Low Strain Rates Research Articles

Mechanical response in tension of twin-induced Mg alloys in wide strain rate regimes

Effect of twin boundary with/without segregation of solute atoms on deformation behavior in tension is examined in Mg–3Al–1Zn (AZ31) alloys from low strain rates to high strain rates. Solute atoms (Al and/or Zn atoms) are segregated at {10 1‾ 2} twin boundaries by static annealing at a temperature of 423 K with a holding time of 150 min. The room-temperature tensile mechanical response of the specimens, which have pre-induced twin boundaries, shows detwinning behavior, regardless of the strain rate between 10−5/s and 100/s. The yield strength of these specimens is also unlikely to be affected by strain rate, because twin boundary mobility, i.e., the shrinkage, is an athermal process. On the other hand, the specimen with segregating of solute atoms at twin boundaries exhibits an increased strength and a decreased strain hardening as compared with those in the specimen having non-segregated twin boundaries. Newly formed deformation twins of several types, i.e., the {10 1‾ 2} twins, {101‾ 1} twins and {101‾ 2}-{101‾ 1} double twins, are the origin of fracture in these specimens.

A physically based constitutive model considering dynamic recrystallization of ERNiCrMo-3 alloy

ERNiCrMo-3 alloy is widely used in the welding of nickel-based alloys. This study investigated the hot deformation and discontinuous dynamic recrystallization (DRX) behavior of ERNiCrMo-3 alloy through hot compression tests at deformation temperatures ranging from 990 °C to 1170 °C and strain rates ranging from 0.01 to 10 s−1. Experimental results showed that under conditions of elevated temperatures and lower strain rates, discontinuous dynamic recrystallization was prone to occur upon reaching critical strain, and the distribution of carbide and nitride particles within the alloy matrix affects recrystallization nucleation and grain boundary migration. A two-stage constitutive model was established based on classical dislocation density theory and DRX kinetics. Comparison between predicted and experimental data demonstrated a strong agreement, highlighting the accuracy and utility of the proposed constitutive model.

Development and validation of a nomogram superior to CHADS2 and CHA2DS2-VASc models for predicting left atrial appendage dense spontaneous echo contrast/left atrial appendage thrombus.

Atrial fibrillation (AF) is one of the most frequently encountered arrhythmias in clinical practice, with stroke triggered by detachment of left atrial appendage thrombus (LAAT) after AF being its most critical complication. The purpose of this study was to construct a nomogram model for forecasting left atrial appendage (LAA) dense spontaneous echo contrast (SEC) and LAAT to accurately identify patients at high risk for stroke. A retrospective analysis was conducted on 433 patients with AF receiving transesophageal echocardiography (TEE) in the First Affiliated Hospital of Soochow University from October 2019 to July 2022. These patients were assigned into a non-dense SEC/LAAT group or a dense SEC/LAAT group. We constructed a nomogram model dependent on the odds ratios (ORs) of logistic regression and subsequently compared its performance with two models, CHADS2 and CHA2DS2-VASc. Female gender, high D-dimer level, low left ventricular ejection fraction, low left atrial ejection fraction, and low left atrial reservoir strain rate were found to be independent factors for predicting LAA SEC/LAAT, with OR values and 95% confidence intervals of 2.811 (1.445-5.469), 2.460 (1.230-4.921), 0.961 (0.927-0.996), 0.950 (0.932-0.967), and 0.173 (0.035-0.848), respectively. The consistency statistic of the nomogram based on these given predictive factors was 0.921, and the calibrated consistency statistic was 0.903. According to receiver operation curve analysis and decision curve analysis, the nomogram was demonstrated to be superior to the CHADS2 and CHA2DS2-VASc models in predicting LAA dense SEC/LAAT. The net reclassification improvement and integrated discrimination improvement of the nomogram were 0.449 (0.324-0.575) and 0.461 (0.408-0.515), when compared with the CHADS2 model, and were 0.521 (0.411-0.632), and 0.432 (0.400-0.504), respectively, when compared with the CHA2DS2-VASc models. The nomogram model constructed in this study demonstrated excellent performance in predicting LAA dense SEC/LAAT, displaying a superior ability to that of the CHADS2 and CHA2DS2-VASc models.

Crystallographic texture and multiscale boundaries mediated creep anisotropy in additively manufactured Ni-based Hastelloy C276 superalloy

The microstructure and high-temperature creep mechanisms of Ni-based Hastelloy C276 superalloy fabricated using wire and arc-based directed energy deposition were investigated systematically and innovatively. The microstructural investigation revealed that the as-fabricated samples comprise γ-Ni matrix and topologically close-packed (TCP) P phase precipitates. The γ matrix subgrains and grains are spread over multiple highly textured columnar dendrites, with a majority of γ <001> crystallographic orientations closely aligned along the deposition direction. Moreover, the interdendritic regions exhibit severe Mo segregation, P phase particles, and dislocation bands. Creep tests were conducted on miniature samples under various temperature and stress conditions, loaded either in the deposition direction (DD) or travel direction (TD). DD samples exhibit lower minimum strain rates, greater strains-to-failure, and longer creep rupture lifetimes than TD samples, indicating significant creep anisotropy. Dislocation creep was identified as the primary creep mechanism for both DD and TD conditions. During creep, dynamic precipitation of TCP phases occurred in the interdendritic regions, resulting in varying creep resistance between interdendritic and dendritic core regions. Isostress and isostrain models, considering both crystallographic texture and precipitation strengthening, reasonably predicted the observed creep anisotropy during the secondary creep stage. Additionally, variations in the Schmid factor led to significant deformation incompatibility among dendrites in TD samples. Dislocation accumulation in TD sample interdendritic regions promoted new grain nucleation, triggering dynamic recrystallisation, facilitating grain boundary sliding, and accelerating tertiary creep. Furthermore, TCP phase particles in the interdendritic regions contributed to microcrack development, further accelerating creep fracture, especially in the TD condition.

Characterization of hot workability of a Cu containing high strength low alloy steel using processing map

Hot workability of an experimental Cu containing martensitic high strength low alloy (HSLA) steel was characterized by conducting isothermal hot compression tests at different temperatures (900–1100 °C) and strain rates (0.0003–1 s−1). Flow curves exhibits predominantly single peak behaviour at temperatures for a strain rate > 0.01 s−1. At temperature > 950 °C and for low strain rates of 0.0003 and/or 0.001 s−1, multiple peaks characterised by oscillations in flow stress was observed. The strain rate sensitivity (m), temperature sensitivity (S) of the material was calculated and the processing map was developed to identify optimum condition for thermo-mechanical processing. The material exhibits three suitable processing windows in temperature – strain rate space viz., (1) 1050–1100 °C; 0.1–0.01 s−1 (2) 980–1020 °C; 0.1–1 s−1 and (3) 980–1020 °C; 0.001–0.0003 s−1. The microstructure of the material deformed under all the above mentioned processing conditions exhibited defect free equiaxed dynamically recrystallized grains with an average grain size of 30–40 μm. Any or combination of these processing conditions can be used by the industry for designing suitable forging process (roughing, finishing etc.) based on the infrastructure available. Further, using Avrami approach, the effect of strain, strain rate and temperature on the kinetics of dynamic recrystallization (DRX) was also evaluated. The results obtained are presented and discussed.

Deformation behavior of SmCo compounds via amorphization and recrystallization

In recent years, nanocrystalline magnets based on the critical single domain size theory have received increasing attention. However, nanocrystalline magnets are difficult to enhance the remanent magnetization by forming textures with conventional magnetic field orientation. Texturing of nanocrystalline magnets is usually done using the hot pressing and hot deformation technique, but there are some difficulties in applying this technique to form texture in SmCo systems. To discover and solve the difficulties of obtaining texturized nanocrystalline SmCo-based magnets during the deformation process, samarium cobalt magnets with different degrees of deformation were first experimentally prepared by low strain rate hot deformation method. Then, molecular dynamics simulations were utilized to study the microstructural changes and the multi-phase formation process during hot deformation. The process of deformation together with the reason why it is difficult to form textures in SmCo systems by low-temperature hot deformation is discussed, and the strain energy densities of SmCo multiphase in multiple directions were calculated, which gives a feasible method to form low-temperature hot deformation textures in SmCo systems experimentally.

Effect of Strain Rate on Hydrogen Embrittlement of Ti6Al4V Alloy.

The phenomenon of hydrogen embrittlement (HE) in metals and alloys, which determines the performance of components in hydrogen environments, has recently been drawing considerable attention. This study explores the interplay between strain rates and solute hydrogen in inducing HE of Ti6Al4V alloy. For the hydrogen-charged sample, as the strain rate was decreased from 10-2/s to 10-5/s, the ductility decreased significantly, but the HE effect on mechanical strength was negligible. The low strain rate (LSR) conditions facilitated the development of high-angle grain boundaries, providing more pathways for hydrogen diffusion and accumulation. The presence of solute hydrogen intensified the formation of nano/micro-voids and intergranular cracking tendencies, with micro-crack occurrences observed exclusively in the LSR conditions. These factors expanded the brittle hydrogen-damaged region more deeply into the interior of the lattice. This, in turn, accelerated both crack initiation and intergranular crack propagation, finally resulting in a considerable HE effect and a reduction in ductility at the LSR. The current study underscores the influence of strain rate on HE, enhancing the predictability of longevity and improving the reliability of components operating in hydrogen-rich environments under various loading conditions.

Geochemical Characteristics of Thermal Springs and Insights Into the Intersection Between the Xiaojiang Fault and the Red River Fault, Southeastern Tibet Plateau

AbstractDuring the ongoing uplift and expansion of the southeastern margin of the Tibetan Plateau, the front edge of the Sichuan‐Yunnan rhombic block (SYB) has experienced intense tectonic activity and frequent seismicity. In this study, the fluid geochemistry in the primary active faults at the front edge of the SYB was investigated, with the aim of understanding the tectonic activity and intersection relationship between the Xiaojiang fault (XJF) and the Red River fault (RRF). Thermal spring water and gases exhibit a coupled spatial distribution relationship; relatively high ion concentrations and 3He/4He ratios (Rc/Ra ratios of 0.21 to 0.62Ra) are observed along the RRF, Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Multidisciplinary research results have indicated that mantle‐derived intrusion has been detected in the crust beneath the QJF and SJF. The current tectonic activity in the front edge of the SYB remains intense, with compressive stresses shifting toward the western side of the XJF and accumulating on the QJF and SJF. This has led to the development of fractures, enhancing the water–rock interaction and deep‐derived gas degassing along the faults. The unmixing characteristics of fluids at the intersection area of these two faults suggest the absence of conduits for fluid migration between the faults. Owing to the lower gas 3He/4He ratios, lower shear strain rates, stable reservoir temperature field, and extremely low historical seismicity in the Indo‐Chinese block, it is speculated that the current movement of the XJF may not cut through the RRF and continue southward.

A combined EBSD and machine learning study of predicting deformation twinning in BCC Fe81Ga19 alloy

Compared to face-centered cubic (FCC) metals, body-centered cubic (BCC) metals demonstrate more intricate deformation behavior and microstructural characteristics because of the influence of intrinsic unstable stacking faults and defect structure. To investigate the unique phenomenon of deformation twinning in Fe81Ga19 alloy with BCC structure at moderate temperature and low strain rate, four twin nucleation models were constructed using a combination of electron backscatter diffraction (EBSD) technique and machine learning. These models are aimed to predict twin nucleation of grains and explore the relationship between twin nucleation and microstructural attributes. The study revealed that amongst the 235 grains analyzed during in-situ compressive deformation, 32 grains experienced twinning. Nine attributes influencing twin nucleation were selected and ranked according to their importance. Grain area, average image quality, neighboring grain count, and the Schmid factor of twinning systems exhibited significant influence on twin nucleation. Decision tree and tree ensemble (XGBoost) achieved 94% and 96% accuracy, respectively, on the test set, showcasing robust generalization capability. Due to the optimization of hyperparameters, support vector machine (SVM) and artificial neural network (ANN) exhibited outstanding performance. The ANN model achieved an accuracy of 97% and an F1 score of 0.91 on the test set, while the SVM model achieved an accuracy of 98% and an F1 score of 0.94, indicating superior performance. Furthermore, the study revealed that the twinning stress in Fe81Ga19 alloy exhibited weak responsiveness to temperature during deformation, and the intrinsic factors of grains were identified as crucial factors influencing twin nucleation.

Effects of pressurized water reactor environment and cyclic loading parameters on the low cycle fatigue behavior of 304L stainless steel

Austenitic stainless steels used in light water reactor coolant environments are susceptible to environmentally assisted fatigue due to non-monotonic loading conditions, primarily associated with load-follow, thermal transients, or intermittent plant shutdowns and start-ups. This study investigates the effects of a high-temperature pressurized water reactor (PWR) water environment and cyclic loading parameters on the low cycle fatigue behavior of austenitic 304L stainless steel. Prolonged exposure to a PWR environment and cyclic loading conditions such as a lower strain rate or a higher fraction of slow strain rate enhances the initiation and accelerates the crack growth rate of fatigue cracks, resulting in decreased fatigue life. The deformation-induced α'-martensite is observed in proximity to fatigue crack tips primarily in specimens tested in simulated PWR primary water, while cellular dislocation structures are more frequently observed near crack tips in specimens tested in high-temperature air. The deformation-induced martensitic transformation from γ-austenite to α'-martensite, occurring via the precursor ε-martensite phase, contributes to the accelerated fatigue crack growth rate in a PWR environment with hydrogen.

Effect of Copper Powder Addition on Microscopic Deformation Behavior of Al2O3/Cu‐Dispersion‐Strengthened Copper‐Sintered Billet

In this work, it is aimed to improve the deformation ability of the Al2O3 dispersion strengthened copper sintered billet by building heterogeneous structure with addition of different sizes of particle. Using the modified mixture model and equal work law, the stress distribution model of heterogeneous materials is derived. In the results, it is shown that higher deformation temperature and lower strain rate are conducive to steady deformation. Under the conditions of 950 °C and 0.01 s−1, the stress distribution coefficients from low to high are 10, 25, and 5 μm, respectively, when the strain is 0.1. The strain contribution rates of softness of the sintered billet are 45.5%, 62.1%, and 42.6%, respectively. The addition of 10 μm particle size copper powder can significantly improve the deformation capacity of the sintered billet. It is found that with the increase of the particle size of copper powder, the density of the microgeometrically necessary dislocation of the hot extrusion dispersed copper is lower. The reason is that the different particle size of copper powder leads to the different distribution in powder stacking, which affects the difficulty of harmonizing the deformation of soft and hard and the number of dislocation in the hot‐extrusion process of sintered billet.

Study on hot compressive deformation behavior and microstructure evolution of G13Cr4Mo4Ni4V steel

To solve the problem of poor uniformity of microstructure of high alloy bearing steel G13Cr4Mo4Ni4V after rolling, the deformation behavior of the steel and its effect on the microstructure evolution was studied systematically. Gleeble-3800 thermo-mechanical simulator was used for precise control of deformation temperature ranging from 1000 to 1200 °C and deformation rate 0.01–10 s−1. Based on modified stress and strain curves by temperature and friction, the processing map of tested steel was drawn. Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) were used to analyze the typical microstructure and carbide properties of different hot working domains respectively. The results showed the processing map could be divided into four regions: domain A 1000–1150 °C, 0.1–10 s−1; B 1000–1100 °C, 0.01–0.1 s−1; C 1100–1150 °C, 0.01–0.1 s−1 and D 1150–1200 °C, 1–10 s−1. Domain A was characterized by incomplete dynamic recrystallization (DRX) which included fine recrystallized grains and elongated deformed grains, whose softening mechanism was mainly discontinuous DRX (dDRX) and limited DRV and continuous DRX (cDRV) related to the ferrites and carbides. For domain B, the deformed grains gradually disappear with temperature rising, instead serrated grains appear with dDRX as dominating softening mechanism. A large number of carbides hinder DRX at 1000 °C with low temperature. With the increase of temperature, carbides dissolve and DRX degree increases. Grain coarsening is obvious because of high deformation temperature and low strain rate in domain C, although the nanoscale MC type carbides prevent recrystallization grain coarsening to some extent. Completely DRX resulted in uniform and fine with defect-free deformation microstructure in domain D, whose volume fraction of recrystallization reached up to 0.96 according to EBSD results. By considering the uniformity of microstructure and the distribution of carbide comprehensively, domain D is an ideal region for hot working.

Atomistic insights into the mechanical properties of cross-linked Poly(N-isopropylacrylamide) hydrogel

Poly(N-isopropylacrylamide) (PNIPAM) is a highly versatile thermo-responsive hydrogel with immense potential for applications in biomedicine and tissue engineering. While PNIPAM has been extensively researched, there remains a significant gap in understanding its mechanical behavior at the atomistic scale. To address this challenge, this study employs molecular dynamics (MD) simulations to delve into the mechanical response of cross-linked PNIPAM hydrogels. The uniqueness of this research lies in our emphasis on providing atomic-level insights into the influence of chemical cross-linking and physical entanglements, as well as quantifying their effects during the application of strain. This represents a novel contribution to the study of hydrogels. MD simulations enable us to scrutinize the behavior of individual polymer chains and their intricate interactions in unprecedented detail, shedding light on microscale phenomena that are often inaccessible through experiments alone. To tackle the complexities associated with atomistic simulations of cross-linked hydrogels, we introduce a dynamic cross-linking algorithm. This innovative approach incorporates a nonreactive force field to construct realistic three-dimensional hydrogel microstructures, employing a stepwise bond formation strategy. Our findings underscore the remarkable impact of increasing the Degree of Cross-linking (DoC) and/or the Degree of Polymerization (DoP) on enhancing the robustness and elastic modulus of PNIPAM hydrogels. Additionally, we uncover the stochastic nature of chemical cross-linking, leading to the formation of anisotropic super-fragments when DoC exceeds a critical threshold. Furthermore, this research highlights the pivotal role of low strain rates on the order of 106 s−1 in accurately modeling the mechanical properties of hydrogels using MD simulations. This approach enables us to obtain meaningful quantitative mechanical properties that align with experimental results reported in the existing literature. In summary, this paper offers an unprecedented level of insight into the intricate interplay of chemical cross-linking and physical entanglements, providing a foundation for future research in this domain.

Compressive mechanical response and microstructures in low strain rate plastic deformation of stainless steel 316L fabricated by selective laser melting

Characterization of the mechanical properties plays an essential role in the post-processing and evaluation of the functionality of the additively manufactured metallic parts. A number of studies have been focused on the tensile properties of additively manufactured metals. However, the quasi-static compression test of the additively manufactured 316L blocks with different heat-treatment conditions and scanning strategies seems to be overlooked in the literature. This paper aims to provide a comprehensive study of compressive mechanical response in plastic deformation of SS316L fabricated by selective laser melting (SLM). The mechanical response and microstructures in compressive deformation is analyzed for three printing strategies with 0°-, 90°- and 67.5°- scanning and three heat treatment conditions (450 °C for 3 h, 1100 °C for 1 h with furnace cool and 1100 °C for 1 h with water quenching) for selective laser melted (SLMed) stainless steel 316L in comparison with wrought stainless steel 316L in this work. Alteration of mechanical properties, microstructure evolution and compressive deformation mechanism is studied. Melt pool features are not significantly affected by low-temperature heat treatment (450 °C for 3 h) but fully dissolved through high-temperature heat treatment (1100 °C for 1 h). High-temperature heat treatment provides a higher resistance to compressive plastic deformation for SLMed 316L compared with the low-temperature heat-treated and as-built samples where more twinnings are observed. The compressive plastic deformation mechanism of 90°- and 67.5°-scanning samples is similar, which mainly results from twinning-induced plasticity. For 0°-scanning samples, the strong crystallographic texture is the main cause of anisotropic deformation. Modelling and simulation have been conducted to explain the anisotropic deformation mechanism of the 0°-scanning strategy. Simulation results suggest that the morphology difference of laser-scanning tracks and melt pools, which leads to material flow along the laser scanning direction, explains the anisotropic deformation mechanism.

Mechanical properties of thermally damaged mortar under coupled static-dynamic loading

In buildings that experience fires, cement mortar is subjected to high-temperature environments and not only the weight of the structure above but also blast loads, leading to structural damage and loss of load-bearing capacity. To investigate the static and dynamic mechanical properties of thermally damaged mortar, a series of tests utilizing modified split Hopkinson pressure bar were conducted. These tests included quasi-static, conventional dynamic and coupled static-dynamic loading tests on mortar specimens that were subjected to seven temperature levels: 20°C, 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C. The test results revealed that both the thermal damage and loading method had an impact on the mechanical properties and damage characteristics of the mortar specimens. The compressive strength, elastic modulus and absorbed energy ratio of mortar decreased as temperature increased. Notably, the quasi-static strength loss rate was 60% when the temperature reached 600°C. Under coupled static-dynamic loading, the specimens exhibited higher strength, elastic modulus, reflected energy ratio, and transmitted energy ratio. Conversely, they had lower average strain rates and absorbed energy ratios. Intriguingly, the dynamic growth factor had a relative increase of 0.7–2.0 compared with other loading methods. Furthermore, the higher temperature, the higher fragmentation of the specimens in the fragmentation pattern. Conventional dynamic loading resulted in the greatest degree of fragmentation. The findings provide a scientific basis for the design and evaluation of concrete shockproof and explosion-resistant structures.

Dynamic tensile properties of flax fiber reinforced polymer composites

Flax fibers have been widely used as reinforcing materials due to the growing demand for the development of sustainable materials. They are cost-effective and have excellent mechanical properties. In this study, the dynamic tensile properties of flax FRP coupons were tested using an Instron VHS high rate testing system. The effect of strain rate on the failure process, failure modes, tensile strength, failure strain, and Young’s modulus of flax FRP coupons were discussed and analyzed within the strain rate less than 164.2 s−1. The failure process at different strain rates were captured by a high-speed camera. It was observed that the specimen failed with only one cross-sectional fracture at a relatively low strain rate. At a relatively high strain rate, more than one fracture was observed. The experimental results indicated that the dynamic tensile strength increased, failure strain decreased, and Young’s modulus remained almost unchanged when the strain rate was less than 41.3 s−1. As it was over 41.3 s−1, the dynamic tensile strength, failure strain, and Young’s modulus had a prominent rise. To describe the dynamic tensile strength, failure strain, and Young’s modulus at a certain strain rate, empirical equations based on the experimental data were proposed for reference.

A test on methods for Mc estimation and spatial-temporal distribution of b-value in the eastern Tibetan Plateau

Seismic b-value is one of the most important parameters for seismological research and seismic hazards assessment, while the accuracy of the b-value largely depended on the completeness of seismic catalog. This article compares eight methods for estimating the minimum magnitude of completeness (Mc). The results indicate that the modified maximum curvature method (MMAXC), exhibits greater stability and accuracy, closely approximating the standard Mc obtained from the synthetic seismic catalogs. We then calculate the b-value using the instrumental seismic catalog from 2000–2023 in the eastern Tibetan Plateau. The results indicate that the five major earthquakes occur in regions with lower b-value. In addition, the temporal evolution of b-value before and after major earthquakes exhibits a common trend of decreasing before earthquakes, and increasing after earthquakes, which may reflect the stress accumulation and release during earthquakes. Combining the results of maximum shear strain rate and b-value, we identify five regions characterized by low b-value and high shear strain rate, indicating a higher potential seismic hazard in the future.

Myocardial Injury in Peritoneal Dialysis Patients Assessed by Multiparametric MRI: Relationship With Left Ventricular Phenotypes.

Myocardial injury is common in end-stage renal disease (ESRD) patients, but the presence and severity of myocardial injury in different left ventricular (LV) phenotypes were still not fully explored. To evaluate myocardial tissue characteristics and deformation in ESRD patients on peritoneal dialysis separated into normal geometry, concentric remodeling, concentric left ventricular hypertrophy (LVH) and eccentric LVH patterns by multiparametric cardiac MRI. Prospective. A total of 142 subjects, including 102 on peritoneal dialysis (69 males) and 40 healthy controls (27 males). At 3.0 T, cine sequence, T1 mapping and T2 mapping. LV mass index and LV remodeling index were used to create four subgroups with normal geometry, concentric remodeling, concentric LVH, and eccentric LVH. LV function, strain and strain rate, myocardial native T1 and T2 were measured. Descriptive statistics, analysis of variance and analysis of covariance, Pearson/Spearman correlation, stepwise regression, and intraclass correlation coefficient. P-value <0.05 was considered statistically significant. Even in normal geometry, LV strain parameters still diminished compared with the controls (global radial strain: 30.5 ± 7.7% vs. 37.1 ± 7.9%; global circumferential strain: -18.2 ± 2.6% vs. -20.6 ± 2.2%; global longitudinal strain: -13.3 ± 2.5% vs. -16.0 ± 2.8%). Eccentric LVH had significantly lower global circumferential systolic strain rate than concentric LVH (-0.82 ± 0.21%/-second vs. -0.96 ± 0.20%/-second). Compared with the controls, the four subgroups all revealed elevated native T1 and T2, especially in eccentric LVH, while concentric remodeling had the least changes including native T1, T2, and LV ejection fraction. After adjusting for covariates, there was no statistically significant difference in T2 between the four subgroups (P = 0.359). Eccentric LVH is associated with the most pronounced evidence of myocardial tissue characteristics and function impairment, while as a benign remodeling, the concentric remodeling subgroup had the least increase in native T1. This study further confirms that native T1 and strain indicators can reflect the severity of myocardial injury in ESRD, providing better histological and functional basis for future grouping treatments. 1 TECHNICAL EFFICACY: Stage 3.

Size effect of nickel-based single crystal superalloy revealed by nanoindentation with low strain rates

Size effect of the nickel-based single crystal superalloy DD6 is investigated in this study by performing nanoindentation experiments and finite element (FE) simulations by emphasizing the strain rate effect. An analytical method is proposed to identify whether a material has the indentation size effect (ISE) based on incremental formulations of the indentation strain rate. By taking ISE as a critical factor, the contact area is further described by considering the curvature radius of non-ideal indenters due to wear issues in practice. In order to emphasize the strain rate effect during indentations, the material parameters dominating mechanical properties are adopted from the strain rate dependent Johnson–Cook model, particular for the nickel-based single crystal superalloy. Consequently, the dimensional ISE analysis is performed by proposing a theoretical framework to establish the relationship among the indentation strain rate, the indenter tip curvature radius and the applied load–penetration depth (P–h) curve for characterizing nanoindentation responses. By identifying the indenter curvature radii and loading time as the important external factors of hardness measurement, FE simulations are validated to achieve good agreement with experimental data. The validated FE predictions are reliably employed to calibrate the dimensionless model of hardness with different indenter curvature radii and loading rates. In the proposed form of the dimensional hardness model, it is found that the indenter curvature radius can be perfectly independent of the material constitutive properties and loading rates. It reveals the potential and advantageous determination of characteristic length of materials by using nanoindentation.

Correlation between Strain Rate and Seismicity in Different Tectonic Settings

Abstract Geodetic strain rate characterizes present-day crustal deformation and therefore may be used as a spatial predictor for earthquakes. However, the reported correlation between strain rates and seismicity varies significantly in different places. Here, we systematically study the correlation between strain rate, seismicity, and seismic moment in six regions representing typical plate boundary zones, diffuse plate boundary regions, and continental interiors. We quantify the strain rate–seismicity correlation using a method similar to the Molchan error diagram and area skill scores. We find that the correlation between strain rate and seismicity varies with different tectonic settings that can be characterized by the mean strain rates. Strong correlations are found in typical plate boundary zones where strain rates are high and concentrated at major fault zones, whereas poor or no correlations are found in stable continental interiors with low strain rates. The correlation between strain rate and seismicity is also time dependent: It is stronger in seismically active periods but weaker during periods of relative quiescence. These temporal variations can be useful for hazard assessment.