Rate Sensitivity Research Articles

Is diet related to osteoarthritis? A univariable and multivariable Mendelian randomization study that investigates 45 dietary habits and osteoarthritis.

Diet is a safe intervention for many chronic diseases as a modifiable lifestyle. However, the potential causal effect of many dietary intake habits on the risk of osteoarthritis has not been fully understood. The purpose of this study was to reveal the potential causal relationship of 45 genetically predicted dietary intakes with osteoarthritis and its subtypes. Data on 45 dietary intakes were obtained from the UK Biobank study of approximately 500,000 participants, and data on six osteoarthritis-related phenotypes were obtained from the Genetics of Osteoarthritis Consortium study of 826,690 participants. We performed univariable Mendelian randomization (MR), multivariable MR and linkage disequilibrium score regression (LDSC) analyses. In univariate analyses, 59 potential associations between diet and osteoarthritis were found. After false discovery rate (FDR) correction and sensitivity analyses, 23 reliable causal evidence were identified. In multivariate analyses, controlling separately for the effects of body mass index, total body bone mineral density, and smoking status, eight robust causal relationships remained: Muesli intake was negatively associated with knee osteoarthritis, spine osteoarthritis and total knee replacement. Dried fruit intake had a negative association with osteoarthritis of knee and total knee replacement. Eating cheese may reduce the risk of osteoarthritis in the knee and spine. And alcohol usually taken with meals was associated with a reduced risk of total knee replacement. LDSC analyses showed significant genetic correlations between all exposures and their corresponding outcomes, respectively, in these eight causal relationships. Evidence of dietary effects on osteoarthritis is provided in our study, which has important implications for the prevention, management, and intervention of osteoarthritis in common sites through rational dietary modification.

Microstructural origins of impact resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy

In this work, the mechanical properties and related deformation mechanisms of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) under dynamic loading were systematically investigated at a medium strain rate range from 500 to 1500 s−1. The EHEA presents significant strain rate hardening and continuous strain hardening without any adiabatic shear bands. The yield strength increases from 803.8 MPa at 500 s−1 to 1006.8 MPa at 1500 s−1. The strain rate sensitivity and strain hardening exponent were evaluated to be 0.198 and 0.567–0.683, respectively, responding for the superior capability to withstand dynamic loading. Post-deformation microstructural analysis reveals that increased strain rate induces higher dislocation density. In the FCC phase, dislocation planar slip at {111} planes dominates at 500 and 1000 s−1, while high dense dislocation walls (HDDWs) form at 1500 s−1 from coplanar slip along {111} planes. In the BCC phase, high dense nano-precipitates result in a significant precipitate-strengthening effect, featured by arrow-shaped dislocations, dislocation loops and dislocation tangles.

Strain rate and anisotropic effects on incipient plastic deformation of Zn–Cu–Ti alloy sheets

Zinc alloys shows strong strain rate dependent and anisotropic mechanical behaviours, the mechanistic origin of which is however not fully understood. In this work, a combination of the experiments and crystal plasticity finite element simulations were used to gain an insight into the relation between deformation mechanisms, tensile deformation behaviour and texture evolution, especially for the incipient plastic deformation stage. To this end, specimens were cut from Zn–Cu–Ti alloy sheets at various orientations with respect to the rolling direction, and uniaxial tensile tests were conducted at different strain rates ranging from 10−3 to 5 × 10−2 s−1. The microstructure evolution with the deformation was examined by the electron backscatter diffraction technique. Crystal plasticity model was calibrated considering the effect of strain rate on the flow stress, and finite element simulations were carried out based on a representative volume element of the polycrystal zinc alloy. It is found out that the flow stress increases significantly, as the loading direction approaches the transverse direction, which results in a lower relative activity of basal slip and higher relative activity of non-basal ones. This, in turn, reduces the rotation of the c-axis of the crystallites towards ND during tensile tests. On the other hand, a positive strain rate sensitivity is found in the zinc alloy. Meanwhile, increasing strain rate leads to an obvious decrease in the activity of the pyramidal π-II slip systems, accompanied by more activated twinning systems. The lower activity of the pyramidal π-II slip at a higher strain rate probably hinders the development of CDRX and grain fragmentation at large strain levels.

Has FinTech changed the sensitivity of corporate investment to interest rates?—Evidence from China

Taking into account the differences in the capabilities of FinTech to process standardized and non-standardized information within the credit market, this study introduces a novel perspective: FinTech has dual opposing effects on the interest rate sensitivity of corporate investment. Utilizing data from 2010Q1 to 2020Q4 of China, we empirically test this new viewpoint using the system-GMM and dynamic panel quantile regression methods. The results indicate that, overall, FinTech enhances banks' abilities to process standardized information but does not significantly weaken their capacity to handle non-standardized information. Consequently, banking FinTech amplifies the impact of interest rates on investment. However, further heterogeneity analysis reveals that FinTech does not have a significant impact on the interest rate sensitivity of investment for state-owned enterprises. Contrary to the prevalent belief that FinTech has inclusive benefits, its positive effects on small and medium-sized enterprises (SMEs) are noticeably diminished in regions with lower degrees of marketization, where non-standardized information dominates the credit market. The study's policy implications indicate that the impact of FinTech on alleviating SMEs financing constraints in developing countries may be overstated. Effective FinTech implementation necessitates synergies with market-oriented reforms. Government focus should pivot towards market-driven institutional changes, as relying solely on technological advancements for a 'leapfrog' strategy is likely to prove challenging.

Fracture behavior of a rapidly solidified thin-strip continuous cast AA5182 Al-Mg alloy with the Portevin-Le Chatelier effect under varying strain rates

This study investigates the strain-rate triggered PLC effect and fracture behavior of a rapidly solidified thin strip (TS) cast AA5182 alloy in comparison with those of direct chill (DC) counterparts. Higher cooling rates obtained via TS casting suppress the formation of phases in Al-Mg alloys and significantly enhance the matrix solute supersaturation beyond the equilibrium level, thereby impacting the interaction dynamics of mobile dislocations and solute atoms. This in turn affects the evolution of typical stress fluctuations in Al-Mg alloys, referred to as the Portevin-Le Chatelier (PLC) effect, occurring in specific strain rate-temperature domains, i.e., with type and characteristics dependent upon the microstructure. Tensile testing demonstrated a strain-rate dependent PLC effect, also aligning with the ductility trend in both negative and positive strain-rate sensitivity domains. The characteristics of PLC bands, as well as the magnitude of stress fluctuations, were shown to evolve with strain rate, facilitating distinct fracture mechanisms. In particular, the TS sample exhibited a higher strain rate sensitivity of the fracture mechanisms and PLC band characteristics and, thus, a narrower range of deformation rates for optimum ductility (attributed to increased solute in the matrix). Controlling the deformation rate to favor predominantly Type-B serrations and ensuring their stability with minimal fluctuations was shown to postpone necking and prevent material failure. The significance of rate sensitivity in alloys with reduced microsegregation is emphasized, suggesting the need for further exploration of mechanical properties.

Effects of GLP1RAs on pregnancy rate and menstrual cyclicity in women with polycystic ovary syndrome: a meta-analysis and systematic review

PurposeThis study was aimed to assess the effectiveness of Glucagon-like peptide 1 receptor agonists on pregnancy rate, menses, anthropometric and hormonal parameters in PCOS patients.MethodsWe conducted searches of the published literature in PubMed, EMBASE, Cochrane Library, Web of Science up to September 2022. Data from randomized controlled trials were obtained to assess the effects of GLP1RAs in PCOS women. Weighted mean difference, standardized mean difference, and risks ratio were employed for effect size estimation using a random-effects model.ResultsA total of 840 patients with 469 individuals in GLP1RAs group and 371 individuals in control group from 11 RCTs were included. GLP1RAs usage was associated with an improvement in natural pregnancy rate (RR: 1.72, 95% CI 1.22 to 2.43, P = 0.002, I2 = 0%) and menstrual regularity (SMD: 1.72, 95% CI 0.60 to 2.85, P < 0.001, I2 = 95.6%). There were no statistically significant differences in total pregnancy rate, IVF pregnancy rate between two groups, but total PR elevated in a short time after GLP1RAs as shown in subgroup analysis. Randomization to GLP1RAs treatment was associated with great improvement in HOMA-IR, BMI, WC, SHBG and a slight reduction in TT compared to control group. A decrease in TBF was seen in European population. GLP1RAs monotherapy was not superior to metformin when it came to fT, DHEAS, FAI.ConclusionsPrescription of GLP1RAs improves natural pregnancy rate, menstrual cyclicity and insulin sensitivity, anthropometrics, hormonal indexes in PCOS women.

Novel nanoindentation strain rate sweep method for continuously investigating the strain rate sensitivity of materials at the nanoscale

We introduce a new nanoindentation method to continuously measure the hardness while sweeping through orders of magnitudes of strain rates within a single experiment. While nanoindentation already allows the determination of the strain rate sensitivity of materials by means of strain rate jump tests, these are typically limited to few discrete strain rates. With the new method, the strain rate sensitivity can be measured continuously as a function of the strain rate. Applications to fused silica, Zn-22 %Al superplastic alloy, single crystalline aluminum, various nanocrystalline metals and a palladium-based metallic glass are shown. Besides some discrepancy with the reference measurements, the new method seems only affected by the presence of a strong nanoindentation size effect. Provided this indentation size effect is not excessively large and can be corrected for accurately, the method proves robust, with no suggestion that the direction of the strain rate sweep affects the evaluation of the strain rate sensitivity.

Elucidating the impact of microstructure on mechanical properties of phase-segregated polyurea: Finite element modeling of molecular dynamics derived microstructures

Phase-segregated polyureas (PU) have received considerable interest due to their use as tough, impact-resistant coatings. Polyureas are favored for these applications due to their mechanical strain rate sensitivity and energy dissipation. Predicting and tailoring the mechanical response of PU remains challenging due to the complex interaction between its elastomeric and glassy phases. To elucidate the role of PU microstructure on its mechanical properties, we developed a finite element modeling framework in which each phase is represented by a volume fraction within a representative volume element (RVE). Critically, we used separate constitutive models to describe the elastomeric and glassy phases. We developed a plasticity-driven breakdown process in which we model the glassy phase disaggregating into a new phase. The overall contribution of each phase at a material point is determined by their respective volume fractions within the RVE. We applied our modeling methods to two compositions of PU with differing elastomeric segment lengths derived from oligoether diamines, Versalink P650 and P1000. Our simulations show that a combination of microstructural differences and elastomeric phase properties accounts for the difference in mechanical response between P650 and P1000. We show our model’s ability to predict PU behavior in various loading conditions, including low-rate cyclic loading and monotonic loading over a wide range of strain rates. Our model produces microstructure transformations that mirror those indicated by small-angle X-ray scattering (SAXS) experiments. Fourier transform analysis of our RVEs reveals glassy phase fibrillation due to deformation, a finding consistent with SAXS experiments.

Change in auditory and visuospatial working memory with phases of menstrual cycle: A prospective study of three consecutive cycles

The menstrual cycle is a well-known physiological model used to study working memory (WM) function. The present study examined auditory and visuospatial WM during proliferative and secretory phases of three consecutive menstrual cycles. Forty young adult females with a mean age of 23.4 ± 4.2 years and a history of regular menstrual cycle were selected for this study. Computerized software-based dual-task n-back WM tasks were performed by each participant during the proliferative (day 10th – 14th) and secretory phases (day 21st – 25th) of the menstrual cycle. The above tasks were repeated for three consecutive menstrual cycles during follow-up. Data from the three menstrual cycles were pooled and compared between the proliferative and secretory phases. Significant differences were observed in the hit rate (p = 0.006), Z score (p = 0.004) and parametric sensitivity (p = 0.005) of visuospatial targets and Z score (p = 0.037) and parametric sensitivity (p = 0.028) of auditory targets with better performance during the secretory phase. However, no significant differences were found across the three proliferative or three secretory phases, indicating that the results were consistent across consecutive cycles. This study concluded that visuospatial and auditory WM skills were significantly improved during the secretory phase compared to the proliferative phase of the menstrual cycle.

Strengthening mechanisms and microstructural evolution of medium manganese steel under dynamic and static loading

The study analyzes the deformation strengthening mechanisms of medium manganese steel under dynamic and static loading conditions. Different austenite volume fractions (7.4 %, 19.1 %, 30.9 %, 37.7 %) were obtained by varying the heat treatment temperatures (640 °C, 660°C, 680 °C, 700 °C). Results show a linear increase in austenite volume fraction with higher annealing temperature, while carbon content in austenite decreases. Yield strength initially decreases and then increases with annealing temperature. The mechanical properties of all four temperature-tested steels show a clear strain rate dependence in the high strain rate range, with strength increasing with strain rate. Quasi-static conditions no significant strain rate sensitivity. 680 °C test steel's quasi-static deformation is mainly governed by the transformation-induced plasticity (TRIP) effect and dislocation slip in body-centered cubic (bcc) crystals. Dynamic deformation after a strain of 0.14 shows a weakened TRIP effect, and dislocation strengthening in bcc crystals becomes dominant despite a large amount of untransformed austenite. During quasi-static deformation, 700 ℃ test steel exhibits strain hardening due to the TRIP effect at low strains and significant dislocation strengthening in bcc crystals at high strains. Although the TIRP effect is initially suppressed during dynamic deformation, it lasts for a long time. The combined effects of the TRIP effect and martensite dislocation strengthening determine the deformation strengthening mechanisms. Additionally, an optimized Voce model with strain rate strengthening term is proposed. It can well describe the mechanical behavior under dynamic strain rate.

Simple Contact Sensor for Material on Die in Sheet Hydroforming

A simple material contact sensor on the forming tool was devised for sheet hydroforming. The applicability was investigated for the shallow forming of aluminum alloy sheet. A flat bottom axisymmetric die or a conical one was used. An antistatic electric tape was used as contact sensor. It is flexible and attached to the die cavity in the radial direction. Electrical resistance of the tape between the center and the contact position of the material changes as the forming progresses. The change in voltage of the resistance part corresponding to the contact length was captured continuously. The strain at the center of the circular test piece was also continuously measured using a strain gage for large deformation. A short contact length was captured for the flat bottom die, since the test piece deforms into a dome shape, and the tip of the dome contacts to the center of the die cavity. On the other hand, the captured length was longer in the forming with the conical die. The repetitive separation and contact motion of the test piece to the die in impact forming due to the impulsive water pressure was successfully captured by the contact sensor. The accuracy was relatively coarse due to that the diameter of the die cavity was small. However, it was found that the simple contact sensor can be applied to evaluate the deformation behavior of the material. The measured maximum strain of the test piece was larger in impact forming, and the strain concentration occurred. This may be due to the negative strain rate sensitivity of the material.

Dynamic mechanical properties of concrete with freeze-thaw damage under different low-temperature conditions

The mechanical properties of hydraulic concrete structures in cold regions are affected by low temperature and freeze-thaw cycles, and their mechanical properties differ greatly compared with those of the room temperature state. Especially for concrete structures with being susceptible to dynamic loads such as earthquakes and collisions, the mechanism involved the effect of low temperature on the dynamic mechanical properties of concrete with freeze-thaw damage is still not clear. The design of different low-temperature environment containing different freeze-thaw damage of concrete dynamic load tests are conducted to reveal the change patterns of dynamic mechanical properties of concrete with initial freeze-thaw damage in the low temperature range of 0 °C ∼ −30 °C. The results show that low-temperature conditions can improve the concrete compactness, and weaken the enhancement effect of high strain rate loading conditions on the concrete strength, which will reduce rate sensitivity of the mechanical properties. Meanwhile, the effect of low temperature can improve the brittleness and compressive strength of concrete and make up for part of the strength loss caused by freeze-thaw damage, and containing different freeze-thaw damage in the mechanical properties of the concrete gap with the reduction of the temperature gradually narrows. Quadratic function relationship exists between temperature and compressive strength together with other mechanical parameters, and the minimum value of R2 is 0.9721. The stress-strain relationship curve of concrete under low-temperature condition is narrowed, and the brittleness of concrete increases; the damage process becomes more intense, the integrity of concrete is high after the damage, and the number of cracks on the fracture surface decreases significantly.

Effect of microstructural evolution during melt pool formation on nano-mechanical properties in LPBF based SS316L parts

Laser Powder Bed Fusion (LPBF) based SS316L parts have a wide range of industrial applications, mainly due to their high strength and good structural integrity. However, there is a lack of nano-mechanical studies related to microstructural evolution. The SS316L cubes were examined for grain orientation and phase transformation with the help of OM and FESEM with EDX analysis. Cellular and columnar grains were substantiated by FESEM with EDX. Further, the δ ferrite and γ austenite phases occurrence was evident in XRD analysis. The orientation of grains was further examined through EBSD analysis. The microstructural transformation was substantiated by mapping based on modulus. Cellular grains showed a maximum hardness of 6 Gpa, whereas the transverse columnar grains displayed a minimum elastic modulus of 105.8 GPa. Nano-wear and scratch analysis predicted the functions caused by the occurrence of cellular dendritic microstructure, and the topographic wear and scratch tracks confirmed the soft nature of transverse columnar grains by forming more pile-up of materials. Strain Rate Sensitivity (SRS) of the SS316L specimens was analysed based on three different strain rates (4.1 ×10−5 s−1, 2.08 ×10−4 s−1 and 3.3 ×10−4 s−1). It was concluded that the LPBFed SS316L parts possessed a negative strain rate. In contrast, the simultaneous attainment of maximum Ultimate Tensile Strength (UTS) and ductility was possible in the quasi-static strain rate.

Studies on flow stress behaviour prediction of AZ31B alloy: Microstructural evolution and fracture mechanism

The hot tensile flow behaviour of the AZ31B alloy is investigated at various varying deformation temperatures (200–350 °C) and strain rates (0.1s−1, 0.01s−1, and 0.001s−1). The deformation condition significantly influenced the mechanical properties and microstructural evolution. Observation from the tensile tests indicated a strong dependence of flow stress on deformation temperature and strain rates. At a constant strain rate, flow stress decreased as the temperature increased, while at a constant deformation temperature, flow stress decreased with decreasing strain rates. The strain rate sensitivity varies from 0.01 to 0.25, suggesting a diffusion-controlled dislocation climb mechanism. Dynamic recrystallization (DRX) initiation was observed at 250 °C and a strain rate of 0.001s−1, characterized by the formation of necklace-type grains with low pole intensity. Predominantly, the DRX softening mechanism, including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX), was observed at 350 °C and 300 °C for a strain rate of 0.001s−1. Fracture morphology analysis of the tested samples indicated a micro-void coalescence mechanism. Equiaxed dimples were found at 350 °C and a strain rate of 0.001s−1, while oval-shaped dimples were observed at 300 °C and 0.1s−1. A strain-compensated Arrhenius model was incorporated to estimate the flow stress prediction for hardening and softening regions. Statistical parameters such as the average absolute relative error (AARE = 13.50) and coefficient of determination (R = 0.97) were calculated. Good agreement between experimental and prediction stresses was achieved at a 0.001s−1 strain rate for all deformation temperatures.

An insight into mechanical response and twinning behavior of bimodal textured AZ31 magnesium alloy under quasi-static and high strain rate compression

In this work, the dynamic, quasi-static response and twinning behavior of bimodal textured Mg–3Al–1Zn alloy is comparatively investigated at room temperature. The relationship between yield stress and bimodal texture is quantified and characterized as an increase of the yield stress with the increasing of the percentage of <0002>⊥ED (extrusion direction) component; the ultimate strength under high strain rate (103 s−1) was quite higher than that under quasi-static condition (10−3 s−1); but, the yield stress was just the reverse. The competition between twin nucleation and growth is significantly affected by a coupled effect of strain rate and texture. Twin nucleation shows positive strain rate sensitivity and is largely enhanced by dynamic deformation. However, the twin growth tendency is bimodal texture and strain rate dependent: it is favorable under quasi-static condition for samples with more soft orientations, while for samples with more hard orientations, dynamic deformation promotes twin growth. It is also found that a higher strain rate can stimulate the activation of more twin variant types in bimodal textured magnesium alloys.

Effect of C on the superplasticity of medium Mn steel

We investigated the effect of C content on the superplasticity of medium Mn steel through high-temperature tensile testing of Fe–7Mn-(0–0.35)C (wt%) steels at temperatures ranging from 490 °C to 720 °C with an initial strain rate of 1.0 × 10−3 s−1. Superplasticity became evident at 550 °C for C-added steels and at 634 °C for the C-free steel. As all the C-added steels exhibited the highest elongation at 650 °C, we conducted in-depth analyses using the specimens tested at 650 °C. The elongation significantly increased with increasing C content up to 0.20 wt%. The results of strain rate sensitivity, apparent activation energy, and microstructural observations indicated that the low elongation of the 0C steel was attributed to the occurrence of dislocation creep, whereas the high elongations of both 0.10C and 0.20C steels were due to the occurrence of grain boundary sliding. The 0.20C steel exhibited higher elongation than the 0.10C steel due to its smaller average grain size and a larger area of α/γ interphase boundaries compared to the 0.10C steel. Meanwhile, the elongation of the 0.35C steel was not significantly improved compared to the 0.20C steel, despite having a smaller average grain size. This was because the 0.35C steel had a lower area of α/γ interphase boundaries, which resulted from the higher γ fraction. We believe the optimal C content for enhancing the superplasticity of Fe–7Mn steel is approximately 0.20 wt%, considering the 0.35C_T steel requires an additional tempering process, and its elongation was comparable to the 0.20C steel.

An integrated computational and experimental study of the failure mode in Mg/Al laminated composite under three-point bending

The deformation behavior of hot-roll-bonded Mg/Al laminated metal composites (LMCs) is investigated, focusing on the crack formation around the interface. The material demonstrates a positive strain rate sensitivity mainly arising from the Mg matrix. A diffusion layer was formed at the Mg/Al interface with a serrated morphology during the two-pass rolling process, which consists of the Al3Mg2 and Mg17Al12 phases. The mechanical responses of the LMCs are evaluated using uniaxial tension, interfacial debonding tests (in normal and shear modes), and microstructure characterization techniques, which clarify the interfacial heterogeneity. The fracture constants of the interface were calibrated and incorporated in the finite element models to predict the failure modes of heterogeneous Mg/Al interface under three-point bending. With the increased thickness ratio of the Mg layer, the damage accumulation rate decreases at the interface and increases in the Mg matrix. As a result, the failure mode transferred from interface failure to matrix fracture. The findings of the present work provide new insight into the failure mechanism in laminated metal composites under bending conditions and can provide theoretical guidance for the plastic forming of such materials.

Excellent dynamic properties and corresponding deformation mechanisms in a microband-induced plasticity steel with dual-heterogeneous structure

A dual-heterogeneous structure with dual phases and heterogeneous grains was designed in a high Mn microband-induced-plasticity (MBIP) steel. The heterogeneous structured sample exhibits similar dynamic shear yield strength, while exhibiting enhanced dynamic uniform shear strain and dynamic shear toughness by 36 % and 47 %, respectively, as compared to the homogeneous structured sample. The strain hardening mechanisms contributing to the excellent dynamic shear properties in the heterogeneous structured sample have been revealed. Firstly, the superior hetero-deformation-induced hardening capability of the heterogeneous structured sample arises from a higher density of geometrically necessary dislocations induced in each phase. Secondly, a pronounced strain rate effect is observed in body-centered cubic (BCC) grains and face-centered cubic (FCC) ultra-fine grains, leading to an elevated level of strain rate sensitivity. Finally, the MBIP effect is also observed in FCC coarse grains under dynamic loading. Moreover, the MBIP effect in FCC ultra-fine grains is more likely to occur at high strain rates due to the emergence of single-wall domain boundaries, which is not observed during quasi-static tensile testing. The present results provide new routes for designing impact-tolerant structures in advanced metals and alloys.

Effect of N on hot deformation behavior of high-Mn austenitic steel

The present study dealt with the hot compression deformation behavior of Fe−18.5Mn–7Cr−0.6C and Fe−18.5Mn–7Cr−0.6C−0.21 N high-Mn austenitic steels within a temperature range of 900–1200 °C, a strain rate range of 0.01–5 s−1, and a true strain of 0.7. The accurate constitutive equations were established according to their flow curves, and the deformation microstructures were also analyzed. The results revealed that the dominant softening mechanism for the two test steels without substantial peak stress (higher Zenger-Holloman parameter values) could also be dynamic recrystallization (DRX) rather than dynamic recovery (DRV). The addition of N enhanced the strain rate sensitivity of high-Mn austenitic steel at low temperatures and high strain rates. Furthermore, the addition of N increased the high temperature strength and hot deformation activation energy (Q) of high-Mn austenitic steel. Moreover, the addition of N could also increase the DRX volume fraction and refine the DRX grain size of high-Mn austenitic steel.

Effect of strain rates on mechanical behavior, microstructure evolution and failure mechanism of extruded-annealed AZ91 magnesium alloy under room-temperature tension

Loading rate is usually considered as a significant factor affecting formability of AZ91 magnesium alloy structural components. Herein, uniaxial tensile tests are conducted on extruded-annealed AZ91 alloy under room temperature with strain rates ranging from 1 × 10−4 s−1 to 1 × 10−2 s−1. Mechanical properties, microstructure characteristics, and fracture morphologies tensioned at these different strain rates are investigated. Extruded-annealed AZ91 alloy exhibits a positive strain-rate dependence of strength and a negative strain-rate dependence of elongation. With strain rate increasing, strain rate sensitivity basically decreases while strain-hardening rate increases. At higher strain rate, the larger strength is mainly attributed to the more rapid accumulation of dislocation and the larger dislocation density, and the lower elongation is mostly owing to the more elevated level of inhomogeneous deformation related with dislocations accumulation. As strain rate increases, the area fraction of basal texture increases while that of prismatic and pyramid texture decreases in tensioned samples, which is associated with the dominant room-temperature deformation mode of basal-slip and twinning co-induced lattice rotation. With tension strain rate increasing, there are three kinds of fracture modes including ductile facture with more and deeper dimples at low strain rate, ductile-brittle facture with some dimples and cleavage planes at mediate strain rate and brittle facture with dominant cleavage planes at high strain rate.