Strain Rate Response Research Articles

A strain rate response and self-healing organohydrogel for use in impact-protective materials

Impact-protective materials are used in many fields owing to their excellent mechanical properties, impact resistance, and rapid responses to external stimuli. In this study, a new organohydrogel (PAIG) was designed and prepared through emulsion copolymerization by combining polymer chain segment as a skeleton and oil phase containing IHP as dynamic crosslinking points. The PAIG gel system provided a stable structure and overcame the cold flow property of impact-hardening polymers (IHP) with a tensile stress of 0.48 MPa. In addition, the introduced flexible IHP chains provided a large number of boron–oxygen dynamic bonds and hydrogen bonds, which improved both the impact resistance (the peak force reduction rate of 74 %), speed- response and the self-healing ability (with an efficiency of ca. 90 %). Impressively, PAIG can withstand cyclic twisting and bending even at −20 °C, showing its excellent freezing resistance. These properties make the PAIG promising for intelligent impact-protection applications.

High strain-rate strength response of single crystal tantalum through in-situ hole closure imaging experiments

The properties of crystalline materials often depend on directionality and operating conditions. Specifically, the strength of materials can depend anisotropically on crystal direction and the loading condition. To probe these effects, a preliminary series of high strain-rate (>105/s) strength plate-impact hole closure experiments were performed on high purity single crystal tantalum cubes. The orientation of the single crystals with respect to impact/loading were varied to provide data to inform crystal plasticity modeling efforts. The experiments consist of in-situ high-resolution X-ray radiographic imaging of the hole collapse under dynamic compression conditions to infer the material strength via its resistance to closure at increasing levels of plastic strain. The experiments are compared against hydrocode simulation predictions. A comparison with simple elastic perfectly plastic strength model predictions is presented to elucidate the response of the different crystal orientations at high strain-rate and large plastic strains.

Compressive response of white matter in the brain at low strain rates

The low strain-rate response of brain parenchyma is critical to predicting prognosis in cases of hydrocephalus or cerebral edema, including in the prediction of brain stem herniation. Although rate-dependent responses of brain parenchyma are well known to arise from both viscoelasticity at higher strain rates, and it is not clear whether the tissue behaves as a fluid or a solid when loaded over periods of hours to days, and the extrapolation of rate sensitivity to lower strain rates is not clear. To address this, unconfined compression-isometric hold tests were performed on samples of white matter from porcine brains at strain rates ranging from 2/s to 2 × 10−6/s. Results showed that the apparent Young's modulus dropped from ∼3000 Pa to ∼160 Pa over this range following a power law, and that an equilibrium Young's modulus of ∼100 Pa was reached. Results reveal that brain parenchyma behaves as a compliant solid at low strain rates, and suggest that brain stem herniation is resisted by an elastic energy barrier.

Ti6Al4V interacting with Al2O3 under ambient and vacuum conditions: Effect of plastic deformation and tribo-chemical reactions on wear mechanisms

Tribological interaction is a synergy between several mechanisms. In this paper, those pivotal mechanisms are studied by investigating the sliding interaction of Ti6Al4V (referred to as Ti64) pins against an Al2O3 disc under both ambient and vacuum environments. The impact of sliding speed was examined by altering the rotation rate (measured in ms−1) of the disc. This assessment utilized a 6.6 mm diameter pin, while keeping the load and environmental conditions consistent across all experimental trials. The findings reveal that in ambient environment, the frictional characteristics and wear rate of the tribological pair are intricately influenced by a synergistic interplay between plastic deformation and tribo-chemical reactions (TCR). A transition in wear mechanism occurs from abrasion to composite type (abrasion + oxidative) to oxidative with step-wise increment in sliding velocity (0.01–1.5 m/s). Coupled action of the TCR sub-mechanisms, viz. tribo-oxidation and formation of mechanically mixed layers (MML) play a pivotal role in the aforementioned wear transition. For vacuum-based experiments, the prevailing wear mechanism is exclusively dictated by plastic deformation. This phenomenon is in turn regulated by adiabatic shear banding (ASB)/strain rate response (SRR) at lower speeds, while at higher speeds, temperature-induced effects (phase transformation assisted thermal softening) come into action. Adhesion takes precedence in governing the material removal process, given that the development and activity of tribo-oxides and MML are impeded in the absence of air. Further, additional tests to study the effect of change in the pin-diameter (2.1, 4.6, and 6.6 mm) on the tribological response are performed and analysed.

Effect of temperature on high strain-rate damage evolving in CFRP studied by synchrotron-based MHz X-ray phase contrast imaging

The present study demonstrates experimental evidence of subsurface mesoscale damage initiation and evolution in angle-ply CFRP laminates under high strain-rate loading at low temperatures using synchrotron-based X-ray MHz radiography. A bespoke set of loading, temperature control and in-situ X-ray imaging systems were applied to simultaneously correlate high strain-rate mechanical response with observed subsurface damage in a time-resolved manner. The results demonstrate that independent of temperature, damage evolved following a specific sequence; firstly intra-ply shear cracking along the fibre direction, developing into multi-layer cracking with continued deformation, and finally culminating in inter-ply delamination and complete failure of the specimen. The timescale for this sequence, however, was observed to strongly depend upon temperature, with low temperatures resulting in more rapid damage evolution and loss of mechanical strength.

High strain rate response of ABS-M30i-based 3D printed, bio-inspired, bovine bone structure

To investigate osteoporosis caused by aging and the dynamic behavior of male bovine trabecular bone, three age groups of male bovine trabecular bone were chosen, and micro-computed tomography (CT) analysis was performed to develop an image-based bio-inspired computer-aided design (CAD) model of the bone structure. Further experimental and computational studies were carried out to examine the rate-dependent behavior and compressive energy-absorbing capacity of the structure as a function of age. To evaluate this study, a micro-CT-based CAD model of the structure was 3D printed using ABS-M30i material and subjected to quasi-static compression (low strain rate) and high strain rate (split Hopkinson pressure bar) compression. The findings show that 3D-printed bovine structures have distinct high-rate dependence at strain rates greater than 430 s−1, as well as sensitivity to strain rate in terms of peak stress, plateau stress, and energy absorption capacity. Using rate-dependent properties, the Johnson–Cook damage plasticity model was used in computational analysis to explain the dynamic behavior of bone due to osteoporosis. Overall, there is good agreement between the numerical simulations and the experimental data, which was obtained by verifying and validating the model against the experimental results.

Modeling and simulation of dynamic compression of Bulk Metallic Glasses at room and elevated temperatures using split Hopkinson pressure bar setup

This paper presents a modeling and simulation study of dynamic compression behavior of Bulk Metallic Glasses (BMGs) at room and elevated temperatures using the split Hopkinson pressure bar (SHPB) setup. The primary objective of this study is to develop and validate a constitutive model and simulation methodology capable of predicting the high strain rate response of BMGs at different temperatures. We propose a constitutive model for BMGs that accounts for the effects of high strain rates and elevated temperatures. We numerically implemented this model in ABAQUS/Explicit Finite Element Analysis software by writing a Vectorized User Material (VUMAT) subroutine. The methodology for modeling and simulation of dynamic compression of BMG specimens using the SHPB setup is developed. The present simulations are able to correctly predict the rate-independent response of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vitreloy-1) BMG under dynamic compression at room and elevated temperatures. Furthermore, the present simulations are also able to correctly predict the negative strain rate sensitivity (SRS) of Zr52.5Cu17.9Ni14.6Al10Ti5 (Vitreloy-105) BMG at room temperature. Finally, the present simulations correctly predict that the failure stress of Zr64.13Cu15.75Ni10.12Al10 BMG decreases with increasing temperature and exhibits a minimal positive SRS. The present study is the first successful attempt to model the mechanical response of various BMGs under dynamic compression and at room and elevated temperatures. In particular, the experimentally observed negative SRS in some BMGs has been successfully simulated. The present work has important implications for the design of next generation spacecraft shields that are based on BMGs for mitigating the effects of hypervelocity impacts from debris in space.

Investigation on high strain rate response of lightweight sandwich panel with aluminum corrugated core and smart composite facesheets

Investigation on high strain rate response of lightweight sandwich panel with aluminum corrugated core and smart composite facesheets

The High Strain Rate Response of A Bio-Mimetic Composite Plates

Biological materials are often viewed as composites, consisting of weaker components arranged hierarchically, leading to exceptional mechanical capabilities that are challenging to replicate in synthetic materials. Natural shape and structure develop through the process of striving for improved performance. This paper will provide a summary of observations from experiments conducted on a composite material designed to closely mimic a sophisticated multifunctional biological structure. The Split Hopkinson Pressure Bar (SHPB) was utilized to test strain rates ranging from 102 s-1 to 104 s-1, providing reliable and comprehensible data for analyzing the behavior of the composite material at high strain rates. The Split Hopkinson Pressure Bar (SHPB) device is frequently utilized for evaluating metals and other materials with high strength and mechanical resistance. This study will detail the changes made to a standard Split Hopkinson Pressure Bar (SHPB) apparatus for testing low impedance materials. An aluminum sample was seen to lose its specific stiffness as impact strain rate increased, but the produced material continued to improve.

Characterizing piezoelectric properties of PVDF film under extreme loadings

Polyvinylidene fluoride (PVDF) as a polymer has been proven to be an effective piezoelectric sensor with advantages of good flexibility, high mechanical strength, and high chemical resistance. Numerous studies have focused on the response of PVDF film at high strain rates, but few on low strain rate response, and the response of PVDF film at different strain rates is unknown. To address these limitations, we examine the piezoelectric properties of PVDF film at extreme high and low loading rates. We design quasi-static compression and dynamic split Hopkinson pressure bar (SHPB) test setups to examine the response of PVDF film. Quasi-static compression test results show that PVDF films have good repeatability and linearity. The charge shift phenomenon is observed at quasi-static loading conditions, and the charge shift rate is found to be related to the gain coefficient of charge amplifier. Next, SHPB tests are performed and results show that PVDF film can well capture the propagation of stress wave. Moreover, it is observed that the PVDF film under high loading rate has a higher failure strength in comparison to that of low loading rate. Finally, based on the measured points by quasi-static compression and SHPB tests, the piezoelectric coefficients of PVDF film under extreme low (on the scale of strain rate of 10−2 s−1) and extreme high (on the scale of strain rate 105 s−1) loading rates are found to be 30.79 pC/N and 27.72 pC/N, respectively. Note that, the strain rate difference is seven orders of magnitude, the piezoelectric coefficient difference is only 9.97%. We believe our findings can advance the design and application of PVDF films in practical engineering.

A comparison of high strain rate response and adiabatic shear band formation in additively and traditionally manufactured Inconel 718

3D printing of Inconel 718 has been increasingly commercialized, as such research comparing the mechanical properties of additively manufactured (AM) and traditionally manufactured (TM) components in both quasi-static and high rate regimes should be conducted. Herein, the high strain rate material response, as well as the formation of adiabatic shear bands (ASBs) in AM and TM Inconel 718 are studied using a split Hopkinson pressure bar (SHPB) system. A top-hat cylindrical specimen geometry was used to convert the compressive load to shear and conduct high rate shear tests in the SHPB. The quasi-static and high rate stress-strain data reported herein indicates that TM components have at least a 70 MPa higher compressive yield strength. Interestingly, the AM specimens were more susceptible to ASB formation than their TM counterparts. The critical shear strain at which an ASB forms was higher for the TM specimens compared to the AM specimens. This was attributed to the TM material having a higher critical stress for dynamic recrystallization initiation, which is required to ASB formation. The microstructures of the shear zone in the top-hat specimens were examined using an optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). Dynamic recrystallization was observed at the center of the shear affected zone (SAZ) using TEM from material lifted out from the ASB. Due to the plastic deformation in the shear region, the material strain hardens and therefore has a higher hardness than the bulk material. At the center of the shear region, a peak in nano-hardness of 585 HV was recorded on the ASB. The outcome of this research will lead to the prevention, containment, and control of shear instability in AM structures.

High strain rate responses of some metals and alloys using a plate impact driven ring expansion test (PIDRET)

A plate impact driven ring expansion test (PIDRET) has been developed to investigate the high strain rate response of metals and alloys under radial expansion. Combining photonic Doppler velocimetry (PDV) probes and ultra-high-speed cameras, it allows for measuring the radial expansion velocity of the ring and for recording the different stages of the ring deformation until necking and ultimate fragmentation. Four metallic materials with different physical and mechanical properties are tested under the same loading conditions leading to strain rates around 104 s−1. The materials exhibit different responses in terms of deformation history and fracture. A comparison is made on (i) the postmortem microstructure and ductility between low strain rate tension loaded specimens and high-strain rate expansion loaded rings and (ii) numbers of necks and fragments between experimental results and theoretical estimations.

Highly strain-rate sensitive and ductile composite materials combining soft with stiff TPMS polymer-based interpenetrating phases

The current work investigates the engineering of strain-rate sensitive and ductile composites through the combination of stiff, triply-periodic-minimal-surface (TPMS) with soft, rubber-type material phases. Different interpenetrating phase composite (IPC) designs are considered, with Diamond, Fisher-Koch, and IWP TPMS architectures as reinforcement phase topologies. The loading rate sensitivity of the arising IPCs is evaluated at different strain-rates, revealing an effective composite performance that well separates from the either brittle or substantially low-strength behavior of its constituent materials. Significant strain-rate effects are recorded, which relate to increased stiffness and energy absorption attributes upon substantial ductility, with the actual performance to depend on the underlying reinforcement phase topology. The effective strain-rate IPC constitutive response is well-captured by dedicated, low numerical cost and high accuracy machine learning models, whereas Digital Image Correlation (DIC) and finite element analysis are employed to provide insights in the inner strain and stress fields developed and failure modes observed. Overall, energy absorptions higher than 10 and up to 14 MJ m−3 are reported for strain-rates in the order of 100, furnishing specific energy absorptions (SEA) in the uppermost range of the effective composite material behaviors up to now reported, upon exceptionally high crushing force efficiencies (CFE) at moderate densities.

Strain-rate response of 3D printed 17-4PH stainless steel manufactured via selective laser melting

This research work aims at investigating the strain rate effects on the 17-4PH stainless steel produced by Selective Laser Melting (SLM), with the final goal of adding knowledge about its mechanical performance for applications under certain dynamic conditions. Mechanical characterization of 3D-printed samples was performed using a universal quasi-static electro-mechanical machine, a hydro-pneumatic machines, and a split Hopkinson Tensile Bar device for quasi-static, intermediate (5 s−1) and high strain-rates (100 s−1 and 300 s−1), respectively. The use of this technology represents the most interesting breakthrough of the paper, allowing to identify and to evaluate the performance of 3D-printed metals in relation to impacts or other dynamic conditions typical of different areas of engineering, which are impossible to be obtained by other technologies. The conducted tests allowed to identify the main information on the material behaviour, from the quasi-static to the high strain-rate regime, mainly in terms of stress–strain curves and fracture, and the behaviour after fracture was assessed by applying the Bridgman equations.The effect of horizontal and vertical printing directions, as well as of an annealing heat treatment, are also discussed. According to the evaluation of the main mechanical parameters, the strain-rate increase affects the mechanical behaviour both in the horizontal and vertical directions: samples built horizontally show increased yield stress and ultimate strain and decreased ultimate strain, whereas specimens printed vertically exhibit a remarkable increase in yield stress and a decrease of the ultimate stresses and strains. However, the better behaviour observed, with respect to the horizontally printed specimens, for vertically printed specimens in the quasi-static regime was no longer observed for intermediate and high strain rates. Moreover, all heat-treated specimens present higher strain-rate sensitivity than not heat-treated ones.Finally, the applicability of the existing Johnson-Cook material strength model to represent the mechanical behavior of 3D printed 17-4PH stainless steel is examined. The obtained results represent an important contribution to the current literature, because the dynamic behaviour of 17-4PH stainless steel produced by SLM, under the studied strain rates values, have been scarcely investigated so far.

A Coherent Assessment of the Compressive Strain Rate Response of PC, PETG, PMMA, and TPU Thermoplastics in MEX Additive Manufacturing.

In this study, we successfully address a significant research and engineering gap by quantitatively assessing the impact of varying compressive loading rates on the mechanical behavior of four popular thermoplastic polymers in material-extrusion-based (MEX) 3D printing. Raw powders of polycarbonate (PC), polyethylene terephthalate glycol (PETG), polymethyl methacrylate (PMMA), and thermoplastic polyurethane (TPU) were processed through melt extrusion, and the filaments were used to 3D-print the test samples. For completeness, thermogravimetric analysis and a compressive test following the ASTM-D695 standard were conducted. Ultimately, the compressive strength and yield stress, the compressive modulus of elasticity and toughness, and the maximum compressive sensitivity index were thoroughly documented. Specimens were tested in strain rates from 1.3 mm/min to 200 mm/min. The compressive strength (40% for the PMMA) and stiffness (29% for the TPU) increased with the increase in the strain rate in all polymers tested. PC had the highest strain rate sensitivity. Significant variations in deformation and fracture modes were observed and thoroughly documented throughout this study. Our findings can be useful in industrial engineering as valued design optimization input parameters in various applications involving the above-mentioned polymeric materials.

High strain rate response and mechanical performance of tantalum carbide–hafnium carbide solid solution

Ultra-high temperature ceramics (UHTCs) based on the solid solution TaxHf1-xC have shown great promise as materials for extreme environments (>2500 °C) due to their improved thermo-mechanical properties. However, their dynamic response under high-impact loading remains unknown. In this study, we investigate the dynamic impact behavior and fracturing evolution of TaxHf1-xC samples (with x = 0, 0.2, 0.5, 0.8, and 1) at a strain rate > 103 s-1 using the Split Hopkinson Pressure Bar (SHPB) test. Among the different compositions, Ta0.5Hf0.5C exhibits the highest compressive strength of 1870 MPa, representing a 36% improvement over TaC and 54% over HfC. High frame rate videos and deformation analysis reveal that Ta0.5Hf0.5C, characterized by extensive Ta–Hf bonding, significantly reduces the crack propagation rate by approximately 1435% compared to TaC and 4050% compared to HfC. This effect is attributed to the dislocation pile-ups, nano-twin formation, inter grain twisting exhibited mostly along {111} plane as Hf substitutes Ta in TaxHf1-xC samples. Further, the surface energy is least for {111} plane eliciting the higher probability for bypassing crack propagation along this plane in TaxHf1-xC. The exceptional damage tolerance and improved mechanical properties of Ta0.5Hf0.5C, compared to other solid-solution TaxHf1-xC compositions, make it an extraordinary structural material for hypersonic applications. These findings provide valuable insights into the dynamic behavior of UHTCs and highlight the potential of Ta0.5Hf0.5C as a superior material for extreme environments requiring high-impact resistance.

Time-dependent mechanical behavior of tough hydrogels under multiaxial stretching

ABSTRACT Understanding the time-dependent mechanical behavior of tough and viscoelastic hydrogels under complex external loading is crucial. In this study, we utilized tough and viscoelastic hydrogels synthesized through the copolymerization of methacrylic acid and methacrylamide as a model system to investigate their mechanical behavior under multiaxial stretching across a wide range of strain rates. Three stretching modes examined were uniaxial, pure shear, and equal biaxial stretching. Our findings show that under equal biaxial stretching, the hydrogels exhibit higher mechanical properties and energy dissipation compared to uniaxial and pure shear stretching, owing to the greater contribution of hydrogen bonds to energy dissipation in the former stretching mode. Additionally, employing the time-elongation separability method during the stretching process, we observed that the relaxation of dynamic hydrogen bonds in the hydrogels only depends on stretching time, independent of the elongation ratio and stretching modes. We anticipate that this study will yield valuable contributions to the design of durable load-bearing soft materials, particularly in dealing with complex deformation and strain rate responses.

High strain rate mechanical behaviour of uniform and hybrid metallic TPMS cellular structures

Four different geometries of uniform triply periodic minimal surface (TPMS) cellular structures (Diamond, Gyroid, IWP, and Primitive) and a hybrid Gyroid–Diamond TPMS structure were fabricated and experimentally tested under different compressive strain rates ranging from quasi-static (at 0.005 s−1) to very high strain rates (at 11,000 s−1). Three different testing apparatuses were used: a universal servo-hydraulic testing machine, a direct impact Hopkinson bar (DIHB), and a powder gun. Limited strain rate hardening was observed at quasi-static, low- and intermediate-dynamic deformation, while the shock deformation mode showed significant strain rate hardening of all tested structures. The computational models were developed and validated with the experimental results and then used to predict the TPMS structure’s behaviour even at higher strain rates (up to 35,000 s−1), not attainable by used experimental devices. The Diamond and IWP structures exhibited up to five times higher (an increase from 6.9 to 40.8 J/g) specific energy absorption (SEA) during very high strain rate loading than during the quasi-static and lower dynamic testing. The tests of hybrid samples showed that the sample orientation significantly affects the mechanical high strain rate response, which can be either progressive (less stiff structure at sample impact end) or regressive (stiffer structure at sample impact end).

Linking myosin heavy chain isoform shift to mechanical properties and fracture modes in skeletal muscle tissue.

Muscle fibers play a crucial role in the mechanical action of skeletal muscle tissue. However, it is unclear how the histological variations affect the mechanical properties of tissues. In this study, the shift of myosin heavy chain (MHC) isoforms is used for the first time to establish a linkage between tissue histological variation and passive mechanical properties. The shift of MHC isoform is found not only to induce significant differences in skeletal muscle passive mechanical properties, but also to lead to differences in strain rate responses. Non-negligible rate dependence is observed even in the conventionally defined quasi-static regime. Fidelity in the estimated constitutive parameters, which can be impacted due to variation in MHC isoforms and hence in rate sensitivity, is enhanced using a Bayesian inference framework. Subsequently, scanning electron microscopy and fluorescence microscopy are used to characterize the fracture morphology of muscle tissues and fibers. The fracture mode of both MHC I and II muscle fibers exhibited shearing of endomysium. Results show that the increase in strain rate only leads to stronger rebounding of the muscle fibers during tissue rupture without changing fracture modes.

Soft polyurethane foam reinforced by expanded polystyrene particles: Compression performance, strain rate, and cyclic compression response

AbstractThe incorporation of particles with soft polyurethane (PU) foam aims to mechanically strengthen the PU foam as PU foam falls short of the mechanical expectation of academia and industries. In this study, the expanded polystyrene (EPS) particles are added to soft polyurethane foam, and composite foam with higher mechanical properties is successfully prepared by one‐step foaming process. The results show that under optimal conditions that is, EPS particle size of 0.5 mm and content of 2.5 wt% (EPS‐0.5‐2.5%), the synthesized foam has the smallest bubble pore diameter of 80 μm and has a stress of 0.284 MPa at 75% strain, which is much higher than that of blank polyurethane foam. As a result of a rise in the quantity of EPS particles, the composite PU foam shows a lower dependency on the strain rate. After the multiple cyclic compression test, PU foam exhibits a descending trend on the stress in the deformation plateau region. Besides, the low‐velocity impact test results indicate that the peak contact force of EPS‐0.5‐2.5% is lower than that of the control group by 632 N.