Strain Rate Dependence Research Articles

Determination of the In-Plane Shear Behavior of and Process Influence on Uncured Unidirectional CF/Epoxy Prepreg Using Digital Image Correlation Analysis

The investigation of the in-plane shear behavior of prepreg is crucial for understanding the generation of wrinkles of preforms in advanced composite manufacturing processes, such as automated fiber placement and thermoforming. Despite this significance, there is currently no standardized test method for characterizing uncured unidirectional (UD) prepreg. This paper introduces a ±45° off-axis tensile test designed to assess the in-plane shear behavior of UD carbon fiber-reinforced epoxy prepreg (CF/epoxy). Digital image correlation (DIC) was employed to quantitatively track the strains in three dimensions and the shear angle evolution during the stretching process. The influences of the temperature and stretching rate on the in-plane shear behavior of the prepreg were further investigated. The results reveal that four shear characteristic zones and wrinkling behaviors are clearly distinguished. The actual in-plane shear angle is significantly lower than the theoretical value due to fiber constraints from both the in-plane and out-of-plane aspects. When the off-axis tensile displacement (d) is less than 15.6 mm, the ±45° specimens primarily exhibit macroscale in-plane shear behavior, induced by interlaminar interface shear between the +45° ply and −45° ply at the mesoscale. The shear angle increases linearly with the d. However, when d > 15.6 mm, fiber squeezing and wrinkling begin to occur. When d > 29 mm, the in-plane shear disappears in the completely sheared zone (A). The reduction in the resin viscosity of the CF/epoxy prepreg caused by increased temperature is identified as the primary factor in lowering the in-plane shear force resistance, followed by the effect of the increasing resin curing degree. Higher shear rates can lead to a substantial increase in shear forces, eventually causing cracking failure in the prepreg. The findings demonstrate the feasibility of the test method for predicting and extracting uncured prepreg in-plane shear behaviors and the strain-rate and temperature dependency of the material response.

Constitutive model of an additively manufactured combustor material at high-temperature load conditions

ABSTRACT In this paper, the high-temperature constitutive behaviour of an additively manufactured ductile nickel-based superalloy is investigated and modelled, with application to thermomechanical fatigue, low-cycle fatigue and creep conditions at temperatures up to 800 ∘ C. Thermomechanical fatigue tests have been performed on smooth specimens in both in-phase and out-of-phase conditions at a temperature range of 100 − 800 ∘ C, and creep tests at 625 ∘ C, 700 ∘ C, 750 ∘ C and 800 ∘ C. Additionally, low-cycle fatigue tests at different strain ranges and load ratios have been performed at 700 ∘ C, and tensile tests have been performed at 600 ∘ C, 700 ∘ C and 800 ∘ C. A clear anisotropic mechanical response is obtained in the experiments, where the anisotropic effects are larger at high stress levels in creep loadings. To capture this behaviour, a rate-dependent strain based on a double-Norton model has been adopted in the model, by which the creep and mid-life response of the thermomechanical fatigue tests can be simulated with good accuracy.

Characterization of the layer, direction and time-dependent mechanical behaviour of the human oesophagus and the effects of formalin preservation.

The mechanical characterization of the oesophagus is essential for applications such as medical device design, surgical simulations and tissue engineering, as well as for investigating the organ's pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanical behaviour using fresh, human tissue: as of yet, in the literature, only the hyperelastic response of the intact wall has been studied. Therefore, in this study, the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus was investigated through various mechanical tests. For this, cyclic tests, with increasing stretch levels, were conducted on the layers of the human oesophagus in the longitudinal and circumferential directions and at two different strain rates. Additionally, stress-relaxation tests on the oesophageal layers were carried out in both directions. Overall, the results show discrete properties in each layer and direction, highlighting the importance of treating the oesophagus as a multi-layered composite material with direction-dependent behaviour. Previously, the authors conducted layer-dependent cyclic experimentation on formalin-embalmed human oesophagi. A comparison between the fresh and embalmed tissue response was carried out and revealed surprising similarities in terms of anisotropy, strain-rate dependency, stress-softening and hysteresis, with the main difference between the two preservation states being the magnitude of these properties. As formalin fixation is known to notably affect the formation of cross-links between the collagen of biological materials, the differences may reveal the influence of cross-links on the mechanical behaviour of soft tissues.

Strain rate-dependent failure mechanics of the intervertebral disc under tension/compression and constitutive analysis

BackgroundThe intervertebral disc exhibits not only strain rate dependence (viscoelasticity), but also significant asymmetry under tensile and compressive loads, which is of great significance for understanding the mechanism of lumbar disc injury under physiological loads. ObjectiveIn this study, the strain rate sensitive and tension-compression asymmetry of the intervertebral disc were analyzed by experiments and constitutive equation. MethodThe Sheep intervertebral disc samples were divided into three groups, in order to test the strain rate sensitive mechanical behavior, and the internal displacement as well as pressure distribution. ResultsThe tensile stiffness is one order of magnitude smaller than the compression stiffness, and the logarithm of the elastic modulus is approximately linear with the logarithm of the strain rate, showing obvious tension-compression asymmetry and rate-related characteristics. In addition, the sensitivity to the strain rate is the same under these two loading conditions. The stress–strain curves of unloading and loading usually do not coincide, and form a Mullins effect hysteresis loop. The radial displacement distribution is opposite between the anterior and posterior region, which is consistent with the stress distribution. By introducing the damage factor into ZWT constitutive equation, the rate-dependent viscoelastic and weakening behavior of the intervertebral disc can be well described.

Mechanical Behavior of Hydrate-Bearing Clayey-Silty Sediments in the South China Sea: Strain-Rate Dependency

Mechanical Behavior of Hydrate-Bearing Clayey-Silty Sediments in the South China Sea: Strain-Rate Dependency

Numerical Investigation of the Damage Effect on the Evolution of Adiabatic Shear Banding and Its Transition to Fracture during High-Speed Blanking of 304 Stainless Steel Sheets.

This paper investigates numerically the effect of damage evolution on adiabatic shear banding (ASB) formation and its transition to fracture during high-speed blanking of 304 stainless steel sheets. A structural-thermal-damage-coupled finite element (FE) analysis is developed in LS-DYNA considering the modified Johnson-Cook thermo-viscoplastic model for both plasticity flow rule and damage law, while further, a temperature-dependent fracture criterion is implemented by introducing a critical temperature. The modeling approach is initially validated against experimental data regarding the fracture profile and ASB width. Next, FE simulations are conducted to examine the effect of strain rate and temperature dependence on damage law, while the effect of damage coupling is also evaluated, aiming to highlight the connection between thermal and damage softening and attribute them a specific role regarding ASB formation and transition to fracture. Also, the influence of dynamic recrystallization (DRX) softening is studied macroscopically, while further, a parametric analysis of the Taylor-Quinney coefficient is conducted to highlight the effect of plastic work-to-internal heat conversion efficiency on ASB formation. The results revealed that the implementation of damage coupling reacts to reduced ASB width and provides an S-shaped fracture profile, while it also decreases the peak force and results in an earlier fracture. Both findings are enhanced when accounting further for DRX softening and a higher value of the Taylor-Quinney coefficient. Finally, the simulations indicated that thermal softening precedes damage softening, showing that the temperature rise is responsible for ASB initiation, while instead, damage evolution drives ASB propagation and fracture.

Strain rate dependence of 3D printed continuous fiber reinforced composites

Fused Deposition Modeling (FDM), one of the most popular additive manufacturing technologies in polymer 3D printing, has been increasingly used in fabricating continuous fiber reinforced composites (CFRCs) in recent years. Intensive research has been conducted on the quasi-static mechanical properties of FDM made CFRCs and the corresponding failure mechanisms. However, limited research has been reported on the dynamic mechanical behavior of CFRCs fabricated using FDM. This paper presents a comprehensive experimental study to understand the deformation and load carrying capacity of FDM-fabricated continuous fiber reinforced Onyx (CFRO), with a focus on the dynamic tensile loadings up to strain rate of 100/s. The deformation and failure mechanisms of FDM-fabricated CFROs under dynamic loadings have been identified after microstructural analyses of fractured specimens. The effects of fiber type, fiber volume fraction, and strain rate on the tensile behavior have been revealed for Onyx reinforced by carbon fiber filaments (CFF), glass fiber filaments (GFF), and Kevlar fiber filaments (KFF). Empirical formulas have also been derived to describe the relationships between the elastic modulus, ultimate tensile strength (UTS) and fiber volume fraction. The results demonstrate that increasing the strain rate from 6.7 × 10−4/s to 100/s substantially enhances the UTS of all three types of printed CFRO.

The impact‐induced deformation characteristics of polycarbonate panels

AbstractIn this study, the investigation of damage caused by a spherical steel projectile on the polycarbonate (PC) panels has been undertaken both numerically and experimentally. The material properties are obtained from both static and dynamic tests. High‐velocity impact experiments are performed using a pressure‐based projectile launching system. The effect of panel curvatures and impact locations on the deformation are investigated experimentally. The impact locations are selected as both at the plate center and near the edge of the plate. A validation study is performed by analyzing the impact response of a PC plate as previously presented in the literature and subsequently comparing it with the results obtained. An analysis of the impact behavior of PC panels is carried out through numerical simulations using finite element program (LS‐DYNA). The effect of boundary conditions on the impact response is also investigated numerically. Plastic strains, von Mises stresses, dent depth, and energy absorption are obtained. It is indicated by the results that the deformation behavior of PC panels exhibits a strain rate dependence. Additionally, the deformation behavior is influenced by panel curvatures and boundary conditions, emphasizing the necessity to consider these factors in the design of structures, such as canopies made of PC panels.Highlights Provides a comprehensive understanding of polycarbonate behavior. Emphasizes the influence of impact locations and panel curvatures. Dent depth and stress rise with panel curvature, crucial for design considerations. Emphasizes the significance of strain rate and boundary condition in design.

Anomalous strain rate dependence of ultra-low temperature strength and ductility of an electron beam additively manufactured near alpha titanium alloy

The strain rate (ε˙) dependence of ultra-low temperature strength and ductility was investigated systematically on a cryogenic near alpha titanium alloy Ti-3Al-3Mo-3Zr-0.2Y additively manufactured by electron beam selective melting (EBSM). As ε˙ increases under quasi-static tension at 77 and 20 K, ductility monotonically decreases when yield strength (YS) keeps ascending. As ε˙ increases from 5.6 × 10–4 s−1 once by one order of magnitude, elongation-to-fracture declines from 20.0 % to 16.5 % and 15.7 % at 20 K. However, unlike the regular monotone increase at 298 and 77 K, ultimate tensile strength (UTS) at 20 K rises to 1460 MPa first then drops to 1320 MPa. This study further examined how strain rate affects slipping, twinning and strain hardening behavior. The monotone increase in YS is primarily attributed to the increased CRSS for slips and the enhanced tendency of pyramidal 〈a〉 and 〈c + a〉 slipping and <101¯0 > 34° twinning at 20 K. On the other hand, the monotone decrease of ductility is essentially ascribed to the intensified deformation localization characterized by micro shear bands, multiple necking and single necking. More importantly, the mechanisms of abnormal UTS variation and disappearance of serration flow at 20 K are discussed in terms of strain hardening levels, degree of shear deformation localization and the interaction of slips and twins. This study provides deep insights into strain rate effect on cryogenic mechanical behavior of EBSM-built titanium alloy.

Numerical modelling of vibratory extraction of monopiles from clayey seabed

Understanding and optimizing the extraction of offshore monopiles from the seabed in decommissioning operations give both environmental benefits and cost reduction. The literature highlights the significance of utilizing a vibratory hammer for the complete removal of monopiles in granular or non-cohesive seabed, e.g., sandy soil, offering a cost-effective alternative to the conventional cutting method. However, the available knowledge for applying this method to cohesive soil is limited. The present study examines vibratory pile extraction from cohesive soil, for both soft and stiff clays, with the aim of assessing the resulting extraction force required for pile removal. Coupled Eulerian-Lagrangian (CEL) analyses with two domains of pile and soil are performed using the finite element package ABAQUS. A modified Mohr-Coulomb (MCC) soil model is coded into a VUSDFLD subroutine to properly simulate the soil softening and shear strain rate dependency of seabed soil in an Eulerian domain. The importance of shear strain and softening effects is underscored for soft clay by demonstrating an approximately 20% reduction in the force needed to initiate cyclic extraction of the monopile compared to scenarios where these effects are not included. However, incorporating these effects does not affect the behavior of stiff clay. The present numerical findings show that adopting vibratory extraction method leads to more soil resistance in cohesive soils at the beginning of the extraction. Considering the added weight og the vibratory hammer which should be clamped to the monopile top head leads to exceedance of the required force than the one required for removal of the monopile without vibration (i.e., the pulling-out method). This demonstrates that the vibratory extraction method is not an efficient method for monopile extraction from clayey seabed despite its beneficial effects reported in the literature for sandy soil.

Statistical analysis of serrated flows in CoNiV medium-entropy alloy

The Portevin–Le Chatelier (PLC) effect induced by dynamic strain aging is commonly observed in various alloys. The stress-drop magnitude of serrations and the critical strain at which serrations occur are two pivotal features characterizing serrated flow. This study investigates the temperature (160–460 °C) and strain rate (6 × 10−4 s−1–2 × 10−2 s−1) dependence of the serrated flow behavior in the CoNiV medium-entropy alloy through uniaxial tensile tests. Under the guidance of the mean-field theory, a scale theory has been applied to derive a scale function and scale indices that can be used to predict the distribution of stress drops. A normal PLC behavior of critical strain is fitted using the dislocation pinning model, demonstrating the presence of specific solute atoms conforming to the dislocation pinning model within medium-entropy alloys.

Multiscale Richtmyer-Meshkov instability experiments to isolate the strain rate dependence of strength.

Theoretical analysis of Richtmyer-Meshkov instability (RMI) experiments for solid strength shows that the strain rate for a given shock should be inversely proportional to the length scale of the sine wave perturbations when η_{0}k, the nondimensional amplitude to wavelength ratio, is held fixed. To isolate the effect of strain rate on strength, free-surface RMI specimens of annealed copper were prepared with three perturbation regions with the same η_{0}k but different length scales, characterized by the wavelength λ varying by a factor of 4.9 from 65 to 130 to 320µm. Three such targets with different fixed η_{0}k^{'}s were impacted to a shock pressure of 25 GPa, and the instability evolution was measured with photon Doppler velocimetry. Strengths estimated by comparing hydrocode simulation to the data increased from 700 to 1200 MPa as λ decreased. The different η_{0}k targets exercised increasing amounts of plastic strain yet showed no evidence of strain hardening. Physical regime sensitivity analysis determined that for 320-65µm wavelength perturbations, the effective strain rates increased from 8.7×10^{6} to 3.3×10^{7}s^{-1}, a factor of 3.8. Thus, the predicted strain rate scaling was mostly achieved but slightly suppressed by increased strength at higher rates. The RMI strength estimates were plotted against constitutive testing data on copper from the literature to show striking evidence of the strength upturn at higher strain rates.

Numerical and experimental analysis of inelastic and rate-dependent buckling of thin injection-moulded high-density polyethylene structure

Semi-crystalline polymers is an important group of materials that is used in a vast array of products. In this study, the rate-dependent properties of high-density polyethylene (HDPE) are investigated, both experimentally and theoretically. Experimental compression testing of a three-dimensional HDPE structure is performed and analysed numerically by use of the finite element method. In addition, an Eulerian constitutive material model for isotropic, semi-crystalline polymers is proposed. The model is able to account for such essential phenomena as strain-rate dependence, work hardening, pressure-dependence of inelastic deformations, and damage. The proposed material model was implemented in Abaqus as a VUMAT, which is an explicit implementation. The material model was calibrated by use of uniaxial tensile tests performed on HDPE dog-bone shaped samples, and the model was further explored by applying the VUMAT implementation to the compression tests of the HDPE structure. The simulation model was able to reproduce the experimental results well, both the uniaxial tests and the compression tests. In particular, the friction present in the compression tests seems to play an important role in determining the buckling mode of the structure.

In-situ determination of strain during transient burst testing and the temperature dependence of Zircaloy-4 claddings

Understanding fuel system behavior during postulated loss-of-coolant accidents is pertinent for continued safe and efficient operation of light water reactors, particularly as higher burnups are being pursued and safety margins re-evaluated. Conventional mechanical models for the incumbent Zr alloys typically rely on the assumption that steady-state creep is the dominant fuel cladding response during transient accident conditions. To investigate this assumption, simulated accident burst testing was performed on Zircaloy-4 claddings with balloon behavior measured in-situ. Two distinct loading conditions were utilized during burst testing: (1) constant-gas-inventory where pressure was allowed to increase with temperature and (2) constant pressure. In-situ strains and strain rates were measured via 2-dimensional digital image correlation techniques and synchronized with temperature to determine deformation dependencies. The temperature dependence of strain rate was characterized by a two segment Arrhenius relationship, with a distinct transition between the high and low temperature/strain regimes. The average activation energy of the lower temperature/strain regime was 328 ± 25 kJ/mol, in agreement with the ∼320 kJ/mol used for conventional LOCA models. However, the higher temperature/strain segment, which encompassed most of ballooning, showed increased activation energies as well as a dependence on whether the burst region was in view. For tests that burst away from the camera view, the average high temperature/strain segment activation energy was 635 ± 150 kJ/mol. For samples where the rupture opening formed in view, the average activation energy was 1015 ± 179 kJ/mol. This observed shift in temperature dependence indicates a transition in deformation mechanism at the end of life, possibly to time independent failure mechanisms, which has not yet been visualized in the literature for Zr alloys. Parameters at the transition points were analyzed to determine thresholds for this change in behavior, which occurred at an average hoop strain of 6.9 ± 2.1 %.

Injection moulding process parameter and strain rate dependence mechanical properties measurement and theoretical estimation of EVA polymer foam

Abstract In this study, the combined experimental and theoretical estimation on elastic characteristics of EVA (ethylene-vinyl acetate) copolymer material is demonstrated. Strain rate dependence stress–strain behavior of EVA in raw and foam material form are measured by the quasi static and dynamic compression test. Simultaneously, the influence of different mould temperature and injection pressure on mechanical properties of EVA foam are investigated. According to the usage scenario of EVA foam in sport footwear application, the EVA foam is generally deformed under higher strain rate as compared with the quasi-static compression condition. For this reason, the stress–strain behavior of EVA foam under high strain rates of 2.66 × 10−3 and 2.66 × 10−2 s−1 are estimated. The analytic results revealed that the strain rate slightly enhanced the modulus of EVA foam, and the foregoing strain rate effect is substituting into the classic Young's modulus estimation equation of closed cell cellular solid. Accordingly, the strain rate dependence Young's modulus of EVA foam is successfully estimated by both experiment and theoretical estimation.

Numerical study on microscopic behaviour of non-crushable cemented granular media subjected to direct shear test

ABSTRACT Granular media, though discontinuous and heterogeneous, exhibit discrete behaviour at the grain scale and continuum behaviour at the macroscopic level. Understanding the correlation between micro-macro-mechanical parameters is crucial. The Discrete Element Method (DEM) effectively bridges this micro-macro-mechanical gap. This study simulates the Direct Shear Test (DST) using DEM software PFC2D on synthetic cemented granular media (CGM) under varying normal loads and strain rates. It examines micromechanical features and correlates them with macroscopic observations, focusing on confinement pressure and strain-rate dependency. Significant volumetric dilation is observed during shearing at low normal loads, which diminishes at higher normal loads. Particle-scale shear mobilization is explored through shear band formation in the sample. Grain-scale contact force distribution is highly heterogeneous throughout the sample. A probability distribution study is carried out to explore the bond breakage effect on the global response, which confirms the bond breakage to be a pressure and strain-dependent phenomenon.

Grain boundary plasticity in Mg binary alloys by segregation of p-block element

The effect of p-block elements (Ga, Ge and In) addition on grain boundary structures and room temperature mechanical responses was investigated on extruded Mg binary alloys with fine-grained structures. Grain boundary segregation was confirmed in the Mg–Ga and Mg–In alloys, whereas the Mg–Ge alloy did not show such microstructures associated with solubility. Grain boundary segregation affected the plastic deformation of the Mg–Ga and Mg–In alloys. In particular, the Mg–In alloy had a large strain rate dependency and exhibited good deformability at low strain rate regimens. First-principles calculations indicated that p-block elements produce a bond-weakening effect at grain boundaries, and atomistic distances at grain boundaries varies according to the element. Solute atom which brings about both bond-weakening and bond-expansion effects to Mg atoms is effective in enhancing the contribution of grain boundary sliding in deformation.

An Overview of the mechanism-based thermomechanical fatigue method (DTMF) in the design of automotive components

The DTMF damage Parameter described in the paper is the generalization of the creep fatigue parameter (DCF) proposed by Riedel, which quantifies the amount of damage produced by a non-isothermal loading cycle. The entire design methodology is outlined in the text, starting with the calibration of Chaboche's viscoplastic model and then the determination of the thermomechanical fatigue (TMF) parameters. Chaboche is generally a good choice for its ability to describe well both kinematic and isotropic hardening behaviors, also enabling stress relaxation and strain rate dependency to be considered. The DTMF method is based on the fracture mechanics concept of cyclic crack tip opening displacement (ΔCTOD) where the effective stress range takes the crack closure effect into account. This method is typically used to describe the thermomechanical low cycle fatigue behavior of cast irons, cast steels, stainless steels, Inconel, HiSiMo and nickel-based alloys. These materials are used in components that need to withstand high temperatures (higher than half of the melting point) in service as exhaust manifolds, cylinder heads, valves, turbochargers and disk brakes. Three failure mechanisms are detailed here: oxidation, creep and fatigue. Oxidation is a complex phenomenon that may occur when the material is hot under tensile in-phase loading or hot under compressive out-of-phase loading. Creep is a time and temperature dependent diffusion process which is incorporated into the DTMF parameter as a multiplicative factor. In this context fatigue life is defined as the number of cycles to propagate an existent microcrack up to an arbitrary size that is defined on a case-by-case basis.

Temperature and strain-rate dependence of the superelastic response in EBF3-fabricated and post-heat-treated NiTi shape memory alloy

In the present work, the temperature and strain-rate dependence of the superelastic response behavior of NiTi shape memory alloys prepared via electron beam freeform fabrication (EBF3) technique and post-heat-treated is systematically studied. It is demonstrated that the response hysteresis of the EBF3-fabricated NiTi alloys during superelastic cycling decreases with increasing strain-rate at the same test temperature. However, the superelastic response of material gradually alters to a nearly linear mode with the increase of test temperature under the same strain-rate. The corresponding stable superelasticity recovery ratio decreases from 62.6 % to 47.6 % when the test temperature improves from 100 °C to 150 °C. This is mainly due to the activation of dislocations in the {011}<001> slip system of B2 austenite, in which they become plugged and entangled during plastic deformation, deteriorating the material superelastic recovery ability. These findings provide a selection basis for the service conditions of the rapidly prepared NiTi alloys under EBF3-fabrication and post-heat-treatment technology routes.

Force decomposition and toughness estimation from puncture experiments in soft solids.

Several medical applications, like drug delivery and biosensing, are critically preceded by the insertion of needles and microneedles into biological tissue. However, the mechanical process of needle insertions, especially at high velocities, is currently not fully understood. Here, we explore the insertion of hollow needles into transparent silicone samples with an insertion velocity v ranging from 0.1 mm s-1 to 2.3 m s-1 (with needle radius R = 101.5 μm, thus strain rates ∼v/R ranging from 1 s-1 to 2.3 × 104 s-1). We use a double-insertion method, where the needle is inserted and re-inserted at the same location, to estimate the fracture properties of the material. The deflection of the specimen's free surface is found to be different between insertion and re-insertion experiments for identical needle positions, which is associated with different force magnitudes between insertion/reinsertion. This aspect was previously neglected in the original double-insertion method, thus here we develop a method based on imaging, image analyses and force measurements to decompose the measured force into individual force components, including deflection force Fd, frictional and spreading force Ff + Fs, and cutting force Ft. We estimate that the toughness Γ of our silicone samples, calculated using the cutting force Ft and the crack dimensions, increases with needle velocity, and ranges within observed values in previous literature for the same material and for some soft biological materials. In addition to toughness Γ, other parameters, such as critical force Fc and mechanical work Wc, also show strain-rate dependence, suggesting tissue stiffening, due to accumulated strain energy, at high speeds.