Challenges in Mechanics of Time Dependent Materials, Fracture, Fatigue, Failure and Damage Evolution, Volume 2

This paper explores the performance improvements of a 2013 Ford Mustang Shelby GT500 resulting from changes to the rear axle housing. In previous work, described in (Peters et al., In Optimal Design of an Automotive Rear Axle Housing. Proceedings of the 2018 IAJC International Conference, Orlando, FL, 2018; Patel, In Design, Analysis, & Optimization of 8.8 Inch Rear Axle Differential Housing, MS Thesis, Kettering University, Flint, MI, 2017), the rear axle housing was optimized in order to minimize its weight. It was expected that the decrease in weight would lead to improved fuel economy; in this work, the vehicle was simulated for the EPA highway drive cycle (HWFET) both before and after the optimization of the housing, in order to quantify the changes in fuel economy. It was found that the optimization of the housing did produce a modest improvement in the chassis energy demand and in the fuel energy demand.

Fracture behavior of high-stiffness and low-toughness materials such as soda-lime glass typically involves crack branching, a phenomenon which has not been well-understood. Attempts to shed light on this issue via full-field optical investigation has been hampered by numerous spatio-temporal experimental challenges as crack speeds in these materials reach upwards of 1500 m/s accompanied by highly localized small deformations. In this work, three different optical techniques—transmission photoelasticity, 2D Digital Image Correlation (DIC) and transmission-mode Digital Gradient Sensing (DGS)—are separately implemented to comparatively assess their efficacy to study crack growth and branching in soda-lime glass plates. Each method is implemented in conjunction with ultrahigh-speed photography (1–2 Mfps), flash/pulse illumination and a modified-Hopkinson pressure bar on nominally identical wedge impact experiments. Visualization of results from these experiments along with preliminary observations on their pros and cons of each approach for this material system are presented.

Many syndrome and disorders have been reported by worker due to long time use of the hand tools. These disorders have been collected by the International Standard Organization (ISO) to help workers maintain safe operation. Anti-vibration gloves have been proposed to attenuate vibrations that transfer from hand tools to the human body, but these gloves are not effective for this purpose. Here we report experimental work and calculations done on the weed wacker to devise a method to attenuate the vibration of this hand tools. An absorber was fabricated by 3D printing and installed on the shaft between the engine and the handle. The location of the absorber on the shaft was investigated to find the optimum location of vibrational attenuation. Because the absorber is designed as a ring, it can absorb the vibration in all three directions. The optimized absorber reduced vibration by about 75% compared to the vibration of weed wacker without an absorber. Our results also indicate that the location of the absorber is very important to optimize its effectiveness. We found that the best position is close to the engine and away from the handle.

The crack initiation and growth in single-edge notched unidirectional T800s/3900-2 carbon fiber reinforced polymer composites (CFRP) are studied under stress wave and quasi-static loading conditions. The reflection-mode Digital Gradient Sensing (or, r-DGS) is extended here to study fracture mechanics of fiber reinforced composites by using it in conjunction with ultrahigh-speed photography to perform full-field measurement of crack-tip deformations in the pre- and post-crack initiation regimes. The optical method is capable of measuring two orthogonal surface slopes in the crack-tip vicinity as angular deflections of light rays in two mutually perpendicular planes due to crack-tip deformations. The effect of fiber orientation of 0°–60° relative to the initial notch in different composite coupons and the effect of different loading rates are investigated. Nominally mode-I fracture occurs when the fiber orientation is 0° whereas mixed-mode (mode-I and -II) fracture ensues in others. The fiber bridging effects are quite evident in the energy release rate histories, which conveys that fracture behavior of CFRP with dynamic loading producing a weaker post-initiation response relative to the quasi-static counterparts.

Aluminum materials are utilized across many industries, spanning from the cycling, automotive, aerospace, and the marine industry. In the latter, marine grade aluminum materials are utilized to construct the hull, appendages, and/or specific components. In particular, 5xxx series aluminum materials are relied on by the marine industry for these purposes, where their material properties are advantageous to reducing the overall weight of naval platforms and reducing their operational cost. During its lifetime, a marine vessel will experience a multitude of variable amplitude loading conditions, with occasional overloads and underloads depending on the sea environment encountered. In some cases, these overloads/underloads result affect the catastrophic failure of the structure and associated design lifetime due to changes in the crack growth rate in 5xxx aluminum materials. Existing models, like the Wheeler, Willemborg, and variations of these, have been utilized to predict the crack growth behavior with varying degrees of success. In this study, we created experimental matrices to explore the effects of overload/underload combinations on fatigue crack growth in 5xxx aluminum. Both visual inspection of crack tip location and Digital Image Correlation (DIC) characterization of the crack tip deformation fields were used to characterize the crack growth in center crack tension (CCT) panel specimens. DIC also enabled additional analysis of strain fields to elucidate on the conditions responsible for the change in the crack growth behavior. Future phases of this work will utilize this data to develop new models for fatigue crack growth.

In this work, we investigated microstructural features of elastomeric foam with the goal of identifying descriptors other than porosity that have a significant effect on the macroscale mechanical response. X-ray computed tomography (XCT) provided three-dimensional images of several flexible polyurethane foam samples prior to mechanical testing. The samples were then compressed to approximately 80% engineering strain. Stereo digital image correlation was used to measure the three-dimensional surface displacement data, from which strain was determined. The strain data, which were calculated with respect to the undeformed coordinates, were then overlaid on the corresponding surface generated from XCT. Heterogeneities in the strain-field were cross-correlated with topological quantities such as pore size distribution. A statistically significant correlation was identified between the distance transform of the pore phase and strain fluctuations.

Carbon fiber reinforced thermoplastics are consisted with the carbon fiber and thermos plastics such as PP, PA6, PI, and PC and so on. Mechanical properties, especially viscoelasticity, of CFRTP were depended on the matrix resin, therefore, if the mechanical properties of matrix resin has changed, CFRTP’s properties will be also changed. In this study, carbon fiber reinforced polyamide 6 was used for evaluate the effect of crystallization. The materials were heat treated for crystallization, and the crystallization was controlled by heat treatment time. As the result of dynamic mechanical analysis, storage modulus was decreased with the increase in the heat treatment time, however, longer heat treatment time made the storage modulus increased. As the results of DSC measurement, the peak shape of melting point was different each other. The double peak was observed with the longer heat treatment time, however, the single peak was observed with the short heat treatment time. This is because the mechanical properties of CFRTP was dominated by the peak shape and peak area of the melting point.

For soft adhesives, a Rigid Double Cantilever Beam (RDCB) experiment has recently been shown to be a convenient way for extracting traction-separation (σ-δ) relationships. An implicit expression of the σ-δ relationship is derived by Brock et al. (J. Adhesion, 2018) assuming small rotation of the beams and a linear traction separation relationship in the compressive zone. In this work, an explicit expression of the σ-δ relationship for a Rigid Double Cantilever beam (RDCB) for large deformation of the adhesive including the effect of a compressive zone ahead of the cohesive zone is used for direct extraction of σ-δ relationship. The expression for the σ-δ relationship is in terms of quantities that can be directly measured using the full-field deformation measurement technique, StereoDIC. Using RDCB analysis, the traction at the Sylgard 184-aluminum interface where adhesive failure occurs is obtained by simultaneous measurement of separation of the adherends at the crack tip, separation at the end of the compressive zone (far end of the beam ahead of the crack tip) and load. The true separation of the crack surfaces at the interface is obtained by measuring δ, the relative displacement of two points separated by 0.05 mm across the interface. It is shown that the compressive zone in the adhesive has a significant effect on the σ-δ relationship. The maximum traction and maximum separation are found to be 0.33 MPa and 5.5 μm respectively. The energy release rate obtained by calculating the area under the σ-δ curve is 1.13 J/m².

The method of thin-wall tube torsion to characterize metal’s shear response is well-known. Unfortunately, the thin wall tube specimen tends to buckle before reaching large shear deformation and failure. An alternative technique, which has rarely been considered, is Nadai’s surface stress method (Nadai, Theory of Flow and Fracture of Solids. McGraw-Hill, New York, 1950). It derives shear stress-strain curve from the torque-twist relationship of a solid bar. Although the analysis is more complex due to nonlinear shear stress distribution along the radius, the deformation is stable through large shear deformation to failure.

Solid bar torsion experiments were conducted to study large shear deformation of Al6061-T6. Two experiments were described in this study. Since few tests were available in the literature, these experiments were to explore the large deformation behaviors of an engineering alloy and the application of modern measurement techniques, such as 3D DIC method, under torsion. Results show during twisting, the surface shear strain distribution was uniform initially and then localized on a narrow band; eventually, the specimen was cracked and failed within the band. Depending on the specimen size, the twist could be greater than 360°. Details are discussed.

In this study, a hybrid experimental-numerical approach is used to determine the mixed mode (mode I/III) dynamic fracture initiation toughness of aluminum alloy. Cylindrical specimens with spiral v-notch at a revolution angle of 360°and pitch angles 22.5°(inclined angles) are fabricated from aluminum rod. A torsional Hopkinson bar apparatus is used to generate and apply a dynamic torsional load on the specimens. A stereo digital image correlation is used to measure full-field displacements around the crack tip and to estimate the fracture initiation time. A commercial finite element software (ABAQUS) is used to extract a dynamic stress intensity factors based on interaction integral method. The stress distribution, full-field deformation with time, and the mixed mode fracture toughness are discussed.

The present contribution is toward the systematic characterization and development of a one-dimensional incremental viscoelastic (VE) model for thermo-rheologically complex materials (called “VisCoR”) for the prediction of residual stresses and shape distortions in composites. Traditionally, models that have been developed for this purpose within the composites industry are based on incremental linear elastic methods. While these methods are robust, they fall short in predicting exact behaviour of large composite parts and high temperature composites where relaxation effects also play a vital role in the final shape of the part. Moreover, these models also do not consider the dependency of stresses on temperature and degree of cure. Although viscoelastic models have been formulated, they are not in an incremental form (which is suitable for Finite Element (FE) simulations), hence requiring higher computational efforts. The presented model is an incremental form and requires lesser computational cost and characterization efforts and most importantly takes into account the effect of temperature and degree of cure. Preliminary studies indicate that the incremental 1D viscoelastic model can accurately model VE stress relaxation behaviour when compared to exact solutions.

Despite the many advances made in material science, stainless steel and aluminum remain the structural materials best-suited for the naval fleet. While these metallic materials offer many benefits, such as high strength and good toughness, their persistent exposure to the maritime environment inevitably leads to issues with corrosion. Among the various manifestations of corrosion, pitting corrosion is of particular concern because the transition of corrosion pits to stress-corrosion cracks can lead to catastrophic failures. Traditional pitting corrosion analyses treat the pit shape as a semi-circle or ellipse and typically assume a growth pattern that maintains the original geometrical shape. However, when the underlying microstructure is incorporated into the model, pit growth is related to the grains surrounding the pit perimeter and the growth rate is proportional to crystallographic orientation. Since each grain has a potentially different orientation, pit growth happens at non-uniform rates leading to irregular geometries, i.e., non-circular and non-elliptical. These irregular pit geometries can further lead to higher stresses.

This work presents a detailed look at corrosion pit growth coupled with mechanical load through a numerical model of a two-dimensional stable corrosion pit. Real microstructural information from a sample of 316 stainless steel is incorporated into the model to analyze microstructural effects on pit growth. Through this work, stress distributions and stress intensity factors are examined for a variety of pit geometries, including comparisons of their range of values to a typical, semi-circular pit. The consequences of these stress distributions and concentration factors are discussed.

In an effort to enhance both the experimental testing and computational modeling of small threaded fasteners, a collaborative investigation consisting of experimental tensile testing and computational modeling was conducted to observe the effects of threaded fastener size on load-displacement behavior and failure. This paper focuses on the experimental tests performed on NAS1351N00–4, NAS1352N02–6, NAS1352N04–8, NAS1352N06–10, and NAS1352N4–24 (referred to herein as #00, #02, #04, #06 and #4, respectively) A286 fasteners. Displacement measurements were obtained from three unique sources/locations: Differential Variable Reluctance Transducers (DVRTs) inserted in the top bushing to measure the relative displacement of the bushing faces, Linear Variable Differential Transducers (LVDTs) located on the outside edge of the bushing fixtures to measure a more global response of the bushing displacement, and the stroke of the test frame. This test series clarified many ambiguities in the experimental process and further established a feasible testing method for small fasteners.

The dynamic tensile properties of additively manufactured (AM) and cast Al-10Si-Mg alloy were investigated using high-speed X-ray imaging coupled with a modified Kolsky bar apparatus. A controlled tensile loading (strain rate = 750 s⁻¹) was applied using a Kolsky bar apparatus and the deformation and fracture behavior was recorded using the high-speed X-ray imaging setup. The recorded high-speed frames were used to identify the location of the critical flaw and to capture the dynamics of crack propagation. In all experiments, the critical flaw was located on the surface of the specimen. The AM specimens showed significantly higher crack propagation speed, yield strength, ultimate tensile strength, strain hardening coefficient, and lower ductility compared to the cast specimens under dynamic tension. The microstructures of the samples were characterized by synchrotron X-ray tomography. The correlation between the dynamic fracture behavior of the samples and the microstructure of the samples was analyzed and discussed.

Material characterization by way of fatigue testing is a common practice in materials research. This research is then applied to many different engineered devices, one of which includes the gas turbine engine. In the environment of a turbine engine the fatigue life plays a critical role in the design, operation, and maintenance of the engine. This study uses the fatigue life of two different metals (Titanium 6Al-4 V, Aluminum 6061-T6) with different cross-sectional measurements to assess the fatigue viability of another material (additively manufactured Inconel 718, or AM IN-718). The assessment of AM IN-718 fatigue life is done by normalizing all the fatigue data against respective ultimate tensile strength results obtained from monotonic tests. The data from two different gage section types for Titanium (Ti) 6Al-4 V and Aluminum (Al) 6061-T6 specimens show that the comparability of the normalized fatigue results fit within a 99% prediction interval. The viability assessment of IN-718 highlighted concerns in the material integrity, and this finding, guided by the normalized fatigue data of Ti 6Al-4 V and Al 6061-T6, led to the identification of flaws which were artifacts of poor AM process controls.

Natural rubber (NR) is the most commonly used elastomer in the automotive industry thanks to its outstanding fatigue resistance. Strain-induced crystallization (SIC) is found to play a role of paramount importance in the great crack growth resistance of NR (Lindley, Int J Fracture 9:449–462, 1973). Typically, NR exhibits a lifetime reinforcement for non-relaxing loadings (Cadwell et al., 1940; Ruellan et al., 2019). At the microscopic scale, fatigue striations were observed on the fracture surface of Diabolo samples tested in fatigue. They are the signature of SIC (Cadwell et al., 1940; Le Cam et al., 2013; Le Cam et al., 2004). In order to provide additional information on the role of SIC in the fatigue crack growth resistance of NR, striations are investigated through post-mortem analysis after fatigue experiments using loading ranging from −0.25 to 0.25. No striation was observed in the case of tests performed at 90 °C. This confirms that the formation of striation requires a certain crystallinity level in the material. At 23 °C, two striation regimes were identified: small striation patches with different orientations (Regime 1) and zones with large and well-formed striations (Regime 2). Since fatigue striations are observed for all the loading ratios applied, they are therefore not the signature of the reinforcement. Nevertheless, increasing the minimum value of the strain amplified the striation phenomenon and the occurrence of Regime 2.

In the current study, experiments are performed on the aero-engine compressor blade model which is fastened to the disc using dovetail joint. Using the technique of photoelasticity, the highly stressed zone is found to be at the interface of the disc and the blade. Cyclic loading is then applied to the disc-blade assembly. Initial experimental observations showed formation of small cracks leading to crack growth and subsequent failure. In this region, a small crack is put and then the growth of crack during cyclic loading is studied till the failure of the specimen. The variation of stress intensity factor with respect to crack length and the number of cycles is evaluated for crack perpendicular to the contact length.

High-throughput methods of measuring mechanical properties can accelerate materials discovery and processing route developments. These metrics of material performance get incorporated into both physics-based (ICME) and statistical machine-learning Processing-Microstructure-Properties (PMP) models. Conventional mechanical testing techniques, such as tensile testing, require large material volumes and become expensive and challenging when quantifying a statistically significant number of observations to enable process optimization thru PMP models of homogeneous materials; not to mention the added complexity of purposefully engineered inhomogeneous materials. Instrumented microhardness machines enable the extraction of indentation stress-strain curves from load-displacement curves as a proxy metric for more time/cost intensive uniaxial stress-strain curves. This versatile technique characterizes the local stress-strain behavior from small material volumes by modifying Hertz theory on the stresses between elastic solids. In this paper, an automated algorithm, written in Python (v2.7), is presented to apply modified Hertz’s theory to extract the Elastic Modulus and indentation stress-strain curve from the load-displacement data. Two methods of assuming the contribution of the elastic deformation of the indenter are presented. First, the algorithm works through the assumptions made by Khosravani et al. and presents these results in comparison to a second method of assuming that the contribution of the indenter elastic deformation is sufficiently small that it is assumed constant and can be approximated from the size of the indent on the sample surface. The algorithms are compared using microhardness measurements from a nickel-base superalloy, LSHR and show that the Elastic Modulus and the yield strength values are in reasonable agreement with the reference literature. The assumptions on the effect of the indenter elastic properties has effects on the shapes of the plastic part of the curve; the Khosravani et al. method seems to underestimate the work hardening properties of the material; while the other method overestimates the work hardening properties. Therefore, utilizing both methods provides proxy measurements of the potential upper and lower bounds of the work hardening behavior beyond the yield strength of the material which could be helpful for PMP models.

Several experiments have reported rate dependent roughening of crack surfaces in brittle hydrogels following slow crack propagation, 0.1–1 mm/s. We conduct in-situ 2D imaging of an internal plane of propagating cracks and volumetric imaging of stationary cracks using confocal microscopy for very slow crack speeds, 0.01 mm/s, in thin brittle hydrogel specimens. We seek to better understand the mechanisms at play in these slow crack roughening events by observing both crack propagation and renucleation. Additionally, we study the crack tip region and crack shape to infer fracture toughness of the gel. Observations suggest that toughening mechanisms are at play in these surface roughening events and lead to crack arrest followed by renucleation at a “weak” point in the crack surface. Based on these observations, we hypothesize that there are two interconnected mechanisms at play: The crack is slow enough that the gel “sees” the stress concentrations at the crack tip and water is forced out of the gel while there is also time for viscoelastic and plastic processes to occur.

Maximization of the rate of dissipation is applied to develop a viscoelastoplastic damaging material model with anisotropic properties and finite deformation. The thermodynamic framework suggests a new damage activation criterion based on the sum of stress and an energy release rate based on a damage-based strain measure. The framework combines the usually disjointed ideas of effective stress and damage strain kinematics to track the dimensional changes attributed to damage while retaining the physical link to load-bearing area reduction. Potential applications include large volume change oxidation of SiC CMC composites, high temperature creep and relaxation influences on damage processes in reinforced polymers and ceramics, and opening/closing of cracks via natural elastic behavior as opposed to treatments based on loading criteria.

Maximum rate of dissipation analysis is applied to develop a framework corresponding to a material model incorporating three strain elements characterized by viscoelastic, damage, and viscoplastic behaviors. A push-pull framework associates these behaviors with respective multiplicative deformation gradients with rates determined by Lie material derivatives.

A modular vibration-based fatigue test capability that significantly minimizes the effects of boundary conditions has been developed. The system utilizes a specimen with boundary conditions on its node lines, which isolates the gage section for deflection as a free-free beam in its first bending mode. The thin specimen is suspended inside an electromagnet by 6 lbs. monofilament fishing line, and permanent magnets are bolted to the bottom of the specimen. The alternating current inside of an electromagnet attracts and repels the permanent magnets rapidly (~55 Hz for a 0.016? thick specimen), causing the beam to cycle in first bend. This testing capability is ideal for generating and assessing fatigue life of thin specimens requiring large deflections for failure. Understanding and characterizing fatigue behavior of thin components is important, especially since the emergence of additive manufacturing (AM) for small, fatigue susceptible components. An alternate solution is to suppress the vibratory susceptibility of the component. Therefore, the importance of thin coatings capable of providing damping to components is on par with fatigue characterization. In this study, 0.4 mm cold-rolled Titanium (Ti) 6Al-4 V specimen were fatigued and compared to published data. Also, a thin damping coating (titanium nitride, or TiN) was applied to a few Ti 6Al-4 V specimens to assess the performance. Both the fatigue and damping assessments are necessary to validate the free-free test method.

This research analyzes a novel high-throughput method for vibration-based fatigue testing. This method builds off previous research by Bruns and Zearley, where a carrier plate assembly containing a test specimen vibrates to failure. This method redesigns an aluminum carrier plate to simultaneously load three, instead of one, test specimens in parallel. The redesign was selected, using SolidWorks modal analysis, based on its ability to concentrate cyclic stress on the specimens, rather than on the plate, to extend the life of the plate. For experimental validation, the redesigned plate assembly was fatigued with an electrodynamic shaker following the same procedures as Bruns’ and Zearley’s assembly. The assembly was monitored with stereo digital image correlation to detect mode shape. Although the assembly exhibited the same mode shape as simulation experiments, fatigue tests could not be completed due to the large accelerations required to generate relatively small strains. Additional work is needed to identify other multi-insert designs capable of exerting larger fatigue strains.

This paper outlines an empirical correlation method combining quasi-static tests in tension and compression, and high strain-rate tests in compression, with dynamic mechanical analysis and time-temperature superposition. A generalized viscoelastic model incorporating continuum damage is calibrated. The results show that a model calibrated using data from quasi-static compression and dynamic mechanical analysis can be used to adequately predict both the quasi-static tensile and the compressive high strain rate response.

Hydrogels are hydrophilic polymer networks. They have a defined geometry, which gives them solid like characteristics. Hydrogels also exhibit liquid like nature since certain soluble molecules diffuse through the hydrogel matrix. These characteristics of hydrogel make it extremely difficult to determine the mechanical properties through conventional methods. A new in-plane shear test method that incorporates 3D printed parts and digital image correlation (DIC) was developed. 3D printed parts were used as loading fixture to ensure the appropriate grip on the hydrogel. DIC was used to measure the properties and validate the test methodology. It was identified that shear modulus could be calculated to within 5% coefficient of variation at about 20% strain. Future research will identify ways to increase the limit of the stress-strain curve for calculating shear properties.

Preliminary investigation on mechanical properties of a Nb-strengthened and nitrogen-stabilized Fe-25wt.%Ni-20Cr (Alloy 709) advanced austenitic stainless steel suggests that it might be a potential candidate for Sodium-Cooled Fast Reactor (SFR), which has higher technology readiness level for deployment. However, the creep-fatigue deformation behaviour is unknown for this alloy. To understand high temperature creep-fatigue interaction of the Alloy 709, strain-controlled low-cycle fatigue (LCF) tests were performed at strain amplitudes ranging from 0.15% to 0.6% with fully reversible cycle of triangular waveform at 750 °C in air following ASTM standard E2714–13. In addition, different hold times of 1, 10, 30 and 60 min were introduced at the maximum tensile strain to investigate the effect of the creep damage on the fatigue-life at strain amplitude of 0.5% at 750 °C. During continuous cyclic loading, fatigue life is found to decrease with increase in strain amplitude. The creep-fatigue life and the number of cycles to crack initiation are found to decrease with increasing hold time indicating the rapid initiation and propagation of cracks. The fractographs of the samples deformed at 0.5% strain amplitude indicated that fatigue might have been the dominant mode of deformation whereas, for the sample deformed at the same strain amplitude with different hold times, both fatigue and creep have contributed to the overall deformation of the alloy. Further studies are underway to carry out creep-fatigue tests at different hold times, strain ranges, and temperatures as well as microstructural characterization of the samples following deformation.

Polyurea (PU) is a microphase-segregated elastomer synthesized through bulk polymerization of isocyanates and amines. Polyurea has previously been shown to be an excellent medium in absorbing energy from blast and shock waves, especially when layered with metallic components. The focus of the present work is to evaluate the thermo-mechanical properties of polyurea considering three different hybrid blend formulations. Hybrid polyurea specimens are synthesized by reacting a blend of diamines of long and short chains (Versalink P-1000 and P-250) with weight ratios of 70:30% and 80:20%, with Isonate 143 L and compared with a previously studied blend of 76:24%. This original blend formulation has been shown to have mostly similar properties to a standard PU formulation that uses medium length chain diamines (VP-650) and the same overall hard domain proportion. However, the blend formulation shows wider transition and loss spectra. Thermal phase transition and conductivity measurements are performed to better comprehend the thermal characteristics of the proposed blend formulations. Storage and loss moduli DMA master-curves along with high strain rate data at room temperature using split Hopkinson pressure bar (SHPB) will be presented. The high strain rate experiments are conducted in unconfined and confined configurations to asses shear and bulk responses of material. The overall objective of this approach is to propose fine-tuned blend formulations that can provide a balanced stiff and tough elastomeric response.

Polyurea is one of the widely used materials in the coating industry and is well known to form a mechanically robust elastomeric network. Due to its toughness and ease of application, it has been studied as a potential protective coating in cavitation erosion conditions. The temperature rise within the polyurea under such harsh loading conditions can lead to significant softening and rapid failure of the coating, while in slightly lower intensity situations the coating may not show any signs of damage. Therefore, controlling the temperature rise due to dissipative heating may lead to better and more reliable coatings. Reinforcing the polyurea with milled carbon fibers not only has the benefit of increasing its thermal conductivity (hence distributing localized heating to larger volumes), it could also increase its stiffness, while maintaining its elastomeric nature (in contrast with continuous fiber composites). The milled fibers may be dispersed within the polyurea matrix in 3D randomly oriented arrangements or may be aligned parallel to the coated surface in very thin layers. The aim of this study is to investigate the thermal and mechanical behavior of such composites. The matrix polyurea specimen is synthesized by reacting a mixture of medium length diamine (Versalink P-650) with isocyanate 143 L. Thermal phase transition (DSC) and thermal conductivity measurements (using MDSC) are performed to accurately measure the thermal properties of such composites. DMA tests are conducted to construct the storage and loss moduli master curves. Stress-strain curves under uniaxial loading at high strain rates are obtained using split Hopkinson pressure bar (SHPB). Results show a significant increase in thermal conductivity and stiffness. The presented study assesses the feasibility of improving elastomer-based coatings for protection against harsh cavitation erosion conditions.