Search Results (38)

As a part of the mining-induced stress redistribution process during coal mining, the repeated loading and unloading process with increasing peak stresses will cause more severe deformation and damage to mining roadways, which is different from the findings in other underground engineering practices. Consequently, cyclic triaxial compression tests with increasing amplitudes were carried out to investigate the mechanical behavior, acoustic emission (AE) characteristics, and damage evolution of coal materials. It is found that peak deviatoric stress and axial residual strain at the failure of coal specimens increase with increasing confining pressures, while the changes in circumferential strain are not obvious. Moreover, the failure patterns of coal specimens exhibit shear failure due to the constraint of confining pressures while some local tensile cracks occur near the shear bands at both ends of the specimens. After that, the damage evolution of coal specimens was analyzed against the regularity of AE counts and energies to develop a damage evolution model. It is concluded that the damage evolution model can not only quantify the deformation and failure process of the coal specimens under cyclic loads with increasing amplitudes but also takes into account both the initial damage due to natural defects and the induced damage by the cyclic loads in previous cycles. Full article

This investigation examines the fracture mechanisms of 31,311 tapered roller bearing cages using finite element analysis (FEA) and the Gurson–Tvergaard–Needleman (GTN) damage model. Static, dynamic, modal, and harmonic response analyses identify critical stress concentrations at the contact interface between the rolling elements and the outer ring, with maximum deformation occurring in the inner ring. Modal analysis excludes resonance as a potential failure cause. Crack initiation and propagation studies reveal that cracks predominantly form at the pocket bridge corners, propagating circumferentially. The propagation angle increases under circumferential and coupled loading conditions while remaining constant under longitudinal loading. Based on the GTN model, this study is the first to examine the crack propagation and fracture toughness of the cage under various loading conditions. The results indicate that longitudinal loading (Load II) yields the highest fracture toughness, significantly surpassing those under circumferential (Load I) and coupled loading (Load III). Load II exhibits the strongest crack growth resistance, with a peak CTOD_c of 0.598 mm, attributed to plastic strain accumulation. Fracture toughness decreases with crack depth, as CTOD_c declines by 66.5%, 20.1%, and 58.4% for Loads I, II, and III, respectively. Crack deflection angles show the greatest variation under Load I (35% increase), while Loads II and III demonstrate minimal sensitivity (<10% change). The optimization of the bearing cage pocket hole fillet radius from 0 mm to 0.75 mm demonstrates a maximum stress concentration reduction of 38.2% across different load conditions. This work introduces a novel methodology for predicting cage fracture behavior and optimizing design, offering valuable insights to enhance the reliability and longevity of systems in high-speed, high-load applications. Full article

Background: While left-bundle-branch-block-related contraction patterns as well as echocardiography-derived strain are variably associated with the volumetric response to cardiac resynchronization therapy (CRT), the role of CMR-derived strain parameters is unexplored. Methods: A total of 50 patients receiving CRT implantation were retrospectively analyzed, all of whom had undergone CMR imaging within one year before, and echocardiography within 6 months before and 6–12 months after CRT implantation. We assessed CMR-derived morphological and functional parameters with regard to the echocardiographic response, defined as a reduction in the left ventricular end-systolic volume of ≥15%. Results: Among the standard CMR parameters, the indexed right ventricular volumes in end-diastole (RVEDVi) (74.5 ± 19.5 vs. 94.8 ± 30.2 mL/m², p = 0.006) and end-systole (RVESVi) (43.2 ± 13.3 vs. 61.6 ± 28.8 mL/m², p = 0.003), as well as the left atrial (LA) area (24.8 ± 3.5 vs. 30.4 ± 9.5 cm², p = 0.020), differed significantly between CRT responders and non-responders. In strain analysis, CRT responders showed a significantly better LA global longitudinal strain (GLS) (25.1 ± 10.4 vs. 15.3 ± 10.5, p = 0.002), LA global circumferential strain (GCS) (27.9 ± 14.7 vs. 17.1 ± 13.1%, p = 0.012), RV GLS (−25.0 ± 6.5 vs. −18.9 ± 7.6%, p = 0.004) and RV free wall strain (−31.1 ± 7.9 vs. −24.9 ± 9.5, p = 0.017). Conclusions: CMR-derived peak septal circumferential strain and RVEDVi correlated with the echocardiographic volumetric response to CRT at 6–12 months. Full article

The excavation process for a deeply buried chamber in a high ground stress area is often dynamic. The design of reasonable excavation methods for differing geological conditions and surrounding pressure environments is of great engineering significance in order to improve the stability of surrounding rocks during construction. Based on the findings from conventional triaxial and cyclic loading laboratory tests on marble, this paper obtains a set of mesoscopic parameters that accurately represent the macro-mechanical characteristics of marble, uses the discrete element method (DEM) to establish a numerical model, and carries out numerical tests of triaxial and cyclic loading under varying circumferential pressures. The mechanical parameter evolution, crack propagation mechanism and mesoscopic force field distribution of marble under conventional triaxial stress and cyclic load-reversal conditions are compared and analyzed. The findings suggest that the peak strength, residual strength, peak axial strain, elastic modulus, and Poisson’s ratio of marble increase as the circumferential pressures rises for both stress paths. The peak strength and elastic modulus under cyclic loading at different circumferential pressures are lower than those observed under conventional triaxial conditions, while the Poisson’s ratio is higher compared to conventional triaxial conditions. The cumulative total number of microcracks in marble damage under cyclic loading is higher and the damage is more complete compared to conventional triaxial loading. The rock specimens in both stress paths are dominated by tension cracks. Nevertheless, a greater number of shear cracks are exhibited by the specimens subjected to cyclic loading conditions. The proportion of tension cracks in the rock specimens gradually decreases with increasing circumferential pressure, while the proportion of shear cracks gradually increases. For both stress paths, the angular distribution of microcracks following rock specimen failure is similar, and the force chain becomes progressively denser as the circumferential pressures increase. The force chain distribution within the rock specimens is more heterogeneous under cyclic loading conditions than under conventional triaxial conditions. Full article

Background and Objectives: This study aimed to evaluate the cardiac functions of 7- to 11-year-old children with a history of preterm birth using echocardiography and to assess the relationship between these functions and neonatal factors. Materials and Methods: A total of 64 children were included in the study, consisting of 32 children aged 7 to 11 years with a history of preterm birth and 32 age- and gender-matched term birth controls. Results: While no significant differences were detected between the preterm and term birth groups regarding age, height, and body weight, echocardiographic data revealed higher values of mitral E, mitral A, and tricuspid A by pulse wave Doppler, as well as septal E by tissue Doppler, in the preterm group compared to the term birth group (p < 0.05). Additionally, the left ventricular global longitudinal peak strain, right ventricular free wall and right ventricular 4-chamber strain, IVRT, MPI, MAPSE, and LVESV values were lower in the preterm group than in the term birth group (p < 0.05). No significant differences were detected in circumferential strain measurements. Right ventricular strain measurements were significantly lower in the preterm group (p = 0.001). Conclusions: While conventional echocardiographic examinations did not reveal obvious pathological findings in school-age children with a history of preterm birth, further echocardiographic assessments demonstrated differences compared to term birth controls, particularly in diastolic functions and right and left ventricular longitudinal strain measurements. Full article

Background and Objectives: The complex relationship between three-dimensional (3D) speckle-tracking echocardiography (3DSTE)-derived left ventricular (LV) and left atrial (LA) volumes and functional properties has been demonstrated in recent studies. A better understanding of LV volumetric dependence on systolic peak LA (reservoir) strains in healthy circumstances could complete this knowledge. Therefore, 3DSTE was used for the simultaneous evaluation of these parameters in healthy adults, aiming to examine their complex relationship. Materials and Methods: The present study consisted of 165 healthy individuals with a mean age of 33.1 ± 12.3 years and 90 men. A complete two-dimensional echocardiography with Doppler with 3DSTE was performed in all the cases. Results: The peak LA global radial (GRS), longitudinal (GLS), and 3D (G3DS) strains were increased in the subjects with a mean LV end-diastolic volume (EDV) as compared to those cases with a lower-than-mean LV-EDV. In the cases with a higher-than-mean LV-EDV, no further increase in these peak global LA strains could be detected. The peak LA global circumferential and area strains showed a tendentious (non-significant) increase with an increasing LV-EDV. The peak LA global strains showed similar non-significant associations with the LV end-systolic volume (except the peak LA-G3DS, which proved to be significant). Conclusions: In healthy adults, the 3DSTE-derived peak LA-GRS and LA-G3DS are increased with a larger LV-EDV up to a point, beyond which a further increase cannot be seen, suggesting a working Frank–Starling mechanism in this context similar to that for LA volumes. Similar associations are present for the peak LA-GLS as well. Full article

Introduction: The contraction–relaxation pattern of the left atrial (LA) walls is opposite to that detected in the left ventricle, which includes thinning in radial, lengthening in longitudinal, and widening in circumferential directions in the systolic reservoir phase of LA function as measured by three-dimensional speckle-tracking echocardiography (3DSTE). Global longitudinal strain (GLS) is a quantitative feature of longitudinal wall contraction referring to the whole LA. The present study aims to clarify the expected prognostic impact of peak LA-GLS as assessed by 3DSTE in healthy participants during a long-term follow-up period. Methods: The study consisted of 142 healthy adults (with an average age of 32.1 ± 12.7 years; 72 of the participants were men), in whom complete two-dimensional Doppler echocardiography and 3DSTE were performed on a voluntary basis. Results: Thirteen adults suffered from a cardiovascular event, including two cardiac deaths during a mean follow-up of 8.35 ± 4.20 years. Peak LA-GLS ≥ 20.9%, as assessed by 3DSTE, was found to be a significant predictor for cardiovascular event-free survival by using ROC analysis (specificity 74%, sensitivity 62%, area under the curve 0.69, p = 0.025). Healthy individuals with peak LA-GLS < 20.9% had a lower LV-EF and a significantly higher ratio of cardiovascular events compared to cases with peak LA-GLS ≥ 20.9%. Subjects who experienced cardiovascular events had lower peak LA-GLS and the ratio of subjects with peak LA-GLS < 20.9% proved to be significantly increased compared to that of cases without cardiovascular events. Conclusions: 3DSTE-derived peak LA-GLS representing LA lengthening in the end-systolic reservoir phase of LA function predicts future cardiovascular events in healthy adults. Full article

Background/Objectives: Duchenne Muscular Dystrophy (DMD) is a prevalent fatal genetic disorder, and heart failure is the leading cause of mortality. Peak left ventricular (LV) circumferential strain (E_cc), twist, and circumferential-longitudinal shear angle (θ_CL) are promising biomarkers for the improved and early diagnosis of incipient heart failure. Our goals were as follows: 1) to characterize a spectrum of functional and rotational LV biomarkers in boys with DMD compared with healthy age-matched controls; and 2) to identify LV biomarkers of early cardiomyopathy in the absence of abnormal LVEF or LGE. Methods: Boys with DMD (N = 43) and age-matched healthy volunteers (N = 16) were prospectively enrolled and underwent a 3T CMR exam after obtaining informed consent. Breath-held MRI tagging was used to estimate left ventricular E_cc at the mid-ventricular level as well as the twist, torsion, and θ_CL between basal and apical LV short-axis slices. A two-tailed t-test with unequal variance was used to test group-wise differences. Multiple comparisons were performed with Holm–Sidak post hoc correction. Multiple-regression analysis was used to test for correlations among biomarkers. A binomial logistic regression model assessed each biomarker’s ability to distinguish the following: (1) healthy volunteers vs. DMD patients, (2) healthy volunteers vs. LGE(−) DMD patients, and (3) LGE(−) DMD patients vs. LGE(+) DMD patients. Results: There was a significant impairment in the peak mid-wall E_cc [−17.0 ± 4.2% vs. −19.5 ± 1.9%, p < 7.8 × 10⁻³], peak LV twist (10.4 ± 4.3° vs. 15.6 ± 3.1°, p < 8.1 × 10⁻⁴), and peak LV torsion (2.03 ± 0.82°/mm vs. 2.8 ± 0.5°/mm, p < 2.6 × 10⁻³) of LGE(−) DMD patients when compared to healthy volunteers. There was a further significant reduction in the E_cc, twist, torsion, and θ_CL for LGE(+) DMD patients when compared to LGE(−) DMD patients. In the LGE(+) DMD patients, age significantly correlated with LVEF (r² = 0.42, p = 9 × 10⁻³), peak mid-wall E_cc (r² = 0.27, p = 0.046), peak LV Twist (r² = 0.24, p = 0.06), peak LV torsion (r² = 0.28, p = 0.04), and peak LV θ_CL (r² = 0.23, p = 0.07). In the LGE(−) DMD patients, only the peak mid-wall E_cc was significantly correlated with age (r² = 0.25, p = 0.006). The peak LV twist outperformed the peak mid-wall LV E_cc and EF in distinguishing DMD patients from healthy volunteer groups (AUC = 0.88, 0.80, and 0.72), as well as in distinguishing LGE(−) DMD patients from healthy volunteers (AUC = 0.83, 0.74, and 0.62). The peak LV twist and peak mid-wall LV E_cc performed similarly in distinguishing the LGE(−) and LGE(+) DMD cohorts (AUC = 0.74, 0.77, and 0.79). Conclusions: The peak mid-wall LV E_cc, peak LV twist, peak LV torsion, and peak LV θ_CL were significantly impaired in advance of the decreased LVEF and the development of focal myocardial fibrosis in boys with DMD and therefore were apparent prior to significant irreversible injury. Full article

Taking the tunnels crossing active faults in China’s Sichuan–Tibet Railway as the research background, experimental studies were conducted using a custom-developed split model box. The research focused on the cracking characteristics of the surrounding rock surface under the action of strike-slip faults, the progressive failure process of the tunnel model, and the mechanical response of the tunnel lining. In-depth analyses were performed on the tunnel damage mechanism under strike-slip fault action and the mitigation effects of combined anti-dislocation measures. The results indicate the following: Damage to the upper surface of the surrounding rock primarily occurs within the fault fracture zone. The split model box enables the graded transfer of fault displacement within this zone, improving the boundary conditions for the model test. Under a 50 mm fault displacement, the continuous tunnel experiences severe damage, leading to a complete loss of function. The damage is mainly characterized by circumferential shear and is concentrated within the fault fracture zone. The zone 20 cm to 30 cm on both sides of the fault plane is the primary area influenced by tunnel forces. The force distribution on the left and right sidewalls of the lining exhibits an anti-symmetric pattern across the fault plane. The left side wall is extruded by surrounding rock in the moving block, while the right side wall experiences extrusion from the surrounding rock in the fracture zone, and there is a phenomenon of dehollowing and loosening of the surrounding rock on both sides of the fault plane; the combination of anti-dislocation measures significantly enhances the tunnel’s stress state, reducing peak axial strain by 93% compared to a continuous tunnel. Furthermore, the extent and severity of tunnel damage are greatly diminished. The primary cause of lining segment damage is circumferential stress, with the main damage characterized by tensile cracking on both the inner and outer surfaces of the lining along the tunnel’s axial direction. Full article

Introduction: In systole, when the left ventricle (LV) twists, the left atrium (LA) behaves like a reservoir, having a special wall contractility pattern opposite to that of the LV wall. Accordingly, the objective of the present study was to investigate the associations between LV rotational mechanics and LA peak (reservoir) strains as assessed simultaneously by three-dimensional speckle-tracking echocardiography (3DSTE) under healthy conditions. Methods: In the present study, 157 healthy adults (mean age: 33.2 ± 12.7 years, 73 men) were involved. Complete two-dimensional Doppler echocardiography with 3DSTE-derived data acquisition were performed in all cases. The 3DSTE-derived LV rotational and LA strain parameters were determined at a later date. Results: Global LA peak reservoir circumferential (22.7 ± 6.4% vs. 27.6 ± 6.8%, p < 0.05) and area (57.8 ± 20.0% vs. 66.0 ± 22.7%, p < 0.05) strains proved to be reduced in the case of the highest vs. lowest basal LV rotation; other LA peak reservoir strains were not associated with increasing basal LV rotation. Global LA peak radial strain was highest in the case of the lowest vs. highest apical LV rotation (−19.2 ± 9.4% vs. −13.0 ± 8.2%, p < 0.05). Global LA peak reservoir 3D strain was lowest in the case of the highest vs. lowest apical LV rotation (−9.9 ± 6.8% vs. −5.0 ± 4.2%, p < 0.05). Only apical LV rotation proved to be significantly reduced in the case of the highest vs. lowest global LA peak reservoir 3D strain (8.12 ± 3.23° vs. 10.50 ± 3.44°, p < 0.05). Other global LA peak reservoir strains were not associated with basal and apical LV rotations. Conclusions: In LV systole, LV rotational mechanics is associated with LA deformation represented by LA peak (reservoir) strains even in healthy circumstances. While basal LV rotation is associated with LA widening, apical LV rotation is associated with LA thinning, suggesting the close cooperation of the LV and LA in systole even in healthy adults. Full article

Background: In this study, we examined and compared ex vivo mechanical properties of aortic walls in patients with bicuspid (BAV) and tricuspid (TAV) aortic valve aortopathy to investigate if the anatomical peculiarities in the BAV group are related to an increased frailty of the aortic wall and, therefore, if a different surgical cutoff point for ascending aortic replacement could be reasonable in such patients. Methods: Ultimate stress tests were performed on fresh aortic wall specimens harvested during elective aortic surgery in BAV (n. 33) and TAV (n. 77) patients. Three mechanical parameters were evaluated at the failure point, under both longitudinal and circumferential forces: the peak strain (Pstr), peak stress (PS), and maximum elastic modulus (EM). The relationships between the three mechanical parameters and preoperative characteristics were evaluated, with a special focus on evaluating potential risk factors for severely impaired mechanical properties, cumulatively and comparatively (BAV vs. TAV groups). Results: The patient populations were inhomogeneous, as BAV patients reached surgical indication, according to the maximum aortic dilatation, at a younger age (58 ± 15 vs. 64 ± 13; p = 0.0294). The extent of the maximum aortic dilatation was, conversely, similar in the two groups (52 ± 4 vs. 54 ± 7; p = 0.2331), as well as the incidences of different phenotypes of aortic dilatation (with the ascending aorta phenotype being the most frequent in 81% and 66% of the BAV and TAV patients, respectively (p = 0.1134). Cumulatively, the mechanical properties of the aortic wall were influenced mainly by the orientation of the force applied, as both PS and EM were impaired under longitudinal stress. An age of >66 and a maximum dilatation of >52 mm were shown to predict severe Pstr reduction in the overall population. Comparative analysis revealed a trend of increased mechanical properties in the BAV group, regardless of the position, the force orientation, and the phenotype of the aortic dilatation. Conclusions: BAV aortopathy is not correlated with impaired mechanical properties of the aortic wall as such. Different surgical cutoff points for BAV aortopathy, therefore, seem to be unjustified. An age of >66 and a maximum aortic dilatation of >52 mm, however, seem to significantly influence the mechanical properties of the aortic wall in both groups. These findings, therefore, could suggest the need for more accurate monitoring and evaluation in such conditions. Full article

Adjacent cyclic explosions significantly impact the stability of underground anchored caverns. Based on the similar model test of the vault explosion of the anchored cavern, the dynamic analysis finite element software ANSYS/LSDYNA(18.0) was used to establish a model of the straight wall side explosion of the underground anchored cavern and conduct a numerical simulation. When the total amount of explosion load is the same, we compared the stress time history curve, displacement time history curve, tunnel wall displacement, and circumferential strain curve of the surrounding rock in the underground anchored cavern (under both a high-level single-side blast and a low-level cyclic side blast). We obtained the dynamic response rules of the surrounding rock. By comparing the damage evolution process of the surrounding rock in the two situations, the damage accumulation law of the surrounding rock was analyzed. At the same time, the axial stress distribution characteristics of underground anchor cavern anchors under the action of cyclic explosion were studied. The findings demonstrate that when the total level of blast load adjacent to the cavern is the same, the displacement and circumferential peak strain of surrounding rock and the axial stress of rock bolt in the high-level single explosion are greater than those in the low-level cyclic explosion. However, compared to a single explosion, the rock mass suffers more damage in the cyclic explosion. This study will provide engineers with information that will assist them with a better understanding of the cumulative damage mechanisms of surrounding rock, as well as the stress characteristics of rock bolts under dynamic loads near the explosion site, which will be used to design underground caves with anti-blast features. Full article

Hypereosinophilic syndrome (HES) is considered to be a rare myeloproliferative disease that is characterized by persistent eosinophilia with associated multiple-organ damage. The heart is often involved in HES, representing a major cause of morbidity and mortality. HES is a heterogeneous group of disorders; the majority of the cases are idiopathic. Summarizing the findings regarding myocardial, valvular, and vascular abnormalities in a series of patients with HES, most studies found normal left ventricular (LV) volumes with reduced LV global longitudinal strain and LV apical rotation and twist in HES cases, accompanied by increased left atrial (LA) volumes and stroke volumes, reduced peak LA circumferential strain (representing systolic abnormalities), and mitral annular dilation and functional deterioration. Regarding the right heart, preserved right ventricular volumes and functional properties, increased right atrial volumes, mild RA functional abnormalities, and dilated tricuspid annular dimensions without functional impairment could be seen in these studies. Aortic and pulmonary valves showed no specific disease-related alterations. Vascular abnormalities included increased aortic stiffness without dilation of the aorta and pulmonary hypertension in some cases. These results suggest disease-specific but relatively mild myocardial, valvular, and vascular abnormalities in HES. The present review aimed to summarize the available clinical data about cardiac mechanics and valvular and vascular abnormalities in a series of patients with HES. Full article

Coal penetration enhancement technology is the key to increase the production of coalbed methane. Coal bodies are subjected to different peripheral pressures in the in situ strata, and the study of the changes in the mechanical strength of coal bodies under different peripheral pressures after the action of liquid nitrogen is crucial for the penetration enhancement of liquid nitrogen (LN₂)-fractured coal. In this paper, an MTS universal testing machine was utilized to carry out experiments to obtain the stress–strain curves of the coal under different freezing times under 1 MPa surrounding pressure and different surrounding pressures after 50 min of LN₂ action. The experimental results showed the following: (1) the uniaxial compressive strength and peak strain of coal samples in a frozen state are positively correlated under two conditions. The modulus of elasticity decreased before 100 min at different times of LN₂ action, and the modulus of elasticity was maximum at 5 MPa at different peripheral pressure actions; (2) the uniaxial compressive strength and peak strain of the frozen-thawed coal samples decreased before 100 min of LN₂ action at different times, and the modulus of elasticity continued to decrease. The uniaxial compressive strength and modulus of elasticity of coal samples in freeze–thaw state under different peripheral pressures were the largest at 5 MPa, and the peak strain was negatively correlated. (3) The elastic strain energy of the frozen coal samples under the action of LN₂ at different times was positively correlated with the freezing time before 80 min, and negatively correlated after 80 min. The elastic strain energy of the frozen coal samples was positively correlated with the freezing time. The elastic strain energy and freezing time of the two coal samples under different circumferential pressures were positively correlated before 5 MPa and negatively correlated after 5 MPa, with opposite dissipation energies. (4) The water–ice phase transition and temperature–thermal stresses on the internal structure of the coal in the presence of LN₂ cause significant damage. The degradation of coal samples in the freeze–thaw state is even higher under in situ ground pressure. Full article

Arterial stiffness has received increasing interest as a cardiovascular marker in patients with aortic valve stenosis (AS). So far, studies on the impact of aortic valve replacement (AVR) on arterial stiffness have been equivocal. Two-dimensional speckle tracking (2DST) is a novel, non-invasive method to measure the motion of the vessel wall. In this prospective observational study, we aimed to assess the change in arterial stiffness of the common carotid artery (CCA) measured by 2DST in patients undergoing transcatheter aortic valve implantation (TAVI). A total of 47 patients were included in the study (age 80.04 ± 6.065 years). Peak circumferential strain (CS) was significantly improved after TAVI (4.50 ± 2.292 vs. 5.12 ± 2.958, p = 0.012), as was the peak strain rate (CSR) (0.85 ± 0.567 vs. 1.35 ± 0.710, p = 0.002). Body mass index (BMI), mean arterial pressure (MAP) and hemodynamic parameters were associated with this change. 2DST results did not correlate with aortic pulse wave velocity (aPWV) or augmentation index normalized to heart rate (AIx@75), suggesting a distinct difference between arterial stiffness of the CCA and other stiffness parameters. 2DST seems to be a promising new tool to assess arterial stiffness in TAVI patients. Full article