Rate-dependent Stress Strain Behavior Research Articles

Temperature and strain rate dependent stress-strain behaviour of nitinol

This paper reports on molecular dynamic simulation approach for the modeling and simulation of nanocrystalline Nitinol (NiTi). The relation between stress–strain behaviour of NiTi at the multiple steps of temperature ranging from 300 K to 1300 K at a particular strain rate 1 × 10 -1 sec -1 and observed at a fixed temperature of 300 K with the variation in strain rate in the order of tens. It has been noticed that the value of stress-bearing capacity of NiTi is decreasing slowly with the increasing temperature in the multiple steps from 300 K to 1300 K and the value of strength in the stress-strain curve of NiTi increases with increase in strain rate at that particular temperature. Elastic constant and ultimate strength at different temperatures and strain rates were also recorded to examine their individual dependence on the stress–strain behaviour of NiTi alloy.

Fractional viscoplastic model for soils under compression

Soils in the field are often subjected to time-dependent compression, where the induced shear strength and deformation could be different upon different loading rates. To capture the rate-dependent stress–strain behaviour of soils under compression, a stress-fractional viscoplastic model is developed in this study, based on Perzyna’s overstress theory. The viscoplastic flow direction of soil is modelled with a unit tensor obtained by performing fractional derivatives on the yielding surface. With the increase in the fractional order, the predicted compressive shear strength varies, and a transition from pure strain hardening to strain hardening and softening is observed. Additionally, as the strain rate increases, the predicted shear strength increases, which agrees well with the corresponding experimental observations. Further validation against a series of oedometer and triaxial test results under different strain-rate loads indicates that the fractional-order viscoplastic model can efficiently capture the rate-dependent behaviour of soils.

Material model parameter estimation with genetic algorithm optimization method and modeling of strain and temperature dependent behavior of epoxy resin with cooperative-VBO model

A constitutive model is proposed for modeling rate and temperature dependent stress-strain behavior of amorphous polymers. The model developed here is a modification of cooperative-viscoplasticity theory based on overstress (VBO) model. The modifications are performed to capture the temperature dependent behaviors below and through the glass transition temperature (Tg) of amorphous polymers as well as rate dependency from quasi static to high strain rate loading. In the proposed constitutive model, adiabatic heating due to high strain rate deformations is included to capture the high strain rate behaviors. The temperature dependent behavior below, around and through Tg will be captured with the modifications performed on the viscoplastic strain rate. The model has been shown to be predictive of compression behavior of DER 353 epoxy at quasi and high strain rates and a temperature range from room to Tg. The genetic algorithm (GA) parameter optimization procedure has been proposed to determine material parameters of the models. The model parameters are determined using GA optimization method. The newly modified model is able to capture the mechanical behavior below and through Tg and also all of the features of the large strain behavior, including the initial modulus, yield stress, strain softening and strain hardening.

High Strain Rate Behavior of Aluminum Produced by Powder Metallurgy

The presented study compares the compressive high strain rate behavior of Aluminum (Al) specimen fabricated from the powder as received, with the effect of ball milling and incorporation of high rock salt percent. Four different types of sample specimens were fabricated by compacting Aluminum powder followed by sintering in Argon atmosphere at 600 °C for 3 hours. Sample types comprised of (i) Aluminum powder as received, (ii) ball-milled Aluminum powder for 24 hours, (iii) Aluminum powder with 33% rock salt and (iv) specimen of type three boiled in a water bath, respectively. The compressive high strain rate testing was done on a 16 mm Titanium bars based Split Hopkinson Pressure Bar (SHPB). For identical incident energy, different strain rates and stresses were attained by these four different types of Al samples. Ball milling of Al powder for 24 hours resulted in significant property variation, which enhanced the peak stress under compressive high strain rate loading. However, the damage pattern shifted from ductile in case of non-milled powder to partly brittle damage for ball milled Al specimens. Incorporation of higher rock salt percent was meant to produce relatively low-density Al. The resulting compressive stresses recorded were much lower and the corresponding damage was brittle in nature. Boiling in water bath dissolved salt but could not enhance the properties of Al specimen. The study reveals the importance of Al powder processing on the rate dependent stress-strain behavior of Aluminum specimen fabricated by powder metallurgy route.

Development of a Flow Evolution Network Model for the Stress-Strain Behavior of Poly(L-lactide).

Computational modeling is critical to medical device development and has grown in its utility for predicting device performance. Additionally, there is an increasing trend to use absorbable polymers for the manufacturing of medical devices. However, computational modeling of absorbable devices is hampered by a lack of appropriate constitutive models that capture their viscoelasticity and postyield behavior. The objective of this study was to develop a constitutive model that incorporated viscoplasticity for a common medical absorbable polymer. Microtensile bars of poly(L-lactide) (PLLA) were studied experimentally to evaluate their monotonic, cyclic, unloading, and relaxation behavior as well as rate dependencies under physiological conditions. The data were then fit to a viscoplastic flow evolution network (FEN) constitutive model. PLLA exhibited rate-dependent stress-strain behavior with significant postyield softening and stress relaxation. The FEN model was able to capture these relevant mechanical behaviors well with high accuracy. In addition, the suitability of the FEN model for predicting the stress-strain behavior of PLLA medical devices was investigated using finite element (FE) simulations of nonstandard geometries. The nonstandard geometries chosen were representative of generic PLLA cardiovascular stent subunits. These finite element simulations demonstrated that modeling PLLA using the FEN constitutive relationship accurately reproduced the specimen's force-displacement curve, and therefore, is a suitable relationship to use when simulating stress distribution in PLLA medical devices. This study demonstrates the utility of an advanced constitutive model that incorporates viscoplasticity for simulating PLLA mechanical behavior.

Development of a new 3D model for the prediction of residual stress and fracture behaviour in Ti-6Al-4V after ultrasonic peening treatment

Experimental and numerical studies have been carried out to determine the residual stress in Ti-6Al-4V after Ultrasonic Peening Treatment (UPT). Ultrasonic vibration output from the test equipment transducer was employed as the load to simulate the test conditions and the residual compressive stress in the material was measured by X-ray diffraction (XRD). A Johnson-Cook constitutive model was used to describe the rate-dependent stress-strain and failure behaviour of a sample. Based on motion analysis of the peening needle, a new 3D peen-rebound-peen (PRP) finite element model was developed to predict the stress field during and after the UPT process, using ABAQUS. The residual stresses predicted by the PRP model are in good agreement with the XRD results for the same peening and sample conditions. The effect of the gap width between the needle and the sample, the constitutive model parameters, and the peening duration were also studied.

Development of a flow evolution network model for predicting the viscoplastic behavior of poly(L-lactide)

Event Abstract Back to Event Development of a flow evolution network model for predicting the viscoplastic behavior of poly(L-lactide) Maureen Dreher1*, Srinidhi Nagaraja1*, Jorgen Bergstrom2* and Danika Hayman2* 1 FDA/CDRH, Division of Applied Mechanics/ Office of Science and Engineering Laboratories, United States 2 Veryst Engineering, United States Introduction: Absorbable polymers are increasingly being used for medical implants that perform a structural role[1]. Computational modeling is critical to device development in order to predict the stress distribution under typical loading conditions. This is especially true for absorbable cardiovascular devices, such as stents, which experience significant plastic deformation when crimped onto a delivery catheter and are cyclically loaded in vivo. However, computational modeling of absorbable devices is significantly hampered by a lack of appropriate constitutive models that capture their viscoelasticity and post-yield behavior. Here, we developed a constitutive model that incorporated viscoplasticity for a common medical absorbable polymer. Materials and Methods: Candidate constitutive models were selected based on the experimental response at 37°C observed during multiple tensile test protocols performed on microtensile bars (thickness=0.5mm, width = 1.42mm, length = 3.8mm) fabricated from poly(L-lactide), i.e., PLLA. The dimensions were chosen in order to be relevant for transcatheter cardiovascular devices. Before testing, all specimens were airbrushed to create a speckled pattern and enable local strain measurements through digital image correlation[2]. The protocols encompassed monotonic ramp (strain rate=0.5%/min, 5%/min, 10%/min), stress relaxation, and “yield point” tests consisting of load/ un-load cycles below and above the yield. Yield point tests provide information on the unloading behavior of the polymer prior to and after yield. The experimental stress-strain data were curve-fit to two candidate constitutive relationships, namely, the Three Network Model (TNM) and a Flow Evolution Network Model (FEN)[3], followed by refinement through finite element simulations of tensile experiments. Both the TNM and the FEN models are capable of capturing large strain viscoplastic behavior, but the FEN model has the advantage of capturing strong softening post-yield. Results and Discussion: Monotonic testing demonstrated that PLLA exhibits rate dependent stress-strain behavior with a significant post-yield region (Fig 1). The peak stress increased with increasing strain rate (47MPa vs 62MPa) while the strain at failure decreased (0.75 vs 0.3). PLLA exhibited significant relaxation prior to and post yield with stress decreases of ~75% and 80% over 30 min, respectively (Fig 2). Yield point tests demonstrate that little hysteresis is generated in linear region. Together, these results suggest that PLLA exhibits complex viscoplasticity that influences the stress level and should be accounted for in computational models of PLLA devices. The FEN model was able to capture these relevant behaviors more accurately than the TNM (NMAD fitness_TNM=9.4, NMAD fitness_FEN=3.5). Conclusion: The FEN constitutive model was able to accurately capture the strain rate dependent loading and unloading behavior which suggests its validity for modeling mechanics of PLLA. This study was funded by the CDRH Critical Path program; We gratefully acknowledge the insights and support David Quinn, PhD

Modeling of the Plastic Deformation of Polycrystalline Materials in Micro and Nano Level Using Finite Element Method

Recent experiments on polycrystalline materials show that nanocrystalline materials have a strong dependency to the strain rate and grain size in contrast to the microcrystalline materials. In this study, mechanical properties of polycrystalline materials in micro and nanolevel were studied and a unified notation for them was presented. To completely understand the rate-dependent stress-strain behavior and size-dependency of polycrystalline materials, a dislocation density based model was presented that can predict the experimentally observed stress-strain relations for these materials. In nanocrystalline materials, crystalline and grain-boundary were considered as two separate phases. The mechanical properties of the crystalline phase were modeled using viscoplastic constitutive equations, which take dislocation density evolution and diffusion creep into account, while an elasto-viscoplastic model based on diffusion mechanism was used for the grain boundary phase. For microcrystalline materials, the surface-to-volume ratio of the grain boundaries is low enough to ignore its contribution to the plastic deformation. Therefore, the grain boundary phase was not considered in microcrystalline materials and the mechanical properties of the crystalline phase were modeled using an appropriate dislocation density based constitutive equation. Finally, the constitutive equations for polycrystalline materials were implemented into a finite-element code and the results obtained from the proposed constitutive equations were compared with the experimental data for polycrystalline copper and good agreement was observed.

Constitutive modeling of the rate-dependent resilient and dissipative large deformation behavior of a segmented copolymer polyurea

Phase-separated segmented copolymers comprised of hard and soft segments can be tailored to offer hybrid mechanical performance including a highly dissipative yet resilient large strain behavior. The phase-separated morphology provides multiple relaxation processes which lead to a rate-dependent stress–strain behavior with a transition in rate sensitivity. In addition to the viscoelastic–viscoplastic dissipation pathways, stretch-induced softening due to microstructural breakdown provides a significant source of dissipation as evident in the hysteresis observed during cyclic loading. Extensive shape recovery is observed upon unloading, showing a highly resilient behavior in tandem with extensive dissipation. Here a microstructurally informed three-dimensional constitutive model is developed to capture the remarkable features of the large strain behavior of the segmented copolymers. The model employs multiple micro-rheological mechanisms to capture the time-dependent nonlinear constitutive responses of both hard and soft domains as well as the stretch-induced softening of the hard domains. In direct comparison to experimental data, the model is found to successfully capture the behavior of an exemplar polyurea copolymer over least six orders of magnitude in strain rate (10−3 to 103 s−1) including a transition in rate sensitivity at 1 s−1. The model is also shown to be predictive of the highly dissipative yet resilient stress–strain behavior under a variety of cyclic loading conditions. The microstructurally informed nature of the model provides insights into tailoring copolymeric microstructures to provide tunable energy storage and dissipation mechanisms in this important class of material.

Coarse-grained modeling of model poly(urethane urea)s: Microstructure and interface aspects

Poly(urethane urea) elastomers are versatile and can be tailored to exhibit a broad range of mechanical response under high strain rate deformation. In this work, we utilize coarse-grained molecular dynamics simulations to elucidate the molecular mechanisms, particularly the effects of hard segment content, intermolecular interaction, and rigidity of the interface between the hard and soft segments on local morphology and rate-dependent stress-strain behavior in the ballistic regime. Simulation results qualitatively agree with available experimental data, where analysis of hard segment orientation during tensile and compression deformation and dynamic strain rate sensitivity was also performed. Further study of the intermolecular interaction on the stress-strain behavior reveals that it has a strong effect on strain hardening, particularly for a rigid interface, once the hard segment content reaches the percolation threshold. Simulation results also show that interface intermolecular interaction could become more dominant over interface rigidity in the initial stress-strain response, particularly below percolation.

A Simple Pneumatic Loading System Controlling Stress and Strain Rates for One-Dimensional Compression of Clay

A simple but automated pneumatic loading system that can control the stress and strain rates for one-dimensional (1D) compression of clay was developed. The rate-dependency of stress-strain behaviour due to the viscous property of clay was investigated by 1D compression tests on standard-size specimens by various loading methods: 1) Standard Consolidation Tests (SCTs), stepwise increasing the axial stress two times every one day; 2) ordinary Constant-Rate-of-Strain (CRS) tests at different strain rates; 3) special CRS tests including unloading and reloading cycles with different stress amplitudes at strain rates of which the absolute value was either kept constant throughout respective tests or changed at the start of reloading; and 4) special CRS tests including a number of sustained loading (SL) during otherwise primary loading or unloading or reloading at constant strain rate. Sufficiently low strain rates were employed to ensure essentially fully drained condition. The followings were found. Despite that the newly developed pneumatic loading system is rather simple, 1D compression tests following such various loading histories as above can be performed on four types of clay rather accurately. The stress-strain behaviour of clay is significantly rate-dependent, exhibiting significant creep strains at SL stages. The creep strain rate is significantly different whether SL starts during otherwise primary loading or unloading or reloading, controlled by the magnitude and sign of the initial strain rate at the start of SL. The whole observed trends of rate-dependent stress-strain behaviour can be qualitatively explained by the non-linear three-component elasto-viscoplastic model extended to cyclic loading conditions.

Constitutive modeling of the rate, temperature, and hydration dependent deformation response of Nafion to monotonic and cyclic loading

The elastic–plastic behavior of the polymer electrolyte membrane (PEM) Nafion is characterized via monotonic and cyclic uniaxial tension testing as a function of strain rate, temperature, and hydration. Dynamic mechanical analysis shows that, under dry (30%RH) conditions, the material begins to transition from the glassy to the rubbery state at 75 ° C, with a glass transition of 105 ° C. DMA reveals the fully hydrated state to be significantly more compliant than the dry state, with a glass transition beginning at 40 ° C. Large strain monotonic tensile tests find the rate-dependent stress–strain behavior to be highly dependent on temperature and hydration. The dry state transitions from an elastic–plastic behavior at 25 ° C to an increasingly more compliant behavior and lower yield stress as temperature is increased through the glass transition, until exhibiting a rubbery-like behavior at 100 ° C. At 25 ° C, the stress–strain behavior remains elastic-plastic for all hydrated states with the stiffness and yield stress decreasing with increasing hydration. Increasing hydration at all temperatures acts to decrease the initial elastic stiffness and yield stress. Unloading from different strains reveals the elastic-plastic nature of the behavior even for the elevated temperature and hydrated states. Cyclic loading-unloading-reloading excursions to different strains show significant nonlinear recovery at all strains past yield with a highly nonlinear reloading behavior which rejoins the initial loading path. A micromechanically motivated constitutive model consisting of an intermolecular resistance in parallel with an elastic network resistance is shown to be capable of capturing the rate, temperature, and hydration dependence of the monotonic stress-strain behavior. The intermolecular resistance captures the local intermolecular barriers to initial elastic deformation and also captures the thermally activated nature of yield; these intermolecular barriers are modeled to decrease with increasing temperature and hydration, in particular mimicking the reduction in these barriers as the material approaches and enters the glass transition regime, successfully capturing the strong temperature and hydration dependence of the stress-strain behavior. The highly nonlinear post-yield unloading and reloading suggest the development of a back stress during inelastic deformation which aids reverse plastic flow during unloading. Inclusion of a back stress which saturates after reaching a critical level provides an ability to capture the highly nonlinear cyclic loading stress response. Hence, the proposed model provides the capability to describe the complex evolution of stress and strain that occurs in PEM membranes due to the constrained hygrothermal cyclic swelling/deswelling characteristic of membranes in operating fuel cells.

The effect of microstructure on the rate-dependent stress–strain behavior of poly(urethane urea) elastomers

Segmented poly(urethane urea) materials (PUUs) exhibit versatile mechanical properties and have drawn great interest due to their potential for protection against projectile impacts and blast loadings. To optimize the performance of PUUs for various high rate applications, specific features of their mechanical behavior have to be suitably tailored by altering the microstructure. Hence the micromechanisms governing the mechanical behavior must be identified, understood and leveraged. In this study, the effects of varying microstructure on the rate-dependent mechanical behavior were examined for select PUU materials. As expected, increasing the hard segment content increased the stiffness and the flow stress levels. Interestingly, it was observed that promoting phase mixing among the hard and soft segment domains of the PUU material greatly enhanced its rate-dependent stiffening and strain hardening behavior. These insights can help design PUUs for articles that manifest improved protective abilities under impact, while maintaining their flexibility during normal use. The potential applications for such materials are extensive, including face masks and goggles, which require excellent folding/un-folding capabilities, while also providing superior impact resistance.

Rate dependent rheological stress-strain behavior of porous nanocrystalline materials

To completely understand the rate-dependent stress-strain behavior of the porous nanocrystalline materials, it is necessary to formulate a constitutive model that can reflect the complicated experimentally observed stress-strain relations of nanocrystalline materials. The nanocrystalline materials consisting grain interior and grain boundary are considered as viscoplastic and porous materials for the reasons that their mechanical deformation is commonly governed by both dislocation glide and diffusion, and pores commonly exist in the nanocrystalline materials. A constitutive law of the unified theory reflecting the stress-strain relations was established and verified by experimental data of bulk nanocrystalline Ni prepared by hydrogen direct current arc plasma evaporation method and hot compression. The effect of the evolution of porosity on stress-strain relations was taken into account to make that the predicted results can keep good agreements with the corresponding experimental results.

Constitutive Modeling of Rate-Dependent Stress–Strain Behavior of Human Liver in Blunt Impact Loading

An understanding of the mechanical deformation behavior of the liver under high strain rate loading conditions could aid in the development of vehicle safety measures to reduce the occurrence of blunt liver injury. The purpose of this study was to develop a constitutive model of the stress-strain behavior of the human liver in blunt impact loading. Experimental stress and strain data was obtained from impact tests of 12 unembalmed human livers using a drop tower technique. A constitutive model previously developed for finite strain behavior of amorphous polymers was adapted to model the observed liver behavior. The elements of the model include a nonlinear spring in parallel with a linear spring and nonlinear dashpot. The model captures three features of liver stress-strain behavior in impact loading: (1) relatively stiff initial modulus, (2) rate-dependent yield or rollover to viscous "flow" behavior, and (3) strain hardening at large strains. Six material properties were used to define the constitutive model. This study represents a novel application of polymer mechanics concepts to understand the rate-dependent large strain behavior of human liver tissue under high strain rate loading. Applications of this research include finite element simulations of injury-producing liver or abdominal impact events.

Rate Effects on the Stress-Strain Behaviour of Eps Geofoam

The rate-dependency of the stress-strain behavior of EPS (Expanded Polystyrene) geofoam with densities of 19.3 and 28.0 kg/m 3 was investigated by performing unconventional unconfined compression tests. A set of monotonic loading (ML) tests were performed at different constant values of vertical (axial) strain rate, ε v . The ε v value was stepwise changed many times and several sustained loading (SL) tests were performed during otherwise ML at a constant ε v in other tests. A number of SL tests were performed during global unload and reload cycles to infer the stress-strain relation when ε v =0. The elastic properties were evaluated by applying minute unload/reload cycles during otherwise ML. The rate-dependent stress-strain behaviour observed in these tests was described by an elasto-viscoplastic model (i.e., a non-linear three-component model), for which the vertical (axial) stress, σ v , consists of inviscid and viscous components, σ v f and σ v v , while ε v consists of elastic and irreversible components, ε v e and ε v ir . It is shown that the viscous property of EPS geofoam is of Isotach type in that, under the loading conditions where ε v ir is always positive, the current σ v v value is a unique function of instantaneous ε v ir and ε v ir , therefore the strength increases with ε v . This viscous property was quantified based on the test results and incorporated into the model. The rate-dependent stress-strain behaviour, including the creep behaviour, observed in the experiment is simulated very well by the proposed model. In particular, the fact that the creep strain becomes significant when the sustained σ v value becomes larger than the inviscid yield vertical stress is well simulated.

Modelling and Simulation of Rate-Dependent Stress-Strain Behaviour of Granular Materials in Shear

A constitutive modelling of the elasto-viscoplastic stress-strain behaviour of geomaterials in shear that has been developed within a non-linear three-component model framework is validated by simulating a comprehensive series of drained triaxial compression (TC) and direct shear (DS) tests on a wide variety of granular materials. Illustrative simulations of rate-dependent stress-strain behaviour of geomaterial under typical laboratory test conditions were performed to analyse the structure of the model. The versatility of the proposed model and its applicability to a wide variety of shear loading histories is examined and demonstrated by these simulations. The following results are shown. Commonly with different basic viscosity types, Isotach, TESRA and P&N, the viscous stress component has a positive component that increases with an increase in the irreversible strain rate, which makes feasible stable and realistic simulations of rate-dependent stress-strain behaviour, including creep deformation, based on the proposed model. With different unbound granular material types having similar relative densities, the creep strain in TC tests and creep shear displacement in DS tests that develop by sustained loading at a given shear stress level for a given period tends to decrease with an increase in the particle roundness. This trend of behaviours is explained by a decrease in the viscosity type parameter, θ, associated with an increase in the particle roundness based on the simulations of these tests.

A coupled thermomechanical model for shape memory alloys—From single crystal to polycrystal

A number of shape memory alloys (SMAs), e.g., NiTi, exhibit a rate-dependent stress–strain behavior already at very low loading rates (10 −4 to 10 −2 s −1), leading to a considerable change in the shape of the stress–strain hysteresis. The reason for this phenomenon lies in the strong thermo-mechanical coupling due to the release and absorption of latent heats, and the high temperature sensitivity of the transformation stresses. A correct description of these mechanisms is important for, e.g., the simulation of electrically heated actuators or the dynamics of SMA-based damping elements. This paper presents a model which combines arguments from the theory of thermally activated processes and statistical thermodynamics to describe the kinetics of the martensite/austenite phase transformations responsible for the hysteretic SMA behavior. It starts out at the single-crystal level to introduce the concepts, and subsequently discusses a polycrystalline version based on a statistical homogenization. Finally, a computationally efficient implementation of the latter scheme by means of a parameterization method is derived and compared with results from tensile experiments with NiTi wires.

Constitutive modeling of the finite strain behavior of amorphous polymers in and above the glass transition

A constitutive model is developed to capture the rate-dependent stress–strain behavior of an amorphous polymer (poly(ethylene terephthalate)-glycol (PETG)) at temperatures in and above the glass transition ( θ g). As a polymer goes through its glass transition, it exhibits a dramatic decrease in elastic modulus and yield stress, and continues to show strong dependence on strain rate and temperature. The mechanical recognition of the glass transition phenomenon itself depends on the applied deformation rate. The model is able to capture this strong dependence on temperature, strain rate, and strain state for uniaxial and plane strain compression experiments to very large strains. In particular, it captures the dramatic drop in modulus from below to above θ g and the corresponding drop in yield or flow stress. The model also captures the dependence on rate, temperature, and state of deformation of strain hardening, including the dramatic stiffening that occurs at very large strains. The model predictions are additionally compared to stress–strain data for poly(ethylene terephthalate) (PET) to identify the areas where strain-induced crystallization plays a role in its compressive mechanical behavior. No significant modifications are needed for the model to capture the behavior of PET in uniaxial compression, in spite of the fact that PET undergoes strain-induced crystallization upon deformation near θ g and PETG does not. This suggests that the primary mechanism for dramatic strain hardening in biaxial deformation of PET is not strain-induced crystallization, but rather molecular orientation and alignment.

Large deformation rate-dependent stress–strain behavior of polyurea and polyurethanes

The thermoplastic elastomer polyurethane and the elastomeric thermoset polyurea are finding new applications in increasing the survivability of structures under impact loading, including those encountered in blast and ballistic events. However, the mechanical behavior of polyurea and polyurethane materials under these high rate conditions is relatively unknown. Here, the rate-dependent stress–strain behavior of one polyurea and three representative polyurethane materials is studied by dynamic mechanical analysis, quasi-static compression testing and split Hopkinson pressure bar (SHPB) testing. The polyurethane chemistries were chosen to probe the influence of the hard segment content on the mechanical behavior, where the volume fraction and the amorphous vs. crystalline structure of the hard segment domains were varied. The large strain stress–strain behavior of polyurea and polyurethane shows strong hysteresis, cyclic softening, and strong rate-dependence. The polyurethane with a non-crystalline well-dispersed hard segment morphology did not exhibit cyclic softening. The materials are observed to transition from a rubbery-like behavior under low strain rate (∼10 −3–10 0 s −1) loading conditions to either a leathery or glassy-like behavior under high strain rate (∼10 −3 s −1) loading conditions.