Strain Rate Dependent Mechanical Behavior Research Articles

On the strain rate-dependent mechanical behavior of PE separator for lithium-ion batteries

The separator is a critical component for ensuring electrochemical cycling performance and preventing internal short circuits in lithium-ion batteries. For the collision safety of lithium-ion batteries, understanding the rate-dependent mechanical behavior of the separator is essential for battery impact modeling and safety prediction. This study conducts a comprehensive experimental investigation into the strain rate–dependent tensile/compressive behavior and failure mechanism of the polyethylene (PE) separator under quasi-static and dynamic conditions. The combination of deformation images recorded by cameras and post-mortem characterization using SEM was employed to clarify the rate-dependent deformation and fracture mechanism of the separator under both tensile and compressive loading. The experimental results demonstrate a significant strain rate effect on the tensile/compressive mechanical properties and damage/failure behavior of the separator. Furthermore, the effect of the strain rate on the mechanical properties, including the tensile strength, tensile fracture strain, tensile elastic modulus, compressive modulus, yield stress and yield strain of separator, was analyzed and discussed. A significant strain rate-dependent tensile damage and fracture behavior of the separator was observed, where the fracture site exhibited an obvious phase transition and skeletal lamella fracture under extremely high strain rate tensile loading. The separator underwent severe damage under dynamic compressive conditions. The results of this study provide an important basis for the establishment of rate-dependent safety criterion and short circuit prediction of lithium-ion batteries under impact loading, and shed light on understanding separator failure-induced short circuit issues in battery collision safety scenarios.

Effect of inelastic deformation on strain rate-dependent mechanical behaviour of human cortical bone

In this study, the role of inelastic deformation of bone on its strain rate-dependent mechanical behaviour was investigated. For this, human cortical bone samples were cyclically loaded to accumulate inelastic strain and subsequently, mechanical response was investigated under compressive loading at different strain rates. The strain rate behaviour of fatigued samples was compared with non-loaded control samples. Furthermore, cyclic loading-induced microdamage was quantified through histological analysis. The compression test results show that the strength of fatigue-loaded bone reduced significantly at low strain rates but not at high strain rates. The difference in microcrack density was not significant between fatigued and control groups. The results indicate that the mechanism of load transfer varies between low strain rate and high strain rate regimes. The inelastic deformation mechanisms are more prominent at low strain rates but not at high strain rates. This study shed light on the role of inelastic deformation on the rate-dependent behaviour of cortical bone.

Effect of Pore Pressure on Strain Rate-Dependency of Coal

Viscoelastic strain rate-dependent behaviour of coal is critical in several subsurface engineering applications especially coal seams gas production. Such rate dependency is controlled by the interaction between coal bulk and gas sorption (a sorbing gas) or gas pressure (a non-sorbing gas). Despite the research conducted to date, the gas pressure effect (non-sorbing) on the viscous behaviour of sediments in particular coal remains unexplored. We, therefore, investigate the strain rate-dependent mechanical behaviour of coal under isotropic loading to specifically explore the effect of gas pressure (Helium) on its rate dependency eliminating the sorption effect. We perform a set of triaxial experiments on coal specimens at dry and pressurised gas (Helium) conditions under different strain rates under isotropic loading. The experimental results show that all coal specimens have viscoelastic strain rate dependency at a dry condition where viscous effect increases with strain rate. As a result, the bulk modulus of the specimens increases with the increase in strain rates. This strain rate dependency response, however, reduces with an increase in pore pressure and vanishes at a certain pore pressure under the same effective stress to that of dry specimens. We further employ X-ray micro-Computed Tomography (XRCT) to 3D scan a coal specimen saturated with Krypton gas undergoing different loading rates to shed light on the micro-mechanisms of gas pressure effect on specimens’ rate dependency. The XRCT results show that gas can be trapped in small-scale fractures and pores during the loading process leading to a localised undrained response that can stiffen the specimen and reduce its ability to show viscous rate dependency. The obtained results are significant in optimizing coal seam gas production and coal seam gas drainage applications.

Viscoelastic-viscoplastic modeling of epoxy based on transient network theory

The expansion of the application of polymers instead of metals has warranted the evaluation and modeling of their mechanical behaviors under various conditions. In the present study, the strain-rate- and temperature-dependent nonlinear mechanical behavior of a glassy polymer from small to large strain ranges is investigated experimentally and numerically. The effects of strain rate and temperature on the mechanical responses and development of the strain field under monotonic and cyclic uniaxial tensile tests of epoxy are evaluated experimentally. In addition, the stress relaxation test is performed to evaluate the time-dependent mechanical behavior of epoxy. In the previous work (Uchida et al. 2019), the concept of the transient network (TN) theory was applied to demonstrate the nonlinear behavior of the thermosetting glassy polymer. In this model, the time-dependent mechanical behavior of the thermosetting glassy polymer was assumed to be characterized by the debonding and rebonding of intermolecular secondary bonds (SBs). In the present study, the TN model is extended to represent the temperature- and strain rate-dependent mechanical behavior of the thermosetting glassy polymer below the glass transition temperature Tg. The decrease in the deformation resistance of a polymer at a higher temperature is represented by a decrease in the SB density. Furthermore, the fixation parameter is introduced to accurately predict the residual strain in the cyclic tensile test. The mechanical responses in the monotonic and cyclic tensile tests and the stress relaxation test predicted by the extended TN model are consistent with the experimental results. The proposed model is further verified using additional experimental results provided in references. The obtained results demonstrate the nonlinear deformation behaviors of glassy polymers under wide ranges of temperature and strain rate.

Effect of organic matrix alteration on strain rate dependent mechanical behaviour of cortical bone

The organic matrix phase of bone plays important role in its mechanical performance, especially in the post-yield regime. Also, the organic phase influences loading rate-dependent behaviour of bone which is relevant during the high-speed loading events. Many diseases, as well as aging, affect the matrix phase of bone which causes compromised mechanical properties. Improved understanding of alterations in the organic matrix phase on mechanical response of bone will be helpful in the mitigation of fractures associated with inferior matrix quality. In the present work, effect of alteration in organic matrix of cortical bone on its strain-rate dependent behaviour was investigated. To produce different amounts of collagen denaturation, bovine cortical bones were heated at the temperature of 180 °C and 240 °C. Further, compression testing was performed at quasi-static strain rates of 10−4 s−1 to 10−2 s−1 using a conventional testing machine whereas a modified Split Hopkinson Pressure Bar (SHPB) was used for high strain rate (∼103) testing. Thermal treatment-induced changes in the mineral and organic phases of bone were assessed using X-ray diffraction (XRD) and Fourier-transform infrared-attenuated total reflection (FTIR-ATR) techniques respectively. Compression test results show that thermal treatment of bone up to 180 °C did not affect mechanical properties significantly whereas treating at 240 °C significantly reduced elastic modulus, failure stress and failure strain. Also, thermal denaturation of collagen reduced the strain rate sensitivity of cortical bone at high strain rates. Similar to the compression test observations, nanoindentation results show a significant reduction in elastic modulus and hardness of denatured samples. Further, FTIR results revealed that with the heat treatment of bone, collagen structure undergoes conformational changes at the molecular level. The initial helix structure breakdowns into unordered/random coil structures which subsequently reduced the mechanical competence of bone. The present study provides insight into the effect of organic matrix modification on mechanical behaviour of cortical bone which could be helpful in understanding bone disorders associated with organic matrix phase and development of therapeutic interventions.

Constitutive equations for strain rate and temperature dependent mechanical behaviour of porous Ag-sintered joints in electronic packages

Sintering of silver attracts increasing attention in electronic packaging owing to superior bonding quality and high operation temperatures. However, the mechanical properties of sintered joints strongly depend on fabrication parameters like sintering temperature, pressure or organic solvents in the silver paste. In consequence, the mechanical characterization of this material is a challenging task. In the present article, unified constitutive equations for plasticity and creep of sintered silver are established. Thereby, particular interest is devoted to the influence of porosity on the mechanical properties. The assumptions of the model are validated by mechanical tests carried out with samples prepared under constant sintering conditions. The model parameters are fitted to test results performed in tension mode, in shear mode and under conditions of stress relaxation. This material model is implemented in the commercial software ABAQUS through user subroutines UMAT and VUMAT. In conclusion, the constitutive material model can be used as prerequisite for reliability predictions of Ag-sintered joints in electronic packages.

Experimental study of the stress state and strain rate dependent mechanical behaviour of TRIP-assisted steels

This paper presents an investigation into the effect of different stress states and strain rates on the austenite-to-martensite transformation during plastic straining of a Q&P steel. Different stress states are imposed to the steel using purposed-designed samples. The sample geometries, including in-plane shear, dogbone and plane strain samples, are optimised by finite element modelling. Tensile tests are performed at different strain rates of 0.001 s-1, 10 s-1 and 500 s-1. Digital image correlation is used to capture the strain fields during the entire deformation process. The mechanical results indicate a positive strain rate sensitivity for both the shear and plane strain specimens and a negative strain rate sensitivity for the dogbone sample. In addition, the influence of the strain rate on the strain level is more pronounced for the shear than for the plane strain specimens and for the dogbone samples.

Experimental characterization and constitutive modeling of an aluminum 7085-T711 alloy under large deformations at varying strain rates, stress states, and temperatures

The strain rate, stress state, and temperature dependent mechanical behavior of a hot rolled aluminum 7085-T711 alloy is experimentally observed and subsequently modeled using a continuum Internal State Variable (ISV) plasticity-damage constitutive model. Structure-property relationships for the alloy are quantified using a series of microstructural analyses and mechanical property experiments. The calibrated ISV model for the Al 7085-T711 alloy is implemented in an implicit finite element code (Abaqus) to simulate the deformation of notch Bridgman tension specimens at a variety of stress states and temperatures. The ISV model accurately captures the material's elastoplastic behavior by predicting the stress state difference between tension, compression, and torsion and temperature dependent microstructure evolution under large deformations.

Strain rate dependent mechanical behavior of B. mori silk, A. assama silk, A. pernyi silk and A. ventricosus spider silk

In this study, the effect of strain rate on the mechanical behavior of B. mori silk, A. assama silk, A. pernyi silk and A. ventricosus spider silk were systematically investigated. Dynamic tensile tests were conducted for these natural silk fibers to obtain their mechanical properties under five strain rates. Tensile test results indicated that the stiffness, tensile strength, failure strain and rupture energy of A. ventricosus spider silk all increase with increasing strain rates. A. ventricosus spider silk was found to have the highest average Weibull modulus among these silk fibers, showing its excellent reliability. Then, based on Zener model and Weibull statistics, this study theoretically characterized and analyzed the influence of strain rate on their mechanical properties including stress-strain responses, tensile strengths, Weibull parameters, failure strains and rupture energies. Some insights that can be helpful for better understanding their strain rate dependent mechanical behavior were provided.

A novel dynamic constitutive micromechanical model to predict the strain rate dependent mechanical behavior of glass/epoxy laminated composites

In the present research, a novel dynamic constitutive micromechanical (DCM) model was developed to predict the strain rate dependent mechanical behavior of laminated glass/epoxy composites. The present model is an integration of the generalized strain rate dependent constitutive model as a constitutive model for the neat polymer, the plasticity model of Huang as a micromechanical model, and dynamic progressive failure criteria. This model is able to predict the longitudinal and transverse tensile and in-plane shear behaviors of unidirectional glass/epoxy composites with arbitrary fiber volume fractions at arbitrary strain rates. The present model can also predict the stress-strain behavior of laminated composites with different layups and fiber volume fractions at arbitrary strain rates. A comparison between the results predicted by the present model and the available experimental data showed that the model predicts the strain rate dependent mechanical behavior of glass/epoxy composites with very good accuracy.

A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin, China

Shale, as a kind of brittle rock, often exhibits different nonlinear stress‐strain behavior, failure and time‐dependent behavior under different strain rates. To capture these features, this work conducted triaxial compression tests under axial strain rates ranging from 5×10−6 s−1 to 1×10−3 s−1. The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates. These strain rate‐dependent mechanical behaviors of shale are originated from damage growth, which is described by a damage parameter. When axial strain is the same, the damage parameter is positively correlated with strain rate. When strain rate is the same, with an increase of axial strain, the damage parameter decreases firstly from an initial value (about 0.1 to 0.2), soon reaches its minimum (about 0.1), and then increases to an asymptotic value of 0.8. Based on the experimental results, taking yield stress as the cut‐off point and considering damage variable evolution, a new measure of micro‐mechanical strength is proposed. Based on the Lemaitre's equivalent strain assumption and the new measure of micro‐mechanical strength, a statistical strain‐rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established. Numerical back‐calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.

Mechanical Behavior of Shale at Different Strain Rates

The strain rate-dependent mechanical behavior of shale is characterized using triaxial compression tests under a constant confining pressure of 50 MPa and axial strain rates $$\dot{\varepsilon }_{1}$$ ranging from 5 × 10−6 s−1 to 1 × 10−3 s−1. This study is conducted on the Longmaxi shale from Dayou in China, which is predominantly composed of brittle minerals including quartz (55%), albite (15%) and cristobalite (3%). The experimental results show that higher axial loading strain rates $$\dot{\varepsilon }_{1}$$ lead to higher elastic modulus and higher peak shear strength, both following exponential relationships with $$\dot{\varepsilon }_{1}$$ . When $$\dot{\varepsilon }_{1} \le 1 \times 10^{ - 5} {\text{s}}^{ - 1}$$ , failure results in a single linear fracture, whereas a more complex multiple crisscrossing fracture network is formed when $$\dot{\varepsilon }_{1} \ge 1 \times 10^{ - 4} {\text{s}}^{ - 1}$$ . Failure in shale specimens can be described by a damage parameter $$D$$ , which is strongly affected by the axial strain $$\varepsilon_{{1{\text{s}}}}$$ . In addition, the strain rate $$\dot{\varepsilon }_{1}$$ had different effects on $$D$$ , which also depends on axial strain $$\varepsilon_{{1{\text{s}}}}$$ . Energy accumulation and dissipation are also closely related to $$\dot{\varepsilon }_{1}$$ with the total absorbed energy $$U_{\text{A}}$$ , the recoverable elastic strain energy $$U_{\text{A}}^{\text{e}}$$ and the dissipated energy $$U_{\text{A}}^{\text{d}}$$ at the peak stress increasing with $$\dot{\varepsilon }_{1}$$ . As for the total energy accumulation $$U_{\text{A}}$$ , the recoverable elastic energy $$U_{\text{A}}^{\text{e}}$$ decreases while the dissipated energy $$U_{\text{A}}^{\text{d}}$$ increases with increasing strain rate.

Influence of ordered L12 precipitation on strain-rate dependent mechanical behavior in a eutectic high entropy alloy

Recent studies indicate that eutectic high-entropy alloys can simultaneously possess high strength and high ductility, which have potential industrial applications. The present study focuses on Al0.7CoCrFeNi, a lamellar dual-phase (fcc + B2) precipitation-strengthenable eutectic high entropy alloy. This alloy exhibits an fcc + B2 (B2 with bcc nano-precipitates) microstructure resulting in a combination of the soft and ductile fcc phase together with hard B2 phase. Low temperature annealing leads to the precipitation of ordered L12 intermetallic precipitates within the fcc resulting in enhanced strength. The strengthening contribution due to fine scale L12 is modeled using Orowan dislocation bowing and by-pass mechanism. The alloy was tested under quasi-static (strain-rate = 10−3 s−1) tensile loading and dynamic (strain-rate = 103 s−1) compressive loading. Due to the fine lamellar microstructure with a large number of fcc-bcc interfaces, the alloy show relatively high flow-stresses, ~1400 MPa under quasi-static loading and in excess of 1800 MPa under dynamic loading. Interestingly, the coherent nano-scale L12 precipitate caused a significant rise in the yield strength, without affecting the strain rate sensitivity (SRS) significantly. These lamellar structures had higher work hardening due to their capability for easily storing higher dislocation densities. The back-stresses from the coherent L12 precipitate were insufficient to cause improvement in twin nucleation, owing to elevated twinning stress under quasi-static testing. However, under dynamic testing high density of twins were observed.

Strain rate dependent mechanical behavior of glass fiber reinforced polypropylene composites and its effect on the performance of automotive bumper beam structure

In this study, the strain rate dependent mechanical behavior of glass fiber reinforced thermoplastic polypropylene (GFPP) was investigated under the high strain rate. The split Hopkinson pressure bar (SHPB) apparatus was used in order to investigate the effects of strain rate based on the dynamic tensile, compressive and bias-extension shear behavior. The failure mode in fracture surface of each specimen was analyzed by using the scanning electron microscopy with respect to the strain rate. Additionally, the impact simulation of bumper beam was conducted to verify the measured strain rate dependent mechanical behavior of GFRP by using the commercial finite element analysis software LS-Dyna. Finally, it was found that the impact response of GFRP structures could be accurately predicted by using the strain rate dependent mechanical behavior compared to those of quasi-static properties.

Decellularisation affects the strain rate dependent and dynamic mechanical properties of a xenogeneic tendon intended for anterior cruciate ligament replacement

Development of new replacement grafts for anterior cruciate ligament (ACL) repair requires mechanical testing to ensure they can provide joint stability following implantation. A decellularised porcine superflexor tendon (pSFT) has been developed previously as an alternative to current reconstruction methods and subjected to biomechanical analysis. The application of varied strain rates to biological tissues is known to alter their biomechanical properties, however the effects of decellularisation on strain rate dependent and dynamic mechanical behaviour of tissues have not been explored. This study utilised tensile testing to investigate the material properties of native and decellularised pSFTs at three different strain rates (1%.s−1, 10%.s−1 and 100%.s−1). In addition, dynamic mechanical analysis (DMA) was used to ascertain the relative contributions of the solid and fluid phase components of the tissues.Ultimate tensile strength was significantly reduced in decellularised compared with native untreated pSFTs but was unaffected by strain rate. In contrast, toe region moduli increased with increasing strain rate for native tissues, but this effect was not observed in decellularised pSFTs. Linear region moduli were unaffected by strain rate, but were significantly reduced in decellularised pSFT compared with native tissue.Following DMA, significant reductions in dynamic modulus, storage modulus and loss modulus were seen in decellularised compared with native pSFT. Interestingly, the damping ability of the tendons was unaffected by decellularisation, suggesting that solid and fluid phases of the tissue were affected equally. These results, alongside previous studies, suggest that decellularisation affects collagen crimp, tissue swelling and collagen fibre sliding. However, despite these findings, the biomechanical properties of decellularised pSFT remain sufficient to act as an off-the-shelf solution for ACL reconstruction.

Strain rate-dependent mechanical behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites under off-axis tensile loading

To make a better use of quasi-unidirectional fabrics in structural application, the strain rate-dependent tensile behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites was studied. Monotonic tensile tests were firstly performed on 10°, 20° and 90° off-axis samples of composites. The experimental results show that both mechanical properties and nonlinear stress-strain behavior of composites are dependent of strain rate. A regression function is adopted to describe the variation in overall mechanical properties with the imposed strain rate. A strain rate-dependent coupled damage-plasticity model is built for quasi-unidirectional composites. The damage variables and plastic parameters in the proposed model are determined through cyclic loading-unloading tensile tests and can be represented as a function of the imposed strain rate. In addition, the damage mechanism of composites is observed to evolve with strain rate. Increasing strain rate can hinder the initiation and evolution of damage in composites.

Identification of strain rate-dependent mechanical behaviour of DP600 under in-plane biaxial loadings

The rate-dependent hardening behaviour of dual phase DP600 steel sheet is investigated by means of in-plane biaxial tensile tests, in an intermediate strain rate range (up to 20s−1) and for large strains (up to 30% of equivalent plastic strain) at room temperature. The dynamic biaxial in-plane tensile tests are performed on a dedicated cruciform specimen shape previously developed and validated for large strains at quasi-static conditions. To perform dynamic biaxial tensile tests, a specific device is used to reduce oscillations on measure of forces. Based on these experiments, parameters of two phenomenological strain-rate hardening models (saturated and power law), are identified. Material parameters are obtained from an optimisation process, based on the finite element modelling of the biaxial test, by minimising differences between experimental and simulated principal strains at the specimen centre. A comparison of the strain hardening functions calibrated from both biaxial and uniaxial tensile tests under static and dynamic conditions are then proposed. Results show that the biaxial procedure developed in this work, associated with a specific shape of the cross specimen, are more efficient to determine the rate-dependent hardening behaviour for large strains than the conventional uniaxial tensile test.

A dynamic constitutive-micromechanical model to predict the strain rate-dependent mechanical behavior of carbon nanofiber/epoxy nanocomposites

Polymeric materials have wide applications; therefore, it is necessary to develop a dynamic constitutive model to investigate their strain rate-dependent mechanical behavior. In this study, mechanical behavior of neat epoxy and carbon nanofiber (CNF)/epoxy nanocomposites were studied experimentally and analytically. For this purpose, the Johnson–Cook material model has been modified to develop a generalized strain rate-dependent constitutive model to simulate the tensile and shear mechanical behaviors of the neat epoxy at a wide range of applied loading rates. The present model includes three main components: the first component expresses the elastic behavior of polymers using an empirical equation. The second component models the nonlinear behavior of polymers using the modified Johnson–Cook model. Finally, the third component predicts the ultimate strength of polymers under dynamic loading conditions using another empirical equation. Furthermore, by combining the generalized strain rate-dependent constitutive model and the modified Halpin–Tsai micromechanical model, a dynamic constitutive-micromechanical model is presented to predict the strain rate-dependent mechanical behavior of CNF/epoxy nanocomposites. To evaluate the present model, predicted results for the pure epoxy and CNF/epoxy nanocomposites were compared with conducted and available experimental data. It is shown that the present model predicts the strain rate-dependent mechanical behavior of polymeric materials with a good accuracy.

Holistic Characterization of Carbon Nanotube Membrane for Capacitive Deionization Electrodes Application

ABSTRACTOne of the main areas of improvement in capacitive deionization technologies is the materials used for electrodes which have very specific requirements. In the present work, a wide range of material characterization techniques are employed to determine the suitability of a multiwall carbon nanostructure thin film as electrode material. The electrical, mechanical, surface and wetting characteristics are studied proving the membrane highly conductive (σ=7.25 103 S/m), having competitive electro-sorption capacity (11.7 F/g at 10 mV/s) and surface area (149 m2/g), strain rate dependent mechanical properties and hydrophobic wetting behavior.

A strain-rate dependent micromechanical constitutive model for glass/epoxy composites

The mechanical behavior of polymeric fibrous composites under dynamic loading is not completely investigated. Therefore, in the preset research, a strain-rate dependent micromechanical constitutive model is developed to predict the dynamic mechanical behavior and elastic properties of fibrous composites under arbitrary loading rates. First, strain rate dependent mechanical behavior of matrix and fibers are experimentally characterized and for each constituent a dynamic empirical material equation is presented. Then, the bridging matrix micromechanical model in combination with a constitutive equation for polymers is utilized to predict the elastic properties and mechanical behavior of fiber-reinforced polymeric composites under arbitrary applied strain rates. Moreover, the strain rate sharing of each constituent of composites (matrix and fiber) is calculated. In order to validate the present method, results predicted by the model are compared with the experimental data. It is shown that the present micromechanical method is able to simulate the rate dependent elastic behavior of fiber-reinforced composites with a good accuracy.