High Strain Rate Behavior Research Articles

High strain-rate fracture behavior of a hollow projectile

In this paper, a hollow projectile made of AISI4340 steel was fabricated based on an arbitrary warhead shape, and high-speed impact tests were performed according to various target encounter conditions including velocity and angle. In order to characterize the dynamic fracture behavior, tensile tests were performed on various notch specimens under three strain rates (10–3 s-1, 100 s-1, 103 s-1), and the stress state histories of the specimens were calibrated through a hybrid experimental-numerical analysis. In particular, for the intermediate (100 s-1) and high (103 s-1) strain rate conditions, the local temperature rose due to adiabatic heating until fracture was experimentally measured, and the thermal softening behavior determined from the inverse optimization technique was considered for the dynamic constitutive model. For the comparison with the high-speed impact test results, a rate-dependent ductile fracture model was utilized for numerical simulation. Considering that the model parameters were calibrated with the thermal softening effect, the proposed fracture model implicitly takes temperature into account. The deformation and fracture modes of the projectile from experimental and numerical study showed very good agreement under all impact conditions. It was confirmed that the softening of a material by adiabatic heating should be considered along with strain rate hardening in dynamic fracture simulation.

High strain rate behavior of polycaprolactone reinforced with aramid nanofiber for insight into dynamic behavior

AbstractSelf-healing materials are repairable and extend product lifetimes but are limited in application due to their mechanical properties such as low yield strength. Here, we examined the dynamic mechanical performance of an elastomeric polymer composite containing aramid nanofibers. These studies provided an economically feasible foundation to understand the reinforcement concentration and resultant mechanical properties that would result should aramid nanofibers be used to reinforce a self-healing polymer that requires complex synthesis methods and expensive reactants. The elastomeric polymer used was polycaprolactone containing various weight percent aramid nanofibers. Dynamic mechanical testing of these samples was performed using a split-Hopkinson pressure bar system that enabled quantification of polymer softening and aramid nanofiber reinforcement. Dynamic flow stress and strain rates were also calculated with these data. Crystallinity and thermal softening effects of solvent dissolution of polycaprolactone are explored to further characterize the performance of aramid nanofibers as a fiber in composite materials. Graphical abstract

Resolving high-strain-rate scratch behavior of Ti6Al4V in experiment and meshless simulation

The outstanding strength-to-weight ratio and corrosion resistance of titanium have made it the material of choice in the aerospace industry and medicine. The alpha–beta alloy Ti6Al4V is particularly preferred for its excellent mechanical and bio-compatible properties. Despite its advantages, the low thermal conductivity and poor tribological performance of titanium pose significant challenges during manufacturing and in operation. This research offers deep insights into the high strain rate behavior of Ti6Al4V under abrasive load, such as e.g. experienced in machining, by modifying the standard scratch test setup and using optimized Johnson–Cook material parameters to perform Material Point Method (MPM) simulations. The MPM simulations provide accurate predictions of the data gathered through high strain rate scratch experiments. We found an increase in the von Mises stress distribution as well as the normal and tangential forces required to perform a scratch of the same depth as the strain rate increases. The morphology of the scratch profiles also showed an increase in the height of the ridges that form as the scratching speed increases. These findings are in line with the increase in yield strength and work hardening with growing strain rate. This study bridges the gap between simulation models and experimental observations by providing insights for improved machining strategies and surface treatments that can enhance the performance of Ti6Al4V in demanding applications.

High strain-rate behavior of polycrystalline and granular ice: An experimental and numerical study

We study the stress–strain response of two different types of ice, viz. polycrystalline ice and granular ice, between −1° – 0 °C over a strain-rate range of 100s−1 to 300s−1 employing the split Hopkinson pressure bar (SHPB). Polycrystalline ice samples, prepared by freezing water in plastic moulds, exhibit a compressive strength ranging from 7 to 10 MPa within the considered strain-rate range. The strain at peak stress remains below 0.2%, indicating brittle behavior. The stress-strain curve of polycrystalline ice displays a prolonged tail, suggesting that the damaged ice specimen retains some strength. High-speed imaging during tests reveals the damage mechanism in ice is fragmentation and axial splitting. A user subroutine based on the Johnson–Holmquist II (JH-2) model is implemented in the commercial finite element (FE) software ABAQUS to predict ice's response at high strain-rates, which captures the softening present in the experimental stress–strain curve. Intact strength parameters and strain-rate sensitivity constants in the JH-2 model are determined from our experimental data and literature results, ensuring alignment with experimental peak stress. Fractured strength and damage evolution parameters are determined by matching post-peak responses from simulations to experiments. Temporal damage evolution from FE simulations aligns well with high-speed images from experiments, providing additional validation. Extending the study to granular ice, samples are prepared by crushing polycrystalline ice and refreezing it. The compressive strength of granular ice at a nominal strain-rate of 200±50s−1 is found to be 4±0.7 MPa. The granular ice, which is a mixture of polycrystalline ice and voids, is homogenized using rule-of-mixture to obtain the elastic properties. The FE simulation results utilizing the JH-2 parameters that we determine matches well with the experimental data, demonstrating that the JH-2 model is well suited to predict the high strain-rate behavior of both types of ice.

Mechanical Properties of Doped Solder SAC-Q for High Strain Rate Testing at Extreme Surrounding Temperatures for 6 Months of Isothermal Aging

Abstract In various industries, including automobile industry, oil and gas, aerospace, and medical technology, electronic components are subjected to significant strain during shocks, vibrations, and drop conditions. Electronic components of this type are frequently subjected to extreme temperatures ranging from –65 °C to 200 °C. These electronic equipment are frequently subjected to strain rates of 1 to 100 sec−1 in sensitive conditions. SAC-Q, SAC-R, Innolot, and other doped SAC solder alloys have recently been introduced to electronic components and packages. SAC-Q refers to the addition of Bi to the Sn-Ag-Cu composition. The mechanical characteristic results and statistics for lead-free solder alloys are particularly important for increasing electronic package stability and high-temperature storage and strain rates. Furthermore, the mechanical characteristics of solder alloys can be dramatically altered owing to thermal aging, which causes microstructure alteration. For high-temperature aging for longer durations and testing at extremely low to very high working temperatures, SAC-Q solder alloy data is not available. The SAC-Q solder material was tested and studied at working temperatures ranging from −65 °C to 200 °C, with strain rates of up to 75 sec−1, for this study. A comparison was also done with the SAC305 solder, which had been thermally aged and tested under identical conditions. Isothermal aging specimens were kept at 100 °C for up to 180 days following manufacturing and reflowing when tensile studies were conducted at various operating temperatures. This study develops and describes stress–strain curves for a wide variety of strain rates and test temperatures. In addition, the test results and data collected were matched to the Anand viscoplasticity model, and Anand constants were calculated by estimating high strain rate behavior throughout a wide range of operating temperatures and stress levels. In addition, for BGA package assembly with PCB, FE analysis was performed for drop/shock events. For varied aging circumstances of SAC-Q solder ball joints, hysteresis stress–strain curves and plastic work density curves are generated.

Characterization and constitutive modeling of the high strain rate behavior of granite at low temperatures

Characterization and constitutive modeling of the high strain rate behavior of granite at low temperatures

Compressive Split Hopkinson Pressure Bar Apparatus: Part I - Design and Development

Optimum utilization of composite materials envisages its use under static as well as dynamic loading conditions. Hence, there is a need to assess the behavior of composite materials at high strain rates. Split Hopkinson Pressure Bar (SHPB) apparatus is widely used to assess high strain rate behavior of composites. Even though SHPB apparatus is widely used, its design methodology and development technique are not readily available. Design and devel- opment details of a compressive SHPB apparatus for characterizing mechanical properties of different materials at high strain rate loading are presented. Brief theoretical background necessary for the design of SHPB apparatus is presented based on one-dimensional wave propagation theory in elastic bars. Next, brief working principle of the apparatus and schematic arrangement are presented. Different components of the compressive SHPB appa- ratus are identified. Design, development and commissioning of the apparatus are discussed. Further, different instruments used and the calibration technique used are presented.

Compressive Split Hopkinson Pressure Bar Apparatus: Part II- Experimental Results

Investigations on high strain rate behavior of a typical unidirectional glass / epoxy composite under compressive loading are presented. Compressive Split Hopkinson Pressure Bar (SHPB) apparatus was used for the studies. Compressive properties were evaluated along longitudi- nal, transverse and thickness directions in the strain rate range of 548 - 2645 per sec. It is observed that the compressive strength is enhanced at high strain rate loading compared with those at quasi-static loading. Studies were also carried out on 10° and 45° off-axis specimens. In-plane shear strength was determined based on 10° off-axis compressive results. It is observed that the in-plane shear strength is increased at high strain rate loading compared with that at quasi-static loading. But it remains nearly constant with increasing strain rate at high strain rates.

Modification of the MTS model for high strain-rate behavior of TI-6AL-4V

The Mechanical Threshold Stress (MTS) model provides excellent predictive capabilities for the material constitutive response for a wide range of temperatures and strain rates. However, the MTS model fails to capture the rapidly increasing yield stress at high strain rate behavior as the deformation controlling mechanism transitions from thermal activation to drag mechanisms, only capturing the linear behavior. Further, the model typically over predicts the flow stress behavior at yield and post yield due to its use of a constant work hardening rate parameter derived from the stress–strain response at constant saturation stress. An alternative approach to fitting portions of the MTS model is investigated and mathematical models are developed to address these issues. The results show that with appropriate experimental data, the mechanical threshold stress and work hardening rate parameters within the MTS model can quite easily and accurately be modified to extend applicability to high strain rate behavior and more accurately model the initial flow stress behavior at early work hardening rates without modification of the functions core to the MTS model itself.

High strain rate behaviour of different types of chocolate

The mechanical behaviour of five different chocolate types (dark, extra dark, milk, white, and ruby) at high strain rates was studied. The experimental arrangement known as the Split Hopkinson Pressure Bar (SHPB) method was used. This experimental procedure enables to study the mechanical behaviour of materials at strain rates up to 103 1/s. The use of SHPB technique shows that the mechanical properties of tested chocolates significantly increase with the strain rate. This increase is much higher than that observed during the quasi static testing where the strain rate achieves values about 10−3 1/s.

Anisotropic mechanical response of AA7475-T7351 alloy at different loading rates and temperatures

The mechanical behaviour of aluminium alloy 7475-T7351 along the three principal directions (i.e rolling, transverse and normal) are compared here at different rates and temperatures under tensile and compressive loading. The aluminium alloy is examined in quasi-static circumstances using the Zwick/Roell Z-50 UTM, while the SHPB (for compression and tension) technique is utilised to investigate the high strain rate behaviour of the material under tensile (up to 2950 s−1) and compressive (up to -4438 s−1) loading. Both the quasi-static and dynamic experiments are performed at five different temperatures (25 °C, 100 °C, 150 °C, 200 °C, 250 °C). JC, KHL and m-KL constitutive models are calibrated along different directions. Quadratic and non-quadratic anisotropy model was further modified to incorporate tension–compression asymmetry and constants were also evaluated to predict the yield surface of AA7475-T7351 for temperatures and strain rates. The loading direction (tension/compression), strain rate and temperature are observed to affect the ductility and strength of AA7475-T7351 immensely. The KL phenomenological model is modified to incorporate the tension–compression asymmetry, strain hardening, strain rate hardening and thermal softening of AA7475-T7351. The efficiency of the modified KL model is compared with Johnson–Cook and KHL constitutive models along the principal material directions.

High rate response of elastomeric coatings for wind turbine blade erosion protection evaluated through impact tests and numerical models

The high strain rate (above ∼104/s) behavior of an elastomer is characterized using low strain rate (below ∼101/s) dynamic mechanical thermal analysis and time–temperature superposition. This approach is validated using high strain rate ball impact experiments and finite element predictions of ball deformations and rebound speeds. The ball impact experiments are performed by shooting 6 mm rubber balls with a controlled impact speed of 50–170 m/s at steel and polyurethane targets. An explicit axisymmetric finite element model of the ball impact experiment is established in the commercial code Abaqus. The validated material properties are used to model the viscously dissipated energy and the corresponding temperature increase in the polyurethane target. The region with the largest dissipated energy in the target material is predicted to be in a ring around the impact center with a radius of approximately 1 mm. This region corresponds well to locations of early damage initiation observed in the impact fatigue experiments for similar materials. The predictions are confirmed by the observed temperature distributions using thermal camera imaging of the rubber ball impact experiment. The experimental setup was developed for impact fatigue testing of anti-erosion coatings for the leading-edges of wind turbine blades.

Impact Deposition Behavior of Al/B4C Cold-Sprayed Composite Coatings: Understanding the Role of Porosity on Particle Retention.

This study explores the role of porosity in the impact deposition of a ceramic-reinforced metal-matrix (i.e., Al/B4C) composite coating fabricated via cold spraying. The Johnson-Holmquist-Beissel constitutive law and the modified Gurson-Tvergaard-Needleman model were used to describe the high strain-rate behavior of the boron carbide and the aluminum metal matrix during impact deposition, respectively. Within a finite element model framework, the Arbitrary Lagrangian-Eulerian technique is implemented to explore the roles of reinforcement particle size and velocity, and pore size and depth in particle retention by examining the post-impact crater morphology, penetration depth, and localized plastic deformation of the aluminum substrate. Results reveal that some degree of matrix porosity may improve particle retention. In particular, porosity near the surface facilitates particle retention at lower impact velocities, while kinetic energy dominates particle retention at higher deposition velocities. Altogether, these results provide insights into the effect of deposition variables (i.e., particle size, impact velocity, pore size, and pore depth) on particle retention that improves coating quality.

The yielding behavior of TU00 pure copper under impact loading

Characterizing the high strain rate behavior of metals under complex stress states has always been a challenging subject in solid mechanics. In this paper, dynamic tension-torsion tests with various stress ratios are performed by a newly developed combined tension-torsion Hopkinson bar (C-THB) system. Together with the quasi-static results, the initial yielding envelopes at different strain rates are illustrated for the first time. Tresca, von Mises and Hill yield criterion are established and evaluated. A universal model describing the strain rate hardening of material under complex stress states is proposed. Based on this model, a modified Hill yield criterion is deduced for pure copper (TU00), which fits well with the experimental yielding envelope at different strain rates.

Dynamic compressive behaviour of Rewa shale through SHPB tests

The present work investigates the high strain rate behaviour of transversely isotropic Rewa shale using a split Hopkinson pressure bar. Rewa shale, a type of Vindhyan shale, is collected from Rewa district in the Madhya Pradesh state of India. Samples are loaded at various strain rates ranging from 110/s to 874/s. It is found that the compressive strength is rate-dependent, and it increases as the strain rate rises. The highest compressive strength is exhibited by samples at 0° and 90°. Samples at 30°, 45° and 60° fail at higher strains and strain rates. All samples subjected to dynamic compressive loading are pervasively fragmented. The results can potentially be applied to improve drilling and blasting operations.

Modeling wide range of viscoelastic–viscoplastic behavior of AralditeLY564 epoxy using cooperative viscoplasticity theory based on overstress model

AbstractThe rate‐dependent properties of epoxy (Araldite LY 564) were successfully addressed by dynamic mechanical analysis (DMA), quasi‐static compression tests (strain rates: 1.E‐3, 1.E‐2, and 1.E‐1 /s), Split Hopkinson Pressure Bar (SHPB) testing (strain rates: 875 and 770/s) and stress relaxation experiments (strain levels: 3.16 and 7.15%) are simulated by a micromechanically based constitutive model. The used model is Cooperative‐Viscoplasticity Theory Based on Overstress (VBO) model. The majority of works about modeling polymers are limited to modeling quasi‐static tension‐compression behaviors and predicting elasticity modulus and yield strength. In this work, the effectiveness of the Cooperative‐VBO model is verified and validated by simulating a wide range of material behaviors of Araldite LY 564. Material parameters of the model are determined by using storage modulus obtained from DMA and quasi‐static compression test at a strain rate of 1.E‐1 /s. High strain rate behaviors and stress relaxation behaviors are predicted. The behaviors from quasi‐static to high strain rate, from stress relaxation at different strain levels to storage modulus, respectively, are predicted with a single set of material parameters. Simulation and prediction results revealed the effectiveness of the proposed model.

Effect of Bainite/Martensite/Retained Austenite Triplex Microstructure on the High Strain Rate Behavior of a One Step Quenching and Partitioning Steel

The mechanical properties and microstructure evolution of a one step quenching and partitioning steel containing bainite/martensite/retained austenite mixed microstructure was studied though static and dynamic tensile tests (strain rates ranging from10-3 s-1 to 5×102 s-1 ).Scanning electron microscopy (SEM) and electron-back-scattered diffraction (EBSD) were applied to describe the microstructure evolution near the fracture. XRD characterization shows the volume fraction of retained austenite decrease exponentially with the strain rates increased.EBSD phase maps reveal that the first type of retained austenite is less sensitive to strain rate than the second type.

Dynamic response of Advanced Placed Ply composites

This work investigates the high strain rate behavior of AP-PLY composites. The large representative volume elements and brittle nature of this material necessitated the use of a bespoke Split-Hopkinson bar apparatus. AP-PLY and baseline laminates were subjected to tensile loading at strain rates of 30 s−1. Results were compared with quasi-static data to evaluate whether the laminate architecture introduced any strain rate dependency. In addition, the dynamic experiments were simulated using a multiscale modeling framework, providing further insights into the micromechanisms governing material behavior. The moduli of the AP-PLY composites were found to be strain rate independent, however, strengths were found to be marginally higher than those of their baseline counterparts. At high strain rates, the strain concentrations induced by the geometry of the individual tapes at through thickness undulations and tow boundaries were less significant due to reduced out-of-plane tow straightening and delamination. As a result, no reduction in AP-PLY strength in comparison to the baseline laminates was obtained. These differences in deformation micromechanisms led to an improvement of the damage tolerance when subjected to dynamic loading.

Effect of α Phase on Dynamic Mechanical Properties and Failure of Ti-4Al-5Mo-5V-5Cr-1Nb Alloy after Two-Stage Aging

This work studied the high strain rate behavior of the Ti-4Al-5Mo-5V-5Cr-1Nb (Ti-45551) alloy after two-stage aging, with dynamic tension tests conducted using the split Hopkinson tensile bar. The results show that the microstructure, especially the size and distribution of the α phase, significantly affects the mechanical and failure behaviors of the Ti-45551 alloy under dynamic loading. As the strain rate increases, increasing trends can be observed in both ductility and strength, which is intimately related to the activation of the dislocation slip in the α phase. Moreover, obvious strain softening was found in the Ti-45551 alloy under dynamic loading. In this study, the microstructure observations suggest that dislocation slips are highly active in the α phase under dynamic loading. Fractographic characterization of the fracture surfaces under dynamic loading reveals a uniform distribution of ductile dimples, which indicates that a uniform distribution of the nano-scale α phase can effectively reduce brittle fracture tendency. Our studies provide a comprehensive picture of how strain rate drives dynamic plasticity and failure mode in the Ti alloy.

High strain-rate compression behavior of woven CF/PEEK thermoplastic composites at the glassy state and high-elastic state

A reliable hot air-flow heating approach is creatively carried out for high strain rate tests without environment tank. The out-of-plane and in-plane compression of carbon fiber reinforced polyetheretherketone (CF/PEEK) woven composites are investigated from 400 to 4000/s at the glassy state and high-elastic state. The real-time and in-situ deformation and failure process of the composite specimens under the extreme thermo-mechanical loads are successfully captured, which can reflect the impact dynamic behavior of the material near the ultimate service temperature. Empirical laws for mechanical index of the woven composites are given. The results reveal that the thermal softening effect outperforms the strain-rate strengthening effect. For out-of-plane impact at low strain rates, damage mode transitions from the interface and matrix cracking at glassy state to the “parallel” shear and fiber extrusion at high-elastic state. Under high strain rates, it reveals the “fragmented” shear mode at glassy state. For in-plane impact, the temperature effect leads to the failure mode changing from the delamination and local shear to the mixed feature of kinking bands, delamination, and multiple-band shear with “bulge” behavior. And the multiple-band shear and delamination are more likely to occur along the in-plane direction as the strain rate increased.