Low Strain Rates Research Articles

Effect of Annealing Time on Grain Structure Evolution and Superplastic Response of Al-Mg 5xxx Alloys

The impact of annealing on the recrystallized grain structure and superplastic behavior of two Al-Mg 5xxx alloys used for high-speed blow forming (HSBF) was studied. The results revealed that both alloys demonstrated rapid static recrystallization after only a few minutes of annealing at 520 °C, forming fine and equiaxed grain structures. After four min of annealing, Alloy 2 (Al-4.0Mg-1.18Mn) exhibited a higher fraction of small grains (<10 µm) compared to Alloy 1 (Al-4.5Mg-0.74Mn). Moreover, Alloy 2 displayed enhanced resistance to grain coarsening with increasing annealing times, which was attributed to its higher amount of Al6(Mn,Fe) intermetallic particles and a higher number density of Mn dispersoids. Optimizing the annealing time can effectively develop a fine and stable grain structure in Al-Mg 5xxx alloys. During tensile deformation, Alloy 2 consistently showed higher ductility compared to Alloy 1 at low strain rates (170% vs. 138% at 0.001 s−1 and 163% vs. 134% at 0.01 s−1), whereas at a high strain rate of 1 s−1, both alloys displayed comparable tensile elongation. The high superplastic response of Alloy 2 at low strain rates renders it a superior superplastic alloy for HSBF applications.

Numerical analysis of fixed-end hollow rectangular beam under uniformly distributed load

The purpose of using opening in the reinforced concrete (RC) rectangular beam is the reduction of self-weight, cost, displacement, and strain. Therefore, this research performs linear elastic finite element analysis by using ETABS for fixed-ended RC hollow and solid rectangular beams under uniformly distributed loadings with variable beam lengths, compressive strengths, and opening sizes.The solid and hollow beams are considered to be a 2-nodded line element for the numerical analysis. The maximum range of validation result in case of hollow beam is found to be (3.9 to 7.9) %, which may indicate good accuracy of numerical analysis. The 50 × 50 mm opening size is suitable for 300 × 300 mm RC rectangular beam because of showing the positive normalized deflection of (0–1.45) % and lower strain rates (i.e. 0.13 % and 0.17 %) to compare the solid beam. This research may help professional engineers to use suitable opening size for design and construction works. Although, there is a scope to enhance this research in future by performing nonlinear analysis.

Effect of Cyclic Load Frequency on the Fatigue Crack Nucleation and Growth of Annealed and Prestrained Austenitic SS 304

ABSTRACTThe austenitic stainless steels are widely used in several engineering fields due to their high ductility, corrosion and high temperature performance. Despite its noble properties, components manufactured in austenitic stainless steel are subject to fatigue failure. Studies indicate that loading frequency can impact the austenitic stainless steel fatigue performance. In this scenario, the present study aims to evaluate the effect of frequencies of 3 and 30 Hz on the fatigue behavior of SS 304 alloy under load control in order to identify in which fatigue stage the effect is outstanding. Therefore, fatigue and fracture mechanics tests were evaluated on the alloy annealed at 1000°C. Furthermore, fatigue tests were also applied to the alloy after previous tensile plastic strain of 0.5. The analyses denoted a significant reduction in fatigue strength with increasing frequency, especially for the strained alloy. Fatigue crack nucleation is encouraged with greater load frequency. This behavior may be attributed to strain‐induced martensite and other strain mechanisms such as twinning and slip bands that are encouraged by lower strain rates but are relieved by auto‐heating achieved in higher frequencies, as mentioned in the literature, which decrease the strength to fatigue nucleation.

Microstructure-sensitive crystal plasticity and phase-field modeling of deformation and fracture in polycrystalline ice

The formation of crevasses in Greenland and Antarctica is primarily driven by the brittle failure of ice at low strain rates. Understanding this phenomenon requires exploring the effect of microstructural heterogeneity and anisotropic elastoplastic deformation on the fracture behavior of ice. Here, we have developed a microstructure-sensitive coupled crystal plasticity and phase-field model. This model allows us to study the plastic deformation, damage initiation and propagation under various strain rates in hexagonal open-packed polycrystalline ice, the prevailing phase on Earth. By employing a Bayesian optimization method, we derived the material parameters for the micromechanical model based on experimental results. The modeling results reveal that the activation of basal dislocations results in a brittle to ductile transition in ice at a low strain rate of 10-7s-1 under tension. At higher strain rates, the intrinsic plastic anisotropy of ice leads to heterogeneous deformation among grains and stress concentration near grain boundaries, triggering crack initiation and exacerbating the brittleness of ice. Under compression, cracks usually do not propagate throughout the specimen due to a significant decrease in stress around the crack tip upon propagation. Moreover, we found that the formation of the shear-induced basal texture at the bottom of ice layers and along glacier valley sides intensifies the brittleness of ice. This study provides insights into the micromechanical deformation and fracture mechanisms of ice, elucidating the intricate process of crevasse development in polar ice sheets.

Anisotropic stress corrosion cracking susceptibility of Mg-8Gd-3Y-0.5Zr alloy

This study investigates the stress corrosion cracking (SCC) behavior of a Mg-8Gd-3Y-0.5Zr alloy in a 3.5 wt.% NaCl solution using slow strain rate tensile (SSRT) testing. The results reveal that SCC susceptibility increases as the strain rate decreases, with hydrogen embrittlement (HE) becoming more dominant at lower strain rates, leading to brittle fracture. Anodic dissolution (AD) plays a more significant role at higher strain rates, resulting in mixed fracture modes. Additionally, the mechanical properties and SCC resistance are strongly influenced by the sample orientation. TD-oriented samples show higher SCC susceptibility than RD-oriented ones due to the alignment of Gd- and Y-rich precipitates and grain boundaries, which act as initiation sites for SCC. These precipitates form micro-galvanic couples with the Mg matrix, accelerating localized corrosion and HE. The findings provide insights into the SCC mechanisms of VW83 alloy and highlight the importance of optimizing microstructure and processing conditions to improve its corrosion resistance.

Investigation on the thermal deformation mechanisms and constitutive model of Ti-55511 titanium alloy

This study presents a comprehensive analysis of the hot deformation behavior of the Ti-55511 alloy over a temperature range of 700 °C to 950 °C and strain rates from 0.001 s⁻1 to 1 s⁻1, utilizing isothermal compression testing alongside electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The investigation focuses on the influence of various hot deformation parameters on the microstructural evolution of distinct phase regions within the alloy. At higher strain rates (0.1 s⁻1 to 1 s⁻1), the primary softening mechanisms for β grains in the α+β two-phase region are identified as continuous dynamic recrystallization (CDRX) and dynamic recovery (DRV), while in the β single-phase region, discontinuous dynamic recrystallization (DDRX) and DRV predominate. Conversely, at lower strain rates (0.001 s⁻1 to 0.01 s⁻1), the softening of β grains in the two-phase region is primarily governed by DRV, whereas in the single-phase region, DDRX and CDRX are the dominant mechanisms. Additionally, based on stress-strain data corrected for friction and temperature effects, an elastoplastic constitutive model is developed, incorporating strain rate and temperature to predict peak stress in the two-phase regions of the Ti-55511 alloy. This examination of the thermal deformation behavior and microstructural evolution of the Ti-55511 alloy provides significant theoretical and practical insights for optimizing the manufacturing processes of aviation die forging, tailoring microstructures, and enhancing hot working techniques.

Microstructure evolution and dynamic recrystallization mechanism of tantalum-tungsten alloys under hot compression

Ta-W alloys exhibit outstanding comprehensive properties at high temperatures, allowing them to have great application prospects in the high-temperature field. High-temperature compression tests (1573~1873 K) were conducted to evaluate the high-temperature mechanical properties of Ta-12W alloy, and the strain-compensated Arrhenius-Type model and hot processing map were developed to predict the optimal processing window. The electron backscatter diffraction, Transmission electron microscope, and DEFORM-3D software were performed to investigate the microstructure evolution and distributions of strain. The results demonstrated that the flow stress of Ta-12W alloy presented apparent negative temperature sensitivity and positive strain rate sensitivity. Based on the thermal processing diagrams and EBSD analysis, the results show that the low deformation temperature and high strain rate introduce stress concentration and deformation instability in the Ta-12W alloy. The optimized processing temperature and strain rate are at 1800 ~1873 K/0.001 s-1~0.05 s-1, and the microstructure at 1873 K/0.001 s-1 is more uniform and exhibits a low residual stress level. As the temperature increases, dynamic recovery and dynamic recrystallization cause significant softening effects, and continuous dynamic recrystallization dominates the high-temperature deformation behavior. Moreover, multiple continuous dynamic recrystallizations occur simultaneously, including sub-grain nucleation inside large grains, sub-grain nucleation at grain boundaries, and grain fragmentation accompanied by grain rotation. This study revealed the mechanisms of microstructural evolution during hot deformation of Ta-12W alloy, providing important guidance for optimizing the thermomechanical processing parameters.

Heterogeneous dynamic restoration of Ti-15Mo alloy during hot compression

Near-β titanium alloys have shown low Young’s modulus and good strength, making them excellent implant candidates. However, their processing using thermomechanical routes in single phase β region results in heterogeneous microstructures due to high content alloying elements and consequent slow diffusion-controlled processes such as dynamic recovery. This study investigates the deformation behaviour of a Ti-15Mo alloy through hot compression experiments using a Gleeble ® 3800 device in the single β domain at strain rates from 0.01 s-1 to 10 s-1, reaching final strains of 0.50 and 0.85 followed by immediate water quench. The findings show that the material presents a low strain rate sensitivity. The flow curves show significant strain hardening before reaching a steady-state regime, particularly at high strain rates. The strain hardening exponent calculations support the effect of molybdenum on retarding softening mechanisms such as dynamic recovery. Electron backscatter diffraction (EBSD) measurements of deformed samples revealed that dynamic recovery is the primary restoration mechanism, with continuous and geometric dynamic recrystallisation evidence. Due to the slow restoration process, we observe the subgrain formation for different deformation parameters. Therefore, we introduced an EBSD-based method to quantify dynamic recovery and subgrain size. We concluded that for a given deformation, the areas of dynamically recovered and recrystallised regions decrease with increasing strain rate and decreasing temperature, exhibiting negligible variation at higher strain rates.

Impact resistance study of lime slag–stabilised steel slag mixes

ABSTRACT Given the transient nature of impact loading, exploring the microscopic damage characteristics and damage mechanisms of materials through indoor tests is difficult. In this study, the damage morphology and energy dissipation characteristics of lime slag–stabilised steel slag (LSSS) mixes under vertical impact loading is explored using ABAQUS software, a finite element model of LSSS for falling hammer impact test is established, the validity of finite element calculation is verified by comparing the results of indoor tests, and the strain characteristics, deflection changes, and energy transformation process of LSSS under vertical impact loading are analysed. Results show that the LSSS tensile and compressive strains under impact loading are roughly divided into low strain rate, precracking, and cracking phases with a rapid increase in strain. Under the same impact energy conditions, the LSSS bottom tensile strain, span deflection, drop hammer kinetic energy conversion time, and LSSS plastic energy consumption curve rising slope are sensitive to drop hammer mass. Thus, improvement in drop hammer mass will prolong the impact loading of the drop hammer–LSSS system internal energy conversion time, and the LSSS strain peak range to the central concentration, enhancing span deflection and bottom deformation.

Hot deformation behavior of an ignition resistance Mg–6Zn-0.6Zr-1.2Ca magnesium alloy

The addition of Ca could enhance the ignition point of magnesium alloys but impairing their workability, so it is essential to study the hot deformation behavior of new Ca-containing ignition resistance magnesium alloys. The hot deformation behavior of a new ignition resistance Mg–6Zn-0.6Zr-1.2Ca alloy was investigated by compression experiment in the temperature range of 240 °C–360 °C, strain rates of 10−3 s−1-1 s−1 and height reduction of 10%–60%. The true stress-strain curves show that flow stress decreases as the deformation temperature increases or the strain rate decreases. Microstructure analysis shows that higher temperatures and lower strain rates are favorable for DRX, while higher strain rates promote the fragmentation of the Ca2Mg6Zn3 phase. Meanwhile, the existence of Ca2Mg6Zn3 phase make the DRX process be dominated by the particle-induced subgrain nucleation mechanism. By superposition of the power dissipation map and the instability map, a hot processing map of true strain of 0.6 is generated. According to analyses on the processing map and microstructure evolution, the instability of processing map can be attributed to the greater dislocation motion resistances, insufficient DRX, and Ca2Mg6Zn3 phase with low-melting point. Conversely, the optimal processing parameters for the alloy were determined as 280–360 °C/0.001–0.01 s−1 in safe zone with a high η above 0.3, which can be due to the apparent DRX and good deformation coordination.

Effect of hot deformation parameters on microstructure evolution mechanism and workability in a wear-resistance steel of machinery equipment

Hot compression experiments were conducted to study the flow behavior and hot workability of NM400 wear-resistance steel. A new Zener-Hollomon parameter ( Z) model is developed for coupling strain into the conventional Z model. The NM400 exhibits excellent resistance to instability owing to its low sensitivity to unsafe regions. Conversely, the peak efficiency of the power dissipation (EPD) region expands to the direction of low temperature with increasing of strain. The dynamic recrystallization (DRX) is facilitated at elevated temperatures and lower strain rates. DRX becomes the dominant softening mechanism with the increasing of temperature. Finally, 1050–1175 °C and 0.11–1.82 s−1 are recommended to be the optimal window. The optimal ln Z values for different strains are provided by the new Z model.

Study on hot deformation behavior and dynamic recrystallization mechanism of recycled Al–Zn–Mg–Cu alloy

This study utilized Al–Zn–Mg–Cu alloy chips as raw materials to prepare recycled billets through a solid-state recycling process. Isothermal hot compression tests were conducted using a thermal simulation machine to establish an Arrhenius-type constitutive equation and the hot processing map based on the dynamic materials model. The microstructure of the recycled Al–Zn–Mg–Cu alloy after hot compression was characterized and analyzed using SEM, EBSD, and TEM, exploring the microstructural evolution mechanisms of the recycled alloy at different temperatures and strain rates. The results indicate that the optimal hot deformation parameters for the recycled Al–Zn–Mg–Cu alloy are 300–360 °C at a strain rate of 0.01–0.05 s⁻1 and 400–450 °C at a strain rate of 0.05–0.3 s⁻1. At the same strain rate, as the deformation temperature increases, low-angle grain boundaries gradually disappear, and the grain structure becomes more stable. Dynamic recrystallization replaces dynamic recovery as the dominant mechanism. At the same deformation temperature, low strain rates allow more time for the migration of low-angle grain boundaries, thereby promoting the growth of dynamically recrystallized grains and ultimately forming new, undistorted grains.

Interaction of microstructure evolution mechanism in Ti-0.3Mo-0.8Ni alloy with initial lamellar microstructure during isothermal compression below the β-transus

The flow behavior and interaction of microstructure evolution mechanisms for a near α Ti-0.3Mo-0.8Ni alloy with as-cast lamellar microstructure are investigated at temperatures of 800∼880 °C in the α+β region with wide strain rate range from 0.01s−1 to 30s−1 during isothermal compression. It is demonstrated that the main reasons of flow softening in the true stress-true strain curves are the kinking of lamellar α, dynamic α→β transformation (DT), dynamic spheroidization (DS), and dynamic recovery (DRV) of β grain. The instability phenomena such as adiabatic shear band (ASB) and flow localization (FL) are the main causes of the stress collapse in the curves at higher strain rate. The dislocation density at the kinking position of initial lamellar α is higher. With the increase of strain rate, the mechanism of the DS changes from flat separation to slat shear. The diffusion of the β-stabilizer results in starting the DT, promoted by the thermodynamic coupling. The interactions between different microstructure evolution mechanisms are extremely complex. In the early stage of hot deformation, the DT promotes the kinking of lamellar α. With the increase of deformation amount, the DT inhibits the DS at higher strain rates, and conversely, the DS promotes the DT. At lower strain rates, the DT and DS accelerate each other in the middle and late stages of hot deformation. The DT and DS are restricted by the process of lamellar α kinking in the middle and late stages of hot deformation.

Constitutive modeling of the slip-twinning transition in martensitic transformations

Martensite is the result of a diffusionless displacive phase transition. In Fe-based alloys it transforms the FCC to the BCC, BCT, or HCP structures and occurs at high strain rates. It has two typical morphologies, known as lath and plate. A quantitative constitutive description of the slip-twinning transition in the martensitic transformation is presented. It is based on the temperature and strain-rate sensitivities of slip, which are much higher than those for twinning. Thus, twinning becomes a favored deformation mechanism at low temperatures and high strain rates. The Hall-Petch coefficient, for the inclusion of grain size effects, is two times larger for twinning than slip. Constitutive relationships for slip and twinning are presented and applied to the martensitic transformation in steels; the lath-to-plate morphology change observed with increasing carbon content is successfully predicted as a function of grain size by calculations incorporating the two modes of deformation. A simple calculation of the strain rates during martensitic transformation is also provided. This methodology is applied to the Fe–C system and can be extended to the Fe–Ni–C system and to thermoelastic martensites, where twinning is favored over slip to enhance reversibility.

Characterizing undrained behaviour of imperfectly saturated Palar sand

The occurrence of earthquake-induced soil liquefaction poses a significant threat, leading to extensive damage to building foundations and other structures, resulting in substantial economic repercussions. The seismic performance of geotechnical systems is markedly influenced by the saturation level of the soil. This study examines the impact of dynamic response on Palar sand. Cyclic triaxial tests were conducted on partially saturated fine-grained loose sand with a relative density of 35 % and a degree of saturation ranging from 65 % to 75 %. These tests were carried out at a strain rate of 0.1 % and confining pressures of 50 and 75 kPa. The study findings reveal that an increase in back pressure corresponds to a rise in the excess pore water pressure ratio of the sand. Additionally, the sand undergoes liquefaction as the number of cycles increases, and the degree of saturation decreases for different confining pressures at frequencies of 0.75 and 1 Hz. It was observed that soil liquefies more rapidly at lower strain rates with an increase in effective confining pressure. Conversely, at higher frequencies, soil liquefaction occurs in a smaller number of cycles. Comparing the effects of confining pressure and frequency, a damping ratio of 13 % and a shear modulus of 40 MPa were achieved at a frequency of 0.75 Hz and a confining pressure of 50 kPa. The shear modulus of partially saturated sand decreases with an increase in the initial degree of saturation due to specific characteristics of the Palar sand and the loading conditions.

Hot deformation behavior and microstructural evolutions of a Mg-Gd-Y-Zn-Zr alloy prepared by hot extrusion

The hot deformation behavior of extruded Mg-9.5Gd-4Y-2Zn-0.5Zr alloy was studied through hot compression tests conducted at deformation temperatures of 350–500 °C and strain rates of 0.001–1 s−1. Under most deformation conditions, the flow stress first reached a maximum before decreasing to a stable value, demonstrating characteristics of dynamic recrystallization (DRX). The constitutive equation of the alloy was established as ε.=1.03*1011sinh0.01287*σp2.422exp(−171150/RT) through calculations and derivation. The influences of the deformation temperature and strain rate on the microstructure and DRX of the alloy during the hot compression process were investigated using electron backscatter diffraction. It was found that at temperatures between 350 °C and 450 °C, the alloy texture exhibited multiple {0001} peak rings distributed around the normal axis of the compression direction. When the strain rate was 0.001 s−1, the average equivalent grain diameter significantly increased from 3.3 μm to 22.4 μm with the rise in deformation temperature, whereas when the deformation temperature was 450 °C, the volume fraction of DRX grains noticeably decreased from 87.6 % to 13.2 % with the increasing strain rate. Further research revealed that due to the restriction of strain rate on grain boundary migration, discontinuous dynamic recrystallization and continuous dynamic recrystallization were the predominant DRX mechanisms at low and high strain rates, respectively.

On the nature of nano twin-induced shear band formation in a dispersion strengthened copper alloy under micro-mechanical loading

A key challenge in metallic alloys with high ductility is understanding how microstructural inhomogeneities influence shear localization, leading to localized plastic deformation and material failure. In this study, we explore the phenomenon of shear localization in coarse-grained copper, a material traditionally regarded as having low susceptibility to such behavior. Contrary to conventional understanding, our findings reveal that microstructural inhomogeneities play a pivotal role in inducing extensive strain localization during low strain rate micro-mechanical loading. The presence of fine precipitate particles leads to strain localization at small strains and low strain rates by activating shear localization driven by void formation mechanisms. Furthermore, nanoscale precipitates act as sites for dislocation pile-up within deformed structures of shear bands, leading to the formation of nano twins within these bands. Consequently, precipitate particles serve a dual role: contributing to strain localization and potential cracking, while also enhancing the alloy’s strength and ductility through nano-twinning mechanisms. This investigation offers a novel perspective on the interplay between material microstructure and deformation behavior, challenging existing paradigms in materials science.

Assessment of the mechanical and functional properties of nitinol alloys fabricated by laser powder bed fusion: Effect of strain rates

Laser Powder Bed Fusion-fabricated (LPBFed) nitinol shape memory alloys (SMAs), which undergo solid-solid phase transitions between austenite and martensite, are increasingly utilized in various technical fields and are subjected to a wide range of strain rates during service. This study pioneers the investigation of a comprehensive range of strain rates (3.16 × 10−6-10°/s), encompassing the strain rates used in quasi-static tensile tests reported in the existing literature, to understand their effects on the deformation mechanisms of LPBFed nitinol SMAs. Utilizing multi-scale characterization, including macroscopic mechanical evaluation, mesoscale analysis of deformation surfaces, and microscale examination of microstructure, we reveal distinct deformation behaviors at different strain rates. At lower strain rates, the mechanical behavior exhibits little sensitivity to changes in the strain rates, with stress-induced martensite transformation or martensite detwinning and variant reorientation being the primary deformation mechanisms. However, at higher strain rates, we observe significant variability in mechanical response, dominated by dislocation-induced slip and reduced occurrence of stress-induced martensitic transformation. This study provides the first comprehensive database for the engineering applications of LPBFed Nitinol SMAs and offers critical insights into optimizing mechanical and functional assessments for these advanced materials.

Hot deformation behavior and dynamic recrystallization mechanism of GH2132 superalloy

In order to study the hot deformation and dynamic recrystallization behavior of annealed GH2132 superalloy, this paper conducted hot compression tests of GH2132 superalloy at different temperatures (950°C–1150°C) and different strain rates (0.01/s–10/s) using Thermocmaster Z thermal simulation testing machine, and made an in-depth analysis of recrystallization behavior via electron backscattered diffraction (EBSD). The results indicate that the flow stresses of GH2132 alloy first increase and then decrease at high temperature, among which the curves present a more obvious flow softening at 10/s. Continuous dynamic recrystallization (CDRX) is dominant at high temperature and low strain rate, while discontinuous dynamic recrystallization (DDRX) plays the major role at low temperature and high strain rate. The type of recrystallization has a significant impact on the formation and volume fraction of twinning. In addition, high-temperature constitutive model, hot processing map, and an unified dynamic recrystallization kinetic model of GH2132 superalloy were established. Thus, the optimal range of hot working parameters was obtained. The research results provide guidance for determining the hot working process window of GH2132 superalloy.

High-temperature hot deformation behavior and processing map of Ti-22Al-25Nb alloy

The high-temperature deformation behavior of the Ti-22Al-25Nb alloy was investigated by conducting hot compression experiments. A constitutive equation predicting the flow behavior of the Ti-22Al-25Nb alloy was established by analyzing its stress–strain curves. The strain-compensated constitutive equation effectively predicted the flow stress of the alloy with a correlation coefficient of 0.992 between the measured and predicted values and an average absolute relative error of 6.548 %. A hot processing map was obtained based on a dynamic material model. It demonstrated that the optimal processing region corresponded to the deformation temperatures of 1273–1353 K and strain rates of 0.001–0.01 s−1. Using electron backscatter diffraction data, thermal deformation mechanisms were elucidated under different deformation conditions within the safe region. The obtained results revealed that under the low temperature (T ≤ 1323 K) and low strain rate (ε̇ ≤ 1 s−1) conditions, continuous dynamic recrystallization and dynamic recovery (DRV) were the main thermal deformation mechanisms. Under the medium-to-high temperature (T ≥ 1323 K) and low strain rate (ε̇ ≤ 1 s−1) conditions, the main thermal deformation mechanisms were discontinuous dynamic recrystallization and DRV. At high strain rates (ε̇ ≥ 1 s−1), the primary thermaldeformation mechanism was DRV. The occurrence of discontinuous yielding in the alloy at high strain rates was related to the proliferation of mobile dislocations at grain boundaries.