Strain Rate Dependence Research Articles

Dynamic mechanical response and fracture mechanism of granite with structural plane containing planar and circular filling simultaneously: The influence of extension length

Weakly filled structural planes are an important influence on the stability control of engineering rock mass. Weak fillings with different geometrical characteristics are randomly distributed in the natural rock mass. To investigate the dynamic mechanical response and fracture mechanism of granite containing both planar and circular weak filling, the Split Hopkinson Pressure Bar (SHPB) experimental system was used to conduct the dynamic impact test. In this paper, the dynamic mechanical properties, the fracture process, the energy evolution and the micro-morphological characteristics of the fragments are mainly analyzed. The results show that: (1) the dynamic uniaxial compressive strength (DUCS), peak strain, and deformation modulus are synergistically affected by the extension length (L) of planar filling and strain rate. The presence of planar weak filling leads to a decrease in strain rate dependence while weakening the specimens' DUCS, and improves the overall synergistic deformation capacity of the specimen. (2) Strain rate and L jointly affect the energy distribution and evolution characteristics of the specimen; L has an enhancement effect on the distribution of reflected energy and a weakening effect on the distribution of transmitted energy. The effect of L on the dissipation of energy is transformed by the strain rate. The strain rate and L are the dominant factors in the variability of stress waveform conversion. (3) At a low strain rate, L has a positive effect on the intensification of the degree of fragmentation, however, at a high strain rate, the effect is characterised by a shift between positive and negative. The degree of fragmentation has a strain rate effect. As L increases, L has a “negative effect” on the “strain rate effect” that affects the degree of fragmentation. (4) The degree of fragmentation of macroscopic fragments is closely related to the energy dissipation density, the relationship between the two appears as a logarithmic function change. The presence of weak filling does not significantly change the microscopic morphology of granite fragments. The loose and porous microstructure of gypsum is the main reason for the altered propagation characteristics of the stress waves.

Strain rate and temperature dependence of short/unidirectional carbon fibre PEEK hybrid composites

Short fibre and hybrid carbon fibre PEEK composite materials were tested in tension and compression under quasi-static and high strain rate conditions to observe the strain rate dependence. Multiple temperatures including room temperature, ＋85 and −50 °C were used to investigate the temperature dependence of the materials. The hybrid laminate comprised a consolidated short fibre core reinforced with outer UD plies in the 0°orientation to provide maximum reinforcement whilst minimising the quantity of expensive UD composite used. Under compression, the beneficial effect of the hybridisation strategy was observed for all high-strain rate testing conditions, where the hybrid laminate outperformed the response of the individual constituents in terms of strength and strain rate dependency. The outer unidirectional (UD) layers contributed to confining the short fibre core, providing superior structural integrity. Under tension, the response was dominated by the UD layers with a 288% increase in strength at room temperature over the short fibre material. However, in the high temperature quasi-static case, the strength was dramatically reduced, by 64%, due to the debonding of the UD reinforcement. This study shows the suitability of hybrid composites for impulsive applications and provides material parameters for the future design of composite structures subjected to impact events.

Dynamic response of polymeric railway sleepers under harsh loading and environmental conditions

ABSTRACT Several composite sleeper technologies have been developed, possibly allowing the railway sector to replace wood and concrete sleepers. Although high-magnitude impact loads can occur on the railway track and sleepers due to wheel/rail abnormalities or train derailment, the behaviour of these sleepers under impact loading has not yet been well understood. In this paper, a high-energy drop hammer facility was utilized to investigate the impact behaviour of a polymeric composite rail sleeper made of high-density polyethylene (HDPE) and unidirectional glass fibre reinforced plastic (GFRP). Quasi-static tests and high strain rate tests were conducted on the materials at room and low/high temperatures to gain more insight into the effects of the temperature and strain rate on the mechanical properties of the HDPE and GFRP made of virgin resin. The results suggest that both materials exhibit strong viscoelastic plasticity, temperature softening, and strain rate-hardening effects. High strain rate and low temperature made the GFRP material extremely brittle and prone to develop cracks. Due to the temperature and strain rate dependency of the thermoplastic materials of the sleepers, in addition to impact tests at room temperature (~23°C), impact tests were also performed at low temperatures (~ minus 30°C) on the sleepers. The findings suggest that low-temperature impact assessment should be considered for all polymeric sleepers (to be installed in regions having extremely low temperatures) since these low temperatures affect the ductility of polymers, decreasing the ultimate impact load-bearing capacity of composite sleepers.

Temperature and strain rate dependent tensile properties of titanium carbide/nitride MXenes

MXenes have rapidly gained prominence since their serendipitous discovery in 2011 in the field of 2D materials due to their exceptional properties, which leads to strong applications in energy storage, anti-wear coatings, nanocomposites and electronics sector. This study examined tensile characteristics of wide ranged titanium carbide and nitride pristine MXenes by molecular dynamics investigation where the directional, temperature and strain rate dependencies were explored. The uniaxial tension computations have been performed at temperature of 225–525K with a linear difference of 75K and strain rate of 5 × 10−5 to 1 × 10−2 ps−1 with an approximate regular logarithmic difference. Afterward a two steps graphical method has been proposed from temperature and strain rate dependencies to calculate the strain rate sensitivity and activation energy for both zigzag and armchair directions by using Arrhenius correlation. The temperature exerts a slight influence on the activation energy, wherein a decrease in temperature results in a reduction of the activation energy. After all, the Ti2X (X = N,C) expressed superior mechanical strength compared to their immediate pristine MXenes.

Experimental and numerical analysis of composite fuselage panel impacted by tire burst debris under airworthiness clause

This study focuses on an experimental and numerical simulation investigation on the dynamic response of the composite fuselage panel under the impact of the tire burst debris. According to the parameters specified in the airworthiness clause, the T800/M21C composite material is selected as the research object to carry out the tire debris impact test, and the consistent results are obtained by employing the applicable mesoscopic model of the tire debris, progressive failure model of composite, the interface model and considering the strain rate dependence of the composite material in numerical simulation. The results show that under the airworthiness condition, the peak strain rate of the fuselage panel is about 16 s−1 during the impact of tire debris. The damage modes of the fuselage panel are debonding of the stringers from the skin and local matrix tensile damage. The Puck failure criterion, which considers the angle of the fracture surface of the matrix, is proved to be more suitable for the prediction of matrix damage than the Hashin failure criterion. The developed progressive damage failure impact model can be used in structural analysis and optimization design of aircraft fuselage, providing reference data for airworthiness verification.

High strain rate effects in masonry structures under waterborne debris impacts

Masonry buildings are vulnerable to extreme hydrodynamic events such as floods or tsunamis. Post-disaster surveys have shown that waterborne debris impacts can significantly damage masonry walls during these events. To simulate these actions, the current design or research practice is to compute the force–time diagram of the impact and then use it for dynamic analyses. Standing on the current knowledge, debris impacts are highly impulsive, but it is not clear if such loads are fast enough to activate the high strain rate effects in masonry, i.e. the strain rate dependency of material properties. The present study aims to answer this question, for the first time, following nonlinear Finite Element (FE) simulations. Simulations are conducted on a masonry wall, following a micro-modelling strategy, subjected to water flow and waterborne debris impact under different scenarios. It is found that the strain rates exceed the critical threshold after which strain rate effects are considerable. Such a finding, initially obtained using the minimum design demand for log-type debris imposed by ASCE/SEI 7-22, is further extended to a range of impact force–time diagrams different in impact duration and peak force (corresponding to different debris properties or flow velocity). It is also shown that the impact location (i.e. midspan or close to the boundary) affects the strain rate magnitude because of the changes in the impact stiffness and the activated failure mechanisms. Furthermore, it is found that the dynamic tensile post-elastic behaviour of the materials is the most influencing parameter in the structural response. These results open a new area in the field of assessment and design of masonry structures to waterborne debris and guide the development of future experiments, numerical simulations or design relations.

Tensile Property of Jute Fiber Sliver Reinforced Green Composite Material under Loading Speed

To assess the safety and utility of green composite materials as a sustainable structural material, this study investigated their tensile properties using unidirectional jute fiber sliver and poly (lactic acid) and poly (butylene succinate) under loading speed. The fiber volume fraction of the green composite materials was about 10%. Vacuum compression molding was used for molding. Static tensile tests of green composite materials using poly (lactic acid) and poly (butylene succinate) were conducted with 0.1–10 mm/min test speed at room temperature, yielding the following conclusions. Tensile strengths of green composite materials using poly (lactic acid) and poly (butylene succinate) increased with increased test speed. The strain rate dependence of the green composite using poly (lactic acid) became strong, but the strain rate dependence of green composite material using poly (butylene succinate) became weak. Results suggest that the matrix viscoelasticity might influence the loading speed effects on the tensile properties of these green composite materials.

A crystal plasticity model of Dynamic Strain Aging for a near-[formula omitted] Ti-alloy

Timetal-834, a near-α Ti-alloy, finds use in aeroengines due to its favorable properties. However, the alloy exhibits Dynamic Strain Aging (DSA) in the temperature range of 375-475 °C, that can cause it to fail early during service. As DSA is due to the micro-scale interaction between the diffusing solutes and mobile dislocations, a crystal plasticity model is developed in this work to capture this phenomenon. Additionally, the influence of the α (HCP) and β (BCC) laths of the transformed-β colony of this alloy on the DSA behavior is captured by using an equivalent model based on Taylor’s assumption. The effect of slip system dependent lath and colony size effect due to Burger’s Orientation Relation is also incorporated. Crystal plasticity finite element method simulations of polycrystalline domains, representative of Timetal-834, are performed for calibration and validation of the model using the available temperature dependent experimental data, and successfully capture the flow stress and DSA behavior. The strain rate dependency of DSA predicted by the model also shows an excellent agreement when compared with experimental data. Microstructural analysis of the simulations show that the orientation of grains/colonies have a strong influence on the aging time and hence the DSA response. Also, the initiation of DSA and frequency of serrated slip on the aligned systems of laths show differences due to dissimilar resistances and constraints on plastic flow. Overall, the model developed in this work can capture the microstructure dependent DSA and can be utilized for engineering of Timetal-834.

Impact-dynamic properties of aromatic hyperbranched polyester/RTM6 epoxy nanocomposites

Present study investigates the influence of aromatic hyperbranched polyester (AHBP) nanofillers on the impact-dynamic properties of RTM6 epoxy. The strain rate dependence of the energy absorption capacity of neat RTM6 epoxy and RTM6 nanocomposites with filler weight ratios of 0.1%, 1%, and 5% was determined through compression testing. Additionally, static and dynamic tensile tests were performed on these materials. Universal testing machines were used for the quasi-static tests, split Hopkinson bar setups for the high-strain rate experiments. Furthermore, dynamic single-edge notch bending (SENB) tests were conducted to measure fracture toughness using an adapted split Hopkinson compression bar setup. In addition to global deformation measurements, full-field deformation measurements were also performed in all experiments using the digital image correlation (DIC) technique. The results indicate that the energy absorption capacity, tensile strength, fracture strain, and toughness are significantly influenced by both strain rate and filler content of the RTM6 epoxy.

The Important Role Played by High-Temperature Tensile Testing in the Representation of Minimum Creep Rates Using S-Shaped Curve Models

It is important to characterize the creep life of materials used in power plants and aeroengines. This paper illustrates the important role played by a material’s tensile strength in enabling accurate creep property representations to be made. It also shows that published high-temperature tensile strength values are not always suitable for use in certain creep models due to its strain rate dependency. To deal with the absence of such suitable date on tensile strength, this paper estimates such values directly from minimum creep rate data. When this technique is applied to models that represent the relationship between minimum creep rates and normalized (with respect to tensile strength) stress using S-shaped curves, an improvement in the fit to data on 2.25Cr–1Mo steel was observed. The findings suggest an important need for future research into the most appropriate strain rates to be used in high-temperature tensile testing when the purpose is to use the resulting tensile strength values for use in creep modeling.

Precipitation size and strain rate dependence of dislocation-amorphous nanopillar interaction mechanism in magnesium

Introducing amorphous phases into the crystalline matrix is a new design strategy to improve the mechanical properties of Mg alloys. In this work, the effects of strain rate and amorphous nanopillar size on the interaction mechanism between the dislocation and precipitation in the Mg matrix were investigated by molecular dynamics simulation. The results show that the interaction mechanism between dislocation and amorphous precipitation depends on strain rate and amorphous nanopillar size. At strain rates of 5 × 107/s and 5 × 108/s, the amorphous precipitation strengthens the Mg matrix due to the pinning effect of the amorphous precipitation relative to the dislocation. The interaction mechanism changes from merging and canceling of dislocation to the cross-slip mechanism with the increase of precipitation size. Moreover, the strengthening effect of the large-sized amorphous phase on the dislocation is noticeable. However, the amorphous precipitation softens the Mg matrix at strain rates of 5 × 109/s and 1 × 1010/s. The underlying mechanism varies from the dislocation shearing mechanism to the generation of dislocation loops with the increase of the amorphous precipitation size. This research can provide theoretical guidance for developing and designing new high-performance Mg alloys.

Behavioral analysis of seabed slope subjected to ice gouging

Ice gouging is a phenomenon that occurs when ice drifts to shallow depths due to current, wind and tides, thus resulting in a large deformation. Many previous studies have conducted numerical analysis based on centrifuge model experiment to understand the mechanism of ice gouging. Strain softening and rate dependence are the two important factors that influence ice gouging. However, the effect of these two important factors on the seabed subjected to large deformation was not considered in previous studies. Therefore, in this study, these factors are simulated, and the occurrence of large deformation in soil due to ice gouging is analyzed. In addition, numerical modeling based on two cases from among knowledge gained via various centrifuge model experiments is implemented. To simulate the large deformation of the soil, return mapping algorithm is applied to the ABAQUS subroutine VUMAT in conjunction with the formulas that define strain softening and rate dependence. These factors are reflected in ice gouging simulations and the consistency is reviewed by comparing and analyzing the results of the centrifuge model experiments implemented in previous studies. Based on this, the kinetic energy of ice keel is defined and a subroutine expressing kinetic energy reduction according to seabed soil resistance is additionally reflected. In addition, this method is applied to seabed slope in cold region to analyze the behavior of the slope.

Influence of manufacturing process-induced geometrical defects on the energy absorption capacity of polymer lattice structures

Modern additive manufacturing processes enable fabricating architected cellular materials of complex shape, which can be used for different purposes. Among them, lattice structures are increasingly used in applications requiring a compromise among lightness and suited mechanical properties, like improved energy absorption capacity and specific stiffness-to-weight and strength-to-weight ratios. A dedicated modeling strategy to assess the energy absorption capacity of lattice structures under uni-axial compression loading is presented in this work. The numerical model is developed in a non-linear framework accounting for the strain rate effect on the mechanical responses of the lattice structure. Four geometries, i.e., cubic body centered cell, octet cell, rhombic-dodecahedron and truncated cuboctahedron 2+, are investigated. Specifically, the influence of the relative density of the representative volume element of each geometry, the strain-rate dependency of the bulk material and of the presence of the manufacturing process-induced geometrical imperfections on the energy absorption capacity of the lattice structure is investigated. The main outcome of this study points out the importance of correctly integrating geometrical imperfections into the modeling strategy when shock absorption applications are aimed for.

An atomistic study on the strain rate and temperature dependences of the plastic deformation Cu–Au core–shell nanowires: On the role of dislocations

Abstract Recently, Cu–Au core–shell nanowires have been extensively used as conductors, nanocatalysts, and aerospace instruments due to their excellent thermal and electrical conductivity. In experimental studies, various methods have been presented for producing, characterizing, and strengthening these structures. However, the mechanical behavior and plastic deformation mechanisms of these materials have not been investigated at the atomic scale. Consequently, in the present study, we carried out uniaxial tensile tests on Cu–Au nanowires at various tension rates and temperatures by means of the molecular dynamics approach. The Cu–Au interface was found to be the main site for nucleation of perfect dislocations, Shockley partials, and stacking faults due to the stress concentration and high potential energy arising from the atomic mismatch between shell and core layers. It was observed that an increase in the strain rate from 108 to 1,011 s−1 shortened the time required for the nucleation of dislocations, decreasing the dislocation density. This emphasizes that dislocation nucleation and slip mechanisms are time-dependent. Moreover, it was found that the interaction of Shockley partials can lead to the creation of lock dislocations, such as Hirth, Frank, and Stair-rod dislocations, imposing obstacles for the slip of other dislocations. However, as the tension temperature rose from 300 to 600 K, opposite-sign dislocations removed each other due to thermally activated mechanisms such as dislocation climb and dislocation recovery. Furthermore, the combination of Shockley partial dislocations decreased the stacking fault density, facilitating the plastic deformation of these structures. The yield strength and elastic modulus of the samples increased with the strain rate and substantially decreased as the temperature rose.

Determination of a material constitutive equation that includes the effects of strain rate and temperature using an optimization method

Numerical analysis of impact phenomena such as collisions and grounding of ships requires a material constitutive equation that considers the strain rate and temperature dependence. However, the constants of the material constitutive equation are often obtained from the literature, which reduces the analysis accuracy. This is because methods for selecting the material constitutive equation and determining its material constants have not been established. Therefore, we constructed a method for determining the material constitutive equation through optimization. First, the compression properties of rolled SM490B steel for welded structures at a wide strain rate (10−3–102 s−1) and temperature (-10–60 °C) were investigated. Using these reference data, the constitutive equation was determined by the Nelder-Mead method and a genetic algorithm. It was found that understanding the tendency of the strain rate dependence of material strength through experiments and the use of reference data for the results of high-temperature impact tests where temperature rise is unlikely to occur are effective in determining the constitutive constants. Finally, a flowchart was developed to describe the process for determining a material constitutive equation for hull materials that includes the effects of strain rate and temperature.

Modelling of rate-dependent inelasticity and damage in semi-crystalline polymers using an Eulerian framework

The present paper concerns the mechanical response of semi-crystalline polymers during cyclic loading, and it includes both modelling and experimental testing. The model is Eulerian in the sense that it is independent of measures of total deformation and plastic/inelastic deformations. It is able to account for such essential phenomena as strain-rate dependence, work hardening, and damage. The model was applied to uniaxial tension tests performed on high-density polyethylene (HDPE), which is a semi-crystalline polymer widely used in the industry. Two types of tests were conducted: monotonic tests, and loading–unloading tests. The model was able to reproduce the experimental results very well. The proposed model was also implemented as a UMAT in Abaqus, including an analytic tangent. The UMAT was used for simulating two 3D geometries. The implementation seems to be robust, and no convergence problems were observed.

In situ damage characterization of CFRP under compression using high-speed optical, infrared and synchrotron X-ray phase-contrast imaging

The strain rate dependency and failure modes of carbon fiber reinforced plastic (CFRP) laminate were investigated under out-of-plane compressive loading. Simultaneous high-speed optical and infrared imaging were used to measure full-field deformation and temperature in the dynamically loaded specimens. The damage initiation and propagation inside the CFRP laminates at high strain rates were characterized using in-situ ultra-fast synchrotron X-ray phase contrast imaging (XPCI). The visually observed damage onset occurs at the strain value of 4.2 ± 0.6% as a transverse shear fracture at the free edge of specimens. The local temperature increases significantly to 185 °C due to damage initiation at high strain rates, while at low strain rates the temperature rise occurs after the final shear band forms. The XPCI and post-failure analysis provide an integrated perspective on the formation of a diagonal shear crack and disintegration of the specimen into two pieces with the fracture of plies in the in-plane transverse direction. Scanning electron microscopic (SEM) study was integrated with XPCI results to append the time scale for the post-mortem failure pattern as well as the length scale for microcracks and filament-level failure.

Strain-rate dependence of mechanical characteristics of PLLA with different MW

Abstract Dynamic mechanical properties of polymers for biomedical applications are crucial parameters for development and engineering of new medical devices. Here, the time-dependent material behavior is a key factor for durability. Varying the strain rate is a convenient implementation of time-dependency for uniaxial testing. This study investigates time-dependence of Poly(L-Lactide) (PLLA) through uniaxial testing with different strain rates and PLLA with different molecular weight. The results show strain dependence for elongation at break and yield stress, Young’s modulus however is not rate dependent. An increase in elongation at break is also seen with increasing molecular weight of PLLA. Plastic strain increases significantly only for PLLA with an intermediate inherent viscosity. Results show distinct time dependencies regarding strain rate for PLLA with slightly different inherent viscosities. For stent-related mechanical material characteristics, higher molecular weight PLLA seems to be advantageous. This study only considers base materials, although appropriate thermal, mechanical as well as chemical post processing approaches for further adjustment of different properties have already been shown. A combination of the best possible base material and a suitable post-processing should be targeted.

Safety Performance and Failure Criteria of Lithium-Ion Batteries under Mechanical Abuse

With the increasing global focus on environmental issues, controlling carbon dioxide emissions has become an important global agenda. In this context, the development of new energy vehicles, such as electric vehicles, is flourishing. However, as a crucial power source for electric vehicles, the safety performance of lithium-ion batteries under mechanical abuse has drawn widespread attention. Evaluating the safety performance of lithium-ion batteries requires in-depth research. This paper provides a review of recent experimental and numerical simulation studies on the mechanical abuse of lithium-ion batteries. It showcases the main methods and conclusions of experimental research, compares different response forms under quasi-static and dynamic loading, discusses the causes of strain-rate dependence in lithium-ion batteries, and briefly describes the impact of the state of charge (SOC) on safety performance under mechanical abuse, as well as the influence of mechanical abuse on battery capacity and impedance characteristics. Furthermore, this paper summarizes the methods of numerical simulation research, analyzes the advantages and disadvantages of detailed modeling and homogenized modeling methods, summarizes the strain-based internal short circuit failure criteria, and reviews numerical predictive models based on multiphysics coupling. Finally, it presents the latest progress in studying the safety performance of battery packs through numerical simulations.

The synergistic effect of temperature and loading rate on the mechanical behavior of shear thickening fluid reinforced with graphene nano-platelets using split Hopkinson pressure bar

Fumed silica shear thickening fluids (STFs) have gained significant interest in recent years due to their distinctive rheological behavior and potential applications in various fields. The objective of this study is to build upon previous research by employing the split Hopkinson pressure bar (SHPB) and the squeeze flow theory to investigate the combined effect of the strain rate and the temperature on the mechanical behavior and thickening time evolution of STFs. The study comprises both pure SiO2-STF with varying concentrations and SiO2-STF reinforced with graphene nano-platelets (GNPs). The impact tests were performed at strain rates up to 23,000 s–1 and at a broad temperature range (-50 °C, -25 °C, +0 °C, +25 °C). The results showed that STFs exhibit a strain rate and temperature dependence in peak stress, impact toughness, and fluid-to-solid transition time. At low temperatures, the shear thicknening behavior of the STFs was significantly enhanced, resulting in a reduced thickening period and improved mechanical properties. Additionally, the study showed that the addition of GNPs additives to SiO2-STF enhances the mechanical performance and the dynamic response of the STF at extreme thermal and loading conditions. The GNPs have strengthened the contact coupling force between particle clusters, enabling the fluid to complete a dynamic response within 5 µs with a maximum peak stress of 350 MPa. These findings provide valuable insights into the behavior of these materials under extreme conditions and could be useful for the development of new applications.