaprolactone (PCL) scaffold, hydrogel scaffold, as well as hydrogel scaffold with 22 nm MgO particles. The viability of cells was determined in: hydrogel and hydrogel with 22 nm MgO particles. Tensile test were conducted on: (1) PCL-hydrogel, (2) PCL-hydrogel with cells, (3) PCL-hydrogel with cells and MgO nanoparticles, and (4) PCL-hydrogel with MgO nanoparticles to measure the adhesion strength between these hard tissue and soft tissue constructs. This research found the increase of osteoblast cells adhesion on hydrogel scaffold containing 22 nm MgO particles and decrease of adhesion strength between PCL and hydrogel, when both PCL and hydrogel were seeded with cells and 22 nm MgO particles.

Morshed Khandaker, Kelli Duggan, Melissa Perram

Mechanical Interactions of Mouse Mammary Gland Cells with a Three-Dimensional Matrix Construct

One risk factor associated with breast cancer is tissue or mammographic density which is directly correlated with the stiffness of the tissue. We undertook a study of mammary gland cells and their interactions with the extracellular matrix in a microfluidic platform. Mammary gland cells were seeded within collagen gels inside microchannels, using concentrations of 1.3, 2, and 3 mg/mL, along with fluorescent beads to track strains in the gel. The cells and beads were observed via four-dimensional imaging, tracking X, Y, Z positions over a three to four hour time frame. Three-dimensional elastic theory for an isotropic material was employed to calculate the stress. The technique presented adds to the field of measuring cell generated stresses by providing the capability of measuring 3D stresses locally around the single cell and using physiologically relevant materials properties for analysis.

M. d. C. Lopez-Garcia, D. J. Beebe, W. C. Crone

Tracking nanoparticles optically to study their interaction with cells

Nanoparticles are by definition too small to be visible in an optical microscope and devices such as scanning electron microscopes must be used to resolve them. However electron beams quickly lead to cell death and so it is difficult to study the interaction of nanoparticles with living cells in order to establish whether such interactions could be damaging to the cell. A simple modification to a conventional inverted optical microscope is proposed here which renders the location of nanoparticles readily apparent and permits tracking of them in threedimensions. Particles in the range 100nm to 500nm have been tracked with a temporal resolution of 200ms. The technique, although motivated by the desire to study the interaction of nanoparticles with cells, has a wide range of potential applications in the fields of food processing, pharmaceuticals and nano-biotechnology.

Jean-Michel Gineste, Peter Macko, Eann Patterson, Maurice Whelan

Coherent Gradient Sensing Microscopy: Microinterferometric Technique for Quantitative Cell Detection

Micro-CGS, an integration of the interferometric optical method Coherent Gradient Sensing (CGS) [1-3] with an inverted microscope, is introduced. Micro-CGS extends the capabilities of Classical CGS into the cellular level. As such, it provides full-field, real-time, micro-interferometric quantitative imaging. Micro-CGS is based on the introduction of a microscope objective into the classical CGS setup. An experimental setup is detailed and resulting interferograms are shown. A digital image processing program is created to compute specimen curvature from the given fringe patterns. The experimental method is validated by the successful measurement of the curvature of 30-micron glass microspheres.

M. Budyansky, C. Madormo, G. Lykotrafitis

Rate effects in the failure strength of extraterrestrial materials

—Most simulations of asteroid impacts use the properties of terrestrial analogs to approximate the behavior of the asteroid material because there is currently a lack of data for the mechanical properties of the investigate the mechanical response of a stony meteorite that is believed to be of asteroidal origin. We investigate the mechanical response of a stony meteorite that is believed to be of asteroidal origin. We have measured, at strain rates ranging from 10

–3

-10

–3

S

–1

, the uniaxial (unconfined) compressive strength of specimens cut from an L5 ordinary chondrite, MacAlpine Hills 88118 (MAC88118). Quasistatic compression experiments were conducted using a servo-hydraulic load frame while dynamic compression experiments were conducted using a modified Kolsky bar. Images of the specimen were also recorded during the experiments were conducted using a modified Kolsky bar. Images of the specimen were also recorded during the experiments for visualization of the failure process. A large increase (3-4X) in compressive strength is observed when the strain rate is increased from 10

–3

-10

–3

S

–1

.

J. Kimberley, K. T. Ramesh, Olivier S. Barnouin

Determination of Dynamic Tensile Properties for Low Strength Brittle Solids

We propose an indirect tensile testing method to measure the full dynamic tensile stress-strain curve of low strength brittle solids. In this method, we use the flattened-Brazilian disc (FBD) sample and apply the dynamic load with a modified split Hopkinson pressure bar (SHPB) system. Low amplitude dynamic loading forces are measured by a piezoelectric force transducer that is embedded in the transmitted bar. The evolution of the tensile stress at the center of the disc sample is determined via finite element analyses with the measured stress in SHPB as inputs. In a traditional Brazilian method, a strain gauge is mounted at the center of the specimen to measure the tensile strain, which is difficult to apply for low strength brittle materials. Therefore, a laser gap gauge (LGG) is used to monitor the expansion of the disc perpendicular to the loading axis, from which the average tensile strain is deduced. The numerical simulation reveals a linear relationship between the tensile strain at the center of the specimen and the average tensile strain and the relating factor is not sensitive to the material elastic parameters. The feasibility of this methodology is demonstrated with the SHPB-FBD experiments on a polymer bonded explosive (PBX).

R. Chen, F. Dai, L. Lu, F. Lu, K. Xia

The Mechanical Response of Aluminum Nitride at Very High Strain Rates

In previous work, we have used a modified compression Kolsky bar to determine the dynamic compressive strength of some ceramic materials, including aluminum nitride (AlN), at strain rates of approximately 10

3

s

–1

. However, there is very limited experimental work on ceramics at higher strain rates (of the order of 10

4

s

–1

) because of various technical difficulties. This work seeks to characterize the mechanical properties of AlN within the strain rate range (10

3

~10

4

s

–1

) using the desktop Kolsky bar (DKB), taking advantage of the benefits of miniaturization. Our interest is in the influence of the loading rate on the compressive strength under uniaxial stress conditions. Microstructural analysis is performed to identify the failure mechanisms at different strain rates.

Guangli Hu, K. T. Ramesh, J. W. McCauley

Dynamic and Quasi-static Measurements of C-4 and Primasheet P1000 Explosives

We have measured dynamic and quasi-static mechanical properties of C-4 and Primasheet P1000 explosive materials to provide input data for modeling efforts. Primasheet P1000 is a pentaerythritol tetranitrate-based rubberized explosive. C-4 is a RDX-based moldable explosive. Dynamic measurements included acoustic and split-Hopkinson pressure bar tests. Quasi-static testing was done in compression on a load frame and on a dynamic mechanical analyzer. Split-Hopkinson and quasi-static tests were done at five temperatures from -50°C to 50°C. Acoustic velocities were measured at, above, and below room temperature.

Geoffrey W. Brown, Darla G. Thompson, Racci DeLuca, Philip J. Rae, Carl M. Cady, Steven N. Todd

Dynamic Characterization of Mock Explosive Material Using Reverse Taylor Impact Experiments

The motivation for the current study is to evaluate the dynamic loading response of an inert mock explosive material used to replicate the physical and mechanical properties of LX-17-1 and PBX 9502 insensitive high explosives. The evaluation of dynamic material parameters is needed for predicting the deformation behavior including the onset of failure and intensity of fragmentation resulting from high velocity impact events. These parameters are necessary for developing and validating physically based material constitutive models that will characterize the safety and performance of energetic materials. The preliminary study uses a reverse Taylor impact configuration that was designed to measure the dynamic behavior of the explosive mock up to and including associated fragmentation. A stationary rod-shaped specimen was impacted using a compressed-gas gun by accelerating a rigid steel anvil attached to a sabot. The impact test employed high-speed imaging and velocity interferometry diagnostics for capturing the transient deformation of the sample at discrete times. Once established as a viable experimental technique with mock explosives, future studies will examine the dynamic response of insensitive high explosives and propellants.

Louis Ferranti Jr., Franco J. Gagliardi, Bruce J. Cunningham, Kevin S. Vandersall

Mechanical Behavior of Hierarchically-structured Polymer Composites

As the engineering of hierachically-structured polymer composites advances, so does the need for understanding the evolution of damage in these materials and their mechanical behavior. In natural systems, such as nacre, it is now well-understood that the damage accumulates across multiple length scales due to the nanoscale elastic biopolymers that bind together microscale aragonite crystals in a layered structure. The result is an extremely damage-tolerant microstructure that has a high hardness and fracture toughness. While it is difficult to duplicate this structure in synthetic polymer composites, it is still possible to alter mechanical behavior through structuring the material across multiple length scales. In this paper, the mechanical behavior of a hierarchically-structured polymer composite is studied by dispersing CNFs in a model epoxy system using sonication during solvent processing. A new nanomechanical characterization approach was used to characterize the multi-scale mechanical behavior in order to develop a model that was capable of determining the degree of dispersion and dispersion limit of CNFs that give rise to the hierarchical structure.

A. L. Gershon, H. A. Bruck

Composite Design through Biomimetic Inspirations

Biomimetics is a developing research field where principles of mechanics are used to both study existing natural systems and also design new systems incorporating the desirable attributes. In the current study, examples from nature that could be applied to design new composite materials and structures are presented. Mechanical characterization of bio materials such as Bivalves, bone and keratin were undertaken to understand the role of micro structure in determining the functionality of these bio-composites. Selected results such as failure in multilayered structures, fracture properties in natural FGMs and functional attributes of layering will be discussed. Special attention provided to rational decision making in terms of choice of the materials and methods will also be presented.

S. A. Tekalur, M. Raetz, A. Dutta

Nano-composite Sensors for Wide Range Measurement of Ligament Strain

Biological tissues routinely experience large strains and undergo large deformations during normal physiologic activity. In order to quantify this strain, researchers often use optical marker tracking methods which are tedious and difficult. This paper investigates a new technique for quantifying large strain (up to 40%) by use of piezoresistive composite strain gages. The High Displacement Strain Gages (HDSGs) being investigated are manufactured by suspending nickel nanostrands within a biocompatible silicone matrix. The conductive nickel filaments come into progressively stronger electrical contact with each other as the HDSG is strained, thus reducing the electrical resistivity which is measured using conventional techniques. In the present work, HDSGs measured the strain of bovine ligament under prescribed loading conditions. Results demonstrated that HDSGs are an accurate means for measuring ligament strains across a broad spectrum of applied deformations. The technique has application to most biological tissue characterization applications.

Tommy Hyatt, David Fullwood, Rachel Bradshaw, Anton Bowden, Oliver Johnson

Advanced Biologically-Inspired Flapping Wing Structure Development

This study examines the possibility to develop a manufacturing method to build a complicated composite structure comparable to insect wings. Stimulated by the research in flapping wing micro air vehicles, a wing structure that can be controlled with stiffness and mass distribution during manufacturing can enable complicated kinematics and efficient aerodynamics. Insects demonstrate superior flight performance and therefore their wings are good examples for building an artificial counterpart. Cicada wings are selected in this work for emulation. An artificial composite wing is built with computer numerical controlled tooling and manual fabrication, with similar vein pattern. The wings are compared with measurements of mass distribution in the spanwise direction. The results show that the composite reinforcement topology and cross section variation allow the two wings to have very similar property trends. Several difficulties are overcome in this work: replicating the cicada wing vein pattern, fabricating small composite structure components and measuring their weight distribution.

Lunxu Xie, Pin Wu, Peter Ifju

Characterization of Electrode-Electrolyte Interface Strengths in SOFCs

Planar Solid Oxide Fuel Cells (SOFCs) are composed of multiple layers of dissimilar materials. Interfaces between the different components that make up an SOFC play an important role in the performance and robustness of the cells and stacks. The present study involves the characterization of electrode-electrolyte interfaces in solid SOFCs. Stud-pull test fixture was constructed and mounted on a servo-electric load frame to examine the anode-electrolyte interface. The stud-pull specimens were made of NiO-GDC/Ni-YSZ anodes and ScSZ electrodes and were reduced in either forming gas (5% H2) or H2 fuel. The test was not successful in separating anode from the electrolyte consistently and was inconclusive due to infiltration of glue into the porous anode which changed the interfacial strength significantly. In the Next step the notched four-point bend experiment was utilized to determine the fracture energy at the interface between the anode and the electrolyte. Crack propagation was monitored with acoustic emission and videography. Specimens for the bend experiments consist of unreduced NiO-GDC/Ni-YSZ anode and ScSZ electrolyte bi-layers sandwiched between steel stiffeners. The microstructure was studied using scanning electron microscopy (SEM).

S. Akanda, M. E. Walter

Die Separation Strength for Deep Reactive Ion Etched Wafers

Typical micro-scale devices made via cleanroom processes are often produced in bulk quantities on a single wafer. Depending on the lateral dimensions of a device, as many as a few hundred can be manufactured on an individual wafer. With expensive required facilities and raw materials, industrial manufacturing of siliconbased electrical and MEMS devices demands mass production to remain economical. Fabrication facilities can optimize throughput by performing batch processes on large diameter wafers containing many die. While larger diameter wafers contain more devices, they can require an extensive amount of time and effort to separate the die in a clean and effective manner.

Any improvements in the die separation process can translate to tremendous cost savings for manufacturers. Gains in efficiency may be achieved in a number of ways. In particular, the product yield can be increased by reducing the amount of material wasted between die, or by lowering the number of die typically damaged during the separation process. Additional concerns include the required separation time and any reduction in die strength due to flaws or micro-scale damage induced during separation.

D. A. Porter, T. A. Berfield

Temperature Moisture and Mode Mixity Dependent EMC- Copper (Oxide) Interfacial Toughness

An ongoing root cause of failure in microelectronic industry is interface delamination. In order to explore the risk of interface damage, FE simulations for the fabrication steps as well as for the testing conditions are generally made in the design stage. In order to be able to judge the risk for interface fracture, the critical fracture properties of the interfaces being applied should be available, for the occurring combinations of temperature and moisture preconditioning. As a consequence there is an urgent need to establish these critical interface fracture parameters. For brittle interfaces such as between epoxy molding compound (EMC) and metal (-oxide) substrates the critical energy release rate (or delamination toughness) can be considered as the suitable material parameter. This material parameter is strongly dependent on the temperature, the moisture content of the materials involved and on the so-called mode-mixity of the stress state near the crack tip. The present study deals with experimental investigation of the delamination toughness of EMC-Copper lead-frame interfaces as can directly be obtained from the production line. A small-scaled test setup was designed. The test setup is suitable for actualizing both pure mode I DCB (double cantilever beam) loading and pure mode II ENF (end notched flexure) loading and allows transferring two separated loadings (mode I and mode II) on a single specimen. The setup is flexible and adjustable for measuring specimens with various dimensions. For measurements under various temperatures and moisture conditions, a special climate chamber is designed. In this paper, the experiment and simulation procedure for establishing the interfacial fracture toughness from fracture test results at different temperatures, especially in the glass transition temperature region of epoxy molding compound (EMC) will be shown. In order to calculate accurate interface toughness, the material property of molding compound is characterized as a function of temperature. A detailed discussion of how EMC responses at its glass transition region will be provided. The influence of the material property on interfacial fracture toughness will be given.

A. Xiao, G. Schlottig, H. Pape, B. Wunderle, K. M. B. Jansen, L. J. Ernst

An Integrated Experimental and Numerical analysis on Notch and Interface Interaction in Same-materials

The theory of fracture mechanics has been extensively developed for cracks. However, notches are found a lot more than cracks in real life. Indeed, a crack is only a special case of a notch. Therefore, developing a generalized notch-interface failure criterion is very important for the field of fracture mechanics from a fundamental standpoint. In the current investigation, an integrated experimental and numerical analysis is conducted to determine the crack initiation load and to compare it with theoretical predictions. The angle of the (β), the loading point (S), and the interfacial adhesive are used as variables to understand their effect on the crack initiation load.

Arun Krishnan, L. Roy Xu

Differentiation of Human Embryonic Stem Cells Encapsulated in Hydrogel Matrix Materials

Prior work on many cell types, including stem cells, has definitively shown that mechanical stiffness of the neighboring material and the overall stress state influences cell behavior. There is also evidence that the topology (i.e. 2D vs 3D environment) impacts cell behavior. Our research involves controlling the differentiation of human embryonic stem cells (hESCs) through mechanical stimuli. We employ three-dimensional cultures to better understand how topology and mechanical properties of a surrounding matrix impact stem cell differentiation. For these experiments, H9 hESCs were embedded in hydrogels of varying Young’s moduli with the target of differentiation toward cardiomyocytes. The amount of contractile behavior was quantified, and real-time polymerase chain reaction (qRT-PCR) tests were conducted at various time points. Results show a similar efficiency in cardiomyocyte generation to other methods with the advantages of a three-dimensional matrix environment more conducive to the needs of tissue engineering.

Max Salick, Richard A. Boyer, Chad H. Koonce, Timothy J. Kamp, Sean P. Palecek, Kristyn S. Masters, Wendy C. Crone

Nonlinear Viscoelasticity of Native and Engineered Ligament and Tendon

Ligaments and tendons are non-linear viscoelastic materials and their response functions are typically assessed using creep and stress relaxation tests. Non-linear viscoelastic models such as multiple Maxwell elements in parallel and the quasilinear viscoelastic model (QLV) used to capture the non-linear viscoelastic response of ligaments and tendons frequently employ multiple relaxation time constants determined from curve-fitting the entire available data set and generally lack a clear physiological relevance. Uniaxial load-unload tension tests on ligament and tendon also manifests the viscoelastic response and such experiments suggest that the bulk of the non-linearity in the response of these soft tissues is in the elasticity. We propose physiologically relevant nonlinear viscoelastic models in which the response of the main structural proteins in ligament and tendon (e.g. collagen and elastin) are described using non-linear elasticity. Our approach using a three-element, non-linear solid micromechanical model captures this viscoelastic response in load-unload, stress relaxation and creep with a limited number of physically meaningful parameters. Previous research also shows different viscoelastic responses between native tendon and ligaments. In our model, by varying the properties of the non-linear springs, we are able to capture the differences in the viscoelastic responses of ligaments verses tendon. We will demonstrate the capabilities of our model by comparing to the experimental results from testing native and engineered ligament and tendon.

Jinjin Ma, Ellen M. Arruda

Spinal Ligaments: Anisotropic Characterization Using Very Small Samples

Spinal ligaments exhibit a nonlinear, anisotropic, viscoelastic response, which has yet to be adequately characterized. Characterizing and modeling the material responses of spinal ligaments is essential to understanding both normal and pathological motion of the spine. Current methods for testing connective tissue require large volumes of sample and often experience difficulty in gripping, due to the texture of connective tissue. Consequently a mechanism capable of overcoming these barriers was developed, designated as the Anisotropic Small Punch Test (ASPT). The apparatus consists of a 6-mm diameter tissue sample clamped between two peripheral plates. The center of the sample is displaced by a 1mm rod and renders a multiaxial profile recorded by two cameras at orthogonal angles. The measured force and displacement experienced by the sample then serve as input for an optimization routine to derive constitutive coefficients that characterize ligament behavior. Bovine achilles tendon were used to validate that ASPT is an appropriate method for capturing the nonlinear, anisotropic, viscoelastic response of ligaments. This methodology has the potential to transform current methods of testing biological tissue in addition to quantifying mechanical properties of ligaments.

Rachel J. Bradshaw, Alison C. Russell, Anton E. Bowden

In-Flight Wing-Membrane Strain Measurements on Bats

An efficient system for high-resolution measurements of a bat wing’s membrane during flight is presented, proving the feasibility of dynamic strain measurements on bats wing membranes during flapping. Data were collected from wind tunnel wind-off flights of a Jamaican fruit bat, Artibeus jamaicensis, a nocturnal and frugivorous specie trained by Brown University team to fly back and forth in the test section. Visual image correlation was used for image post-processing providing spatial highresolution three-dimensional displacements and strains on the bat’s wing.

Temporal membrane surface-averaged strain analysis showed a level of strain in the X direction (spanwise) approximately three times larger then the Y direction (chordwise) with values around 10% and 3%, respectively. Strains are estimated from an unknown reference state at the beginning of each recorded sequence. Full surface membrane strain distribution shows a consistent strain-relief effect around the ring finger during downstroke in the X direction (spanwise). Temporal wing section shape analysis during a down stroke revealed a higher camber and a significant pitch-up twist of the ring finger respect to the free membrane between the little and ring finger.

Roberto Albertani, Tatjana Hubel, Sharon M. Swartz, Kenneth S. Breuer, Johnny Evers

The Mechanical Properties of Musa Textilis Petiole

From a structural point of view, banana leaf is an outstanding design of biological system. This work used a procedure based on finite element analysis and inverse problem method to estimate elastic modui of different parts of banana petiole from compression test data. Two phase compression tests on petiole section specimens were performed to get the force-displacement data of petiole for inverse finite element analyses. The inverse analysis method was performed by using a MATLAB procedure to execute ABAQUS to obtain finite element results and read desirable data from finite element results for optimization procedure. The values of elastic moduli of skin and core of petiole estimated by current method are 28 MPa and 0.9 MPa respectively for the particular petiole section under test.

N.-S. Liou, S.-F. Chen, G.-W. Ruan

Analysis of Strain Energy Behavior throughout a Fatigue Process

The dissipation of strain energy density per cycle was analyzed to understand its trend through a fatigue process. The motivation behind this analysis is to improve a fatigue life prediction method, which is based on a strain energy and failure correlation. The correlation states that the same amount of strain energy is dissipated during both monotonic fracture and cyclic fatigue. This means the summation of strain energy density per cycle is equal to the total strain energy density dissipated monotonically. In order to validate this understanding, the strain energy density per cycle was analyzed at several alternating stress levels with fatigue life between 10

3

and 10

5

cycles. The analysis includes the following: Alternating between high and low operating frequencies (50x difference), interruption of cyclic load during testing, and idle/zero-loading for intervals of 20-40 minutes between cyclic loading sequences. All experimental results show a consistent trend of cyclic softening as the loading cycles approach failure, which further validates the theories used in developing the energy-based fatigue life prediction method.

Onome Scott-Emuakpor, Tommy George, Charles Cross, M.-H. Herman Shen

Relating Fatigue Strain Accumulation to Microstructure using Digital Image Correlation

While fatigue has been studied extensively, fatigue life predictions are still phenomenological and relatively simple (

e.g.

Miner’s rule, Paris relationship, etc.). Many improvements have been suggested to such models to incorporate newly discovered phenomena, but fatigue life predictions still have limited accuracy and scope. A quantitative understanding of fatigue at the grain level would lead to models with better predictive capability and/or broader applicability. In this work, fatigue crack growth in Hastelloy X, a high-temperature nickel based alloy, was examined using an ex-situ digital image correlation technique. Electron backscatter diffraction (EBSD) was performed on a region of interest in front of the crack tip in a single edge notched tension specimen to obtain microstructural characteristics. The specimen was then fatigue loaded to advance the crack. At regular intervals of crack growth, the specimen was removed from the load frame and the region of interest was imaged with an optical microscope. By performing digital image correlation on these images, a full-field measure of the accumulated plastic strain was obtained as the crack approached and passed through the region of interest. Strain fields were compared to EBSD results to elucidate the relationship between microstructure and fatigue crack growth. The presence of strain concentrations at grain and (annealing) twin boundaries was seen to be instrumental in the evolution of plastic strain accumulation during fatigue.

Jay Carroll, Wael Abuzaid, Mallory Casperson, John Lambros, Huseyin Sehitoglu, Mike Spottswood, Ravinder Chona

High Cycle Fatigue of Structural Components Using Critical Distance Methods

This study explores the high cycle fatigue strength of crack-like discontinuities in metallic structures as well as those made from powder metals using approaches that are based on theory of critical distances (TCD). The methods used in this study consist of (a) the point method, (b) the line method, and (c) the imaginary crack method. The effective parameter for the methods (a), (b), and (c) is the distance ‘d’ from the material surface, which is a material property and the reference parameter is the fatigue limit. The imaginary crack method involves introduction of a sharp crack at the root of a notch and the length of the crack, ‘lo’ assumed a material constant. In the imaginary crack method, the effective crack length is taken as the sum of the actual crack and the material parameter ‘lo’. It is concluded that the high cycle fatigue has a volumetric character and the proposed methods introduce the volume effect in the determination of stress and strain fields as well as the fatigue life. Using the material parameters from the various approaches, the number of cycles to initiate a fatigue has been determined for a number of materials and compared with experimental results.

Somnath Chattopadhyay

Crack Propagation Analysis of New Galata Bridge

The New Galata Bridge links the two sides of the entrance of the Golden Horn and as a bascule-type bridge, the bridge has four wings, each having a span of 42 meters. The bridge has replaced the Galata Bridge which gave service from 1912 to 1985. After the new bridge has begun to give service, serious cracks located in steel stringers underneath the road surface and near the counterweight blocks were observed during maintenance. As a result, modifications around this area were made. Three dimensional finite element models of the third wing and cracked locations were prepared. Crack analyses were conducted around these points. Based on results, comments were provided.

Kadir Ozakgul, Ozden Caglayan, Ovunc Tezer, Erdogan Uzgider

Stress-Dependent Elastic Behaviour of a Titanium Alloy at Elevated Temperatures

In this study the stress-dependence of the elastic modulus at elevated temperatures during fully-reversed low cycle fatigue of the titanium alloy Ti6242 is examined. The change of the elastic properties with stress manifests itself in a crescent-like shaped hysteresis loop of stress vs. plastic strain at very low amplitudes. A quadratic extension of Hooke’s law with a second constant “

k

” is applied. The parameters are determined all along the unloading curve in tension and compression. The approach allows to align the branches of the hysteresis loop so that they become vertical, i.e. the elastic strain is accurately described. The value and sign of “

k

” depend whether the deformation occurs in tension or compression. Like the Young’s modulus

E

0

, “k” it also depends on temperature. The changes of “k” are correlated with the different mechanisms of dislocation movement activated at different temperatures. At temperatures up to 550°C the values of “

k

” in tension and compression do not change during fatigue life. However, at 650°C thermally activated slip processes lead to changes of both,

E

0

and “

k

”.

Thomas K. Heckel, Aimé Guerrero Tovar, Hans-Jürgen Christ

Numerical and Experimental Modal Analysis Applied to the Membrane of Micro Air Vehicles Pliant Wings

Hyperelastic latex membrane is an integral structure of micro air vehicles and plays an important role in their wings performance. This paper presents finite element analysis (FEA) models for characterizing latex hyperelastic membrane at both static and dynamic loadings, validated by experimental results. The membrane at different pre-tension levels are attached with a circular steel ring and statically loaded using steel spheres of different sizes placed at the center of the membrane. The deformation of the membrane is measured by visual image correlation (VIC), a non-contact measurement system and strain energy is calculated based on Mooney-Rivlin material model. It is found that the deflection and strain energy of the membrane computed by experimental and FEA models are correlated well, although discrepancy is expected among experimental and FEA results within reasonable limits due to the variation of the thickness of the membrane. The experimental modal analysis is conducted by imposing a structural excitation to the ring for investigating the membrane vibration characteristics at both atmospheric pressure and reduced pressure in a vacuum chamber. The three-dimensional shape of the membranes during a burst-chirp excitation at different pre-tension levels is dynamically measured and recorded and the natural frequencies are computed by performing the fast Fourier transform of the out-of-plane displacement at several points of the circular membrane. Experimental results show that the natural frequencies increase with mode and pre-tension of the membrane, but decrease due to increase in ambient pressure. A preliminary FEA model is developed for the natural frequencies of the membrane at different isotropic and nonisotropic pre-tension levels at vacuum environment.

Uttam Kumar Chakravarty, Roberto Albertani

Objective Determination of Acoustic Quality in a Multipurpose Auditorium

Significant differences in listening qualities have been reported by the audience attending wide varieties of functions ranging from orchestral music to stage drama and public announcements at the multipurpose auditorium of the Miami University Hamilton campus. Preliminary investigations have been conducted to examine the difference in sound qualities utilizing impulse responses at various seating sections throughout the auditorium, based on standardized measurement procedures. Detailed comparisons of measured acoustic quality parameters have been made against the available data in literature for statistically determined optimal acoustic conditions. Each measured range of parameter values has been analyzed to determine the distribution characteristics over a pre-determined set of locations on the audience seating area. Recommendations for improvements are presented throughout the paper.

B. Hayes, C. Braden, R. Averbach, V. Ranatunga

Identification and Enhancement of On-stage Acoustics in a Multipurpose Auditorium

The objective of this research is to identify the measurable sound quality parameters of an existing multipurpose auditorium in which the acoustics are not adequate for orchestral purposes. The major problems have been identified as the lack of sufficient projection of sound from the stage area, the inability of the musicians to hear themselves and each other, and the poor reverberation in the auditorium. Objective architectural acoustic parameters have been identified and analyzed by conducting acoustical measurements following standardized procedures. One of the measured objective parameters is 'Musician Support', which depends on the amount of early reflections available on stage for the musicians. An acoustic shell, which is a set of large panels that surround an orchestra, will increase the level of early reflections. The goal of this study is to assess the effectiveness of an acoustic shell in improving the on-stage acoustics of this particular auditorium. An objective analysis of these parameters is presented with and without the shell in place, in order to quantify the overall enhancement for the musicians provided by the acoustic shell.

C. Braden, B. Hayes, R. Averbach, V. Ranatunga

Fractional Calculus of Hydraulic Drag in the Free Falling Process

A new approach to describe the hydraulic drag received by a falling body has been developed through fractional calculus, and the analytical solution has been given. This new method treats the measurement of the hydraulic drag as the fractional derivative of the falling body’s displacement. The existing methods could be classified into two categories. The first ones assume the drag could be described by a quadratic equitation of the body’s velocity and use the classical Newton law to describe the falling process. The second ones do introduce the fractional calculus to describe the dynamic process but still treat the drag as the quadratic of velocity, which make the physics meaning of parameters are obscure. Compared to existing methods, the new approach introduced in this paper is original from the perspectives of basic hypothesis and modeling. To evaluate the performance of this method, series experiments have been conducted with the help of high speed camera. The data fit the new method successfully, and compared to the existing approaches, the new one has the overall better performance on the accuracy to describe the dynamic process of the falling body and owns intuitive physical explanation of its parameters.

Yuequan Wan, Richard Mark French

Fatigue Cracks in Fibre Metal Laminates in the Presences of Rivets and Cold Expanded Holes

In order for new composite materials like fiber metal laminates (FML) to gain acceptance in the aerospace field, it is important to understand the effect on them of common manufacturing techniques such as riveting and cold expansion. A comprehensive research program was initiated using two advanced strain measurement techniques; digital image correlation and thermoelastic stress analysis, to understand the failure mechanisms in FML materials that had been fatigue cycled after having undergone hole cold expansion or riveting. Prior theoretical work has shown the potential for improvement in fatigue life of FMLs, so one standard grade of FML (FML 4-3/2) and a novel FML variant were manufactured and tested. Thermoelastic stress analysis was employed to measure strains on the mandrel exit face while digital image correlation was used to measure strains on the mandrel entry face in the coupons and additional insight was gained regarding the effect of the cold expansion process and of riveting on fatigue crack growth. The results also highlighted the effect of material design on fatigue life as well as the interaction between residual strains and fatigue crack growth.

David Backman, Eann A. Patterson

Effect of Nonlinear Parametric Model Accuracy in Crack Prediction and Detection

The use of nonlinear system identification has been applied to predicting and tracking cracks as they form and propagate through a vibrating cantilevered beam. Continuous Time based nonlinear system identification is used in application to the harmonically excited system. Model parameters are shown to vary as the beam transitions to failure, though no attention has been given to the accuracy of the parameters identified. In this application the effects of fixing sets of model parameters to their known, accurate values is explored as a method to enhance the health monitoring technique.

Timothy A. Doughty, Natalie S. Higgins

Optical Based Residual Strain Measurements

Residual stresses can occur due to either manufacturing, fabrication processes or intentionally engineered into structures in attempts to improve fatigue life. Equally important is that designers understand how to account for the potential effects of residual stresses on the life of structures or products.

This paper describes the theory and practice for residual strain measurements in friction stir welded joints in aluminum and cold worked holes using the split sleeve mandrel expansion for aircraft fasteners. The first application is based on the hole drilling method where a small hole is drilled in the central region of a measuring strain gage array. The optical method described in this paper makes use of a small circular gage that is rapidly applied through a peel and stick process. Once the gage is applied a reference reading is recorded and a second following the hole drilling. The circular gage is capable of measuring thirty-six tangential strain values around the circumference of the hole. This yields an over determined set of equations to calculate the residual strain components.

Cold-working of fastener holes is used extensively to increase the fatigue life and damage tolerance of mechanically-fastened joints in aircraft structural components. Life improvements of up to five or more are possible over a non cold worked hole. An optical method has been developed and presented to measure directly the hole diameters before and after cold working of holes. The diameter changes are then used as boundary conditions as input variables into a finite element code. This combined method of experimental and numerical techniques provide for a complete and accurate description of residual stress distributions around cold worked holes. Experimental examples are used to illustrate the application of each method.

Jason Burnside, William Ranson, Dean Snelling

Correlating Fatigue Life with Elastic and Plastic Strain Data

It is widely accepted that residual compressive stresses in aerospace materials enhance fatigue performance. Conventional shot peening and the cold expansion of holes are two techniques for imparting beneficial compressive stresses. Stresses can be directly measured with x-ray diffraction (XRD), while the corresponding elastic and plastic strains are characterized with XRD peak shifts and widths. This paper presents elastic and plastic strain data, residual compressive stress state, and the resulting fatigue performance of aerospace materials shot peened over a range of common peening intensities. With few exceptions, the data correlated well in that higher intensities provided greater residual compressive stresses and strains. However, the greatest fatigue performance was observed on the lower end of the peening intensity range.

Scott M. Grendahl, Daniel J. Snoha, Beth S. Matlock

Monitoring Crack Tip Plastic Zone Size During Fatigue Loading

Digital image correlation has been used to obtained detailed strain maps around a propagating fatigue crack. The size of the plastic zone has been estimated from the maps and compared with the value calculated using Dugdale’s and Irwin’s models for crack tip yielding and from measurements made using thermoelastic stress analysis.

Ying Du, Amol Patki, Eann Patterson

Studying Thermomechanical Fatigue of Hastelloy X using Digital Image Correlation

Hastelloy X, a nickel based superalloy, has been extensively used in the past for high temperature applications. However, less is known about its thermomechanical fatigue response compared to other structural metals. Generally, the relation between microscale and macroscale is vital in order to identify specific phenomena that contribute to the cracked component fatigue lifetime. In this work, Hastelloy X notched samples were used to investigate fatigue crack nucleation near the notch and subsequent fatigue crack growth. Isothermal experiments at varying temperatures (up to 1,000°C) were performed while the specimen was fatigue loaded to advance the crack. Macroscale Digital Image Correlation (DIC) was performed on images taken at various stages of crack growth. In addition, using images obtained directly behind the crack tip, microscale DIC was used to quantify the effects of crack closure. The interaction of crack closure and far-field loading was investigated as a function of temperature. The combination of full-field macroscale and near-tip microscale measurements will aid in the development and understanding of a multiscale fatigue crack growth model.

Mallory Casperson, Jay Carroll, Wael Abuzaid, John Lambros, Huseyin Sehitoglu, Mike Spottswood, Ravinder Chona

Understanding Mechanisms of Cyclic Plastic Strain Accumulation under High Temperature Loading Conditions

In-depth analysis of deformation mechanisms, such as slip deformation and slip/twin interaction, on the micro-level can greatly enhance the understanding of the physics behind thermomechanical fatigue damage accumulation in ductile metals. This improved understanding is essential for the development of new fatigue models that are not phenomenological, and have better predictive capability than the current ones. Hastelloy X, a nickel based superalloy has been experimentally studied using multiscale experimentation under different cyclic plasticity and thermomechanical fatigue loading conditions. High resolution

ex-situ

Digital Image Correlation (DIC) was used to measure plastic strain accumulation as a function of load and temperature. By performing DIC experiments with sub-grain resolution we can relate the measured strain fields to the underlying microstructure through comparison with EBSD scans of the same region of interest. The results reveal a highly heterogeneous material response at the grain level and even at the sub-grain level with high strain concentrations at regions such as twin boundaries and triple points, and with strain variations even within particular grains. By making such measurements at regular intervals of load, the evolution of plastic strain during loading was observed. As loading increased heterogeneity also increased (i.e. regions with high strain became more strained and regions with low strain remained relatively unstrained).

Wael Abuzaid, Huseyin Sehitoglu, John Lambros, Jay Carroll, Mallory Casperson, Ravinder Chona

Simulated Corrosion-Fatigue via Ocean Waves on 2024-Aluminum

The combined effect of corrosion and fatigue loading can be extremely detrimental to the service life of structures in and around bodies of salt water. 2000-series aluminum alloys are of special concern due to their tendency for pitting, which can lead to widespread crack initiation sites with relatively little loss in mass. In the current work, we present results from a series of experiments on 2024-T351 aluminum simulating the corrosive environment and wave loading of a structure in the North Sea. Details are presented about the method for constructing the simulated wave loading as well as the incorporation of periodic overloads. The effects of loading rate and grain orientation of the material on fatigue life are explored.

E. Okoro, M. N. Cavalli

The Effect of Processing Conditions on the Properties of Thermoplastic Composites

Ultra high molecular weight polyethylene (UHMWPE) composites are produced from SpectraShield 3124 to evaluate the influence of the magnitude of the temperature and the pressure used to consolidate the composite on selected mechanical and physical properties. In this study, properties of composites processed using higher and lower temperatures and pressures than is the industry standard are examined. Differential scanning calorimetry (DSC) is used to examine differences in crystallinity, and dynamic mechanical analysis (DMA) is used to examine creep compliance response of the different materials. Tensile properties of the composites are also evaluated. Results indicate that higher processing pressure may result in more favorable tensile properties, but that the impact of processing temperature is relatively small.

Frederick P. Cook, Scott W. Case

Calculation of Shells and Plates Constructed from Composite Materials

In the article is considered the analysis problem of having irregularity plates when the plate consists from the various strength separate elements which are connected with each other by ideal hinges. The simultaneous equations are solved by developed by Sh. Mikeladze for discontinuous functions generalized Maclaurin series which automatically considers in points of interfaces the values of functions and jumps of their derivatives.

R. Tskvedadze, G. Kipiani, D. Tabatadze

Reducing Build Variation in Arched Guitar Plates

The objective of volume production is to produce identical products with little to no build variation in their parts. However, in instrument manufacture, this can be a challenging task due to the natural variation in wood properties. The purpose of this paper is to illustrate an approach to reduce build variation in the production of arched plates for acoustic guitars by using CAD/CAM software and the CNC machine. To accurately machine the arched plates, a family of curves called curtate cycloids was used during the design phase. The paper will also discuss the effort to reduce build variation during the manufacturing process by placing the arched plates under load while being machined. A series of arched back plates has been produced using this approach, and the build variation, as measured by resonant frequency, is notably reduced.

Eddy Efendy, Mark French

Rotation Angle Measurement Using an Electro-Optic Heterodyne Interferometer

An electro-optic heterodyne interferometer based on phase-locked extraction for measuring low optical rotation angle is successfully developed. The validity of the proposed design is demonstrated by a half-wave plate with the average relative error of 0.74%. When applied to the measurement of glucose solutions with concentrations ranging from 0 to 1.2 g/dl, the average relative error in the measured rotation angle of glucose solutions is determined to be 1.46%. The correlation coefficient between the measured rotation angle and the glucose concentration is determined to be 0.999991, while the standard deviation is just 0.00051 degrees. Overall, the current proposed system is capable of measuring glucose concentration as low as 0.01 g/dl with an error of 6.67%.

Jing-Fung Lin, Chun-Jen Weng, Kuo-Long Lee, Yu-Lung Lo

Digital Shadow Moiré Measurement of Out-of-Plane Hygrothermal Displacement of TFT-LCD Backlight Modules

As the light source device of the thin film transistor-liquid crystal display (TFT-LCD), backlight modules (BLM) suffers not only the heat produced by itself own but also the possible high temperature and/or high humidity of the operating environment. In this paper, based on the specially designated hygrothermal reliability test conditions, the digital shadow moire method was applied to inspect out-of-plane displacement fields of BLMs installed in 4.3” TFT-LCDs which are commonly employed in smart phones and navigators. Three hygrothermal reliability test conditions were selected in this paper, i.e. (1) high temperature storage; (2) high temperature operation; (3) high temperature and high humidity. In addition, test specimens of three different tolerances in the normal direction inside the BLMs were prepared to investigate the tolerance effects on the out-of-plane displacement. The current inspection procedures adopted in the TFT-LCD industry is to remove BLM periodically from the oven to measure the variation of the illumination of the BLM after experiencing the hygrothermal effects. With the whole-field and real-time inspection features, the digital shadow moire inspection system developed in this paper can be employed to replace the current inspection procedures adopted by the TFT-LCD manufacturers. The experimental results showed that the out-of-plane displacement of the BLM under the high temperature and high humidity condition is the largest one among three conditions.

Wei-Chung Wang, Ya-Hsin Chang

Theory and Applications of Universal Phase-shifting algorithm

Phase shifting technique provides a fully automatic analysis for fringe pattern or interferogram processing. In practice, due to the imperfections of phase shifter, optical elements, experimental setup and other various reasons, typical phase-shifted interferograms generally contain nonlinear phase shifting errors, variations and fluctuations of background intensities and modulation amplitudes, optical nonlinearities between intensities and phases, and so on. These errors in practice severely violate the assumptions in the principles of the existing phase shifting algorithms. To cope with these problems in applications, this paper presents a simple, rigorous, precise yet unveiled universal phase-shifting algorithm for retrieving desired phase distributions with ultrahigh accuracies from actual interferograms. The algorithm is based on a least-squares approach and a generic governing equation for the description of practical interferograms. Computer simulation shows a perfect performance of the universal algorithm, and applications to selected experiments demonstrate its validity and practicability.

Thang Hoang, Zhaoyang Wang, Dung Nguyen

Evaluation of Crash Energy Absorption Capacity of a Tearing Tube

This paper deals with the numerical prediction of energy absorption capacity of a tearing tube, which can absorb the crash energy through expanding and axial splitting processes. It is important to consider the dynamic material behavior and fracture characteristics of tube material in order to simulate the deformation behavior of a tearing tube accurately. Uniaxial tensile tests are performed in order to obtain the flow stress curve and the fracture strain of a tube material according to the strain rate. Quasi-static tensile tests were carried out in the range of strain rates from 0.001/sec to 0.01/sec using a static tensile testing machine. Dynamic tensile tests were conducted at strain rates ranged from 0.1/sec to 300/sec using a high speed material testing machine. These dynamic material properties are utilized to finite element analysis through a user material subroutine of ABAQUS/Explicit. Especially, ductile fracture criteria are adopted in order to describe the fracture characteristics of a tube material during axial splitting process. Dynamic tearing cases are simulated and the reliability of numerical results is verified by comparing them with the experimental results in dynamic tearing tests. The simulated results accurately predict the onset of fracture in axial splitting process and the energy absorption capacity has a good agreement with experimental results.

Younki Ko, Kwanghyun Ahn, Hoon Huh, Wonmok Choi, Hyunseung Jung, Taesoo Kwon

Fracture Studies Combining Photoelasticity and Coherent Gradient Sensing for Stress Determination

An experimental study of in-plane tensorial stress determination from full-field phase-shifting photoelasticity and transmission Coherent Gradient Sensing (CGS) for stress intensity factor estimation is presented. Phase-shifting photoelasticity determines principal stress directions and the difference of principal stresses, while transmission CGS measures the x and y first derivatives of the sum of principal stresses. Combining these two methods for the same field of view allows for principal stress separation and, using the principal stress directions, the full in-plane stress tensor. The present study, which is the first experimental study for full-field tensorial stress determination around sharp cracks in a photoelastic material, applies this hybrid method for millimeter-scale fields of view including Mode I-dominant cracks in Homalite-100, a linear elastic brittle bulk polymer. The cases presented here range in Mode I stress intensity factor from about one-quarter of the fracture toughness to just below the fracture toughness. This experimental method can detect and determine mode-mixity ratios as small as 0:0043 with a range of –0:010 to 0:020. The experimental stress fields have excellent global agreement with the full-field 2D asymptotic crack solution using the experimentally calculated Mode I and Mode II stress intensity factors.

Sharlotte Kramer

Strength and Fracture Behavior of Diffusion Bonded Joints

Current high temperature alloy systems for turbines and powerplant heat exchangers are typically titanium-, nickel- or iron-based. The extreme performance environments in these applications demand exacting control of both alloy composition and microstructure. This can be problematic when fabrication or repair requires the joining of multiple parts. Traditional welding processes destroy the desirable microstructure in the region of the weld and may lead to the formation of undesirable phases. Diffusion bonding has been gaining increasing interest in this area as a means of both preserving the joint microstructure and controlling second phase formation. The current paper presents the results of initial experimental studies on diffusion bonding of commercially pure titanium, iron and nickel samples.

A. H. M. E. Rahman, M. N. Cavalli

Fabrication and Characterization of Novel Graded Bone Implant Material

A solid structure and porous core graded porosity materials were fabricated and characterized for potential bone replacements. Stainless steel is considered as a model material for generating graded porosity structure in this study. Powder metallurgy concepts were employed to generate constant porosity metallic implant materials and later they were sintered using a high temperature furnace with inert gas environment. Sintered materials were densified on the surface using a novel indentation tool. To verify the feasibility of our methodology, pure iron powder was used in preliminary studies. Preliminary results obtained using scanning electron microscopy images and image analysis of MATLAB indicated that the densification process generated gradation of porosity from the surface. The gradation of porosity is continuous and the gradient is high for higher densification depths. Preliminary results also indicated that hardness values changed gradually from the surface to certain depth. To control the process parameters of densification process in the fabrication, a numerical model is developed using a flow rule associated with porous materials. Micro-indentation tests will be conducted to study variation mechanical properties along the porosity gradation. Both quasi-static flexure and fracture experiments will also be conducted to understand the effect of gradation on fracture toughness and flexure strength.

S. Bender, S. D. El Wakil, V. B. Chalivendra, N. Rahbar, S. Bhowmick

A Dynamic Design Model for Teaching

There is a need to include inverse design problems of vibration engineering into undergraduate and postgraduate education of mechanical and structural engineers. It has not been hitherto possible due to lack of economical dynamic testing equipment and absence of several of dynamic design technologies. With the emergence of laboratory compatible modal testing equipment and the emergence of technologies like those of finite element model updating, structural dynamic modification, operational modal analysis and laser vibrometery it is now feasible to include dynamic design procedures into curriculum. The present paper proposes a dynamic design model based on three decades of research in the area. The paper discusses several cases of application to vibration engineering design employing the above mentioned emerging technologies. It then proposes a vibration design model which is well integrated with satisfaction of other design requirements and constraints of machines/ structures based on yield strength, fatigue strength, surface fatigue strength and other modes of failure. The concept of concurrent mechanical/ structural design to include dynamic soundness of the equipment/ structure is also discussed.

T. K. Kundra

Video Demonstrations to Enhance Learning of Mechanics of Materials Inside and Outside the Classroom

Using video to present demonstrations holds a significant number of advantages, particularly when class size or demonstration complexity prevents students from having hands on access. In video format delivered via the web, students have the capability to pause and repeat videos. Used in a classroom setting, the video provides the instructor more ease in set up and ensures high quality viewing in a large lecture hall forum. We have created videos of mechanics of materials demonstrations from a collection used in both introductory and advanced mechanics of materials courses. A wide range of topics are represented in the video collection, but three topics in particular (thermal effects, transverse shear in bending, combined loading) have been identified for use teaching where an assessment of learning outcomes can be measured.

Michael Dietzler, Wendy C. Crone

Experimentation and Product-making Workshop Simplified for Easy Execution in Classroom

In this study, we introduced the students to experimenting with and manufacturing of real products. The products are a "Model Car" and a "Walking Model.” With this specific objective and using no special equipment, students can learn and utilize mechanics which is one of the fundamental discipline in engineering. We introduced these two products in a lecture format and evaluated the effectiveness of the learning process. Results of the evaluation administered before and after the class showed that the students obtained a greater understanding of mechanics by using the two products. A resulting concept map and survey questionnaire showed that the students had improved their ability to apply scientific knowledge through their practical experiences in experimental and manufacturing processes. Moreover, detailed analyses including factor analysis suggest an improvement in the students’ confidence in their scientific knowledge and activities in product making.

Tsuyoshi Nakazawa, Masaaki Matsubara, Sumiyoshi Mita, Katuo Saitou

Illustrating Essentials of Experimental Stress Analysis Using a U-Shaped Beam

A graduate-level homework assignment and follow-on laboratory experiment involving a flat

U

-shaped specimen is described. The base of the

U

can be considered a curved beam. The specimen is loaded such that a known bending moment

M

and shear force

V

are applied to the curved beam. Closed-form elasticity solutions exist for these two loading conditions. The homework assignment is to superimpose these two solutions and plot the inplane principal stresses and orientation angle of the principal stress coordinate system along a specified radial line within the curved section. During the follow-on lab experiment an aluminum

U

-shaped beam is instrumented with several 3-element strain gage rosettes along the specified radial line. The rosettes are used to measure principal strains and orientation of the principal strain coordinate system. The corresponding principal stresses are then calculated using the plane stress form of Hooke’s law and compared with theory. Together the homework assignment and lab experiment illustrate many essential elements of the experimental stress analysis process.

Mark E. Tuttle

Demonstration of Rod-Wave Velocity in a Lecture Class

There was a discussion of Wave Propagation in Solids in a Graduate Class of Structural Engineering. Propagation of Longitudinal Wave (Rod-wave) was demonstrated by the author using a piece of Chalk and Wooden Duster.

Dulal Goldar

Influence of Friction-Stir-Welding Parameters on Texture and Tensile Behavior

A series of friction stir welding (FSW) was conducted on AZ31B Mg alloy plate by varying its key parameters, i.e., rotation speed and travel rate of the weld tool, to investigate the influence of thermo-mechanical input during welding process on the resulting texture and tensile behavior. Neutron diffraction texture measurements show that, with the systematic changes in the thermo-mechanical input during welding, there are corresponding changes in crystallographic texture that correlates well with the expected changes in deformation and recrystallization mechanisms. Furthermore, tensile behavior along the longitudinal direction was examined as a function of FSW parameters, and the results show dramatic changes in the strength and ductility in a way that is consistent with the changes in texture.

Zhenzhen Yu, Hahn Choo, Wei Zhang, Zhili Feng, Sven Vogel

Comparing Two Different Approaches to the Identification of the Plastic Parameters of Metals in Post-necking Regime

In the past 20 years the growing computation power availability encouraged experimental mechanics specialists to couple full field measurements with FE methods to raise the so called hybrid experimental-numerical methods. A typical example is the identification of the plastic parameters of metals starting from experimental data.

In this work a comparison of two different inverse approaches is presented. A global method, called Kali, identifies the parameters of a plastic law (e.g. Ramberg-Osgood, Hollomon,...) fitting the global experimental data (load, clip-gauge) with FE results obtained using the trial parameters. Instead a full field method, called PlastFemDIC, prescribes DIC measured displacement data of the specimen surface as well as the global ones.

To judge the best approach, the silhouette of a round axial-symmetric specimen is compared at various load levels with the FEM results obtained with the parameters identified by the global and local approaches.

Antonio Baldi, Andrea Medda, Filippo Bertolino

Determination of hardening behaviour and contact friction of sheet metal in a multi-layered upsetting test

This paper describes the identification of hardening parameters of DC05 sheet metal and contact friction coefficients using a multi-layered upsetting test (MLUT), the modified two specimen method (MTSM) and a finite element based inverse method. The MLUT is an alternative compression test that is based on the stacking of small circular specimens on top of one another. This test was designed in order to identify frictional and material behavior under severe local forging of sheet metal as encountered during a clinching operation. The MTSM is adopted in order to identify the friction coefficient between the tools and the stacked circular specimens which are cut from the base material by spark erosion. Next, the hardening behavior is identified inversely by combining the results of a MLUT and finite element simulations of the test setup. Finally, the results are compared with standard tensile tests and it is shown that the MLUT is a viable alternative for the identification of the local hardening behavior of sheet metal where standard test specimens cannot be prepared due to size limitations of the specimen.

S. Coppieters, P. Lava, H. Sol, P. Van Houtte, D. Debruyne

Measuring the Elastic Modulus of Soft Thin Films on Substrates

The use of instrumented indentation to measure the mechanical properties of thin films supported on substrates where the Young's modulus of the film (E1) is substantially less than that of the Young's modulus of the substrate (E2) with modulus ratios from E1/E2 = 0.0001 to 1 is important for investigating materials such as soft polymers, cellulosic sheets, and biological materials. Most existing models for determining the elastic properties of films or sheets on substrates from indentation measurements were developed for the analysis of metal and dielectric films on semiconductor substrates and thus have been used in cases where E1/E2 is ~0.01 to ~10. In the present work, flat punch indentation of systems with E1/E2 = 0.0001 to 1 is investigated via finite element (FE) modeling and experiments. A FE parametric study in which E1/E2 was varied from 0.0001 to 1 was performed to quantify the effect of substrate stiffness on the measurement of the elastic film properties. A semi-analytical model that treats the thin film and substrate as two springs in series was fit to the FE results to allow for use of the results presented. Preliminary experiments, in which a series of film/substrate systems with various modulus mismatch (E1/E2 from ~0.0005 to ~1) were characterized using instrumented indentation, were performed to evaluate the effectiveness of the model for extracting films properties from indentation measurements. The results of the parametric FE study show that for very stiff substrates, the measured stiffness becomes insensitive to changes in substrate modulus. The analytical model and FE model agree to within 7% for E1/E2 values between 0.0001 to 1 and a/t ratios from 1 to 100. Comparison of the preliminary experimental results and FE model show reasonable agreement, but further investigation is required to obtain better correlation.

M. J. Wald, J. M. Considine, K. T. Turner

Characterization in Birefringence / Diattenuation of an Optical Fiber in a Fiber-Type Polarimetry

An analytical technique based on the Mueller matrix method and the Stokes parameters is proposed for extracting five effective parameters on the principal axis angle, phase retardance, diattenuation axis angle, diattenuation and optical rotation angle of anisotropic optical materials. The linear birefringence (LB) / circular birefringence (CB) properties and linear diattenuation (LD) properties are decoupled within the analytical model. The analytical method is then integrated with a genetic algorithm to extract the optical properties of samples with linear birefringence property using a fiber-based polarimeter. The result demonstrates the feasibility of analytical model in characterizing five effective parameters of anisotropic optical material. Also, it confirms that the proposed fiber-based polarimeter provides a simple alternative to existing fiber-based probes for parameter measurement in the near field or the remote environment. A low birefringence fiber-based polarimeter based on effective parameters and genetic algorithm without using a fiber polarization controller is first proposed confirmatively.

Thi-Thu-Hien Pham, Po-Chun Chen, Yu-Lung Lo

Predictive Fault Detection for Missile Defense Mission Equipment and Structures

Equipment failures in defense systems result in loss or reduction of operational capability, impacting system readiness. Faults in critical equipment can impact system performance and reliability, as can structural failures. Predictive fault detection (PFD) provides prognostic capability to identify components and internal structures that exhibit either degradation or increased variability of parameters, in advance of actual faults occurrences. It has the power to reduce facility down times significantly, enhancing system availability and reducing maintenance costs. PFD enables maintainers to take corrective action before actual failures occur, thus improving system availability and reducing maintenance costs for the covered facility. The authors have applied an integrated approach to PFD, including multiple-phenomenology sensing and data acquisition; generalized multivariate statistical treatment of waveform shapes, continuous variable values, and discrete event occurrences; and maintenance decision-making techniques that balance performance and cost factors. An engineering prototype PFD product has been developed and tested under an MDA-sponsored Small Business Innovative Research project sponsored by the Missile Defense Agency.

Jeffrey S. Yalowitz, Roger K. Youree, Aaron Corder, Teng K. Ooi

Portable Maintenance Support Tool Enhancing Battle Readiness of MDA Structures and Vehicles

Handheld Portable Maintenance Support Tool (PMST) incorporates microcontroller unit providing a wireless interface between a sensor node network, consisting of Analatom micro-LPR corrosion sensors combined with off-the-shelf sensors, and portable computer databases for high value asset monitoring and matériel management. PMST will be able to provide the user real-time capability to evaluate health status and operability of future MDA hardware including structures and vehicles such as Launch Platform, and Future Interceptor. This assessment capability provides early warning of structural and component deterioration or failure traditionally encountered during time of use. PMST system results in reduced maintenance, maintenance costs, downtime, and vulnerability of MDA’s stockpile, while increasing inventory condition-awareness and battle readiness. Clear benefits are improvements in safety and security while expanding field readiness and operational capacity. Future extensions to PMST system will provide new prognostics, readiness predictions, matériel inventory management, and mobilization capabilities.

Trevor Niblock, John O’Day, Duane Darr, Bernard C. Laskowski, Harsh Baid, Ajit Mal, Teng K. Ooi, Aaron Corder

A Compact System for Measurement of Absorbance of Light

In this work a compact device to measure absorbance based on light emitting diodes – LED - is proposed. Measurand is the concentration of specific chemical or biochemical components within the test fluid. The advantage of such a system lies in the use of low-cost standard optic-mechanical and electronic components that contribute to its compactness and robustness.

The proposed system measures absorbance (or transmittance) of monochromatic light inside a standardized cuvette of 10 mm light path within a temperature ranging from 25 to 40ºC (±0,2ºC). Some important features, such as stability, accuracy and precision of the measurement system are discussed. It is shown that the measurement stability is governed by the stability of the light source. An acceptable value is 0,002 units of absorbance per hour, which can be verified by measuring a dummy cuvette during a suitable long period. The accuracy and precision are estimated by means of traceable calibration standards throughout the desired spectrum of wavelengths. The wavelengths required for the target application of the proposed system are 340, 405, 505, 546, 600 and 700nm. Basic variables of influence are identified and a brief metrological analysis is presented in form of an uncertainty balance. First results obtained with the proposed system demonstrate uncertainties below 1,6 % relative to the measured value of absorbance.

Adriano Jotadiemel Masi, Meinhard Sesselmann, Denilson Laudares Rodrigues

Fracture Mechanics Analysis in Frost Breakage of Reservoir Revetment on cold regions

Reservoir revetment on cold regions are often frost damaged resulting from the joint action of low-temperature and cryogenic environment in winter, and then reservoir revetments are often broken to decline the usage function, even to lose the function completely. In this paper, practical problems in engineering were analyzed for the drainage pumping station of Tuanjie Reservoir. Based on traditional method in analysis and calculation, fracture mechanics was brought to make quantitative analysis and calculation on the problems of anti-freeze damage from the viewpoint of fracture mechanics. So as to put forward a new idea to resolve anti-freezing of reservoir slope protection on cold regions, doing meaningful exploration.

Liu Xiaozhou, Liu Peng

Combined Experimental/Numerical Assessment of Compression After Impact of Sandwich Composite Structures

An integrated experimental and computational study of residual compressive strength of composite laminate sandwich structures after low velocity impact (CAI strength) is performed using samples consisting of 8 ply graphite/epoxy face sheets bonded to aluminum honeycomb core. The study encompasses characterizing the indentation damage (dent depth and laminate fractures), measuring the CAI strength for a range of layups and core densities and computational modelling of indentation and CAI strength.

Michael W. Czabaj, Alan T. Zehnder, Barry D. Davidson, Abhendra K. Singh, David p. Eisenberg

Mechanical Behavior of Co-Continuous Polymer Composites

Natural and synthetic composite materials consisting of two or more different materials are a major avenue for achieving materials with enhanced properties and combination of properties. The combination of hard and soft materials enables outstanding combination of mechanical performance properties including stiffness, strength, impact resistance, toughness, and energy dissipation. In this work, we demonstrate the potential to achieve materials with enhancements in stiffness, strength and energy dissipation. We consider co-continuous structures with simple cubic (SC), body-centeredcubic (BCC), and face-centered cubic (FCC) lattices, which are generated by 3D printing technology. The linear and nonlinear mechanical behavior of these composites including their elastic stiffness, yield, post-yield, and dissipative behaviors are investigated by compression tests. The experimental results are compared with finite element based micromechanical modeling of large elasticviscoplastic deformation. We show that these 3D periodic cocontinuous composites can provide enhanced improvement in combinations of mechanical performance achieving a unique combination of stiffness, strength and energy absorption. These results provide guidelines for engineering and tailoring the nonlinear mechanical behavior and energy absorption of the composites for a wide range of applications.

Lifeng Wang, Jacky Lau, Nicholas V Soane, Matthew J. Rosario, Mary C. Boyce

Laboratory Evaluation of a Silicone Foam Sealant for Field Application on Bridge Expansion Joints

A silicone foam sealant was developed to provide an alternative small-bridge joint sealant that was effective, easy-to-use, and economical. In the previous study various laboratory tests including tension, bonding, compression, shear, stress relaxation, and other were conducted to determine the engineering characteristics of the sealant. All these tests were limited to the concrete as the substrate to which the sealant was bonded to. In the present study, laboratory tests on the sealant were conducted using other substrates found in practice, including steel, asphalt and polymeric concrete. Some of the tests conducted included tension (pull to failure) test, oven-aged bonding test, salt water immersion test, and a performance-during-curing test that evaluated the strength and strain of the sealant.. Through the laboratory tests, it has been observed that the silicone foam can exhibits good bonding to various substrate materials and can easily accommodate small movement bridge expansion joints. In addition to these tests in small specimen, a procedure to produce larger quantity of sealant and apply it to an actual bridge expansion joint was developed using a simulated joint built in the laboratory. Through the development of this procedure and the eventual application of the sealant into various bridge expansion joints, it can be determined that the silicone foam presents an alternative sealant that is east-to-use and allows for quick installation.

Ramesh B. Malla, Brian J. Swanson, Montgomery T. Shaw

Effect of Prior Cold Work on the Mechanical Properties of Weldments

Heat exchanger units used in steam raising power plant are often manufactured using many metres of austenitic stainless steel tubes that have been plastically formed (bent and swaged) and welded into complex shapes. The amount of plastic deformation (pre-straining) before welding varies greatly. This has a significant effect on the mechanical properties of the welded tubes and on the final residual stress state after welding. The aim of the present work was to measure and understand the combined effects of pre-straining and welding on the properties and residual stress levels in stainless steel tubing weldments. Effects of plastic deformation were simulated by plastically straining three identical stainless steel tubes to different strain levels (0%, 10% and 20#x0025;). Then each tube was cut into two halves and welding back together. The variation in mechanical properties across weldments was measured using digital image correlation (DIC) and a series of strain gauges (SG). Residual stresses were measured on the 0% (undeformed) and 20% prestrained and welded tubes by neutron diffraction. It was found that the welding process had a marked effect on the tensile properties of parent material within 25mm of the weld centre-line. Evidence of cyclic strain hardening was observed in the tube that had not been pre-strained, and evidence of softening seen in the 10% and 20% pre-strained tubes. Macroscopic residual stresses were measured to be near zero at distances greater than 25 mm from the weld centre-line, but measurements in the 20% pre-strained tube revealed the presence of micro residual stresses having a magnitude of up to 50 MPa.

M. Acar, S. Gungor, P. J. Bouchard, M. E. Fitzpatrick

Use of Viscoplastic Models for Prediction of Deformation of Polymer Parts

Polymers are extensively used in engineering applications, ranging from sealing rings to dampers and springs in centrifugal separators as well as in micro robots with piezoelectric excitation. The mechanical behaviour of these materials is highly non-linear and may be described by integral equations, taking into account the load history of the part considered. Paper shows taht long-term deformation in creep and relaxation can be derived from tensile tests at several loading rates. The influence of cyclic loading is discussed. Tests show that material can fail in fatigue.

Nils G. Ohlson

Mechanical Characterization of SLM Specimens with Speckle Interferometry and Numerical Optimization

This paper describes the process of mechanical characterization of specimens built via Selective Laser Melting (SLM). An hybrid approach based on the combination of phase-shifting electronic speckle pattern interferometry (PS-ESPI) and finite element analysis is utilized. Three-point-bending experimental tests are carried out. The difference between displacement values measured with ESPI and their counterpart predicted by FEM analysis is minimized in order to find the values of the unknown elastic constants.

C. Barile, C. Casavola, G. Pappalettera, C. Pappalettere

Torsion/compression Testing of Grey Cast Iron for a Plasticity Model

To characterize the yield surface, combined torsion/compression experiments were conducted to help develop a plasticity model for grey cast iron. Loadings were sequential, allowing for better exploration of yield under different conditions. Hollow cylindrical specimens were machined and strain measurements were taken with multiple strain gages and verified with a digital image correlation system. With the use of effective and von Mises stresses and strains, test results produced intermediate data points for a plasticity model, such as the Johnson-Cook model. The data is shown to follow the predicted relationship qualitatively.

Timothy A. Doughty, Willamette Blvd, Mary LeBlanc, Lee Glascoe, Joel Benier

Nucleation and Propagation of Portevin-Le Châtelier Bands in Austenitic Steel with Twinning Induced Plasticity

Twinning induced plasticity (TWIP) steels have high manganese content and exhibit extreme strain hardening and elongation. Tensile flow curves show serrations due to dynamic strain aging associated with solute-dislocation interactions. Highly inhomogeneous plastic flow is manifested by Portevin-Le Chatelier (PLC) band nucleation and propagation. In this research, TWIP steel tensile specimens were quasi-statically deformed to fracture at room temperature. Images of one specimen surface were recorded with a variable framing rate high speed digital camera and custom image acquisition software. A digital image correlation technique was used to compute incremental strain rate maps that enabled study of PLC band nucleation and propagation. The impact of tensile specimen geometry on the location of band nucleation along the specimen gauge section was also explored. Fracture surfaces and material chemistry were examined with SEM and energy dispersive mapping.

Louis G. Hector, Pablo D. Zavattieri

Identification and Enhancement of On-stage Acoustics in a Multipurpose Auditorium

The objective of this research is to identify the measurable sound quality parameters of an existing multipurpose auditorium in which the acoustics are not adequate for orchestral purposes. The major problems have been identified as the lack of sufficient projection of sound from the stage area, the inability of the musicians to hear themselves and each other, and the poor reverberation time of the auditorium. The final goal of this study is to implement a solution which will produce a measurable and audible improvement of the on-stage acoustics for the musicians by implementing an acoustic shell which will surround the orchestra, thereby increasing the early reflections on-stage. During this study, one of the objective parameters used is 'Support', which depends on the amount of early and late reflections relative to the direct sound. The studied objective parameters have been used to assess the effectiveness of the acoustic shell by conducting acoustic measurements following the guidelines specified by ISO 3382-1:2009 for performance spaces. In the final paper, an objective analysis of these parameters will be presented with and without the shell in place, in order to verify the overall enhancement for the musicians provided by the acoustic shell.

C. Braden, B. Hayes, R. Averbach, V. Ranatunga

Determination of Objective Architectural Acoustic Quality of a Multi-Purpose Auditorium

Significant differences in listening qualities have been reported by the audience attending wide variety of functions ranging from orchestral music to stage drama and public announcements at the multipurpose auditorium of the Miami University Hamilton campus. Preliminary investigations have been conducted to examine the difference in sound qualities utilizing impulse responses at various seating sections throughout the auditorium, based on the measurement procedures set forth by ISO 3382-1:2009 for performance spaces. Detailed comparisons of measured acoustic quality parameters have been made against the available data in literature for statistically determined optimal acoustic conditions. Each measured range of parameter values has been analyzed to determine the distribution characteristics over a pre-determined set of locations on the audience seating area. In the final paper, a detailed study of the acoustical parameters, including the enhancements proposed as a result of this investigation are presented.

B. Hayes, C. Braden, R. Averbach, V. Ranatunga

Notch-interface experiments to determine the crack initiation loads

The theory of fracture mechanics has been extensively developed for cracks (Williams, 1952; Hutchinson and Suo, 1992). However, notches are found a lot more than cracks in real life. Indeed, a crack is only a special case of a notch (notch angle being 0o for a crack). Recent experiments on composite laminates have indicated that impact-induced delamination will propagate under compressive loading (Krishnan and Xu, 2010,

Submitted to 2010 SEM Annual Conference

). This delamination front is a notch and not a mathematically sharp crack. Therefore, developing a generalized notch-interface failure criterion is very important for the field of fracture mechanics from a fundamental standpoint.

Arun Krishnan

Mechanical Characterization of Alternating Magnetic Field Responsive Hydrogels at Micro-scale

Magnetically responsive hydrogels has become an interesting subject of study as they offer several potential advantages over other material systems for the controlled release of drugs, local heating of the tumors leaving all other regions unaffected and the temperature control within as well as outside the target region due to their response to the magnetic stimuli [1]. Magnetite provides the most attractive magnetic material of common use due to its strong magnetic property and low toxicity [2]. The integration of magnetic nano-particles in hydrogel therefore provide a new generation of material system for many potential applications, like magnetic pump, mimmicking muscular movements, soft robotic actuators and magneto-optical sensors or to develop magnetic force based immunoassay [3]. Hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) is a well known thermoresponsive polymer that undergoes a volume phase transition across the lower critical solution temperature (LCST, 32-33). Therefore, the inherent temperature-sensitive swelling/shrinkage properties of PNIPAM offer the potential to control gel performance with an alternating electromagnetic field.

Shannon Meyer, Luke Nickelson, Rakim Shelby, Jon McGuirt, Jian Peng, Santaneel Ghosh

Investigation of a force hardening spring system

This paper reports on the jump phenomenon as seen in a geometrically nonlinear mass spring system. Analysis and simplification of the governing differential equation results in two coupled equations, which were solved in MATLAB using various values for mass of the oscillator (M), effective spring stiffness (K), mass of the flywheel (m), radius of gyration of the flywheel (r), and damping (C) of the system. Depending on values of the parameters used, various theoretical system responses were seen for the cart amplitude as a function of driving frequency. Based on the output of the MATLAB program, components were chosen to implement into a mass spring system that would physically illustrate the jump phenomenon. The result is a nonlinear spring system that was able to show the jump down effect, but not the jump up.

E. Jones, D. Prisco

Resonance Behavior of Magnetostrictive Sensor in Biological Agent Detection

The growing threat of biowarfare agents and bioterrorism has led to the development of specific field tools that perform rapid analysis and identification of encountered suspect materials. One such technology, recently developed is a micro scale acoustic sensor that uses experimental modal analysis. Ferromagnetic materials with the property to change their physical dimensions in response to changing its magnetization can be built into such sensors and actuators. One such sensor is fashioned from Metglas 2826MB, a Magnetostrictive strip actuated in their longitudinal vibration mode when subjected to external magnetic field. Due to mass addition, these magnetostrictive strips are driven to resonance with a modulated magnetic field resulting in frequency shifts. In Vibration Mechanics the frequency shift for a certain amount of mass will have a tolerance limit based on their distribution and discrete position over the sensor platform. In addition, lateral positioning of same amount of mass does not influence the resonant frequency shift of the sensor. This work concentrates on developing a model correlating theoretical, experimental and numerical simulations to determine the mass of

E. Coli O157:H7

cells attached to the sensor platform.

M. Ramasamy, B. C. Prorok

Detection of Damage Initiation and Growth of Carbon Nanotube Reinforced Epoxy Composites

The effect of nano-deformation, damage and growth of carbon nanotubes (CNT's) reinforced polymer composites is investigated using electro-mechanical response at different loading conditions. Three different polymer systems namely epoxy, epoxy reinforced with gas bubbles (that induces porosity) and epoxy reinforced with Aluminum Silicate hollow microspheres (Cenospheres) are used in this study. CNT's of different weight percentages are loaded into above three polymer systems and a combination of shear mixing and ultrasonication processes are used to fabricate composites. A four-point probe method is used to measure high resolution electrical response when the above polymer systems are subjected to mechanical loads. The effect of various types of mechanical loading on different stages of deformation of test samples, onset of damage and growth as a function of either glass bubbles or cenospheres in epoxy are discussed using high-resolution electro-mechanical response of polymer systems.

V. K. Vadlamani

Nano-mechanical Characterization of Polypropylene Fibers Exposed to Ultraviolet and Thermal Degradation

Nano-indentation studies using atomic force microscopy (AFM) was conducted to investigate the effect of accelerated ultra violet (UV) and thermal degradation on mechanical properties of Polypropylene textile fibers. The Polypropylene fibers with initial stabilizers were exposed to UV degradation using Q-UV Panel Weatherometer. The effect of degradation on gradation of Young’s modulus values across fiber cross-section was investigated by doing progressive nano-indentation from the surface to the center of the fiber. It was identified that UV degradation initially increases the Young’s modulus values from center to surface of the fibers until 120 hours of exposure and the values show decreasing trend at 144 hours of exposure. The Young’ modulus values at 144 hours of exposure are less than those of unexposed fibers. To investigate thermal degradation effect on Polypropylene fibers, the fibers were exposed to 125oC as a function of number of weeks in increments of one week to four weeks. Results indicate that the thermal exposure did not have much impact on variation of Young’s modulus values for the first three weeks and showed an increase in Young’ modulus values at the surface when they are exposed to four weeks. Fourier Transform Infrared Spectroscopy (FTIR) and Wide Angle X-ray Spectroscopy (WAXS) were performed to identify the oxidation bonds and crystallinity. The increase in Young’s modulus values of Polypropylene fibers exposed to UV and thermal degradation is attributed to increase in crystallinity.

N. D. Wanasekara

Detachment Dynamics of Cancer Cells

Cell adhesion and detachment are crucial components in cancer spreading, often leading to recurrence and patient death [1]. Probing the mechanical behavior at the whole cell level while the cell is undergoing spreading and detachment during would enhance our understanding on cancer metastasis. However, these processes are not well understood in a quantitative sense, especially for the cancer cells [2]. In this article, we propose a biohybrid micro-device for the investigation of cellular attachment and detachment dynamics. This device comprises of silicon nanowires as electromechanical strain sensors, embedded in a suspended doubly-clamped silicon dioxide (SiO

2

) microbridge (Fig. 1A & Fig. 2A) for breast cancer (MCF-7) cells seeding and attachment (Fig. 1B).

Chee Chung Wong, Julien Reboud, Jeffrey Soon, Pavel Neuzil, Kin Liao

Compression Testing of Biomimetic Bones with 3D Deformation Measurements

Knowledge of mechanical properties of trabecular bones is important for the designing of bone replacements and implants as well as the research of bone diseases such as osteoporosis. However, due to difficulties on harvesting and preparing trabecular bone specimens, as well as uniqueness on microstructure and mechanical properties of each trabecular bone specimen, it is expensive to use real trabecular bone specimens to validate and to calibrate the experimental technique. In this research we use the open-cell aluminum foam as a replacement of the trabecular bone. Two 45° mirrors and two CCD cameras are used in our experimental setup to acquire images of four surfaces during the compression. Two-dimensional digital image correlation technique is used to measure surface deformations based on these images.

Hang Yao, Wei Tong
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