Strain Rate Research Articles

Prognostic impact of echocardiographic predictors of subclinical systolic dysfunction in patients with moderate aortic stenosis

Abstract Introduction Moderate aortic stenosis (AS) marks a critical point in AS severity spectrum, paralleled by significant cardiac structural changes. Concentric left ventricular (LV) hypertrophy, in response to the increased afterload, enables the preservation of a normal ejection fraction (EF) despite significant underlying myocardial dysfunction. Reductions in LVEF may serve as early indicators of the LV's diminished capacity to withstand this increased afterload, potentially leading to LV fibrosis and irreversible myocardial damage. Research has shown that LVEF may not recover in some patients following aortic valve replacement (AVR). Consequently, there is a growing debate concerning higher LVEF thresholds for triggering AVR in patients with severe AS, aiming to intervene before clinical systolic dysfunction ensues and irreversible damage occurs. Meanwhile, a combination of objective indicators may help to identify those patients AS at high risk before a decline in LVEF occurs. Aim To explore the role of baseline left ventricle global longitudinal strain (GLS) and strain rate (SR) as markers of subclinical LV dysfunction, as predictors of LVEF depression, and their impact on survival of patients with moderate AS. Methods Patients with moderate AS and LVEF ≥ 50% at least in 2 echocardiograms were retrospectively identified. Prosthetic and bicuspid valves were excluded. Baseline LV GLS and SR were used as covariates in cox regression models to predict the cumulative incidence of LVEF depression over 5 years and overall survival after multivariable adjustment including time-dependent AVR. Results 574 patients were included (age 76 ± 9 years; 51% female; median follow-up time of 8.97 years). The average baseline aortic peak velocity was 3.4±0.8 m/s, mean pressure gradient was 25±9 mmHg, aortic valve area was 1.1± 0.3 cm2, and LVEF 60±5%. The average GLS was -17±7 % while the peak systolic SR was 1.2 ± 0.5/s. Both baseline GLS (HR= 0.88 for each -1%; 95% CI= 079-0.99; p= 0.04) and SR (HR= 0.89 for each +0.1/s; 95% CI= 0.80-0.99; p=0.03) were associated with 5-year incidence of LVEF depression (<50%). Risk discrimination improved by incorporating SR on top of GLS (increase in area under curve from 0.78 to 0.84; 95% CI= 0.01-0.10; p= 0.04). Furthermore, a nonlinear relation was found between GLS (optimal boundary <-15.8%; p=0.35) and SR (optimal boundary >0.96/s; p=0.34) and overall survival. Conclusions This study identifies baseline GLS and SR as predictors of LVEF depression in moderate AS underscoring their importance in detecting subclinical LV dysfunction. The combination of GLS and SR may enhance the prediction of cardiac function decline, suggesting their potential utility in guiding early intervention strategies. Although their direct relationship with survival needs further exploration, these findings advocate for incorporating GLS and SR in AS management to inform timely AVR decisions and improve patient outcomes.

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.

Left ventricular late diastolic strain rate predicts cardiovascular mortality in patients with heart failure with reduced ejection fraction

Abstract Background Left ventricular (LV) strain rate measures provide detailed information regarding LV contraction and filling pressures. These include global systolic strain rate (GSRs), early and late diastolic strain rates (GSRe and GSRa), and ratio of transmitral early filling velocity to GSRe (E/GSRe). Purpose To investigate the prognostic value of strain rate measures with regard to cardiovascular mortality in patients with heart failure with reduced ejection fraction (HFrEF). Methods The study population was retrospectively included from a HF clinic and consisted of patients with LV ejection fraction (LVEF) ≤45%. Echocardiography was obtained within 1 year of referral. The study endpoint was cardiovascular mortality, which was analysed using univariable and adjusted Cox proportional hazards models. Incremental prognostic information was assessed using Harrell’s C-index and continuous net reclassification improvement (NRI). Cubic spline analysis was used to dichotomise variables at a hazard ratio (HR) of 1 for better interpretability. Results The final study population consisted of 1160 patients with HFrEF (mean age 68±11.8 years, 72.7% male, LV ejection fraction (LVEF) 28.6±9.9%). During follow-up (median 10.1 years, IQR: 4.7-13.0), 333 (28.7%) met the outcome. Subjects who met the outcome generally had higher age and prevalence of male sex, a higher burden of comorbidities, and more severely impaired conventional echocardiographic parameters. All four strain rate measures were significantly associated with cardiovascular mortality (GSRs: HR 16.88 95% CI [8.42, 33.84] per 1 s-1 increase, GSRe: HR 0.29 [0.18, 0.47] per 1 s-1 increase, E/GSRe ratio: HR 1.31 [1.22, 1.41] per 1 unit increase, GSRa: HR 0.15 95% CI [0.23, 0.65] per 1 s-1 increase, p<0.0001 for all). However, only GSRa remained an independent predictor in multivariable Cox regression after adjustment for clinical risk factors including sex, age, mean arterial pressure, heart rate, body mass index, cigarette pack years, diabetes mellitus, total cholesterol, ischemic heart disease, and echocardiographic factors including LVEF, global longitudinal strain, tricuspid annular plane systolic excursion, LV mass index, LV internal diameter index, E/e’ ratio and left atrial volume index (HR 0.39 [0.23,0.65], p=0.0003). Furthermore, GSRa provided incremental prognostic information to a model containing all aforementioned parameters (Harrell’s C-index 0.789 vs. 0.792 and continuous NRI 0.158). GSRa was dichotomised at 0.5 s-1, and a Kaplan-Meier curve stratified according to this was plotted (log rank p<0.0001)(Figure 2). Conclusion GSRa is an independent predictor of cardiovascular mortality in patients with HFrEF after multivariable adjustment. GSRa provides incremental prognostic value over conventional echocardiographic measures in risk stratification of HFrEF patients. Our results suggest an increased risk of cardiovascular mortality associated with a GSRa below 0.5 s-1.Figure 1:Spline of HR according to GSRaFigure 2:Kaplan-Meier curve

Cocoa flavanols alleviate early diastolic dysfunction by decreasing left atrial volume in healthy elderly individuals

Abstract Background Enlargement of the left atrium (LA) predicts future cardiovascular events. Current guidelines recommend cocoa flavanol (CF) intake as it provides cardiovascular and metabolic benefits, although underlying mechanisms are not fully revealed. In this study, we hypothesized that CF intake reverses LA enlargement as a surrogate marker for diastolic dysfunction in elderly individuals without cardiovascular diseases. Methods and Results In a randomized, double-blinded trial, we investigated the effects of CF on systolic and diastolic heart function in healthy elderly individuals. Precise assessment of left-atrial and left-ventricular volume as well as strain rates, all together as emblems of early subclinical cardiac impairment, and markers of systolic function were measured by high-resolution cardiac magnetic resonance (CMR) imaging before and after CF intake. Sixty-three participants (59% male) aged ≥ 55 years received either 500 mg CF (n=30) or a placebo (n=33) twice daily for 30 days. CF counteracted subclinical cardiac dysfunction, evidenced by a reduction in maximal LA volume and LA volume index by 12.6±3.5% (p=0.0063 and p=0.0067) and LV end-diastolic volume (LVEDV) and LVEDV index by ~4.9±1.9% (p=0.049 and p=0.0413). CF intake did not influence strain, strain rate, and systolic function parameters, while the systolic blood pressure decreased by 7 mmHg [~4.7±1.9% (p=0.04)]. Conclusion We provide evidence that CF intake mitigates early changes of diastolic dysfunction and improves cardiovascular health by reversing left atrial and left ventricular remodeling. Cocoa flavanol consumption may prevent age-related cardiac changes in healthy elderly individuals and promote a health span free from cardiovascular diseases.

Investigating the Effects of Boron Nitride on Mechanical Properties of CoCrFeNiMn Composites

High‐entropy alloys (HEAs) are gaining attention for their exceptional properties but achieving precision and surface quality in powder metallurgy (PM) can be challenging. This study investigates the mechanical properties of CoCrFeNiMn HEAs produced through the flake powder metallurgy (FPM) technique and laser powder bed fusion (LPBF) preservative industrial, which established outstanding antiwear properties. To assess the enhancement of mechanical behavior and wear resistance by incorporating boron nitride (BN) into CoCrFeNiMn composites is fabricated via FPM. By incorporating BN into the composites, the mechanical behavior is significantly enhanced, leading to improved resistance against wear. Furthermore, the study delivers comprehensions into the serration behavior microstructure and shear localization in a high‐strain‐rate‐deformed CoCrFeMnNi entropy‐high alloy produces through metallurgy in powder. The serration behavior of the CoCrFeMnNi HEA is discussed concerning strain rate and temperature. Accordingly, the study employs the LPBF technique to fabricate the CoCrFeMnNi alloy from the prepared flakes. Microstructural characterization using scanning electron microscopy and X‐ray diffraction techniques to explore phase distribution, grain size, and possible segregation in the CoCrFeMnNi alloy produced through FPM‐LPBF is performed. In this particular investigation, a gradient microstructure is achieved through fusion in a laser‐powder bed of CoCrFeMnNi HEA onto highly deformed equal‐atomic HEA sheets. The resulting combination of partially recrystallized regions, exhibiting elevated yield strength, and fully recrystallized regions, demonstrates enhanced strain hardenability and elongation, and yields superior mechanical properties. The results obtained from the FPM‐LPBF CoCrFeMnNi alloy will be compared with those of conventionally processed CoCrFeMnNi to highlight the advantages and improvements achieved through the proposed method. The study findings reveal that the fundamental understanding of HEAs’ behavior under LPBF with FPM affords valuable insights into optimizing the processing parameters and achieving superior mechanical attributes.

Additive effect of metabolic dysfunction-associated fatty liver disease on left ventricular function and global strain in type 2 diabetes mellitus patients: a 3.0 T CMR feature tracking study

Abstract Purpose Type 2 diabetes mellitus (T2DM) represents the most prevalent form of diabetes, exerting a significant influence on cardiovascular health. Concurrently, metabolic dysfunction-associated fatty liver disease (MAFLD) is closely linked to heightened cardiac dysfunction risk. Our study aimed to explore the additive effect of MAFLD on left ventricular (LV) deformation among T2DM patients, utilizing cardiac magnetic resonance (CMR) feature tracking technology. Methods This study retrospectively included 270 patients with T2DM, comprising 110 individuals with MAFLD and 160 without, alongside 80 age- and sex-matched healthy controls, all of whom underwent CMR examination. Parameters derived from CMR encompass those related to LV function and global strain metrics. LV global strain parameters include global radial peak strain (GRPS), longitudinal peak strain (GLPS), and circumferential peak strain (GCPS), peak systolic strain rate (PSSR), and peak diastolic strain rate (PDSR), measured across radial, circumferential, and longitudinal directions. Intergroup analysis, employing the Mann-Whitney U test, was utilized to compare LV function and global strain parameters. Results The LV function parameters, including LV end-diastolic volume (LVEDV), LVEDV index, LV end-systolic volume (LVESV), LVESVI, LV mass, and LV mass index, displayed a progressive augmentation from controls through T2DM patients without MAFLD, to those with MAFLD. In parallel, LVEF showed a declining trajectory across these groups. In contrast, LVSV and LVSVI were comparable among the three groups. In a similar vein, when examining global strain parameters derived from CMR, a significant and progressive deterioration is observed across the groups. GRPS, GCPS and GLPS, along with PSSR and PDSR in radial, circumferential, and longitudinal directions, manifest a pronounced decline moving from control subjects to T2DM patients without MAFLD, and further deteriorating in those with T2DM and MAFLD (All p-values < 0.05). To assess the effect of MAFLD severity on global peak strain, patients with T2DM and MAFLD were stratified into two groups: a mild MAFLD group (N=77) and a moderate to severe MAFLD group (N=33). Although there was a noticeable decline in GRPS, GCPS and GLPS, as well as in PSSR and PDSR across the three groups—from those without MAFLD to those with mild and then moderate to severe MAFLD—the observed differences did not reach statistical significance. The absence of statistical significance is likely due to the small sample sizes of the groups categorized by severity of MAFLD. Conclusions This study revealed that MAFLD has additive worsening effects on LV function and LV global strains in T2DM patients evaluated by CMR. Besides, moderate to severe MAFLD, compared to mild MAFLD, exhibits worse global strain parameters. Early detection and intervention of MAFLD might improve the prognosis of T2DM patients.

Verification of intra- and inter-atrial conduction during Bachmann's bundle pacing using longitudinal bi-atrial strain

Abstract Introduction Although atrial septal pacing has been reported to reduce atrial fibrillation (AF) burden, there is less evidence regarding its effect on the prevention of permanent AF and the improvement of long-term clinical outcomes. However, Bachmann's bundle pacing (BBp), which features P-wave morphology similar to sinus rhythm and shortened P-wave duration (PWD), was reported to significantly reduce permanent AF recurrences and occurrences compared with right atrial appendage pacing (RAAp) and non-specific right septal pacing. Purpose Possible mechanisms for AF suppression with BBp are that fast inter-atrial conduction through BB decreases global atrial activation time and the dispersion of the overall atrial refractoriness, and it prevents the decrease in left ventricular filling and increase in left atrial pressure associated with delayed left atrial contraction. Intra-and inter-atrial conduction during BBp was evaluated using longitudinal bi-atrial strain. Methods In patients with successful BBp implantation defined by electrocardiographic criteria using SelectSecure pacing lead and C315 delivery catheter (Medtronic, Inc), both left atrium (LA) and right atrium (RA) global longitudinal strain (GLS) in simultaneous phases were measured using Philips Ultrasound Workspace 2D Strain in apical 4-chamber view during atrial pacing to assess intra- and inter-atrial conduction delay. The atrial GLS were measured semi-automatically, and the strain rate was analyzed in the three segments of septal wall, lateral wall, and roof and their average. The negative peak of strain rate during atrial systole was the starting point of atrial contraction, and time to peak (TTP) was measured. The difference in TTP between septal and lateral walls in each atrium was measured as intra-atrial conduction delay and the difference in average TTP between LA and RA as inter-atrial conduction delay. Results Ten patients who underwent successful BBp were enrolled (Sick sinus syndrome: 3, advanced atrioventricular block: 2, complete atrioventricular block: 5). At implantation, bipolar atrial electrogram amplitude was 2.03±0.93 mV, atrial lead impedance was 632.7±157.6 Ω, and atrial pacing threshold was 0.7±0.2 V at 0.4 ms. The PWD during sinus rhythm on the 12-lead ECG was 132.8±10.6 ms, while during BBp it was 108.0±11.9 ms, which was significantly shorter in the BBp group (p<0.001). The intra-atrial conduction delay in RA and LA was 10.9 ± 12.1 ms and 12.1 ± 17.3 ms, respectively, and the inter-atrial conduction delay was 6.6 ± 8.6 ms. On the other hand, for the 10 RAAp and 10 sinus rhythm patients as control groups, the inter-atrial conduction delay was 29.7±13.8 ms and 8.5±9.5 ms, respectively. BBp had significantly less inter-atrial conduction delay than RAAp (p=0.005) and was comparable to sinus rhythm (p=0.719). Conclusion Longitudinal bi-atrial strain suggested that BBp significantly reduced inter-atrial delay and it might be effective in AF suppression.Longitudinal bi-atrial strain

Interaction between right atrial function reserve and liver stiffness after complete repair of tetralogy of fallot: a pilot study

Abstract Background Impaired right atrial mechanics is reported in patients with repaired tetralogy of Fallot (TOF) and is associated with liver stiffness. However, whether right atrial functional reserve correlates with liver stiffness is unknown. Purpose This study tested the hypothesis that right atrial reserve capacity is limited in patients with repaired TOF and explore its relationships with right ventricular function and liver stiffness. Methods 10 patients (45% male) aged 19.04 ± 3.76 at 16.70 ± 4.30 years after repair and 15 controls (60% male, aged 20.31 ± 1.25 years) were studied. RA mechanics was assessed by speckle-tracking echocardiography (STE) at rest and during bicycle exercise, with quantification of positive, negative, and total strain, and strain rates at ventricular systole (aSRs), early diastole (aSRed), and atrial contraction (aSRac). Right atrial function reserve (RAFR) is calculated as (∆RA total strain x [1-1/ RA total strain at baseline]). RV systolic and diastolic function was quantified using Doppler interrogation and STE. Hepatic shear wave velocity (c) and tissue elasticity (E) were measured using two-dimensional shear wave elastography. Results At rest, patients had significantly lower RA positive, negative and total strain, aSRs and aSRed than control subjects (all P<0.02). Shear wave velocity and hepatic E value were significantly higher in patients than controls (both P<0.02). Compared with controls, patients had significantly lower RA positive, negative and total strain, aSRs, aSRed, and aSRac at exercise (all P<0.05). No significant difference in hepatic shear wave velocity and tissue elasticity were found between patients and control subjects at exercise (all P>0.05). Both baseline liver stiffness indices correlated negatively with RAFR, RA positive and total strain and aSRed at exercise (p<0.05 for all). RV function parameters, including baseline trans-tricuspid early and late diastolic inflow velocity (E, A), systolic, early and late diastolic tricuspid annular velocity (s, e, a), isovolumetric acceleration (IVA), RV systolic and diastolic reserve correlated significantly with RA positive and total strain at exercise (P<0.05 for all). Conclusions In young adults with repaired TOF, right atrial function reserve is impaired, and is associated with increased liver stiffness and RV dysfunction.RA mechanics from rest to exerciseStress RA mechanics and liver stiffness

Echocardiographic assessment of the right heart pulmonary circulation unit in mitral regurgitation due to mitral valve prolapse

Abstract Background Right ventricular evaluation is essential in the context of chronic mitral regurgitation (MR). Chronic MR is associated with a progressive cardiac remodeling with enlargement and dysfunction of all cardiac chambers, and the development of functional tricuspid regurgitation (TR). Besides, right ventricle (RV) dysfunction and functional TR have been shown to influence patient prognosis. Purpose The aim of this study was to evaluate simple and combined echocardiographic parameters analysing the right heart – pulmonary circulation unit, according to the severity of MR. Methods In this monocentric retrospective study, echocardiographic studies of patients followed for a mitral valve prolapse (with or without MR) were reviewed. Usual parameters analysing RV morphology, load and function were obtained. Combined parameters of RV – pulmonary artery (RV-PA) coupling were calculated: TAPSE/PASP and RVFWS/PASP. Comparison between MR grades were performed with ANOVA or Kruskal Wallis tests as appropriate. Two-by-two post-hoc comparisons of continuous variables across the 5 groups were made using the Bonferroni correction. Results 158 patients with mitral valve prolapse (MVP) were included: 37 without MR, 28 with mild MR, 23 with mild-to-moderate MR, 21 with moderate-to-severe MR and 49 with severe MR. Clinical and echocardiographic results are presented in Table 1. Patients with a higher-grade MR tended to be older and were more likely to be men. They were also significantly more symptomatic. Most echocardiographic parameters were significantly different between grades of MR. RV remodeling, studied with morphologic parameters, started with the first grade of MR and had a linear progression between levels of MR severity (Figure 1A). Load parameters were stable until grade 2 and then showed progressive increase of RV afterload. RV free wall strain slightly increased with MR grade 1, and then decreased with each grade of MR (Figure 1B). RV fractional area change, Tissue Doppler MPI and RV free wall strain rate tended to stagnate between grade 0 and 2, and then they progressively decreased. Combined parameters of RV-PA coupling including load and function, increased with the first grade of MR, and then gradually decreased (Figure 1C). Conclusion In this study, multiparametric assessment of the cardiopulmonary unit in patients with MVP showed that RV morphologic remodeling starts with the first grades of MR, before any significant increase of pulmonary pressure. This remodeling seemed to initially enhance RV function (evaluated with parameters of RV – pulmonary artery coupling) in the first grade of MR and was then followed by a progressive decrease of RV function with the increasing severity of MR.

3D geometry of the Dugald River Shear Zone, Mount Isa Inlier, Australia

The Dugald River Shear Zone is a structurally complex, anastomosing shear zone that hosts high-grade Zn mineralisation within the Dugald River Slate. The Dugald River Zn–Pb–Ag mine is situated within the Mount Isa Inlier, Australia and developed through two phases of mineralisation with high-grade Zn mineralisation intimately associated with the development of the brittle–ductile Dugald River Shear Zone. The first phase of mineralisation occurred during the regionally extensive, D2 ductile fold and axial planar cleavage forming event and resulted in the development of a sulfide horizon. This horizon was a preferential site for strain partitioning during early D4 ductile deformation, which resulted in transposition-related concentration and thickening of a sulfide horizon marking the second phase of mineralisation. The Dugald River Shear Zone developed during D4 wherein strain rate incompatibilities between a ductile-deforming sulfide horizon and the brittle-deforming Dugald River Slate resulted in the development of a Riedel shear zone. A high-resolution 3D model of the shear zone was constructed from robust drilling and mapping datasets in which releasing and restraining bends highlight the thickening and thinning of ore lenses, respectively. The 3D model with detailed structural analysis and observations allows for predictive modelling of dilational zones within throughgoing Y-shears, which are prospective sites for remobilisation of high-grade Zn sulfides as the ore body developed coevally with progressive shearing.

Dynamic statistical damage constitutive model based on the Hoek–Brown criterion at high strain rates

Dynamic statistical damage constitutive model based on the Hoek–Brown criterion at high strain rates

Fenofibrate modulates cardiac energy metabolism in moderate-severe aortic stenosis: a mechanistic double-blinded randomised controlled MR trial

Abstract Background Aortic stenosis (AS) is associated with impaired cardiac metabolism and high-energy phosphate production which can further exacerbate the progression to HF. Myocardial lipid accumulation and reduced production of high-energy phosphates have important implications for both systolic and diastolic heart function in AS. Peroxisome proliferator-activated receptor alpha (PPAR-alpha agonist, has the potential to optimise cardiac substrate metabolism, thereby, may be effective in improving cardiac dysfunction and functional capacity in AS. Methods In this prospective, randomized, double-blind, placebo-controlled study, patients with moderate-to-severe asymptomatic AS (n=72) were randomly assigned to Fenofibrate 200 mg daily or matching placebo for 6 months in 4:1 fashion. Of the total 72 participants, 59 received Fenofibrate and 13 received placebo. All subjects underwent cardiac magnetic resonance (CMR) and exercise testing at 0 and 6 months, with follow-up data available in 47 patients. The primary end point was change in myocardial triglyceride content (MTG) determined by proton magnetic resonance spectroscopy (1H-MRS). Secondary outcome measures included change in cardiac energetics (PCr/ATP) determined by phosphorus magnetic resonance spectroscopy (31P-MRS), left ventricular strain determined by myocardial tagging and exercise capacity i.e. peak VO2 assessment via cardiopulmonary exercise testing. Results Cardiac energetics (PCr/ATP) showed statistically significant improvement in the Fenofibrate group (0.14 ± 0.48; CI: - 0.03, 0.30; p=0.05) vs placebo group (0.11 ± 0.75; CI -0.42, 0.65; p=0.64). There was also significant reduction in MTG in the Fenofibrate group (mean change -0.40 ± 0.97; 95% CI -0.74, -0.06; p=0.02). MTG content also reduced in the placebo group (mean change -0.41 ± 0.26, 95% CI -1.10, 0.18, p 0.13), but the reduction was not statistically significant. Though no significant changes were seen in the systolic function parameters, there was a significant improvement in diastolic function in the fenofibrate group only (peak diastolic longitudinal strain rate 9.6, 95% CI: 1.13, 18.1; p = 0.02). Peak VO2 did not show any significant improvement in either group. Conclusions Fenofibrate works as a metabolic modulator upregulating fatty acid metabolism in pressure overload AS hearts. Such modulation is associated with an improvement in cardiac energetics and diastolic function in moderate-severe AS.Main results from baseline to 6 monthsBaseline demographic and CMR parameters

Inclined bending seismic reflection layer in the crust illuminated by distributed fibre-optic-sensing measurements in western Japan

Distributed acoustic sensing (DAS), which enables a single fibre-optic cable to function as multiple sensors, is a technique to measure the strain rate distributed along the cable. This technique is applied to record ground motions in western Japan via a 50 km-long fibre-optic cable beneath a national road. The measured values are strain changes along the cable every 5 m, corresponding to 9788 sensor deployments. This high-density measurement along the long cable successfully recorded the 2021 M2.8 and M3.2 earthquakes that occurred in the crust within the distance of the cable in southern Kyoto. The direct S waves were followed by seismic waves approximately 8–14 s later, which were reflected by lower crustal structures. These waveforms were previously reported by observing many earthquakes via multiple seismometers, but the DAS observations clearly illuminate reflected wavefields from single earthquake observations for the first time. The numerical simulation of the strain-rate wavefields of these earthquakes reveals the existence of a north-dipping thin layer with a slow seismic velocity in the lower crust, which becomes steeper in the shallower part. This layer might represent the path of slab-derived fluid to the shallow fault zone.

Thermal processing behaviour and microstructural evolution of high W and high γ’ content extruded nickel-based powder metallurgy superalloy FGH4109

ABSTRACT Nickel-based powder metallurgy superalloys with high W and high γ’ content exhibit excellent high-temperature properties, but their high deformation resistance poses significant challenges for hot processing. In this study, the hot compression behaviour of an extruded nickel-based powder superalloy FGH4109 with high W (6.1%) and high γ’ phase contents (60%) was systematically investigated at temperatures ranging from 1060 ℃ ~ 1140 ℃, strain rates from 0.001 s−1 ~1 s−1, and maximum true strains of 0.7. Combined with the hot working map and the microstructure evolution in different hot working zones, the optimal hot working window for the alloy was determined to be in the temperature range of 1060 ℃ ~ 1140 ℃ and strain rates of 0.001 s−1 ~0.012 s−1, where the power dissipation efficiency η was greater than 0.5, and the dominant deformation mechanism was discontinuous dynamic recrystallisation.

High‐precision numerical simulation method for thermal–mechanical coupling in rubbers

AbstractImproving the precision of numerical simulations in thermal–mechanical coupling for amorphous polymer materials is crucial for their effective utilization. To enhance the precision of rubber numerical simulations, this study proposed a method considering the temperature and strain rate to establish tensile testing conditions based on the principle of time–temperature equivalence. Additionally, to obtain more precise parameters for hyperelastic constitutive equations, stress relaxation experiments were conducted to determine a set of stress values under complete rubber stress relaxation, which were used to fit the hyperelastic components of the hyper‐viscoelastic algorithm. A finite element model of rubber rebound was established, and a hyperelastic model based on loss factor and a hyperelastic model based on Prony series (hyper‐viscoelastic) were used to calculate the temperature changes caused by rubber rebound coefficient and energy dissipation during the rebound process at 110, 120, and 130°C. We compared the calculation results of these two algorithms with experimental data to verify their accuracy. The research results show that the average error of the rebound coefficient of the hyperelastic algorithm at three temperatures is 3.63%, and the average error of the rebound coefficient of the hyper‐viscoelastic algorithm at these three temperatures is 0.93%. The comparison with the rebound test results shows that the hyper‐viscoelastic method is more accurate and better captures the viscoelastic hysteresis of rubber, but the model calculation time is longer. In addition, at the moment of rebound sample impact, the maximum temperature rise amplitude of the hyperelastic algorithm sample impact position is 2.60, 1.75, and 0.91°C, which are 110, 120, and 130°C, respectively; The maximum heating amplitudes of the hyper‐viscoelastic algorithm are 2.05, 1.35, and 0.61°C. The hyper‐viscoelastic algorithm is closer to the actual test results.Highlights Applied the principle of time–temperature equivalence. Determination of material parameters using the hyper‐viscoelastic algorithm. Calculated the temperature change during the rubber rebound process.

A Transition State Theory-Based Continuum Plasticity Model Accounting for the Local Stress Fluctuation

Based on the transition state theory, a continuum plasticity theory is developed for metallic materials. Moreover, the nature of local stress fluctuation within a material point is considered by incorporating the probability distribution of the stresses. The model is applied to investigate the mechanical behaviors of 316 L stainless steel under various loading cases. The simulated results closely match the results obtained by the polycrystal plasticity model and experiments. The mechanical behaviors associated with strain rate sensitivity, temperature dependence, stress relaxation, and strain creep are correctly captured by the model. Furthermore, the proposed model successfully characterizes the Bauschinger effect, which is challenging to capture with a conventional continuum model without additional assumptions. The proposed model could be further employed in the design, manufacturing, and service of engineering components.

Analysis of Stress Corrosion Cracking Growth Rate in the Heat-Affected Zone of 316L Based on the Heterogeneity of the Mechanical Properties

The heterogeneity of the microstructure and mechanical properties of safe-end dissimilar metal welded joints (DMWJs) presents a challenge to the quantitative prediction of the stress corrosion cracking (SCC) growth rate directly from laboratory data. This study investigates the effect of the heterogeneity of the mechanical properties of the 316L-welded heat-affected zone (HAZ) in safe-end DWMJs on the SCC tip stress-strain field and the SCC growth rate. First, based on the analysis of microstructures in localized regions within the 316L-welded HAZ and the acquisition of material mechanical properties through microhardness testing, a user-defined material subroutine was developed to characterize the heterogeneous material properties within the 316L-welded HAZ. Then, using this finite element model with an inhomogeneous distribution of the mechanical properties of the material, the crack tip strain rates (CTSRs) at different locations within the 316L-welded HAZ were obtained. In conjunction with the FRI model, the SCC growth rates at various locations within the HAZ were determined. The results show that the closer to the 52Mw/316L fusion boundary within the 316L-welded HAZ, the greater the yield strength of the material and the higher the CTSR and predicted SCC growth rates at the characteristic distance.

Dynamic compressive impact behavior of CFRP composite under high strain rate loading

Carbon Fiber Reinforced Plastics (CFRP) composite exhibits significant sensitivity to strain rate. In this work, authors investigated the CFRP composite’s dynamic compressive impact behavior under a high strain rate. The vacuum bagging technique was used to fabricate the composite specimens to reduce the presence of voids. Compressive mechanical behavior was examined for the CFRP composite for strain rate ranging from 1384 to 1953 s−1 using a Split Hopkinson Pressure Bar (SHPB) test setup. The experiment aims to investigate the effect of strain rate on stresses, strains, failure strengths, fracture energies, and failure of quasi-isotropic CFRP composites. Furthermore, the specimens’ strength initially increases and achieves its maximum strength, followed by a decrease in strength value. Moreover, an optical microscopic examination reveals that damage in composite laminate grows as the strain rate increases.

Recrystallization Behavior of Computationally Optimized Low‐Alloy Steel at Various Temperatures and Strain Rates

The dynamic recrystallization (DRX) behavior of SA508‐III steel, a critical material for reactor pressure vessels (RPVs) normally treated by hot forging, is thoroughly examined in this article. In the investigation, elevated temperatures and the coarsening of metallic phases and carbides are revealed to contribute to the degradation of the steel's strength–toughness relationship. Utilizing computational thermodynamics, the stability of secondary phases, including carbides and brittle inclusions, is simulated to enable precise phase equilibrium calculations and accurate prediction of key mechanical properties such as yield strength, tensile strength, and hardness. These simulations facilitated targeted modifications to the alloy composition to enhance the steel's strength and hardenability under high‐temperature, high‐pressure conditions. In this study, alloy composition and processing parameters within the CALculation of PHAse Diagram framework, utilizing the ThermoCalc and JMatPro software packages, are optimized. In the microstructural investigations conducted under various isothermal deformation conditions (1173–1473 K) and strain rates (0.001–1 s−1), it is demonstrated that DRX mechanisms led to varied grain size developments, with a critical strain rate identified at 0.01 s−1 during high‐temperature deformations. In these findings, significant insights are provided into optimizing the mechanical performance of SA508‐III steel for RPV applications.

Experimental research on deformation response of hot dry rock (HDR) geothermal reservoir during hydraulic modification at 300 °C and depth 2500 m

In the stages of reservoir construction and geothermal exploitation, the rock deformation is an important factor in the study of the reservoir stability. However, the existing laboratory research in this area pay far less attention to the macroscopic deformation of the reservoir rock mass. Hydraulic fracturing experiments have here been conducted at a temperature of 300 °C, an axial pressure of 65 MPa, and a confining pressure of 60 MPa. The quantitative relationship between the granite strain (axial, radial, and volumetric) and the water injection pressure during hydraulic fracturing has then for the first time been determined experimentally. Meanwhile, the deformation response of granite geothermal reservoir during hydraulic modification has also been discussed. As a result, the maximum opening of the hydraulic fractures was in the range of 10−1 μm - 10−2 μm and the maximum volumetric strain rate of the rock mass was 1.71 × 10−4 s−1. Microseismic events preferably occurred during periods of high volumetric strain rates when the injection pressure fluctuated repeatedly. During geothermal exploitation, the structural changes caused by hydraulic fractures and thermal cracks resulted in greater potential for contraction of the rock mass. These research results provide a reference for geothermal reservoir reconstruction and stability assessment.