Mechanical Behavior Evolution Research Articles

Dynamic Compressive Mechanical Behavior and Microstructure Evolution of Rolled Fe-28Mn-10Al-1.2C Low-Density Steel.

In this study, the quasi-static and dynamic compressive mechanical behavior of a rolled Fe-28Mn-10Al-1.2C steel (low-density) was investigated. X-ray diffraction, optical microscopy, electron backscattered diffraction and transmission electron microscopy were conducted to characterize the microstructure evolution. The results displayed that the steel has remarkable strain rate sensitivity and strong strain hardenability under high strain rate compression. Most specifically, the deformation behavior was changed with the increase in the strain rate. A feasible mathematical analysis for the calculation of stacking fault energies and the critical resolve shear stresses for twinning was employed and discussed the nucleation of the twinning. The microband-induced plasticity and twinning-induced plasticity controlled the deformation under high strain rate compression and provided a strong strain hardening effect. The higher mechanical response can increase the broad use of low-density steel in automobile applications.

Mechanical Behavior and Microstructure Evolution during Hot Torsion Deformation of Aluminum Alloy AA2219

This study comprehensively analyzes the mechanical behavior and microstructural evolution of aluminum alloy AA2219‐T87 undergoing high deformation and strain rates at elevated temperatures via hot torsion tests. An integrated experimental and modeling approach is employed, where a finite element model (FEM) is developed with ABAQUS to address local deformation and nonuniform temperature distribution along the specimen gauge section. A Johnson–Cook constitutive material model is calibrated based on the calculated and measured torque curves at different conditions. The grain structure distribution is characterized through optical microscopy and electron backscatter diffraction (EBSD) analysis. Combined with the ABAQUS calculated local thermomechanical conditions, microstructure modeling, using established literature‐based equations, is established to provide insights into grain size distribution and recrystallization mechanisms. The calibrated material constitutive model, recrystallization model, and grain size model can be utilized to model various manufacturing processes, which involve hot deformation of aluminum alloys in the intermediate strain rate range of 14–78 s−1. The constitutive model shows adequate matching of the experimental torque curves at 400, 450, and 500 °C. The recrystallization prediction model functions at over 94% accuracy and the grain size model provides an average deviation between predicted and measured grain size reduction of 11.5%.

Research on Mechanical Behavior and Energy Evolution of Coal and Rocks with Different Thin Spray-On Liners Thickness under Uniaxial Compressive Loading

Compared with the traditional supporting materials such as the bolts, mesh, and concrete, thin spray-on liners (TSLs) have the advantages of improving impact energy bearing and absorption capacity of rocks. In this study, the uniaxial compressive mechanical response feature of white sandstone, yellow sandstone, and coal with different coating thickness of TSLs were investigated through laboratory tests and theoretical analysis. The hard segments and soft segments of TSLs induced microphase separation, and formed the physical cross-linking. The hard segment evenly dispersed in the soft segment, which improved the mechanical strength of the TSLs. The confining pressure was affected by the TSL-coated coal and rocks, which improved the mechanical strength of the rocks and coal under UCS loading. It was discovered that the uniaxial compressive strength (UCS) increases with an increase in the TSL coating thickness, and UCS increments of the coated white sandstone, yellow sandstone and coal were 4.6%, 25.51%, and 43.75%, respectively. The energy absorption capacities of the coated coal, and yellow and white sandstones gradually decreased with an increase in their TSLs coating thickness. Meanwhile, the energy-absorbing capacity of a coated rock reduced gradually as rock coating decreases. Furthermore, the energy-absorbing capacity of coal is greater than that of yellow sandstone or white sandstone. By increasing the coating thickness, the total and dissipative energies in the yellow sandstone, white sandstone, and coal specimens were gradually increased, and energy increment was significantly more in coal (2–3 times), while the elastic energy remained nearly unchanged.

Influence of loading direction on mechanical behavior, microstructure characteristic and texture evolution of WE43-T4 magnesium alloy undergoing uniaxial compression

To elucidate the influence of loading direction on deformation behavior of WE43-T4 magnesium (Mg) alloy, compressive tests, optical microstructure (OM), X-ray diffraction (XRD) and electron backscattered diffraction (EBSD) characterizations and Schmid factor (SF) analysis have been conducted in the present study. All samples (0° sample, 45° sample and 90° sample) exhibit minor plastic anisotropy during uniaxial compression at room temperature. The difference about 0.2% proof yield stress is closely related to various activities of prismatic <a> slip, {10−12} extension twinning (ET) and {11−21} ET, while the difference about strain hardening response is attributable to various activities of basal <a> slip. The solid solution of Y element strengthens the critical resolved shear stress of {10−12} ET harder than that of {11−21} ET, resulting in their synchronous activation in 8%-deformed samples. The SF values for {10−12} ET and {11−21} ET possess a decreasing tendency, resulting in a decreasing tendency about their activities from 0° sample to 90° sample. These activated ETs are mainly responsible for the observed texture with different degrees of concentration for c-axes of most grains towards compression direction. In these 20%-deformed samples, the formation of tilted basal texture is mainly associated with the activities of pyramidal <c+a> slip and {10−11}-{10−12} double twinning.

An interacting wing-crack based semi-analytical meso-scale model for describing elasto-plastic damage behavior of brittle rocks

An interacting wing-crack based mesoscale model was developed for describing the elastoplastic damage behaviors of brittle rocks under compressive loading. In the present model, the main deterioration process of the rock is assumed to be induced by the wing-crack propagation, attributing the macroscopic inelastic strain to the nucleation and growth of tensile ‘wings’ of the initial flaws. The initial flaws are assumed to follow a periodic distribution in space. To account for the interaction between microcracks, a spatial evolution law as a function of the wing length is introduced, and the influences of the wing-crack propagation on the discontinuous slip of the crack surface are taken into consideration. On this basis, the increment of the compliance tensor caused by wing-crack propagation is proposed, and an incremental-based constitutive model is constructed so that the total stress-strain relations involving post-peak softening and residual behavior can be reproduced. Further, through appropriate parameter selection, the proposed model can reasonably simulate the triaxial test results of Taiwan sandstone, and the correctness of the model is effectively validated. Finally, the intrinsic features of the model are explored through a series of parametric analyses, and the macroscopic mechanical behavior and damage evolution of the rock characterized by the model are investigated. The conclusions show that this model is of significant usage to describe the whole strain-stress relation and inelastic strain analysis. It is full of potential to deem various rock macroscale mechanisms to mesoscale crack evolution.

Mechanical behavior, failure pattern and damage evolution of fiber-reinforced cemented sulfur tailings backfill under uniaxial loading

In order to explore the mechanical properties of cemented sulfur tailings backfill (CSTB), uniaxial compression tests of cemented sulfur tailings backfill (CSTB) were carried out in the laboratory, and the effects of sulfur content and polypropylene fiber on the mechanical properties, failure pattern and damage evolution of the CSTB were systematically studied. Moreover, fiber factor γ is introduced to measure the impact of polypropylene fiber on mechanical behavior of CSTB. The peak stress, residual stress and elastic modulus of the CSTB all increase initially and decrease afterwards with the fiber factor γ increasing. When the fiber content is 0%∼0.6%, the three factors show exponential and quadratic function with the fiber factor γ increasing. The total strain energy, elastic strain energy and dissipative strain energy of CSTB at the peak stress point all increase first and then decrease with the fiber factor γ increasing, and all reach the maximum value when the fiber content is 0.6%. Under uniaxial loading, the elastic strain energy of CSTB presents a change characteristic of “gentle - rapid increase - slow increase - rapid decline” with the increasing axial strain, while the dissipative strain energy presents a change characteristic of “gentle - steady increase - rapid increase”. In addition, each strain energy (dissipative strain energy, total strain energy and total strain energy) of CSTB at the peak stress point all increase initially and decrease afterwards with the fiber factor γ increasing. Then, the piecewise damage constitutive model taking fiber factor γ into consideration was established. Under uniaxial loading, the damage evolution of backfill can be divided into four stages: no damage stage, slow growth stage, acceleration stage and damage failure stage. It shows that polypropylene fiber can effectively inhibit the damage and failure of CSTB, thus improving the bearing capacity and anti-deformation and failure ability of CSTB. The CSTB without fiber shows obvious shear failure characteristics, and there are obvious large-scale “Y-shaped” and “linear” failure cracks on the sample surface. There is not only one or two major large-scale cracks in the failure of CSTB containing fiber, but also the range of fracture surface is very limited, indicating that adding fiber can effectively inhibit the crack propagation of CSTB during failure and improve the overall anti-crack ability of CSTB.

Constitutive behavior and microstructural evolution of 2060 Al–Li alloy under high strain rate: Experiment and simulation

Being impacted at higher strain rates, the dislocation density in the metal material increases, which leads to the phenomenon of grain refinement. The refined grains demonstrate the hardening effect of the material processed by high-velocity impacts well. However, the mechanical response and the microstructure evolution of the new material, 2060 Al–Li alloy, under high-velocity impact remain to be unclear. In this study, the mechanical behavior of 2060 Al–Li alloy at high strain rates was investigated by split Hopkinson pressure bar (SHPB), and the influence of higher strain rates on the microstructure evolution of 2060 Al–Li alloy was further revealed by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) experiments. Meanwhile, a coupling constitutive model was proposed to correlate the macro and micro properties of the material and was applied to characterize the mechanical behavior and microstructure evolution of 2060 Al–Li alloy. The experimental results showed that when the strain rate increased from 3189 s−1 to 9053s−1, a significant strain rate hardening phenomenon was exhibited in 2060 Al–Li alloy, which could be ascribed to the significant increase in the dislocation density. Meanwhile, as the strain rate increases, the proportion of low-angle grain boundaries (LAGB) in the material increases, along with the augmented sub-grains. After the impact, the Goss texture {110}<001> became conspicuous, while the Cube texture {100}<001> in the material became gradually eclipsed. When the strain rate is up to 9053s−1, the Goss texture took on orientational dominance. Finally, based on the coupling constitutive model, the dislocation density and grain size of the specimen after impact were predicted, and the calculated results were in good agreement with the experiments.

A strain rate and temperature-dependent crystal plasticity model for hexagonal close-packed (HCP) materials: Application to [formula omitted]-titanium

The mechanical responses of hexagonal close-packed (HCP) materials are highly anisotropic, as well as strain rate and temperature-dependent, because of inherently asymmetric slip and twinning in constituent crystalline grains. How slip and twinning are affected by strain rate/temperature and how they alter the deformation response of HCP materials are still not well understood. To provide greater insights, a novel crystal plasticity model is proposed to describe the mechanical behavior and microstructure evolution of single-crystal and polycrystalline HCP materials under different loading conditions. A new flow rule is developed, which incorporates the effects of strain rate and temperature on the activation of specific deformation mechanisms. Both dislocation density-based and empirical hardening laws are adopted to describe the overall hardening contributed by slip, twinning, and their interaction, taking into consideration loading conditions and the difference between tension and compression twinning. The proposed model is implemented in the commercial FE package ABAQUS via a user-defined subroutine. The mechanical response and microstructure evolution of single-crystal titanium with different orientations, and polycrystalline titanium comprising grains with 350 random orientations, subjected to deformation at different strain rates and temperatures, are numerically explored. The numerical results display good agreement with published experimental data. The simulations indicate that an increase in strain rate or decrease in temperature will retard the activation of slip systems, thereby promoting twinning instead. A higher twinning volume fraction leads to a larger amount of lattice reorientation, more pronounced hardening, and higher stress levels. This effort has yielded a greater understanding of the influence of strain rate and temperature on the mechanical response of HCP materials and facilitated mesoscale simulations that couple slip and twinning.

Pore structure, mechanical behavior and damage evolution of cemented paste backfill

In this paper, the internal pore structure and mechanical properties of cemented paste backfill (CPB) with different mix proportions are studied by low field nuclear magnetic resonance (NMR) and unconfined compressive strength (UCS) test, and the relationship between UCS, pore structure characteristics and curing time is quantitatively characterized. The following conclusions are obtained: (1) The internal pores of CPB are divided into micropores, secondary pores, and macropores, among which secondary pores account for the largest proportion, accounting for about 70% of the total pores. The proportion of macropores is inversely proportional to the UCS, while the proportion of micropores is proportional to the UCS. (2) The porosity of CPB decreases with the increase of curing time, and UCS increases with the increase of curing time. The curing time has an exponential function relationship with porosity. UCS decreases exponentially with the increase of porosity. (3) A damage model of CPB is established considering the initial pore damage, which is highly consistent with the experimental results. The total damage evolution curve presents an “S" type distribution. The total damage change rate evolution curve showed a normal distribution.

The permeability properties of bedded coal and rock: Review and new insights

AbstractIt is beneficial to understand deeply the permeability properties of coal and rock for the stability control of mining engineering, underground engineering, oil and gas engineering, nuclear waste storage engineering, and so on. Therefore, new insights for the permeability properties of bedded coal and rock are summarized and proposed. (1) "Five guarantees" coring technology is worth for vigorous promotion and application. (2) The internal spatial fabric has the significant effect on the mechanical behavior evolution law of (bedded) coal and rock, but the effect is not dominant. (3) The permeability‐energy evolution models of (bedded) coal and rock should be constructed considering the idea of initial high in situ stress reduction, which is helpful for the energy visualization characterization of (bedded) coal and rock. Meanwhile, it can be combined with the structural evolution theory for in‐depth characterization and disclosure. (4) Researches on the permeability properties of (bedded) coal and rock under multi‐field or multi‐phase or phase‐field coupling conditions should be strengthened based on considering the initial damage produced and the distribution characteristics of in situ stress under the coring environment. (5) More accurate and scientific permeability evolution models of (bedded) coal and rock should be vigorously constructed based on the above insights.

Experimental study on mechanical behaviour and pore evolution of borehole-sealing materials under different confining pressures

Experimental study on mechanical behaviour and pore evolution of borehole-sealing materials under different confining pressures

Mechanical behavior and microstructural evolution during cyclic tensile loading-unloading deformation in metastable Ti–10V–2Fe–3Al alloy

The mechanical behavior and microstructural evolution for Ti–10V–2Fe–3Al (Ti-1023) alloy with a single metastable β-grains obtained by β solution treatment (β-ST) were discussed by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) during the various early stages of cyclic tensile loading-unloading deformation (abbreviated as cyclic deformation) at ambient temperature. The main deformation product is stress-induced martensite transformation (SIMT) by coupling mechanical characterization and microstructure observation. With the cycles increasing, the trigger stress of SIMT (σSIMT) decreases with a stress plateau (120 MPa ±10), and the volume fraction of SIMT gradually increases until a nearly complete α″ martensite microstructure. Besides, the deformation-induced martensite twins (DIMT) in the α″ martensite have been generated until reaching a certain strain value. Moreover, there is specific orientation relationships (SORs) between β matrix and α″ martensite with <100>β//<100>α″, <110>β//<010>α″, and <110>β//<001>α″. And the geometrically necessary dislocations (GNDs) structure evolution is sensitive to cyclic strain and grain orientation. Moreover, GNDs synergizes the microstructure evolution and mechanical behavior.

Strain rate effects on mechanical behavior and microstructure evolution with the sequential strains of TWIP steel

Dynamic and quasi-static mechanical behaviors and microstructural mechanisms of the TWIP steel were investigated at strain rates from 0.001 to 3000 s-1 by using a split Hopkinson tensile bar paired with interrupted strain fixtures and electron backscattered diffraction technology. The positive strain rate sensitivity of dynamic yield stress is significantly different from that of quasi-static stress at a transition strain rate of about 100 s-1 for the different yield mechanisms. Owing to the high stress from dynamic loading, the smaller twin onset strain and the higher twin fraction as well as the more intense twin boundary-dislocation interaction are responsible for the enhanced strain hardening behavior in the early stage of strain. Nevertheless, the rapid decrease of the strain hardening rate in the later stage and the resulting negative strain hardening rate sensitivity are due to the decreasing growth rate of the twin boundary fraction. It is closely associated with the softening effect of adiabatic temperature rise (∼117 °C) by raising the stacking fault energy and inhibiting twinning activity. In addition, the fuzzy regions caused by high-density dislocations within interfaces between twin and grain boundaries may lead to the lower elongation of the dynamic tensile specimen. The grains with a high Schmid factor are conducive to slip rather than twinning, which enables the twin region orientation for slip-mediated plastic deformation. This study thus advances the understanding of the strain and strain rate dependence of the mechanical behaviors and twinning mechanisms of TWIP steels for the safety performance of automobiles.

Mechanical behaviour and energy evolution of polyurethane-mixed ballast under revised bonding constitutive model

The bonding contact presents complex modes in polyurethane-mixed ballast. The commonly used parallel bond model is revised and four different contact models are developed including Ballast-Ballast Contact Bonding, Ballast-Ballast Noncontact Bonding, Ballast-Sleeper Contact Bonding, and Ballast-Sleeper Noncontact Bonding. The mechanical behaviour and energy evolution of polyurethane-mixed ballast with various amounts of glue are studied from the macro and mesoscopic properties. Results show that the elastic strain energy has always been the main form in polyurethane-mixed bed, followed by viscous strain energy, frictional energy, and damping energy. Compared with the common ballast bed, there are more contacts in polyurethane-mixed ballast bed and, when more glue is used, the amount of contacts is further increased while the maximum contact force is reduced. After bonding, the amount of contacts is significantly increased and all forms of energy become more evenly distributed at different surfaces of the sleeper. The kinetic energy of polyurethane-mixed ballast fluctuates with smaller amplitude and convergences more quickly under cyclic loading, which is reflected in the macroscopic aspect that the settlement of polyurethane-mixed ballast bed is relatively small and can be fast completed.

Dynamic mechanical behavior and microstructural evolution of additively manufactured 316L stainless steel

Dynamic mechanical behavior and microstructural evolution of additively manufactured 316L stainless steel

Study on Mechanical Behavior and Microstructure Evolution of QP Steel under Low-frequency Vibration Assisted Tension

Study on Mechanical Behavior and Microstructure Evolution of QP Steel under Low-frequency Vibration Assisted Tension

Experimental And Numerical Modelling of Cyclic Softening and Damage Behaviors for a Turbine Rotor Material at Elevated Temperature

In order to better understand the physical process of deformation and cyclic softening a 12% Cr martensitic stainless steel FV566 has been cyclically tested at high temperature in strain control. Increase in temperature was found to increase the cyclic life, softening rate and viscous stress magnitude. An increase in the dwell time led to the acceleration of the material degradation. The microstructure changes and dominating deformation mechanisms were investigated by means of scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results have revealed a gradual sub-grain coarsening, transformation of lath structure into fine equiaxed sub-grains, and misorientation angle development in blocks and packets until material failure. Further, a unified viscoplastic constitutive model coupled with a physically-based damage variable, is proposed to capture the cyclic mechanical behavior and microstructural evolution of the material at elevated temperature. The mechanical strength can be reduced by the decrease in the dislocation density, the coarsening of the martensitic lath and the loss of the martensitic structure under cyclic loading. The proposed physically-based damage variable is driven by the evolutions of dislocation density and martensitic lath width. The good comparisons with test results mean that the proposed model can reasonably model the cyclic elastic-viscoplastic constitutive behavior of the material at high temperature.

Experimental and numerical investigation of severe plastic deformation of copper sheets processed by modified-constrained studded pressing

In this study, mechanical behavior and microstructural evolution of copper sheets, produced by modified-constrained studded pressing (modified-CSP) as a severe plastic deformation (SPD) method, were investigated by experimental and numerical methods. A finite element model (FEM) was established to analyze distribution of equivalent total strain, distribution of equivalent plastic strain and residual stress for the complete first pass of the process. Local stress concentration was predicted by FEM. Also, copper sheets were deformed by the modified-CSP from the first to the tenth passes. The distribution of residual stress on the surface of the copper sheets was measured at each step of the process. Crack initiation and propagation were investigated by the non-destructive penetration test (PT). The residual stresses were predicted by X-ray diffraction (XRD) via sin2 Ψ method. The residual stresses were determined for the annealed and the first pass samples, +128.2 and +80.4 MPa, respectively. The maximum compression residual stress was −62.5 MPa for the tenth pass sample. The microstructural evolution including grain size and dislocation density of samples during the process were investigated by XRD pattern analysis. The average grain size had a significant decrease from ∼35 to ∼76 nm for annealed sample and tenth pass of modified-CSP, respectively.

Ageing of PEEK/Carbon Fibre composite under electronic irradiations: Influence on mechanical behaviour and charge transport

Polymer used in satellite manufacturing are exposed to surface charging phenomenon due to electronic irradiations. This phenomenon can induce electrostatic discharges (ESD) which can lead to failures. In order to limit this phenomenon, we propose to develop PEEK composite reinforced with Short Carbon Fibres (SCF). We studied the behaviour of these composites in pristine state and after electronic irradiations compared to PEEK. In pristine state, fibres induce a faster surface electron relaxation. This behaviour shows that SCF can reduce ESD risks in space which is a first validation of the concept. After irradiations, PEEK ageing mechanisms are not modified by the presence of fibres. However, SCF stabilise both the evolution of mechanical behaviour and surface potential relaxation compared to irradiated PEEK. This stabilisation comes from two contributions: fibres stabilise the ageing of the matrix and hides the influence of this ageing on composite mechanical and electrical behaviours.

Study on mechanical behavior and microstructure evolution of Al-Mg-Li alloy during electropulsing assisted uniaxial tensile

The mechanical behavior and microstructure evolution of Al-Mg-Li alloys under the effect of electric current was investigated using an electropulsing-assisted uniaxial tensile (EAUT) test combined with microstructure observations. It was found that the localized Joule heating-induced microscale high temperature at the grain boundaries in the necking zone significantly accelerated the grain boundary weakening when necking occurred, which resulted in rapid intergranular fracture and relevant decrease in elongation. Electropulsing induced continuous dynamic recrystallization (CDRX) in the both side layers and the discontinuous dynamic recrystallization (DDRX) in the intermediate layers of the Al-Mg-Li sheet during EAUT testing at 460 °C and higher, promoting the formation of newly near-equiaxed recrystallized grains and weakening of β-fiber texture components. For the conventional high temperature tensile test, only a small amount of recrystallized grains formed along the grain boundaries of the coarse parent grains under the control of DDRX. The occurrence of CDRX during EAUT was substantially attributed to the promoted effect of electropulsing on dislocation glide and climb, which resulted from the combined effect of microscale localized Joule heating around dislocations and the electro-induced enhancement effect on vacancy diffusion.