High Strain Rate Deformation Research Articles

Thermomechanical characterisation of a thermoplastic polymer and its short glass fibre reinforced composite: Influence of fibre, fibre orientation, strain rates and temperatures

Polycarbonate composites are widely used in products exposed to high strain rate deformation. This paper investigates the thermomechanical properties of polycarbonate and 20 wt% glass fibre reinforced polycarbonate to provide characterisation data and improved mechanistic understanding of the response to load, supported by Dynamic Mechanical Analysis and time–temperature superposition. Compressive behaviour is characterised from 0.001 to 5000 s−1 at room temperature and from −60 to 120 °C at 0.01 s−1; and a thermal imaging camera used to obtain temperature rise data. Quasi-static tensile experiments were also performed in different orientations relative to the injection flow direction. High-rate compression experiments are performed with X-ray imaging. As well as information about rate dependence of yield stresses and softening in the two materials, these data show how adiabatic shear band formation can cause significant softening in the composite. These data will enhance application of these polymers and facilitate development of advanced thermo-mechanical models.

Molecular dynamics informed calibration of crystal plasticity critical shear stresses for the mesoscopic mechanical modeling of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) single crystal

An extension of a constitutive law for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is proposed with a focus on the calibration of a crystal plasticity law. TATB, a highly anisotropic energetic molecular crystal used in explosive formulations, can be subjected to high-pressure and high-temperature conditions, either under high strain-rate deformation or shock loading. The existing thermodynamically consistent model, fully informed by molecular dynamics (MD) simulations, includes nonlinear elasticity as well as a phase-field by reaction pathway formalism under large strain for the modeling of TATB behavior upon pressure as well as its well-known twinning–buckling deformation mechanism. However, it has been observed that TATB single crystal can accommodate large deformations through dislocation-mediated plasticity, a feature not included in the mesoscale model. In the present work, we take advantage of the microscopic flow surface, previously computed through MD calculations, to calibrate a crystal plasticity law, extending the capability of the continuum model currently limited to low velocity impacts and moderate strain rate. Indeed, the microscopic flow surface, defined as a 3D stress-at-first-defect-nucleation contains all information about TATB single crystal mechanical response under directional shear loading, including twinning, buckling, and plastic events. The calibration process uses differential evolution optimization to calibrate TATB basal and transverse slip systems critical stresses to reproduce the microscopic flow surface. Finally, the response of a TATB single crystal to directional loading is investigated in order to evaluate the new model.

In situ synchrotron investigation of tensile deformation and failure mechanisms in cold spray Cr-coated Zr-alloy system

High energy synchrotron X-ray diffraction in the transmission mode was performed in situ during uniaxial tensile testing to understand the deformation and cracking behavior of cold spray Cr-coated Zr-alloy specimens in both the as-deposited and annealed conditions. The fracture surface of the specimens, examined using scanning electron microscopy, revealed that the Cr coatings in both samples remained strongly adherent to the substrates through the completion of the tensile test. Both elastic and plastic deformation mechanisms during tensile deformation were quantified using detailed X-ray line profile analysis. High dislocation density with a unique distribution of edge and screw fractions and non-zero lattice strain was determined to be present in the cold spray Cr coating due to high strain-rate deformation during cold spray deposition. The annealing treatment reduced both residual lattice strain and dislocation density (with preferentially higher reduction in edge fractions) in the Cr coating. This led to a heterogeneous distribution of dislocation density and character among different grains, that enhanced resistance to crack propagation in the annealed Cr coating. The mechanical properties of the Zr-alloy in both specimens were not significantly altered by the presence of the cold sprayed Cr coating on the surface.

Dynamic Mechanical Properties and Modified Johnson-Cook Model Considering Recrystallization Softening for Nickel-Based Powder Metallurgy Superalloys.

The material undergoes high temperature and high strain rate deformation process during the cutting process, which may induce the dynamic recrystallization behavior and result in the evolution of dynamic mechanical properties of the material to be machined. In this paper, the modified Johnson-Cook (J-C) model for nickel-based powder metallurgy superalloy considering dynamic recrystallization behavior in high strain rate and temperature is proposed. The dynamic mechanical properties of the material under different strain rates and temperature conditions are obtained by quasi-static compression test and split Hopkinson pressure bar (SHPB) test. The coefficients of the modified J-C model are obtained by the linear regression method. The modified model is verified by comparison with experimental and model prediction results. The results show that the modified J-C model proposed in this paper can accurately describe the mechanical properties of nickel-based powder metallurgy superalloys at high temperatures and high strain rates. This provides help for studying the cutting mechanism and finite element simulation of nickel-based powder metallurgy superalloy.

High–strain–rate deformation of a nanoprecipitate–strengthened dual–phase steel

High–strain–rate deformation of steels is prone to generating localized adiabatic shear bands (ASB) due to strain localization, leading to plastic instability and fracture. Nanoprecipitate–strengthened austenite–martensite dual–phase (DP) steel is a kind of promising impact–resistant materials due to their high strength and excellent plasticity. In this study, the effects of a combination of nanoprecipitates and the frame structure of DP steels with the hard martensite as the support framework on the dynamic mechanical properties were systematically investigated. The nanoprecipitate–strengthened DP steel exhibited excellent dynamic performance. At a strain rate of 3800 s−1, the maximum flow stress of the DP steel with nanoprecipitates reached ∼ 4067 MPa, which was 1146 MPa higher than its counterpart without nanoprecipitates. High–strain–rate deformation induced the transformation of Cu–rich nanoprecipitates from body–centered cubic (B2) to 9R twin structure, alleviating the stress concentration. Upon high–strain–rate deformation, the high strength of nanoprecipitate–strengthened DP steel induced the formation of a narrow shear band with sever–deformed microstructure. The frame–structure of DP steel restrained the transformation of deformed shear bands (DSB) to transformed shear bands (TSB) due to the deformation–induced martensitic transformation of austenite, delaying the crack formation and propagation.

A Review of Numerical Simulation and Modeling in High Strain Rate Deformation Processes

Numerical simulation and modeling play a crucial role in understanding and predicting the behavior of materials subjected to high strain rate deformation processes. These processes involve rapid deformation and loading rates, typically encountered in scenarios such as impact events, explosive detonations, metal forming, and crash simulations. By employing advanced computational techniques, researchers and engineers can gain insights into complex material behavior under extreme loading conditions. This paper provides an overview of numerical simulation and modeling approaches used in studying high-strain rate deformation processes. It discusses the challenges associated with capturing dynamic material response, the development of constitutive models, and the use of finite element analysis and computational fluid dynamics. The paper also highlights the importance of material characterization, model validation, and sensitivity analysis for accurate and reliable simulations. Additionally, it explores the application of numerical simulations in optimizing material properties, designing protective structures, and improving the performance of impact-resistant materials. Overall, this review paper emphasizes the significance of numerical simulation and modeling as powerful tools for advancing the understanding and design of high-strain rate deformation processes.

Revealing the dynamic behavior and micromechanisms of enhancing the formability of AA1060 sheets under high strain rate deformation

Developing high strain rate (HSR) forming technologies is significant for efficient and high-quality aerospace sheet metal parts manufacturing. Research on the deformation behaviors and micromechanism of materials under HSRs will contribute to the further application of HSR forming technologies. In this study, the mechanical behavior of AA1060 pure aluminum at low strain rates (LSRs, 0.001 s−1 and 0.1 s−1) and high strain rates (HSRs, 2400 s−1 and 3300 s−1) was tested utilizing quasistatic tensile tests and Hopkinson bar tests at room temperature. The results of the mechanical properties showed that the elongations were 30.01 %, 37.91 %, and 46.61 %, corresponding to strain rates of 0.1 s−1, 2400 s−1, and 3300 s−1, respectively, which were 29.86 % at a strain rate of 0.001 s−1. The maximum amplification of AA1060 elongation reached 56.10 % at the HSR. Microstructure characteristics, including the Schmid factor distribution, geometrically necessary dislocation (GND) distribution, slip band, and dislocation cell, were observed by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM) under the condition of the same elongation with strain rates of 0.001 s−1 and 3300 s−1. In addition, the reasons for the plastic improvements during HSR loading were also investigated. The hard-oriented grains participate in plastic deformation at HSRs, providing additional space for dislocation multiplication and movement, increased dislocation density, and interaction between dislocations. In addition, the deformed hard-oriented grains also coordinated the strain gradient with soft-oriented grains. This improved the overall deformation uniformity, thus avoiding the premature occurrence of strain localization, namely, the elongation increase.

Investigation on the microstructure evolution and mechanical properties of electromagnetic rail material in a launch environment

The failure issue of electromagnetic railgun rails is a widely researched problem, but effective research methods are lacking in studying the microstructure of rail materials. The high current and high strain rate tensile (HCHST) testing platform was designed to simulate the high current density and high strain rate deformation service conditions of pure copper rails used in electromagnetic guns. The microstructural and mechanical properties of commercially pure copper were analyzed using TEM and EBSD under high current density (2680 A/mm2) and various high strain rates (ε̇=3404s−1,ε̇=6808s−1)using the HCHST test platform. The obtained results were then compared with those obtained from the as-received state and the quasi-static current-assisted tensile (QCAT) test. The findings indicate that the deformation mechanism of pure copper specimen under HCHST is similar to that of QCAT, where dislocation and slip are the main mechanisms. However, distinct differences in microstructure were observed. Specifically, a significant number of dislocation walls were present in the grains under QCAT, whereas numerous dislocation cells were formed in the grains under HCHST. In the high-current density environment of 2680 A/mm2, as the strain rate increased, the number of dislocation cells increased while their size decreased. The grains became extremely refined, and the KAM value also increased. Furthermore, the Vickers hardness of pure copper significantly improved after undergoing the HCHST. Based on the experimental findings, it was observed that during the service process of the pure copper rail in electromagnetic railguns (under the influence of high current density and high strain rate deformation), the surface of the rail material experienced significant dislocation entanglement. This resulted in a significant increase in the strength and hardness of the surface of the rail with high strain rate deformation. However, the uneven distribution of strength and hardness throughout the surface layer of the rail eventually made it more susceptible to deformation and failure.

Surface crack analysis of 8Cr4Mo4V steel based on Crystal/Phase microstructure model by grinding

Metal polycrystalline materials tend to be homogeneous and isotropic at the macroscopic level, which leads it difficult to visually characterize the sprouting and expansion of cracks by traditional grinding simulation. In this study, the Johnson–Cook constitutive model was used for the finite element method (FEM) based on grinding characteristics with a high strain rate and large plastic deformation. The models are focused on the actual microstructure distribution, one of them contains grains and grain boundaries, and another contains phase organization (martensite and acicular martensite) and carbides. The study pinpoints the changes in microstructure under different grinding parameters during the grinding process and the influences on the formation of microscopic cracks. Ultimately, it was found that the shedding of large primary carbide is a critical factor for inducing surface cracks. The uncoordinated deformation between brittle carbides with the other phases is the main cause of carbide shedding. Therefore, this article visualized shows the influence of grinding parameters on surface cracks from the perspective of microstructure modeling, which is of great significance in guiding practical processing.

Improvements in bonding through ultrasonic additive manufacturing of titanium by stabilizing displacive phase transformations

The development of advanced materials to operate in extreme environments (temperature, pressure, strain rate, irradiation, etc.) is essential to meet future energy challenges. In addition to being an advanced solid state bonding technique, ultrasonic additive manufacturing (UAM) can be considered as a type of extreme environment due to the high strain and high strain rate deformation that is created. Understanding the physical processes that occur in this extreme environment can be valuable to creating new desirable microstructures and/or phase changes. Although UAM has demonstrated great success in bonding a variety of materials, the underlying science mechanisms controlling the bonding are not well quantified. We observed crystal structure changes from hexagonal closed packed (HCP) to body centered cubic (BCC) in Ti and Ti alloy specimens occurring within ∼0.5 s following UAM bonding with an estimated peak temperature of ∼400 °C. Extensive interdiffusion of elements (0.2 µm – 2 µm depending on location) occurred that does not conform to thermal equilibrium bulk or grain boundary diffusion. We present evidence that a significant concentration of deformation induced vacancies Xv (between 10−4 - 10−6 atomic fraction) was created during UAM, approximately ten orders of magnitude higher than the Xv value of ∼10−15 expected for thermal equilibrium conditions. This caused pronounced metallurgical changes including rapid elemental diffusion, strain induced phase transformation, and bonding. We examined this UAM-induced severe plastic deformation on a variety of materials and performed uncertainty calculations from the measurements.

Dynamic Properties of Low-Alloyed Copper Alloys with Submicrocrystalline Structure Obtained by High Strain Rate Deformation

Dynamic Properties of Low-Alloyed Copper Alloys with Submicrocrystalline Structure Obtained by High Strain Rate Deformation

Microstructure and formation mechanisms of nanotwins in the shear band in the NiCrFe medium-entropy alloy

Introducing nanotwins to metallic materials can significantly improve strength and ductility. Nanotwins exist in the shear band after high strain rate deformation in some NiCrFe-based alloys, while the formation mechanism of nanotwins has not been revealed. In this work, nanotwins appear in the shear band of NiCrFe medium-entropy alloy (MEA) and are investigated by a series of characterization. The thickness of nanotwins is 8 nm − 10 nm. The nanotwins are of a single face-centered cubic (FCC) phase without phase transformation. Combined with experiments and molecular dynamics (MD) simulation, formation mechanism of nanotwins in the shear band is revealed. These findings provide theoretical guidance for rapid preparation of nanotwinned MEAs.

Explosive fragmentation of additively manufactured stainless steel

Properties of fragmentation from an explosively driven 316L stainless steel spherical shell section fabricated by a laser powder bed additive manufacturing process with minimal surface finishing are investigated. This shell is driven by an insensitive high explosive, resulting in high strain rate deformation (>8 × 103 s−1) and failure of the stainless steel. Photonic Doppler velocimetry measures the expansion rate; dynamic radiography and high-speed imaging capture the fracture behavior of the stainless steel. The fracture response of the additively manufactured stainless steel shell is compared to published experimental results on additively manufactured 316L stainless steel and conventionally manufactured wrought 316L and 304 stainless steel shell fragmentation. Despite preferred crack orientation, suggesting the influence of surface grooves on fracture time, fragment size is identical to that measured in a similar experiment on wrought 304 stainless steel. Further analysis indicates that the 316L additively manufactured stainless steel shell exhibits comparable spall strength and fragmentation toughness to conventionally manufactured stainless steel yet lower failure strain due to surface stress concentrations.

Influence of high strain rate deformation on the microstructure and mechanical behavior of NiCoCrFe high entropy alloy

The paper reported a high-entropy alloy, NiCoCrFe, which was produced in a Vacuum Induction Melting (VIM) furnace. In order to homogenize the microstructure, the as-cast ingot was rolled, annealed and machined to appropriate dimensions. Then the Split Hopkinson Pressure Bar (SHPB) was used to evaluate the specimens under various strain rates. True stress–strain curves of this test showed similar patterns in all strain rates, with two peaks that can be assigned to the competition between strain hardening and thermal softening. Modified Johnson–Cook model applied to characterize flow behavior of the alloy. X-ray diffraction results indicated that the alloy was single-phase with FCC crystal structure at the casting condition, after thermomechanical operation and after high-strain rate tests. The specimens were further examined by EBSD. The results indicated the impressive presence of twins in the samples deformed at strain rate of 1500 s−1, confirms the significant contribution of twinning in the strengthening process; Regarding the low SFE of the mentioned alloy, it can be said that Twin-Induced Plasticity (TWIP) has occurred. By strain rate enhancement to 3000 s−1, finer and elongated grains were observed while twinning decreased because of SFE increase as a result of temperature elevation due to adiabatic heating during deformation. According to KAM map, there was strain gradient in mentioned sample, which results in production of GNDs and GNDs pile-up leading to strain hardening by creating obstacles to further slip. Moreover, in the hat-shaped samples, which used for shear localization resistance evaluations, bundles of nano-twins were observed whose formation largely prevented strain localization and make the above alloy suitable for applications exposed to high-speed impacts.

Microstructure evolution and grain fragmentation induced by the co-activation of slip and [formula omitted] nanotwin during cryo-forging of a Ti-6Al-4V alloy

The nanostructured titanium alloy usually exhibits superior mechanical properties than the coarse-grained titanium alloy. In the present work, the α-grain fragmentation induced by slip/nanotwin co-activation during cryo-forging was studied in a bimodal Ti-6Al-4V alloy, in which the nanosized (022‾1‾) deformation twin was revealed. The results show that the lamellar α-grains fragmented to small globular grains after 25% compression at 0.1 mm/s and 0.5 mm/s. The high strain rate and large deformation increased the dislocation density and flow stress, therefore strengthened the deformation texture and promoted the grain fragmentation. The (0001) <112‾0> basal slip system was regarded as the dominant slip mode during cryo-forging, which activated more intensely in lamellar α-grains than that in equiaxed α-grains, and was promoted as the deformation ratio and stain rate increased. In addition, the activation of basal slip system was inhomogeneous in lamellar α-grains. The partial lattice rotation caused high angle grain boundary (HAGB) formation and grain fragmentation. On the other hand, the (022‾1‾) nanosized deformation twins appeared within fragmented α-grains after 25% cryo-forging at 0.5 mm/s, in which the (011‾1) planes between matrix and twin existed a ∼27° misorientation. The (022‾1‾) deformation twins contributed to grain fragmentation by twin boundary grooving and twin-twin intersection. This work demonstrated an available route to achieve refined or gradient grained structure in Ti-6Al-4V alloy by slip/twinning co-activation.

Evaluating the effect of environmental conditions on high compressive strain rates in unfilled and filled neoprene rubbers.

Elastomers are known for their strain-rate-dependent properties not only to quasistatic but also to high strain rate deformations, where mechanical behavior is significantly affected by inertia. Concurrently, environmental changes, such as temperature and humidity variations, can impact their stress response to deformation. This study investigates the effects of material layers within neoprene samples on mitigating these environmental changes. While the presence of an intermediate layer proves effective against temperature and humidity influence, it fails to block the impact of increasing high strain rates. Moreover, the different humidity levels at room and elevated temperatures do not significantly alter the mechanical behavior of filled neoprene samples compared to pure neoprene. Notably, in unfilled neoprene, an increase in humidity levels, other than an absolutely dry environment, leads to a notable stress level rise at room temperature, while under elevated temperature conditions, there is a significant stress decrease with increasing humidity. However, neoprene filled with polyester/cotton or nylon displays resilience to diminishing mechanical behavior under various temperature and humidity regulations, indicating that the material layer within these samples effectively "protects" the rubbers from potential stress lapses observed in unfilled neoprene. While a high strain rate compression affects the behavior of the filled variants significantly, increasing humidity and temperature have minimal impact on their stress levels. These findings offer valuable insights into the dynamic responses of elastomers to environmental changes, highlighting the advantages of using filled rubbers in diverse applications.

Self-force of high-speed dislocation in anisotropic media based on configurational mechanics

Subsonic, transonic, and supersonic dislocations play a critical role during super high strain rate (>105/s) deformation. For these high-speed dislocations, the self-force is history dependent, which is different from and much more complex than the quasi-static dislocations. Solutions to the self-force of high-speed dislocation in continuum media are only known for some special cases, i.e., subsonic dislocation moving in isotropic infinite crystals with a constant speed. However, metals are generally anisotropic, and high-speed dislocations may have complicated histories and interact with the free surface. How crystal anisotropy, complicated motion history and free surface influence their self-force has so far received little attention. In the current work, we proposed an effective calculation method of self-force on high-speed dislocation based on the discrete-continuous model of three-dimensional dislocation elastodynamics and the dynamic J-integral of configurational mechanics. It is applicable to arbitrarily moving subsonic, transonic and supersonic dislocation, in both isotropic and anisotropic crystals, and can automatically consider the image force if the dislocation is close to the free surface. The effectiveness of the method is carefully verified by comparing it with the existing theoretical solutions and the molecular dynamics results. The effect of crystal anisotropy on the elastodynamic stress field, as well as the self-force of high-speed dislocation close to or far from free surface are studied.

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.

Investigation of the twin-induced adiabatic shear bands evolution in a Mg-Al-Mn alloy under ballistic impact

The formation and evolution of twin-induced adiabatic shear bands (ASBs) in a Mg-Al-Mn alloy under ballistic impact were investigated by analyzing the microstructures at three representative locations with different distances from the crater rim. Results show that localized shear deformation occurred at the twin boundaries, resulting in the formation of ASBs. The ASBs thicken at the expense of the deformation twins with increasing plastic deformation, forming ASBs which are mainly composed of subgrains, ultra-fine recrystallized grains and Mg17Al12 precipitates. The appearance of the twin-induced ASBs is mainly attributed to the twin-twin intersections caused by high strain rate deformation. The twin-twin intersections under high strain rate deformation lead to a different twinning activity in which the subsequent plastic deformation mainly occurs by shear deformation along the twin boundaries rather than thickening the twins. These results and analysis can shed new light on understanding the nucleation and evolution of ASBs in Mg alloys under dynamic loadings.