High Strain Rate Deformation Behavior Research Articles

Tungsten heavy alloys for kinetic energy penetrators: a review

Tungsten heavy alloys are preferred materials for kinetic energy penetrators owing to the combination of high density, tensile strength, good impact strength and inert nature. The factors affecting shear band formation in the material and strategies to aid their early emergence by various alloy and process modifications to sustain a self-sharpened head during penetration are the main focus of this review article. Changes in the microstructural features such as tungsten grain size, dihedral angle and contiguity and mechanical properties by the addition of various alloying constituents and post-processing are critically discussed, along with high strain rate deformation behaviour analysis. This article also captures recent developments in the last decade and future prospects in the field of tungsten heavy alloys.

Dynamic Impact Properties of Carbon-Fiber-Reinforced Phenolic Composites Containing Microfillers.

The addition of nano- and microfillers to carbon-fiber-reinforced polymers (CFRPs) to improve their static mechanical properties is attracting growing research interest because their introduction does not increase the weight of parts made from CFRPs. However, the current understanding of the high strain rate deformation behaviour of CFRPs containing nanofillers/microfillers is limited. The present study investigated the dynamic impact properties of carbon-fiber-reinforced phenolic composites (CFRPCs) modified with microfillers. The CFRPCs were fabricated using 2D woven carbon fibers, two phenolic resole resins (HRJ-15881 and SP-6877), and two microfillers (colloidal silica and silicon carbide (SiC)). The amount of microfillers incorporated into the CFRPCs varied from 0.0 wt.% to 2.0 wt.%. A split-Hopkinson pressure bar (SHPB), operated at momentums of 15 kg m/s and 28 kg m/s, was used to determine the impact properties of the composites. The evolution of damage in the impacted specimens was studied using optical stereomicroscope and scanning electron microscope. It was found that, at an impact momentum of 15 kg m/s, the impact properties of HRJ-15881-based CFRPCs increased with SiC addition up to 1.5 wt.%, while those of SP-6877-based composites increased only up to 0.5 wt.%. At 28 kg m/s, the impact properties of the composites increased up to 0.5 wt.% SiC addition for both SP-6877 and HRJ-15881 based composites. However, the addition of colloidal silica did not improve the dynamic impact properties of composites based on both phenolic resins at both impact momentums. The improvement in the impact properties of composites made with SiC microfiller can be attributed to improvement in crystallinity offered by the α-SiC type microfiller used in this study. No fracture was observed in specimens impacted at an impact momentum of 15 kg m/s. However, at 28 kg m/s, edge chip-off and cracks extending through the surface were observed at lower microfiller addition (≤1 wt.%), which became more pronounced at higher microfiller loading (≥1.5 wt.%).

High strain rate deformation behavior of Al0.65CoCrFe2Ni dual-phase high entropy alloy

An industrially-cast high entropy alloy with a nominal composition of Al0.65CoCrFe2Ni, having FCC and BCC phases, was compressed at high strain rates using a split Hopkinson pressure bar under a range of test temperatures. The strain rate sensitivity and strain hardening behaviour of the alloy were analyzed. The alloy exhibited high strain hardening and excellent strain rate sensitivity owing to its large solid solution strengthening and low athermal strength contributors. The alloy also displayed outstanding dynamic strain rate sensitivity compared to similar dual-phase high entropy alloys of the AlCoCrFeNi alloy system. The alloy exhibited excellent resistance to thermal softening at high strain rate loading due to higher phonon drag associated with an increase in the operating temperature. The substructures formed in the alloy during high strain rate deformation at room temperature comprised of Lomer-Cottrell (L-C) locks, deformation twins, planar deformation bands, and high dislocation pile-ups at interphase boundaries and subgrain boundaries. The high strain rate deformation at high temperatures resulted in the formation of dislocation cells, kinks and jogs, enabling the alloy to retain strain hardening behavior. The Johnson-Cook (J-C) model accurately predicted the plasticity behavior of the alloy under high strain rate loading.

Numerical simulation of fracture in Taylor rod impact problem with stochastically distributed inherent damage

High strain rate deformation behavior studies in structures always hold importance in many areas of science and technology. The high strain rate deformation behavior is generally determined by the Taylor rod impact tests. During the impact process, the front portion of the Taylor rod undergoes a large deformation that results in the evolution of the voids leading to damage/fracture in the rod. A process of fracture phenomenon and mechanics of blunt-shaped projectile impacting a rigid target at high-velocity results in different fracture modes viz. mushrooming, petalling, shear cracks, tensile splitting, fragmentation, or mixed modes of failure. The deformation and evolution of these practically observed fracture modes are investigated due to the introduction of stochastically distributed inherent damage in the flat-faced Taylor rod. The process is simulated in the mild steel Taylor rod using continuum damage mechanics. The evolution of the damage and fracture growth has been presented. The process of deformation, the phenomenon of stress propagation, and the effect of stochastically distributed inherent damage on the fracture mode in the Taylor rod have been discussed. As the stresses initially evolve at the outer edge of the Taylor rod, the damage initially grows at the outer edge leading to the tensile splitting and petal formation. It is found that the introduction of stochastically distributed inherent damage and critical damage inside the Taylor rod changes the fracture modes. The results are found to be consistent with the literature.

High strain rate deformation behavior of 2195 Al-Li alloy: Constitutive behavior and grain fragmentation

The high-speed forming process is a promising method for the preparation of high-performance Al-Li alloy components. However, the high-strain rate deformation behavior of the material is complex and difficult to accurately predict, which significantly restricts its development. In this paper, using the split Hopkinson pressure bar apparatus, the constitutive behavior and microstructure evolution of as-annealed and solution treated 2195 Al-Li alloy during high strain rate deformation was studied. As the strain rate increases, the flow stress first decreases and then increases for both two-state materials, showing a local strain rate softening behavior. Based on the Johnson-Cook model, a modified constitutive model is proposed, in which a correction term for the C value related to strain rate and strain is introduced. The modified Johnson-Cook model can accurately capture the abnormal strain rate sensitivity behavior observed in the experiment. In addition, it was found that the heat treatment state has a significant effect on the microstructural evolution behavior of 2195 Al-Li alloy. The as-annealed material shows the deformation behavior based on the evolution of dislocation cells. In addition to dislocation cells, there is also deformation behavior based on the evolution of submicron lath deformation bands for solution treated material. Dislocation cross slip is suppressed in the solution treated material, and its slip mode tends to be the plane slip. Through the analysis of dislocation density, mean slip distance of dislocation slip, and the interaction between solid atoms and dislocation, the mechanism of the abnormal deformation behavior of the solution treated material is revealed.

High Strain Rate Deformation Behaviour Analysis of Recycled Aluminium Alloys AA6061 Reinforced Alumina Oxide Al2O3 Using Taylor Cylinder Impact Test

High Strain Rate Deformation Behaviour Analysis of Recycled Aluminium Alloys AA6061 Reinforced Alumina Oxide Al2O3 Using Taylor Cylinder Impact Test

High strain rate deformation behavior, texture and microstructural evolution, characterization of adiabatic shear bands, and constitutive models in electron beam melted Ti-6Al-4V under dynamic compression loadings

The results of an investigation on the influence of strain rate on the microstructural and texture evolution, adiabatic shear band characterization, and deformation mechanism of electron beam melted Ti-6Al-4V vertically built cylindrical rods are presented and discussed in this paper. Typical initial microstructure includes a mixture of α (aluminum-rich) and β phases (vanadium-rich) and grain boundary α along with the columnar prior β-grain boundaries. High strain rate compressive loadings were applied using a Split-Hopkinson pressure bar at the strain rates of 700 s−1 and 1650 s−1 at room temperature. By increasing the strain rate from 700 s−1 to 1650 s−1, the maximum stress and total strain in the alloy increased by 510 MPa and 141%, respectively. The higher dislocation density in the more severely deformed sample led to a more considerable amount of dislocation cells and consequent subgrains, high-angle grains, and piled-up dislocations. Intense shear strain localization leading to the adiabatic shear bands formation that occurred at higher strain rates. Texture investigations of the ASB region proposed that α→β phase transformation occurred within the ASB. Flow behavior prediction and experimental data revealed reasonable accordance, using the Gao-Zhang-Yan and the Chang-Asaro model.

High strain rates deformation behavior of an as-extruded Mg–2.5Zn–4Y magnesium alloy containing LPSO phase at high temperatures

Mg–Zn–Y magnesium alloys comprising long-period stacking ordered (LPSO) phase have shown excellent strengthening effects, however, their deformation behavior and microstructure evolution under different strain rates and temperatures have not yet been thoroughly investigated. This work is based on the investigation of elevated temperature and high strain rate deformation behavior of an as-extruded Mg–2.5Zn–4Y magnesium alloy comprising LPSO phase, with the strain rates lying in the 700 s−1 to 2100 s−1 range, and temperature ranging from 293 K to 623 K. Electron backscattering diffraction (EBSD), scanning electron microscopy (SEM), and optical microscopy (OM) was employed for investigating the deformation microstructure. The results show that at early deformation the extension twinning coordinates the plastic deformation first, subsequently, pyramidal < c+a > slip and kinking of LPSO phase can also coordinate deformation for the experimental alloy at high strain rates at high temperatures. A peculiar phenomenon of misaligned LPSO phase structures (1600 s−1, 623 K) was also discovered. The fracture mode of the experimental alloy is mainly the cleavage fracture or the mixed ductile-brittle fracture during high-speed impact. A modified Johnson–Cook (J-C) constitutive model of the as-extruded Mg–2.5Zn–4Y was found to appropriately analyze the stress–strain values by comparing the computed results with the experimentally obtained data. It was, thus, demonstrated that the modified J-C model can make a reasonable prediction about the dynamic mechanical behavior of a Mg–2.5Zn–4Y magnesium alloy in its as-extruded condition throughout a range of high temperatures and strain rates with a high degree of accuracy.

Effect of printing parameters on the structure and high strain rate deformation behavior of additively manufactured 316L stainless steel

High strain rate deformation is characterized by strain localization and formation of adiabatic shear bands (ASBs), as opposed to the movement of slip systems seen in quasistatic deformation. Several studies have been done on the effect of printing parameters on the structure and properties of 316L stainless steel, little attention has been paid to the high-strain rate deformation behaviour of this material. In this study, the effect of printing parameters on the microstructure and high strain rate deformation behavior of 3D-printed 316L stainless steel alloy was investigated. Printing parameters such as hatch spacing, laser power, scan speed and build direction, and their effect on the microstructure, density, hardness, and high strain rate compressive behaviour of 316L stainless steel alloy are established. The results show that even though increasing laser power leads to a reduction in part porosity and better part consolidation (density), scan speeds had a significant effect on porosity production regardless of laser power and hatch spacing. A scan speed of 750 mm/s generally resulted in the lowest porosities regardless of laser power and hatch spacing (150 W ≤ P ≥ 250 W and 0.08 mm ≤ h ≥ 0.14 mm respectively). Scan speeds of 1250 mm/s would have to be coupled with higher laser powers (P ≥ 200 W) to get relatively similar porosities obtained at 750 mm/s. Regardless of the laser power and hatch spacing, scan speeds ≥1750 mm/s resulted in higher porosities. In addition, increasing hatch spacing, generally, resulted in increasing levels of porosity in the printed samples, with a hatch spacing of 0.08 mm resulting in the lowest levels of porosities while hatch spacing of 0.14 mm resulted in the highest levels of porosities. In terms of Volumetric Energy Density (VED), VEDs between 44 and 139 J/mm3 resulted in the lowest porosities, highest densities, and hardness, regardless of the build directions. In addition, increasing laser power resulted in thicker and tightly packed sub-grain structures whereas, an increase in hatch spacing and scan speed resulted in thinner/loosely packed sub-grain structures, and thinner/tightly packed sub-grain structures, respectively. Regardless of the printing parameters, samples perpendicular to the build direction had higher maximum flow stresses and lower strains when compared with the samples parallel to the build direction during high strain rate impact. Also, any combination of individual printing parameters that result in finer sub-grain structures resulted in a relatively brittle deformation behaviour during high strain rate impact. The formation of ASBs is characterized by refined grains within the region of the ASBs and coarser grains away from the ASBs region.

Local deformation of Mg–7Gd–5Y–1.2Nd–0.5Zr magnesium alloy under high speed impact along extrusion direction

The high strain rate deformation behavior of Mg–7Gd–5Y–1.2Nd–0.5Zr alloy was carried out at several temperatures. Through the truncated test of cap specimen, it was found that the local deformation occurred in the design shear zone, but no adiabatic shear band was observed. The deformation mechanism was mainly pyramidal slip, supplemented by prismatic slip, basal slip, and dynamic recrystallization. Among them, pyramidal 〈c + a〉 slip could coordinate deformation through the slip component along the 〈c〉 direction. The Johnson–Cook constitutive model and failure model were modified, and then the local deformation of the cap specimen along the extrusion direction was simulated by LS-DANY software. The results showed that the local severe deformation occurred in the area of the cap specimen with sharp change in shape, which was at an angle of 45 ° with the impact compression loading along extrusion direction. The temperature increased continuously with the amount of deformation until fracture occurred. The results showed that the alloy had high resistance to local high strain deformation and fracture.

High Strain Rate Deformation Behavior of 2195 Al-Li Alloy: Constitutive Behavior and Grain Fragmentation

High Strain Rate Deformation Behavior of 2195 Al-Li Alloy: Constitutive Behavior and Grain Fragmentation

High Strain Rate Deformation Behavior, Texture and Microstructural Evolution, Characterization of Adiabatic Shear Bands, and Constitutive Models in Electron Beam Melted Ti-6al-4v Under Dynamic Compression Loadings

High Strain Rate Deformation Behavior, Texture and Microstructural Evolution, Characterization of Adiabatic Shear Bands, and Constitutive Models in Electron Beam Melted Ti-6al-4v Under Dynamic Compression Loadings

High Strain Rate Deformation Behavior and Recrystallization of Alloy 718

To study the deformation behavior and recrystallization of alloy 718 in annealed and aged state, compression tests were performed using Split-Hopkinson pressure bar (SHPB) at high strain rates (1000 to 4000 s−1), for temperatures between 20 ^circ C and 1100 ^circ C (293 K to 1373 K). Optical microscope (OM) and electron back-scatter diffraction (EBSD) technique were employed to characterize the microstructural evolution of the alloy. The stress–strain curves show that the flow stress level decreases with increasing temperature and decreasing strain rate. In addition, up to 1000 ^circ C, the aged material presents higher strength and is more resistant to deformation than the annealed one, with a yield strength around 400 MPa higher. For both states, dynamic and meta-dynamic recrystallization occurred when the material is deformed at 1000 ^circ C and 1100 ^circ C, leading to a refinement of the microstructure. As necklace structures were identified, discontinuous recrystallization is considered to be the main recrystallization mechanism. The recrystallization kinetics is faster for higher temperatures, as the fraction of recrystallized grains is higher and the average recrystallized grain size is larger after deformation at 1100 ^circ C than after deformation at 1000 ^circ C.

A computational investigation on the influence of the l/d ratio and strain rate on the deformation behavior of rolled and homogeneous armor steel in the split Hopkinson pressure bar test process

The present investigation deals with the finite-element analysis of the high strain rate deformation behavior of the quenched and tempered armor-grade rolled and homogeneous armor steel. The rolled and homogeneous armor steel is extensively used in civil and military structures such as battle tanks, armament combat vehicles, combat helicopter, etc. The dynamic deformation behavior of rolled and homogeneous armor steel, that is, resistance against ballistic circumstances relates to its mechanical behavior under high strain rate conditions. In the present research work, a finite-element analysis investigation (using Abaqus finite-element analysis code) has been carried out to evaluate the influence of specimen l/d ratios and high loading strain rates on the deformation behavior and stress–strain responses of the rolled and homogeneous armor steel. Further, an attempt has also been made to check the high strain rate and specimen l/d ratio influence on the strain amplitudes of incident, reflected, and transmitted pulses. The numerical investigation has been carried out with the rolled and homogeneous armor steel specimen with l/d ratios of 1, 0.8, and 0.6. In addition, three high impact strain rates of 2130, 2907, and 3105 s−1 are considered to evaluate the stress–strain responses. The results revealed that the l/d ratio and strain rate have a significant influence on the specimen stress–strain response and the strain amplitudes of incident, reflected, and transmitted pulses. The peak stress value is increased with the increase in the l/d ratio and strain rate. The developed finite-element analysis model has predicted the stress–strain responses with &lt;3% percentage error. The obtained finite-element analysis results have been validated with the experimental investigation with an l/d ratio of 0.6 and a strain rate of 3105 s−1 for rolled and homogeneous armor steel.

High Strain Rate Response of In-Situ TiB2/7055 Composite by Taylor Impact

The high strain rate deformation behavior and microstructure evolution of in situ TiB2 particle reinforced Al-Zn-Mg-Cu composite were investigated by means of Taylor impact. The dynamic tests were performed at three different impact velocities. Under three different velocities, no obvious shear failure occurred in the composite, indicating a good impact resistance. Compared to the quasi-static compression test, the dynamic yield strength increased obviously with the rise of velocity, even more than 1 GPa. The dislocation multiplication, phonon drag effect and ceramic reinforcement increased the flow stress of composite. Fine, equiaxed grain structure developed after impact, resulting from grain fragmentation or dynamic recrystallization. Finite element simulation of Taylor impact was qualitatively in agreement with the experiments, which was useful to elucidate the formation of equiaxed grain structure.

Effect of Stress-Relieving Heat Treatment on the High Strain Rate Dynamic Compressive Properties of Additively Manufactured Ti6Al4V (ELI)

A study was undertaken on the compressive high strain rate properties and deformation behaviour of Direct Metal Laser-Sintered (DMLS) Ti6Al4V (ELI) parts in two separate forms: as-built (AB) and stress relieved (SR). The high strain rate compression tests were carried out using a Split Hopkinson Pressure Bar test system at ambient temperature. The average plastic strain rates attained by the system were 400 s−1 and 700 s−1. Comparative analyses of the performance (flow stresses and fracture strains) of AB and SR specimens were carried out based on the results obtained at these two plastic strain rates. Microstructural analyses were performed to study the failure mechanisms of the deformed specimens and fracture surfaces. Vickers microhardness test values were obtained before and after high strain rate compression testing. The results obtained in both cases showed the strain rate sensitivity of the stress-relieved samples to be higher in comparison to those of as-built ones, at the same value of true strain.

Compressive Behaviour of Closed-Cell Aluminium Foam at Different Strain Rates.

Closed-cell aluminium foams were fabricated and characterised at different strain rates. Quasi-static and high strain rate experimental compression testing was performed using a universal servo-hydraulic testing machine and powder gun. The experimental results show a large influence of strain rate hardening on mechanical properties, which contributes to significant quasi-linear enhancement of energy absorption capabilities at high strain rates. The results of experimental testing were further used for the determination of critical deformation velocities and validation of the proposed computational model. A simple computational model with homogenised crushable foam material model shows good correlation between the experimental and computational results at analysed strain rates. The computational model offers efficient (simple, fast and accurate) analysis of high strain rate deformation behaviour of a closed-cell aluminium foam at different loading velocities.

Analysis and constitutive modeling of high strain rate deformation behavior of Haynes 282 aerospace superalloy

Haynes 282 is a relatively new γ′- strengthened superalloy used in static and rotating components of jet turbine engines. An understanding of its high strain rate behavior is required to develop constitutive model to predict and optimize its response under dynamic loading applications. Using the direct impact Hopkinson pressure bar, this study investigates the high strain rate behavior of Haynes 282 at strain rates from 2000/s to 10,000/s and temperatures from 25 to 800 °C under three heat treatment conditions (solutionized, standard aged, and special aged). Experimental results show that the flow stress of Haynes 282 remains nearly constant or decreases with increases in strain rate, a remarkable feature that could increase its resistance to impact damage. This contrasts with Inconel 718, the most-widely used superalloy, which show positive strain rate sensitivity. An Arrhenius-type and modified Johnson-Cook constitutive models are developed to predict the combined effects of work hardening, strain rate softening, and temperature on the high strain rate behavior of Haynes 282. The model prediction shows good agreement with the experimental observations. The modified JC model has a higher correlation coefficient and lower average absolute relative error than the Arrhenius-type model, a statistical indication of higher predictability. Nevertheless, both models present powerful tool for designers to simulate and optimize high impact load-bearing applications.

Analysis and constitutive modelling of high strain rate deformation behaviour of wire–arc additive-manufactured ATI 718Plus superalloy

A fundamental prerequisite for obtaining realistic finite element simulation of machining processes, which has become a key machinability assessment for metals and alloys, is the establishment of a reliable material model. To obtain the constitutive model for wire–arc additive-manufactured ATI 718Plus, Hopkinson pressure bar is used to characterise the flow stress of the alloy over a wide range of temperatures and strain rates. Experiment results show that the deformation behaviours of as-deposited ATI 718Plus superalloy are influenced by the applied strain rate, test temperature and strain. Post-deformation microstructures show localised deformation within the deposit, which is attributable to the heterogeneous distribution of the strengthening precipitates in as-deposited ATI 718Plus. Furthermore, cracks are observed to be preferentially initiated at the brittle eutectic solidification constituents within the localised band. Constitutive models, based on the strain-compensated Arrhenius-type model and the modified Johnson–Cook model, are developed for the deposit based on experimental data. Standard statistical parameters, correlation coefficient (R), root-mean-square error (RMSE) and average absolute relative error (AARE) are used to assess the reliability of the models. The results show that the modified Johnson–Cook model has better reliability in predicting the dynamic flow stress of wire–arc-deposited ATI 718Plus superalloy.

Effect of α phase on high-strain rate deformation behavior of laser melting deposited Ti-6.5Al-1Mo-1V-2Zr titanium alloy

Laser melting deposition (LMD) technology enables the use of complex titanium alloy parts in ballistic applications such as lattice armors and warheads. The effect of the α phase of a LMD Ti-6.5Al-1Mo-1V-2Zr titanium alloy during compression at a high strain rate of 3000 s⁻1 was investigated. Various morphologies and textures of the α phase of the LMD alloy were obtained by annealing at different temperatures at the β transus, followed by furnace cooling. It was found that all the α phases of the annealed microstructures exhibit two fiber textures, <21̄1̄0>α and <16 0 16¯ 19>α, parallel to the building direction. The reason is that the <100>β directions of the prior-β grains were parallel to the building direction. Due to a high Schmidt factor, {101̄2} twinning occurs in the α phases with the <21̄1̄0>α fiber texture during the high-strain rate deformation. After annealing at 970 °C, the volume fraction of the α phases with the <21̄1̄0>α fiber texture increases significantly to 51.4 vol%, which leads to a significant improvement of 14.3% in the uniform ductility strain. Moreover, with an increase in the annealing temperature from 930 °C to 970 °C, the flow strength of the sample decreases slightly by 2%.