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About this book

Mechanics of Composite, Hybrid, and Multifunctional Materials, Volume 5 of the Proceedings of the 2018 SEM Annual Conference & Exposition on Experimental and Applied Mechanics, the fifth volume of eight from the Conference, brings together contributions to this important area of research and engineering. The collection presents early findings and case studies on a wide range of areas, including:

Recycled Constituent Composites


Mechanics of Composites

Fracture & Fatigue of Composites

Multifunctional Materials

Damage Detection & Non-destructive Evaluation

Composites for Wind Energy & Aerospace Applications

Computed Tomography of Composites

Manufacturing & Joining of Composites

Novel Developments in Composites

Table of Contents


Chapter 1. Stimulus-Responsive Interfacial Chemistry in CNT/Polymer Nanocomposites

The enhancement of interfacial interactions in carbon nanotube (CNT)/polydimethylsiloxane (PDMS) polymer matrix composites was investigated. The approach taken was to functionalize the CNTs with the photoreactive molecule benzophenone in order to anchor the CNTs to the polymer chains on demand. The anchoring reaction was activated by the use of externally applied UV irradiation. A comparison was done on randomly dispersed and aligned CNTs in order to observe the effect of orientation on interface mechanics and overall enhancement. The effect of interfacial interaction on the mechanical response was determined through analysis of static mechanical experiments, as an increase in interfacial interaction resulted in an observable change in elastic modulus and yield stress. An increase of 22% in elastic modulus was observed in randomly oriented CNTs while an increase of 93% was observed in aligned CNT composites after exposure to UV light. In addition, alignment of CNTs lead to a more discreet yield stress which allowed for a clearer identification of the onset of interfacial failure. This work provides insight into the intelligent design of composites, starting at the nanoscale, to provide desired on-demand macroscale response.

Frank Gardea, Zhongjie Huang, Bryan Glaz, Shashi P. Karna, Xiyuan Cheng, Zhiwei Peng, YuHuang Wang

Chapter 2. Devulcanized Rubber Based Composite Design Reinforced with Nano Silica, Graphene Nano Platelets (GnPs) and Epoxy for “Aircraft Wing Spar” to Withstand Bending Moment

This paper aims a new composites design by using devulcanized recycled rubber (90 wt %) and epoxy 20 wt %) based composites reinforcement with nano silica and graphene nano plates (GnPs). The toughening effects of nano-silica/graphene hybrid filler at various ratios on this composite were investigated for aircraft engineering applications especially aircraft wing spar. As well known, wing spar is used two of them; one front, other rear in order to control torsional effect of the wing. Nano-silica and graphene nano plates (GnPs) have been used as the main reinforcing fillers that increase the usefulness of recycled rubber composite. As each filler retains its specific advantages, the use of nano-silica/graphene combinations should improve the mechanical and dynamic properties of recycled rubber composite.In aircraft and aerospace applications, graphene nano plates can be used effectively new design of electrically conductive composites which can improve the electrical conductivity of these composites designed for the fuselages that it would replace copper wire which is generally used for the prevention of damage caused from lightning strikes. There are many advantages and possibilities that graphene nano plates (GnPs) can prevent water entering the wings, which adds weight to the aircraft.In the frame of this present common research, a new devulcanized recycled rubber based composite design for aircraft wing spar has been proposed and wing load due to structure weight was calculated analytically to tolerate bending moment under the service conditions. The toughness properties and tribological behaviour indicating the reinforcement of recycled rubber based composite were evaluated. Microstructural and fractural analyses were made by Scanning Electron Microscopy (SEM).

A. B. Irez, E. Bayraktar, I. Miskioglu

Chapter 3. Study of Mechanical Characteristics of Banana and Jute Fiber Reinforced Polyester Composites

Composite materials are gaining utmost prominence in many fields of application, nowadays, due to their surpassing traits have acquired relevance in various spheres of Engineering. The present study consists of assessment of the mechanical characteristics of Banana and Jute Fiber reinforced Polyester Composites. Banana and Jute Fiber reinforced Polyester Composites were fabricated using banana fibers of length 10 mm and jute fibers of length 10 mm as reinforcements and polyester resin as matrix respectively. Thickness of composite panels varied from 3 to 5 mm and fiber volume fractions were adopted as 5%, 10%, 15%, 20% and 25% respectively. It is observed that Jute Fiber reinforced Polyester Composites exhibit higher values of tensile and flexural strength compared to Banana Fiber reinforced Polyester Composites. However, both Banana and Jute Fiber reinforced Polyester Composites revealed optimum tensile and flexural strength at a fiber volume fraction of 25% and 20% respectively.

G. L. Easwara Prasad, B. E. Megha, B. S. Keerthi Gowda

Chapter 4. Toughening Mechanism in Epoxy Resin Modified Recycled Rubber Based Composites Reinforced with Gamma-Alumina, Graphene and CNT

In this research, low cost devulcanized recycled rubber based composites were designed with fine gamma alumina (d < 5–10 μm) reinforcements containing minor reinforcements such as nano graphene platelets and Carbon Nano Tubes. After determination (in different wt% percentages) of the reinforcements with matrix, a special process was applied to complete successfully the manufacturing of the composites. After that, the relevant toughening mechanisms for the most suitable reinforcements were analyzed in detail for aeronautical engineering applications. For this purpose, certain mechanical and physical properties (ISO 13586:2000, KIc – Fracture toughness stress intensity factor and GIc- Critical energy release rate in mode I) have been determined by fracture toughness tests (static 3P bending test with single edge notch specimens, Charpy impact, etc.). Microstructural and fracture surfaces analysis have been carried out by means of Optical Microscopy (OM) and Scanning Electron Microscopy (SEM).

A. B. Irez, E. Bayraktar, I. Miskioglu

Chapter 5. AlSi10Mg Nanocomposites Prepared by DMLS Using In-Situ CVD Growth of CNTs: Process Effects and Mechanical Characterization

Carbon Nanotube (CNT) reinforced AlSi10Mg Metal Matrix Composites (MMCs) were fabricated through direct metal laser sintering (DMLS), and select mechanical properties were compared to those of virgin DMLS AlSi10Mg. The MMCs were prepared by initially depositing CNTs homogeneously on the bulk AlSi10Mg powder through the chemical vapor deposition (CVD) process. The CNT-reinforced AlSi10Mg (CNT-Al MMC) powder was then fused together through DMLS using an EOS M290 additive manufacturing printer. Virgin AlSi10Mg powder was processed as a separate build via DMLS for baseline comparison. Scanning Electron Microscopy was conducted and material property characterization was performed to observe surface morphology, microstructure and mechanical property variation of these materials. Further analysis via Scanning Electron Microscopy and Energy-Dispersive X-ray spectroscopy revealed homogeneously distributed voids within the microstructure of the CNT-Al MMC and large quantities of oxygen near these voids. The growth of CNTs directly onto powder particulates, via CVD, allows for the uniform distribution of reinforcement, which is critical to cohesive 3D printed builds. However, this process requires refinement to limit the presence of excess oxygen, which can cause microstructural defects, thereby hindering the reinforcing capabilities of CNTs.

P. Thompson, R. Poveda, I. Bezsonov, M. Rossini, D. Orthner, K. Cobb, B. Leng, Z. Iqbal

Chapter 6. Optimization of Surface Integrity of Titanium-Aluminum Intermetallic Composite Machined by Wire EDM

This study investigate the influence of the machining parameters on Ti-Al intermetallic composite based using a wire electrical discharge machining. This process is typically used for very hard material, which are hard to machine using a more traditional process. The aim of the work is to optimize the integrity of surface of Ti-Al intermetallic composite machined by WEDM. The first step is defined the machining parameters of the process: Start up voltage U, Pulse on time Ton or T, advanced speed S and flushing pressure P (pressure of injection of dielectric) are chosen to determine their effects on surface roughness Ra. The second step is using integrated method, which mixed Taguchi method and response surface methodology RSM, the RSM model was developed as a tool to predict the integrity of surface of Ti-Al intermetallic composite machined by WEDM. The significance of the machining parameters was obtained using analysis of variance (ANOVA) based on S/N ratio, which show that flushing pressure P, Pulse on Time T and Voltage U were the most significant parameters. Microstructure of surface and subsurface, cracks, craters, and debris and roughness surface of the samples machined at the different condition has been realized by scanning electron microscopy (SEM), and 3D-Surfscan. The integrate method of Taguchi and RSM was validated by conducting validation experiment to ensure that it can work accurately as a prediction tool.

S. Ezeddini, E. Bayraktar, M. Boujelbene, S. Ben Salem

Chapter 7. Design of Cost Effective Epoxy + Scrap Rubber Based Composites Reinforced with Titanium Dioxide and Alumina Fibers

In last decades, aerospace and automotive industries are in search of multi-functional high performance, low cost materials due to certain environmental regulations. Epoxy-recycled rubber based structural composites (ERCs) are used in these type of engineering applications thanks to their favorable properties such as corrosion resistance, low cost and light weight. In addition, the use of recycled materials gives an economic and environmental aspect to the manufacturers. The data for basic material parameters of these composites is essential in order to realize an efficient engineering development process. For this reason, this paper is focused on the design of ERCs reinforced with ceramic powders in different ratios in a matrix of epoxy-fresh scrap rubber. The mechanical and some physical properties of these composite systems were studied in this research. Titanium dioxide (titania-TiO2) and alumina fibers (Al2O3) are used as reinforcements in pre-defined weight percentages. During this study, mechanical and wear properties of these composite systems are studied. Three-point bending tests and nanoindentation were conducted to evaluate mechanical properties. After that, wear resistance is examined by means of nano-scratch tests. As the final step, fracture surfaces were observed with scanning electron microscopy (SEM) to identify damage mechanisms of these composites.

A. B. Irez, I. Miskioglu, E. Bayraktar

Chapter 8. Reinforcement of Recycled Rubber Based Composite with Nano-Silica and Graphene Hybrid Fillers

Nano-silica and Graphene have been used as the main reinforcing fillers that increase the usefulness of recycled rubber composite. As each filler retains its specific advantages, the use of nano-silica/graphene combinations should improve the mechanical and dynamic properties of recycled rubber composite. But, the optimum nano-silica/graphene ratio giving rise to the optimum properties requests to be explained. In this work, reinforcement of recycled rubber composite with nano-silica/graphene hybrid filler at various ratios was studied in order to determine the optimum nano-silica/graphene combinations. The toughness properties and tribological behaviour indicating the reinforcement of recycled rubber based composite were evaluated. Microstructural and fractural analyses were made by Scanning Electron Microscopy (SEM).

A. B. Irez, E. Bayraktar, I. Miskioglu

Chapter 9. Testing the 2-3 Shear Strength of Unidirectional Composite

In this study, the objective was to measure the “out-of-plane” 2-3 shear strength of unidirectional composite, working within constraints in supplied material geometry. Unidirectional carbon/epoxy composite material was tested using a sandwich-type beam specimen under 3-point bending with a low span-to-thickness ratio to achieve failure under 2-3 shear. Specimens were carefully designed to deliberately cause shear failure near the midplane, avoiding other possible failure mechanisms. A photoelastic coating and post-mortem microscopy were used to verify failures. Results were compared with a simple analytical description of failure and found to have good agreement. Notably, this approach was able to accommodate the limitations of the supplied material (thin sheets) while still providing an accurate means of obtaining the F23 shear strength of the material. The results also imply the possibility of testing the transverse tensile strength (F2t) in lieu of performing a shear test, which is far simpler, and inferring the out-of-plane shear strength F23.

Joel S. Fenner, Isaac M. Daniel

Chapter 10. Nondestructive Damage Detection of a Magentostricive Composite Structure

The integrity of composite structures gradually degrades due to the onset of damage such as matrix cracking, fiber/matrix debonding, and delamination. Over the last two decades, great strides have been made in structural health monitoring (SHM) community using various sensing techniques such as acoustic emission, eddy current, strain gages, etc., to diagnose damage in aerospace, mechanical and civil infrastructures. Embedded sensing offers the prospects of proving for real-time, in-service monitoring of damage were weight savings is a major factor in Aerospace Industry. It also provides for a new nondestructive indication of early stage damage. Defect detection and monitoring of fatigue in structural materials can be captured through local indicators of a change of the magnetic properties within the damaged sites. In this present work, magnetostrictive particles such as Terfenol-D were embedded in a composite structure, along with acoustic emissions technique, to validate the damage in a composite system undergoing qausi static and fatigue loading. As the applied load and fatigue cycles increased, the change in the magnetization flux density was captured using a non-contact magnetic field sensor. It was confirmed through numerous tests that a change in the magnetic properties of the composite served as an indicator of early stage damage detection.

Michael Coatney, Asha Hall, Mulugeta Haile, Natasha Bradley, Jin Hyeong Yoo, Brandon Williams, Oliver Myers

Chapter 11. Thermo-Mechanical Properties of Thermoset Polymers and Composites Fabricated by Frontal Polymerization

Thermoset polymers are commonly used as the matrix material in fiber-reinforced polymer composites (FRPCs) due to their good mechanical properties, chemical stabilities, and ease of manufacturing. Conventional curing of thermosets and their composites requires heating the matrix monomers at elevated temperatures during long cure cycles for producing fully crosslinked polymers, resulting in high manufacturing cost in terms of time, energy, and capital investment. Frontal polymerization (FP) is a promising approach for rapid, energy-efficient fabrication of high-performance thermosets and FRPCs. In FP, a thermal stimulus (trigger) causes a self-propagating exothermic reaction wave that transforms liquid monomers to fully cured polymers, eliminating the need for external energy input by large ovens or autoclaves. We have used the FP of dicyclopentadiene (DCPD) to successfully fabricate thermoset polymers and composite parts. In this novel curing strategy, the final degree-of-cure of the polymer, and thereby its mechanical performance, is governed by the heat transfer phenomenon that occur at the polymerization front. During the fabrication of FRPCs some fraction of the generated heat is absorbed by continuous fibers or lost through the tooling. In this work, we will discuss the characterization of the thermo-mechanical properties of DCPD polymer manufactured by FP curing.

M. Yourdkhani, B. Koohbor, C. Lamuta, L. M. Dean, P. Centellas, D. G. Ivanoff, I. D. Robertson, S. R. White, N. R. Sottos

Chapter 12. Design of Magnetic Aluminium (AA356) Composites (AMCs) Reinforced with Nano Fe3O4, and Recycled Nickel: Copper Particles

New classes of aluminium matrix composites (AMCs – 356) were designed by three different manufacturing techniques; only sintering, through combined method called here after “Sinter + Forging” and/or “sinter + thixoforming”. Main reinforcement was magnetic iron oxide, Fe3O4 (10, 20 and 30 wt %) and two recycled reinforcements, nickel, Ni and pure electrolytic copper, Cu, given by French Aeronautical Society were also used and preceded under the constant process parameters such as hot compaction, sinter-forging, sintering time, Forging temperature and Force, etc. As auxiliary element, hybrid graphene nano-platelets, GNPs, was added in the structure. Microstructural analyses (by using SEM), magnetic, mechanical and physical properties of the composites were compared with three different manufacturing processes. Static compression tests, Micro hardness tests, measurement of magnetic permeability and also electrical conductivity, have shown that the mechanical and physical properties of these composites can be improved with the optimization of process parameters. In the present work, an alternative and a low cost manufacturing process were proposed for these composites.

L-M. P. Ferreira, E. Bayraktar, I. Miskioglu, M-H. Robert

Chapter 13. Reinforcement Effect of Nano Fe3O4 and Nb2Al on the Mechanical and Physical Properties of Cu-Al Based Composites

In the present work, Copper-Aluminium based composites(CAMCs) were designed through 3 different manufacturing processes; “Sintering, “Sinter + Forging” and also “sinter + thixoforming” was made a pre alloy from pure electrolytic copper that was doped with atomized recycled aluminium alloy chips (AA7075) that was given by French Aeronautical Society. After that, a typical composite was created by adding nano magnetic iron oxide (Fe3O4) with a special treatment. Nb2Al intermetallic was also used as reinforcements to increase the wear resistance of the final structure. Graphene Nano Plates (GNPs) and nickel were also added to the CAMCs structures to improve mechanical behaviour and wear resistance of these novel composites. The addition of hard ceramic and/or intermetallic particles to soft copper matrix can significantly improve the mechanical properties and wear resistance, without any serious deteriorating of both magnetic, thermal and electrical conductivities of copper based composites.Briefly, Cu-Al based composite can be successfully used to produce as high quality metal matrix composites in an economic way in the electronic field. Microstructural evaluation was performed by Scanning Electron Microscopy (SEM) and EDS analyses to optimize influence of the major reinforcements distributed in the matrix.Mechanical and physical properties of the composites designed here can be improved with the processing method and reinforcement volume fractions. Macro scratch, nano wear and micro hardness tests were also made for these composites.

L.-M. P. Ferreira, I. Miskioglu, E. Bayraktar, D. Katundi

Chapter 14. Recycled Ti-17 Based Composite Design; Optimization Process Parameters in Wire Cut Electrical Discharge Machining (WEDM)

This work present a comprehensive study on the effect and optimization of machining parameters on the kerf (cutting width) and material removal rate (MRR) in wire electrical discharge machining (WEDM) process by using the response surface methodology (RSM) and Taguchi method. The experimental studies were conducted under varying parameters. The main input parameters on this model are the cutting parameters such us pulse on time (Ton), servo voltage (U), Speed of advance or feed rate (S) and injection pressure or flushing pressure (P). Recycled Titanium based composite (an alloy Ti17) was used for machining operations and the combined effects of cutting parameters on the material removal MRR rate and kerf were investigated while using the analysis of variance ANOVA. Mathematical models were used for the objective of minimum kerf and maximum MRR, Cut edge surface analysis was carried out using an optic microscope and Scanning Electron Microscope (SEM) to evaluate the kerf.

Sonia Ezeddini, Mohamed Boujelbene, Emin Bayraktar, Sahbi Ben Salem

Chapter 15. Alternative Composite Design from Recycled Aluminum Chips for Mechanical Pin-Joint (Knuckle) Applications

In this work, an alternative aluminum matrix composite (AMCs) was designed from the recycled chips of the aluminium series of AA7075 (90 wt %) and AA1050 (10 wt %) given by French aeronautic company through combined method of powder metallurgy followed by Sintering + Forging. We aimed for the application for the connection link in a mechanism to transfer motion, for example; between the two railways wagons etc. and also some connecting link in aeronautical pieces as an alternative replacement for conventional alloys used in this area. First of all, A typical Al-Zn-Mg-Si-Ni matrix was developed and reinforced basically with B2O3 (5, 10%). Chip milling was performed using high energy milling in a planetary ball mill with an inert argon atmosphere to prevent oxidation of the powders. Two compositions were prepared with two different percentages of B2O3 and also one composition was kept without reinforcement for comparison with the reinforced ones. Mechanical properties, compression and dynamic drop weight tests of these composites designed here can be improved with the doping process and doping volume fractions. Micro-hardness results were compared according to the optimization conditions of the doping and the reinforcement. Static compression and impact-drop weight tests were carried out. The microstructure analyses have been carried out by Scanning Electron Microscope (SEM).

D. Katundi, A. B. Irez, E. Bayraktar, I. Miskioglu

Chapter 16. Manufacturing of Copper Based Composites Reinforced with Ceramics and Hard Intermetallics for Applications of Electric Motor Repair Parts

In the present work, a recycled copper based composites reinforced with ceramic as an alternative replacement for the application of electric motor repair parts with the use of novel processing techniques.A practical solution was proposed as cost effective economic manufacturing of the composites for this type of applications. Copper based composite design (Cu-Al-Nb2Al) was based on the ceramic reinforcements such as titanium carbide (TiC) in different percentages and niobium aluminate intermetallics (Nb2Al). Because TiC and Nb2Al make a good combination of thermal and electrical conductivities, microstructural stability and strength retention at elevated temperatures, etc. These reinforcements increase considerably wear resistance of the composites for electrical contact applications. Otherwise, certain percentage of fresh scrap aluminium powder, the mixture of AA1050 (80 wt% + AA7075 (20 wt %) chips were used to create an exothermic combustion reaction in the process for helping diffusion bonding process of the ceramics to the copper matrix. At the first stage of the present work a preliminary study has been carried out for developing a cost effect and high wear resistant electrical brushes for aeronautical applications. Microstructural and wear analyses have been carried out to optimize the process conditions for a practical tool that will be used for final industrial applications. Three basic compositions were prepared depending on the percentage of TiC. The microstructure and damage analyses have been carried out by Scanning Electron Microscope (SEM).

G. Zambelis, E. Bayraktar, D. Katundi, I. Miskioglu

Chapter 17. Damping and Toughening Effect of the Reinforcements on the Epoxy Modified Recycled + Devulcanized Rubber Based Composites

This paper discusses damping effect of the reinforcements on the epoxy modified (10, 20 and 30 wt. %) devulcanized recycled rubber based composites. Within this study, the influence of Boron, γ-alumina and hollow glass microspheres (HGM) added in the matrix as the reinforcement elements were examined. As well known, devulcanization process is an efficient method of micronized rubber that can be used as useful products in a highly valued form. In this study, a combined process (chemical treatment + microwave) was used in order to modify the structure of the scrap recycled rubber. To characterize toughening and impact behaviour, quasi static 3P bending tests and choc tests were used for obtaining the principal values KIc and GIc and also damping capacity due to the reinforcement particles. Additionally, Shore-D hardness tests were measured. Scanning Electronic microscopy (SEM) was used to check dispersion quality and fracture surfaces, in scanning mode.

A. B. Irez, E. Bayraktar, I. Miskioglu

Chapter 18. Impact and Post-impact Behavior of Composite Laminates Reinforced by Z-Pins

Delamination, i.e. the separation between layers that occurs by failure of the resin-rich interlaminar interface, is a direct consequence of the lack of out-of-plane reinforcements and, undoubtedly, the most common damage mode in laminated composites.Delaminations induced by low-velocity impacts are of primary concern in structural applications, since impact damage, often miss-detected, may propagate, impairing the load bearing capacity of the component, particularly under compressive loads. Preventing delamination, as well as delaying and limiting its propagation, are thus key issues in the design of composite structures. Over the last decades, many strategies have been proposed to address this problem. Among them, the introduction of through-thickness reinforcements (stitching, pinning and stapling) has proven to be effective in improving the interlaminar properties of composite materials. In particular, recent studies have shown that Z-pinning, which consists in inserting high stiffness pins through the thickness of uncured laminates, may significantly enhance the delamination resistance of laminated components.In this study, conventional and Z-pin reinforced [02/902]s graphite/epoxy laminates were subjected to low-velocity impact and compression after impact (CAI) tests in order to examine the effect of the reinforcements on the impact response and the residual post-impact properties of the laminate. The results show that Z-pinning significantly reduces the extent of delamination induced by impact, while, on the contrary, it appears to only marginally improve the post-impact compressive strength of the laminates.

L. Francesconi, F. Aymerich

Chapter 19. Layered Jamming Multifunctional Actuators

Recent advances in additive manufacturing have enabled the realization of concepts in layered materials that were not previously viable. We have created a layered manufacturing process using robots to fabricate actuators using pre-fabricated materials, e.g. solar cells and batteries. This has allowed us to design and fabricate multifunctional structures that can encompass new capabilities for applications, such as pneumatic actuators for robotics. One way to enhance the functionality of these actuators is to use layers that are not fused together to create “variable stiffness” components when a vacuum is drawn. Studying the mechanics of these components is important in understanding how to configure the layers of the jamming multifunctional actuators. We have prototyped and characterized the mechanics of a layered jamming multifunctional actuator to model the effects of layering on the multifunctional performance of these new actuation materials. The proposed model is for a soft actuator with opposing jamming layers, and the predictions of actuation performance were found to be consistent with measurements from the prototype structures. Three different types of composite jamming materials were investigated, consisting of polyurethane rubber, silicone, or paper with paper. It was found that the order of magnitude difference in the stiffness of the polyurethane rubber and silicone with paper reduced the predicted curvature of the more compliant material under transverse load by approximately 50%, which increases the shear strain between the stiffer materials due to the reduced shear stiffness of the more compliant material. Two prototype actuation structures were fabricated: (1) a programmable array of layered jamming actuators to control the 3D shape of a flexible solar cell for energy harvesting, and (2) a multi-mode actuator capable of bending and extensional deformations. We have also demonstrated the viability of these actuators on a robotic platform known as “ArmadilloBot” that is capable of walking, and then morphing into a rolled-up structure, just like a real Armadillo.

Hugh A. Bruck, Ruben Acevedo, Jasmin Rohwerder, Lena Johnson, Satyandra K. Gupta

Chapter 20. 2D Microscale Observations of Interlaminar Transverse Tensile Fracture in Carbon/Epoxy Composites

This study presents a new experiment to image and analyze the evolution of transverse tensile fracture in tape-laminate carbon/epoxy composites at the microscale. To this end, a miniature double cantilever beam specimen is developed to produce stable transverse tensile fracture and various amounts of crack turning through a stack of 90° plies. The specimen is wedge-loaded with a custom micromechanical tester, while the crack growth is optically monitored at both the micro- and macro-scale. Post-test, microscale images are analyzed to determine the transverse crack path relative to the applied loading, and to directly measure local strains using 2D digital image correlation. The experimental data sets obtained in this study enable direct validation of finite element simulations of transverse tensile cracking in fibrous composites at the microscale and provide impetus for their further model development.

Austin J. Smith, Caitlin M. Arndt, Danielle Benson, Michael W. Czabaj

Chapter 21. Electro-Mechanical Response of Polymer Bonded Surrogate Energetic Materials with Carbon Nanotube Sensing Networks for Structural Health Monitoring Applications

The addition of carbon nanotubes throughout the binder phase of energetic particulate composites is investigated in an effort to develop real-time embedded sensing networks for detection of small-scale damage in polymer bonded explosives undergoing mechanical load. The experimental effort herein focuses on the exploration of multi-walled carbon nanotube (MWCNT) concentration in energetic composite material; the fabrication of such specimen include the substitution of sugar as a mock energetic for the crystal particulate Ammonium Perchlorate (AP), an oxidizer most often used in solid rocket propellants. Further explored was the particulate embedded into a binder of PDMS, a polymeric silicone, as well as the addition of aluminum powder, a common combustive fuel in solid propellants, in the particulate. Electrical and mechanical properties of neat (no MWCNTs) energetics and MWCNT hybrid energetics were quantitatively evaluated under monotonic compression, and tension to failure. Noteworthy electro-mechanical response was obtained for these MWCNT AP hybrid energetics, justifying further study of CNT binder network formation for real-time electro-mechanical sensing in an effort for structural health monitoring (SHM) in energetics.

Samantha N. Rocker, Nishant Shirodkar, Tanner A. McCoy, Gary D. Seidel

Chapter 22. Strength and Energy Absorption Capability of Porous Magnesium Composites Reinforced by Carbon Nanofibers

Porous magnesium-carbon nanofiber (CNF) composites were manufactured to investigate the variation of compressive mechanical properties with the change of porosity and CNF concentration. When the CNF concentration changed from 0% to 2%, the average yield strength significantly increased for the porous composites with the porosity of either 24%, 34%, or 50%. The yield strength and the ultimate compressive strength decreased at an increasing rate with the increase of porosity. For each studied porosity, the addition of CNF to porous magnesium composite samples increased energy absorption capability when the samples underwent any given strain level. Four theoretical strengthening models were utilized to estimate yield strength of the studied porous composites and the results indicated that the shear lag model and the rule of mixture model provided better yield strength estimations than the Strengthening factor model and the Zhang & Chen model.

Huiru Xu, Qizhen Li

Chapter 23. Mechanical Characterization of Open Cell Aluminum Foams Using X-ray Computed Tomography

Open-cell aluminum foams show excellent potential for use in a variety of applications. In order to accelerate the use of aluminum foams in engineering industry, it is important to accurately understand the relationship between the manufacturing processes and the resulting foam properties. Two tests are developed to support development of finite element (FE) models that will be used to design foam geometries optimized to meet specific design criteria. A bulk crush test is created for small foam blocks which uses in situ X-ray computed tomography (CT) imaging. A tensile experiment is developed to test individual foam ligaments, which measures the aluminum’s mechanical behavior and will be used to improve the simulation’s accuracy beyond what is possible using published bulk material properties of aluminum.

Kristoffer E. Matheson, Michael W. Czabaj

Chapter 24. Damage Detection and Visco-Elastic Property Characterization of Composite Aerospace Panels Using Ultrasonic Guided Waves

Composite materials are widely used in commercial and military aircraft. A major concern is the detection and quantification of damage in these panels caused, for example, by foreign object impacts. A related issue is the characterization of the composite visco-elastic properties, whether the ply-by-ply properties or the laminate’s engineering properties. Both of the aforementioned tasks can be accomplished by careful use of ultrasonic guided waves that are multimode and dispersive waves propagating in the composite waveguide. The test piece for these studies is a carbon-reinforced plastic (CFRP) panel with co-cured stiffeners representative of modern commercial aircraft construction (e.g. B787). The wave dispersive properties of this panel were first determined from broadband ultrasonic tests and 2D Fourier Transform techniques. A Semi-Analytical Finite Element (SAFE) analysis was then performed to calculate dispersion curves and cross-sectional mode shapes of relevant guided modes propagating in the panel. The SAFE analysis allowed to iteratively change the elastic properties of each layer in the panel so as to identify the layer-by-layer properties from the experimental extraction of the dispersive guided waves propagating in the test panel. A scanning inspection system using air-coupled ultrasonic transducers operating at specific frequencies was also developed to detect and quantify impact-induced damage in the skin or the stringer of the panel.

M. Capriotti, R. Cui, F. Lanza di Scalea

Chapter 25. Microscale Investigation of Transverse Tensile Failure of Fiber-Reinforced Polymer Composites

In this study, two experimental approaches are used to understand fracture mechanisms that govern transverse tensile failure of fiber-reinforced polymer composites at the microscale. These observations are used to directly measure, and indirectly estimate, the magnitude and scatter of the transverse tensile strength, YT, and the associated effective flaw size, a0. To this end, static three-point bend tests are performed on pristine and notched 90° unidirectional IM7/8552 carbon-epoxy samples. In the pristine specimen study, tensile microcracks are observed to initiate well before the ultimate failure load used to compute YT is reached. In the notched specimen study, a comparison is made between experimentally measured strengths with known notch lengths and a linear elastic fracture mechanics solution. The fracture mechanics solution significantly over-predicts the apparent YT for notch lengths less than a ply thickness, suggesting that this approach may not be appropriate for estimation of transverse tensile strength at the microscale. The observations made in this study suggest that YT may not be a true material property, but rather, a structural property dependent on specimen geometry and microstructural variability.

Caitlin M. Arndt, Paige DaBell, Michael W. Czabaj

Chapter 26. Optimization of Kerf Quality During CO2 Laser Cutting of Titanium Alloy Sheet Ti-6Al-4V and Pure Titanium Ti

CO2 laser cutting is an advanced processing technology, which can, according to the computer-aided design graphics, cut a variety of shapes in the surfaces of many metallic sheets. Laser cutting of various materials including the Titanium alloy Ti-6Al-4V and pure Titanium Ti is carried out to assess the kerf width size variation along the cut section. This work aims to analyze the effect of laser power, cutting speed, and gas pressure on the kerf quality of Ti-6Al-4V alloy and Ti with CO2 laser cutting process. The kerf width size is formulated and predicted using the lump parameter analysis and it is measured from the experiments. The influence of laser output power Pu and laser cutting speed V and pressure nitrogen assisting gas p on the kerf width size variation is analyzed using the analytical tools including scanning electron and optical microscopes. The quality of laser cut kerf mainly depends on appropriate selection of process parameters. Uniform kerf with minimum kerf width is always demand. It has been found that the kerf width during CO2 laser process is not uniform along the length of cut. A considerable improvement in kerf quality has been achieved.

B. El Aoud, M. Boujelbene, E. Bayraktar, S. Ben Salem

Chapter 27. A Study of the Surface Integrity of Titanium Alloy Ti-6Al-4V in the Abrasive Water Jet Machining Process

The abrasive water jet (AWJ) cutting technique is one the most rapidly improving technological methods of cutting materials. In this cutting technique, a thin, high velocity water jet accelerates abrasive particles that are directed through an abrasive water jet nozzle at the material to be cut.Using the abrasive water jet machining process, this work investigated the effect of machining conditions, specially the cutting speed and the material thickness, on the integrity surface (including surface microstructure alterations and surface roughness) of work piece of the Titanium alloy Ti-6Al-4V. The GMT garnet was used as an abrasive material with 80 mesh. Surface integrity is defined as the inherent or enhanced condition of the surface produced in a machining or other surface generating operation. It is very important to examine the influence of cutting conditions on surface roughness and microstructure. Photographs of cut surfaces were analyzed and roughness parameters were measured in different locations across depth of cut. Differences between surface geometric structures and measured roughness parameter values obtained were presented and discussed.

M. Douiri, M. Boujelbene, E. Bayraktar, S. Ben Salem

Chapter 28. Process Reliability of Abrasive Water Jet to Cut Shapes of the Titanium Alloy Ti-6Al-4V

Titanium alloys have been widely used in industries, especially aerospace, energy and medical industries, due to their good mechanical and chemical properties. However, titanium alloys are typically difficult-to-cut materials. That is why, in industries we are using many process to cut this alloys. In fact, several studies have made a comparisons between the various machining processes currently used in industries to cut Titanium alloys.Remains the abrasive water jet process is the most answered in terms of quality quantity and reliability. In this cutting technique, a thin, high velocity water jet accelerates abrasive particles that are directed through an abrasive water jet nozzle at the material to be cut. Advantages of abrasive water jet cutting include the ability to cut almost all materials, no thermal distortion, and high flexibility, small cutting forces and being environmentally friendly. The mechanism and rate of material removal during AWJ cutting depends both on the type of abrasive and on a range of process parameters.The presented work aims at studying the behavior machinability in Ti-6AL-4V alloys using the GMTas an abrasive material with 80 meshes. Photographs of cut shapes were taken with a 2D machining which show the impact of parameters conditions on surface geometric in different location. A comparative measurement of the kerf and the precision of the angle was taken with a profile projectors, and the defects of cut was discussed.In order to increase the relibility of the abrasive water jet process, and to anticipate an estimation of the machinability of the material, a mathematical model of the Kerf width has been put in place, which aims at optimization of cutting parameters by minimizing the Kerf.

M. Douiri, M. Boujelbene, E. Bayraktar, S. Ben Salem

Chapter 29. Optimization of the High Energy Milling Process of Chips of a Stainless Steel Using the Response Surface Modeling

The present paper discusses response surface methodology as an efficient approach for predictive model building and optimization of the high energy milling process from the chip duplex stainless steel with a carbide vanadium addition willing to obtain the smaller particle size. The process parameters studied was milling time of 10 h and 50 h. Rotations were performed at 250 and 350 rpm. Vanadium carbide was added from 0% to 3% in weight, and a mass/ball ratio of 1/10 and 1/20. An analysis of particle size and a scanning electronic microscopy were used to measure and characterize particle size. With addition of carbide in milling process resulted on a reduction of particle size compared to the material without carbide added around 66%. The results predicted using factorial regression model showed high values of regression coefficients (R2 = 0.952) indicating good agreement with experimental data. The minimum value of particle size was obtained for following optimal conditions: rotation of 325 rpm, time of 42 h, ball/mass 18:1 and carbide 2, 67%wt. The particle size of fabricated powders after 50 h of milling with 3% vanadium carbide addition was about 186 times lower than that the initial chips.

Fábio Gatamorta, C. S. P. Mendonça, M. M. Junqueira, E. Bayraktar, B. G. Andrade, M. de L. M. Melo, G. Silva

Chapter 30. Iron Contents on Recycle Aluminum and Influence on Mechanical Properties

This study aims to investigate the influence of iron content on the mechanical property of the recycle AA356 aluminium alloy. The recycle Alloys enriched with iron were prepared by casting and samples were chemically analyzed by mass spectrometry to confirm their composition. The alloy tixoability was evaluated by thermodynamic simulation via Thermocalc®, and then other alloys samples were prepared by partial melting. The samples were analysed metallurgically and mechanically. Through microstructural analysis, it was noted the presence of Fe-rich intermetallic in the alloys enriched with iron, which were not found in the alloy as received. The presence of these intermetallic contribute to improve the mechanical strength.

Claudomiro Alves, Bruna Vilas Boas, Fábio Gatamorta

Chapter 31. Experimental Comparison of the Microstructure and Surface Roughness in CO2 Laser Cutting of the Titanium Alloy Ti–6Al–4V and the Pure Titanium Ti

Titanium and its alloys have over the years proven themselves to be technically superior and cost effective materials for a wide range of applications spanning the industries of aerospace, industrial, marine, and even commercial products. In this paper, the surface integrity of titanium alloys Ti-6Al-4V and pure titanium Ti, cut with high power CO2 laser is determined and the results are presented and discussed. The aim of this experimental investigation is to compare the microstructure and the cut surface quality of both titanium based on the variation of three different cutting parameters namely, laser power (Pu), cutting speed (V) and gas pressure (p).The microstructure analysis is evaluated by investigating the cut edge microstructure and the cut section roughness for both Titanium alloy Ti-6Al-4V and pure Titanium Ti. An experimental analysis is carried out to identify the main effects and interactions of these parameters. Optical microscopy and scanning electron microscopy (SEM) are carried out to examine the cutting defects.

B. El Aoud, M. Boujelbene, E. Bayraktar, S. Ben Salem, A. Boudjemline

Chapter 32. Influence of Crumb Rubber Reinforcement on the Properties of Medium Density Fiberboard

Recycling of scrap tires in the form of crumb rubber is one way to address the environmental concern of tire disposal. In this investigation we have utilized crumb rubber to reinforce medium density fiberboard (MDF). For the purpose of comparison, a baseline MDF material is prepared by mixing polypropylene pellets and wood flour in the ratio of 1:2 by weight using a double helical screw mixer at 165 ∘C. The crumb rubber reinforced MDF (CR–MDF) material is prepared by adding crumb rubber particles of a size between 1.2 to 1.4 mm, into to the polypropylene pellets and wood flour mixture. Subsequently, the prepared samples are molded into the desired dimension using a hot press. The bulk density of CR–MDF materials is found to be 19% higher than the baseline MDF samples. This indicates that crumb rubber assists in the consolidation process. Prepared MDF and CR–MDF specimens are mechanically characterized as per ASTM D 1037. Compressive modulus of CR–MDF shows an increase of 200%, as compared to baseline MDF. With the addition of crumb rubber, flexural modulus and flexural strength of the MDF samples are improved by 120% and 75%, respectively. Scanning electron microscopy (SEM) on failed CR–MDF samples indicates extensive tearing of crumb rubber particles which suggests that particle bridging is the dominant strengthening mechanism. In addition, water immersion experiments show that the presence of crumb rubber improves the resistance to moisture absorption. Finally, Fourier Transform Infrared Spectroscopy (FTIR) of CR–MDF samples indicates sulfur–sulfur bonds and the CN group from the nitrile component of the crumb rubber.

Libin K. Babu, Kunal Mishra, Raman P. Singh

Chapter 33. Sub-components of Wind Turbine Blades: Proof of a Novel Trailing Edge Testing Concept

Wind turbine rotor blade sub-component testing (SCT) confines the structural validation to design critical blade parts. Unlike full-scale blade testing, SCT can be adjusted to replicate the stress state of the local structure closer to field conditions and thus augment towards increasing the structural reliability. One of the blade regions often subjected to fatigue loads is the trailing edge bond line. In this work, the proof of concept of a novel trailing edge sub-component test is presented. An outboard specimen of 3 m length was cut out of a 34 m wind turbine rotor blade. The sub-component was installed on a customized test rig and loaded statically with an hydraulic actuator. The imposed strain field along the specimen length is found in a good agreement to the strain distribution in the corresponding area developed during the static full-scale blade test. The experimental setup was simulated by analytical and finite element models. Data recordings with electrical strain gauges and a four-camera digital image correlation system were obtained to validate the predicted structural response of the specimen.

Malo Rosemeier, Alexandros Antoniou, Catherine Lester

Chapter 34. Toughening Mechanisms on Recycled Rubber Modified Epoxy Based Composites Reinforced with Alumina Fibers

Environmental and economic concerns has been a motivation for the material manufacturers to produce new, robust, lightweight and cost-effective materials. Therefore, aeronautic and automobile industries are investigating multifunctional composite materials that can meet their expectations. In this regard, polymer based composites can have high specific strength with the contribution of resistant fillers. As a polymer, epoxy is considered an appropriate matrix, which can be modified by different agents. First option is the addition of hard particles and second is that the inclusion of thermoplastics or the addition of elastomeric materials. Since, epoxy exhibits high brittleness due to its highly cross-linked nature, modifiers less rigid than the matrix can serve as unique tougheners enhancing the ductility. In this study, a good combination of both hard and soft modifiers is used. In addition to mechanical characteristics, using of fresh clean scrap EPDM rubbers adds an economic and environmental value to this study. Also, due to its favorable structural characteristics such as interlocking effects of fibers, addition of alumina fibers (AF) ensures desired mechanical properties in case of a homogeneous distribution. This paper primarily explains the mechanical behavior as well as damage mechanisms of epoxy-fresh scrap rubber composites. The mechanical and physical properties of these composite systems are studied in the present work. Dynamic Mechanical Analysis (DMA) analyses were carried out to determine thermal-mechanical properties. Three-point bending and fracture toughness tests were realized with single edge notched beam (SENB) and smooth specimens. Finally, scanning electron microscope (SEM) was used to observe fracture surfaces and the microstructure.

A. B. Irez, I. Miskioglu, E. Bayraktar

Chapter 35. Toughening Mechanisms on Recycled Rubber Modified Epoxy Based Composites Reinforced with Graphene Nanoplatelets

Recycling is a subject undergoing intense study in terms of sustainable development. In every area, recycling is strongly encouraged by governments due to the international agreements on environmental issues. For example, many industrial manufacturers have a tendency to find clean and cost-efficient solutions by utilizing recycled materials to produce new components. In this regard, rubbers have very wide usage in aeronautic and automotive industries both in structural and in interior body components. Rubbers are also used to modify brittle polymer components in the existence of hard, resistant fillers. In this study, fresh scrap EPDM rubbers are used to manufacture novel composites by modifying epoxy resin with the inclusion of graphene nano platelets (GnPs). Rather than micro sized particles, nanoparticles have high surface area, which means that a low content of these nanoparticles may enhance the material’s properties more efficiently. Besides, due to its superior structural, thermal and physical characteristics, addition of graphene promises improved mechanical properties if they can be dispersed homogeneously. This paper is focused on the fracture characteristics and toughening mechanisms of epoxy – fresh scrap rubber composites. The mechanical and physical properties of these composite systems are studied in the present work. Mechanical properties are examined by means of three-point bending tests with smooth and single edge notched beam specimens (SENB). Also, nano indentation tests were realized to see the creep compliance and viscoelastic properties. Finally, scanning electron microscope (SEM) was used to observe the fracture surfaces and the microstructure.

A. B. Irez, I. Miskioglu, E. Bayraktar

Chapter 36. Damage Accumulation in CMCs

Silicon carbide/ silicon carbide ceramic matrix composites (SiC/SiC CMCs) are a subgroup of structural ceramics that are well-suited for high-temperature aerospace applications, due to their low weight, excellent creep resistance, damage tolerance, and high specific strength. Damage initiation and accumulation in CMCs depends on a number of factors, including constituent architecture, thermo-mechanical loading parameters, and environmental conditions. However, much is still unknown about the impact of these factors and the interactions between them. In order to accurately predict life of these advanced composites, it is critical to understand the relationships between damage initiation/accumulation and key microstructural features, and to characterize which early damage mechanisms subsequently lead to crack coalescence and macroscopic failure. In this study, SiC/SiC minicomposites, which are representative of a fundamental element of the macroscopic CMC, are characterized via an experimental approach combining acoustic emission (AE) with microscale deformation tracking via digital image correlation inside a scanning electron microscope (SEM-DIC) in order to examine early damage initiation at room temperature below the proportional limit. This dual technique enables the capture of multi-modal data on early damage mechanisms in CMCs at both the subsurface and surface levels. This research provides the foundation for characterization of damage in SiC/SiC CMCs under more complex testing conditions.

B. Swaminathan, J. D. Kiser, A. S. Almansour, K. Sevener, S. Daly

Chapter 37. Investigating Intralaminar Crack Growth in Biaxially Stressed Composites

Permeability concerns of fiber-reinforced composites has delayed their implementation into next-generation space launch vehicle structures. Namely composite cryotanks, which could help achieve significant weight savings, are not being implemented due to a deficient understanding of the mechanisms that lead to the generation of through-thickness crack networks and permeation paths. A novel in-plane cruciform test method was developed to investigate intralaminar crack growth under biaxial load using ex situ X-ray computed tomography (CT). Specimens were tested at predefined load levels, determined from a progressive damage model, then imaged with X-ray CT. 3-dimensional representations of the specimen after each load interval were reconstructed to capture damage accumulation as a function of load. The CT data were then used to establish initial hypotheses of crack initiation and growth in biaxially stressed composites.

Jordan French, Jessica Christensen, Michael M. Czabaj

Chapter 38. Determination of Stress Free Temperature in Composite Laminates for Residual Stress Modeling

As the complexity of composite laminates rises, the use of hybrid structures and multi-directional laminates, large operating temperature ranges, the process induced residual stresses become a significant factor in the design. In order to properly model the initial stress state of a structure, a solid understanding of the stress free temperature, the temperature at which the initial crosslinks are formed, as well as the contribution of cure shrinkage, must be measured. Many in industry have moved towards using complex cure kinetics models with the assistance of commercial software packages such as COMPRO. However, in this study a simplified residual stress model using the coefficient of thermal expansion (CTE) mismatch and change in temperature from the stress free temperature are used. The limits of this simplified model can only be adequately tested using an accurate measure of the stress free temperature. Only once that is determined can the validity of the simplified model be determined. Various methods were used in this study to test for the stress free temperature and their results are used to validate each method. Two approaches were taken, both involving either cobonded carbon fiber reinforced polymer (CFRP) or glass fiber reinforced polymer (GFRP) to aluminum. The first method used a composite-aluminum plate which was allowed to warp due to the residual stress. The other involved producing a geometrical stable hybrid composite-aluminum cylinder which was then cut open to allow it to spring in. Both methods placed the specimens within an environmental chamber and tracked the residual stress induced deformation as the temperature was ramped beyond the stress free temperature. Both methods revealed a similar stress free temperature that could then be used in future cure modeling simulations.

Brian T. Werner, Helena Jin, Timothy M. Briggs

Chapter 39. Calibration of a Simple Rate Dependent Elastic-Plastic Constitutive Model for a Toughened Carbon Epoxy Composite System

The concept of progressive failure modeling is an ongoing concern within the composite community. A common approach is to employ a building block approach where constitutive material properties lead to lamina level predictions which then lead to laminate predictions and then up to structural predictions. There are advantages to such an approach, developments can be made within each step and the whole workflow can be updated. However, advancements made at higher length scales can be hampered by insufficient modeling at lower length scales. This can make industry wide evaluations of methodologies more complicated. For instance, significant advances have been made in recent years to strain rate independent failure theories on the lamina level. However, since the Northwestern Theory is stress dependent, for adequate use in a progressive damage model, a similarly robust constitutive model must also be employed to calculate these lamina level stresses. An improper constitutive model could easily cause a valid failure model to produce incorrect results. Also, any global strain rate applied to a multi-directional laminate will produce a spectrum of local lamina level strain rates so it is important for the constitutive law to account for strain rate dependent deformation.

Brian T. Werner, Joseph D. Schaefer

Chapter 40. Imaging the Life-Cycle of CMCs Using High-Resolution X-Ray Computed Tomography

In this study, the entire life cycle of a ceramic matrix composite (CMC) manufactured using polymer infiltration and pyrolysis (PIP) is imaged using high-resolution X-ray micro-computed tomography (μCT). The entire PIP process is imaged ex situ to capture the evolution of voids and shrinkage cracks during laminate densification. After manufacturing, two specimens are extracted from the CMC laminate, and subsequently tested to failure in flexure and tension at 1000°C. Gray-scale image segmentation methods are used to quantify the evolution of porosity within the microstructure during PIP processing. X-ray μCT image results from in situ testing are qualitatively examined to quantify presence of individual fiber breaks, fiber pull-outs, matrix cracking, fiber-matrix decohesion, to name a few. These results are used to motivate development of new algorithms for segmentation of microstructural features from X-ray μCT data sets.

Peter J. Creveling, Noel LeBaron, Michael W. Czabaj

Chapter 41. Effect of Process Induced Residual Stress on Interlaminar Fracture Toughness on Hybrid Composites

Delaminations are of great concern to any fiber reinforced polymer composite (FRPC) structure. In order to develop the most efficient structure, designers may incorporate hybrid composites to either mitigate the weaknesses in one material or take advantage #of the strengths of another. When these hybrid structures are used at service temperatures outside of the cure temperature, residual stresses can develop at the dissimilar interfaces. These residual stresses impact the initial stress state at the crack tip of any flaw in the structure and govern whether microcracks, or other defects, grow into large scale delaminations. Recent experiments have shown that for certain hybrid layups which are used to determine the strain energy release rate, G, there may be significant temperature dependence on the apparent toughness. While Nairn and Yokozeki believe that this effect may solely be attributed to the release of stored strain energy in the specimen as the crack grows, others point to a change in the inherent mode mixity of the test, like in the classic interface crack between two elastic layers solution given by Suo and Hutchinson. When a crack is formed at the interface of two dissimilar materials, while the external loading, in the case of a double cantilever beam (DCB), is pure mode I, the stress field at the crack tip produces a mixed-mode failure. Perhaps a change in apparent toughness with temperature can be the result of an increase in mode mixity. This study serves to investigate whether the residual stress formed at the bimaterial interface produces a noticeable shift in the strain energy release rate-mode mixing curve.

Brian T. Werner, Kevin Nelson, Ciji Nelson

Chapter 42. Analysis of Interfaces in AA7075/ Recycled WC Particles Composites Produced via Liquid Route

Casting of composites is a simple and low cost route to produce composites, which allows numerous possibilities in terms of reinforcement location in the cast part and high geometry flexibility of the products. However, interfaces between reinforcement and metal depend on the behaviour of the particles in liquid metal during processing. The work investigates the effects of parameters such as temperature and time of contact between WC particles and liquid aluminium, and reinforcement content, in the production of cast AA7075/WC composites. WC particles coming from recycled cutting tools are used as reinforcement for aluminium alloys AA 7075, widely used in aeronautical domain. Reinforcement contents of 15 and 30 wt %, temperatures of 700, 740 and 780C, and contact time of 1, 2, 3 and 4 h were the values of the investigated variables. Microstructure of cast composites produced under these conditions were analysed by OM, SEM and EDS microanalysis. A reaction layer was found in the interface between metal and WC, with composition and micro constituents depending on the studied parameters. A mechanism of formation of the reaction layer is proposed.

Marina Ferraz Viana, Maria Helena Robert

Chapter 43. Investigation on Microstructure and Interfaces in Graded FE50007 / WC Composites Produced by Casting

Graded composites of grade FE50007 nodular ductile iron reinforced with WC granules grinded from recycled cutting tools, were produced by casting, using lost foam technique. Reinforcement granules were forced to be located in a specific region of the part by controlling flow during pouring. Different casting conditions were investigated (reinforcing granules content and dimensions). Resulting microstructures were extensively analysed to investigate eventual phases modifications in the iron matrix among reinforcing particles and interface interactions or possible reactions. Results show that WC granules deteriorates in contact with liquid metal, by diffusion of binder elements, detaching WC individual particles, resulting in a smooth and continuous interface; any kind of reaction is observed in the interface. The presence of the ceramic particles modifies the alloy microstructure within the reinforced region due to thermal and chemical local features. Preliminary studies on wear behaviour for a specific cast product developed (an impact crusher) are also presented, indicated superior performance compared to commercial crushers.

Rodolfo Leibholz, Henrique Leibholz, Emin Bayraktar, Maria Helena Robert

Chapter 44. In-Situ Imaging of Flexure-Induced Fracture in Fiber-Reinforced Composites Using High-Resolution X-Ray Computed Tomography

This work presents a new test method which allows for in situ high-resolution X-ray computed tomographic imaging of flexure-induced fracture in tape-laminate composites. Specimens with two distinct stacking sequences were tested to visualize, in 3D, the evolution of intralaminar ply cracks and delaminations as a function of the applied bending moments. The first laminate, which had small angle changes between adjacent plies, produced a fracture pattern that consisted solely of intralaminar cracks. The second laminate, having a more traditional quasi-isotropic stacking sequence, evolved a fracture surface that contained interacting intralaminar cracks and delaminations. The vastly different fracture surfaces obtained from both laminates provide invaluable, and previously unobtainable, 3D information for validation of existing and future progressive damage models.

Brian P. Wingate, Michael W. Czabaj
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