Search Results (82)

The soil water characteristic curve (SWCC) is a key foundation in unsaturated soil mechanics describing the relationship between matric suction and water content, which is crucial for studies on effective stress, permeability coefficients, and other soil properties. In natural environments, colluvial and residual soils typically exhibit high pore heterogeneity, and previous studies have shown that the SWCC is closely related to the distribution of pore sizes. The SWCC of soils may display either a unimodal or bimodal distribution, leading to different hydraulic behaviors. Past unsaturated slope stability analyses have used the unimodal SWCC model, but this assumption may result in evaluation errors, affecting the accuracy of seepage and slope stability analyses. This study proposes a novel bimodal hydro-mechanical coupling model to investigate the influence of bimodal SWCC representations on rainfall-induced seepage behavior and stability of unsaturated slopes. By fitting the unimodal and bimodal SWCCs with experimental data, the results show that the bimodal model provides a higher degree of fit and smaller errors, offering a more accurate description of the relationship between matric suction and effective saturation, thus improving the accuracy of soil hydraulic property assessment. Furthermore, the study established a hypothetical slope model and used field data of landslides to simulate the collapse of Babaoliao in Chiayi County, Taiwan. The results show that the bimodal model predicts slope instability 1 to 3 h earlier than the unimodal model, with the rate of change in the safety factor being about 16.6% to 25.1% higher. The research results indicate the superiority of the bimodal model in soils with dual-porosity structures. The bimodal model can improve the accuracy and reliability of slope stability assessments. Full article

This study explored the effects of the finishing deformation temperature on the microstructure and properties of CrVNb micro-alloyed steel following thermomechanical processing (TMP). The investigation encompassed the influence of the deformation temperature on the ferrite grain size, precipitate characteristics, hardness and flow stress. The microstructure characterization was performed using optical and electron microscopy techniques. The results show that decreasing the deformation temperature refined the ferrite grains, though a bimodal ferrite grain structure formed when the deformation temperature fell to about 100 °C below the Ar3 temperature. Additionally, lower deformation temperatures increased the number density of strain-induced precipitates (SIPs), whereas the density of finer precipitates (random and interphase precipitates (IPs)) decreased. The highest hardness was observed in a sample deformed at 950–850 °C temperatures. These findings highlight the impact of the finishing deformation temperatures on the microstructural and mechanical properties, providing valuable insights for optimizing steel processing conditions. Full article

Welding and cutting behaviour may affect the mechanical properties of titanium alloy welded structures, which may have some impact on the safety assessment of the structure. This study analyses changes in residual stress in Ti80 butt-welded thick plates before and after wire-cut electric discharge machining, using numerical simulations based on thermo-elastoplastic theory and the element birth and death method, validated by X-ray non-destructive testing. The transverse residual tensile stress near the weld exhibits an asymmetric bimodal distribution, while the longitudinal stress is significantly higher than the transverse stress. Wire-cut electric discharge machining had minimal influence on the transverse residual stress distribution but led to partial relief of the longitudinal residual tensile stress. The maximum reductions in transverse and longitudinal welding residual tensile stresses are approximately 60% and 36%, respectively. The findings indicate that wire-cut electric discharge machining can alter surface residual stresses in Ti alloy butt-welded thick plates. This study also establishes a numerical simulation methodology for analysing welding residual stresses and their evolution due to wire-cut electric discharge machining. The results provide a theoretical basis for analysing the structural strength and safety of Ti-alloy-based deep-sea submersibles. Full article

Wheat exhibits moderate tolerance to salinity. The increasing salinization of arable land poses a significant risk to future wheat production. Therefore, it is imperative to expedite the genetic breeding of wheat for enhanced salt tolerance. This study investigates the genetic and phenotypic diversity of 90 wheat varieties under salt stress, utilizing a comprehensive approach involving trait distribution analysis, hierarchical clustering, kinship estimation, and low-density association analysis. The phenotypic analysis of key agronomic traits revealed significant variability in traits such as leaf area index, canopy temperature, grain area, dry weight, harvest index, grain yield, and tiller number. Most traits exhibited a near-normal distribution, with a few parameters showing skewed or bimodal distributions, indicating the presence of subpopulations with distinct trait profiles. The hierarchical clustering analysis identified five distinct genetic clusters among the wheat varieties, highlighting the complex genetic relationships and variations in salt stress tolerance. Kinship estimates further confirmed the presence of genetic divergence among the accessions, with a majority showing weak or null relationships. Statistical models for association analysis revealed the effectiveness of the Generalized Linear Mixed Model (GLMM) in detecting a greater number of significant genetic markers associated with key agronomic traits, with the GLMM explaining a higher proportion of phenotypic variation. The findings underline the importance of genetic diversity in wheat breeding programs aimed at improving salt stress tolerance and agronomic performance. These results provide valuable insights for future breeding strategies, focusing on the optimization of key traits and marker-assisted selection for the development of salt-tolerant wheat cultivars. Full article

This study explored the innovative foaming behavior of a novel biodegradable polymer blend consisting of polylactic acid/poly(butylene succinate)/poly(butylene adipate-co-terephthalate) (PLA/PBS/PBAT) enhanced with nanohydroxyapatite (nHA), using supercritical carbon dioxide (SCCO₂) as an environmentally friendly physical foaming agent. The aim was to investigate the effects of various foaming strategies on the resulting cell structure, aiming for potential applications in tissue engineering. Eight foaming strategies were examined, starting with a basic saturation process at high temperature and pressure, followed by rapid decompression to ambient conditions, referred to as the (1T-1P) strategy. Intermediate temperature and pressure variations were introduced before the final decompression to evaluate the impact of operating parameters further. These strategies included intermediate-temperature cooling (2T-1P), intermediate-temperature cooling with rapid intermediate decompression (2T-2P), and intermediate-temperature cooling with gradual intermediate decompression (2T-2P, stepwise ΔP). SEM imaging revealed that the (2T-2P, stepwise ΔP) strategy produced a bimodal cell structure featuring small cells ranging from 105 to 164 μm and large cells between 476 and 889 μm. This study demonstrated that cell size was influenced by the regulation of intermediate pressure reduction and the change in intermediate temperature. The results were interpreted based on classical nucleation theory, the gas solubility principle, and the effect of polymer melt strength. Foaming results of average cell size, cell density, expansion ratio, porosity, and opening cell content are reported. The hydrophilicity of various foamed polymer blends was evaluated by measuring the water contact angle. Typical compressive stress–strain curves obtained using DMA showed a consistent trend reflecting the effect of foam stiffness. Full article

High-speed electrical discharge machining (EDM) is crucial for drilling aerospace components, but the fatigue effects of its recast layer are still not well understood. This study investigates the fatigue behavior of high-speed EDM-processed specimens using ultrasonic fatigue testing and microscopic analysis. The recast layer showed a 20.4% increase in hardness and a 16.5% decrease in elastic modulus compared to the base material. Fatigue cracks originated from microcracks, pores, and inclusions within the recast layer, as well as at its interface with the substrate. Microscopic crack initiation was influenced by defect interactions, while macroscopic crack initiation occurred near the maximum hole diameter perpendicular to the loading direction due to stress concentration. The specimens exhibited bimodal fatigue life: shorter lifetimes were observed when macroscopic stress concentrations overlapped with recast layer defects such as cracks and voids, while defect-free regions significantly extended durability. The non-uniform distribution of the recast layer critically links microstructural heterogeneity to variations in fatigue failure. These findings highlight how recast layer characteristics influence crack nucleation and life variability in EDM-processed components, offering valuable insights for optimizing machining parameters to reduce fatigue risks in critical aerospace applications. Full article

This study explored the effects of T5 and T6 heat treatments on the microstructure and tensile properties of a laser powder bed fusion (LPBF)-fabricated Al–Mn–Mg–Sc–Zr alloy. The as-built condition exhibited a bi-modal grain structure of equiaxed and columnar grains. Specimens after T5 heat treatment also had a bi-modal microstructure with slight grain growth and the precipitation of secondary Al₃Sc, which enhanced the yield strength via precipitation hardening but reduced ductility. In contrast, T6 treatment triggered recrystallization, and the microstructure was only coarse equiaxed α-Al grains. This microstructure change was accompanied by coarsened primary Al₃X and Al₆(Mn, Fe) precipitates, partial Mg₂Si dissolution, and significant secondary Al₃Sc particle growth. Consequently, T6-treated specimens showed lower strength than their T5 counterparts and the poorest ductility due to brittle fracture induced by the stress concentration effect of coarse precipitates at grain boundaries. Full article

To investigate the dynamic characteristics, energy dissipation patterns, and failure modes of granite with filled joints of varying thicknesses under impact loading, we utilized the Split Hopkinson Pressure Bar (SHPB) test setup for impact tests on both unfilled and filled granite samples. Additionally, a high-speed camera was used to capture the dynamic failure and crack propagation processes of the rock samples in real time. The results indicate that the thickness of the filling material significantly affects the stress–strain behavior of jointed rock masses, particularly in terms of characteristics of stress variation and post-peak morphology. In comparison to unfilled jointed rock samples, a distinct “stress bimodal” phenomenon is present, and the rebound of strain following the peak gradually decreases. The fracture patterns observed in the jointed rock samples are primarily characterized by tensile failure. Damage is notably more pronounced on the left side of the samples (near the incident bar), the lower side, and in the areas filled with gypsum. The most severe degree of damage occurs when the filling thickness is 7.56 mm. As the thickness of the filling increases, the dynamic compressive strength of the rock mass diminishes, and the peak strain first increases and then decreases. Concurrently, the energy reflection coefficient of the rock mass increases linearly, while the energy transmission coefficient declines linearly. Furthermore, the energy dissipation ratio first increases and then decreases. The test data reveal that the critical filling thickness influencing the dynamic properties, energy absorption characteristics, and damage degree of jointed rock samples falls within 4.91 mm to 7.56 mm. Full article

In the process of deep mining, the dynamic disasters of coal and rock occur frequently under the action of high stress and high seepage pressure, the essence of which is energy-driven coal rock failure. In order to explore the energy evolution law and damage mechanism of sandstone with intermittent cracks under the coupling effect of stress and seepage, in this paper, by comparing the differences in mechanical characteristics between fractured rock and intact rock, the energy evolution characteristics, crack propagation, and micro-damage mechanism of fractured rock under different confining pressures and seepage pressures are analyzed. The research shows that: (1) The local stress drop phenomenon occurs in the fractured rock during the loading process, and the stress–strain shape is ‘bimodal’. At the same time, there is stress concentration at both ends of the fracture. (2) The energy conversion of the fractured rock changes in stages during loading. As confining pressure rises, the energy storage limit and the maximum dissipation energy go up. The increase in seepage pressure reduces the energy storage limit, while the dissipation energy shows an upward trend. The energy consumption ratio curve shows ‘concave’ evolution during the loading process. (3) Based on the dissipation energy and residual stress, the damage state of the specimen is analyzed, and the proposed damage variable can reasonably explain the whole process of the damage evolution of intermittent fractured rock under stress and seepage. (4) The increase in confining pressure increases the friction between the particles inside the sample and promotes the transformation of the sample from tensile failure to shear failure. The seepage pressure reduces the friction between the particles in the sample through the air wedge effect to deepen the damage degree, thus promoting the tensile failure of the sample. Full article

Background: Hearing loss in children can have a detrimental impact on their development, thus lowering the psychological well-being of parents. This study examined the amount of parental stress, learned helplessness, and perceived social support in mothers of children with hearing loss (MCHL) and mothers of typically developing children (MTDC), as well as the relationship between various possible contributing factors to parental stress such as learned helplessness and perceived social support. Method: Three questionnaires measured parental stress (Parental Stress Scale; PSS), learned helplessness (Learned Helplessness Scale; LHS), and perceived social support (Perceived Social Support-Friends PSS-Fr and Perceived Social Support-Family PSS-Fa Scale) in 100 MCHL and 90 MTDC. All mothers had normal hearing and children aged 1 to 12 years. Mothers of children with any degree of bilateral sensorineural hearing loss, using hearing aids and/or cochlear implants, were included in the MCHL group. Children with hearing loss did not have any additional disabilities. Results: Parental stress and learned helplessness were not significantly different between the groups. The perceived social support was significantly lower in MCHL as compared to MTDC. Pearson correlation analysis with pooled data from both groups showed a small but significant negative correlation between parental stress and perceived social support. A moderately significant positive correlation existed between learned helplessness and parental stress. The relationship between learned helplessness and perceived social support was negative, being small but significant. Conclusions: The study findings indicate that parental stress was similar in both groups. As perceived social support increased, parental stress and learned helplessness decreased. Thus, the present study findings indicate the need for developing greater social support for MCHL. Full article

The development of high-strength aluminum alloys with improved ductility is a crucial challenge for modern materials science, as high strength and ductility tend to be mutually exclusive properties. In this work, the composite material was fabricated using wire arc additives manufactured from AA1050 (commercially pure aluminum) and AA5056 (an Al–Mg system alloy) aluminum alloys. It was demonstrated that the addition of a lower-strength material into a high-strength matrix enhances the potential for deformation localization and results in an increased plasticity of the composite material. A further strengthening of the composite material was achieved through its deformation by a high-pressure torsion (HPT) technique. The mechanical properties of the material were thoroughly investigated before and after the HPT treatment. Static strength and plasticity were analyzed as a function of the deformation degree. Microstructural analysis was performed using scanning electron microscopy and X-ray diffraction. The optimal deformation route, providing the best combination of mechanical properties, was experimentally identified, along with key microstructural parameters of the formed composite with a bimodal grain structure. A deformation level corresponding to 36% of shear stress provides a yield stress of up to 570 MPa, an ultimate tensile strength of up to 664 MPa, and a relative elongation to failure of up to 7%. As a result of the deformation treatment, characteristic substructures with dimensions of ~250 nm and >1000 nm are formed, with a volume ratio of approximately 80/20. Full article

The trimodal grain-structured (TGS) carbon nanotube-reinforced aluminum matrix composites (CNT/Al) exhibit better strength–ductility synergy compared to bimodal grain-structured (BGS) composites. The addition of fine grain (FG) to the TGS composites effectively facilitates strain hardening and reduces strain/stress concentrations. In order to address the strain incompatibility in TGS composites, a significant accumulation of geometrically necessary dislocations (GNDs) occurs at the hetero-zone boundaries. This accumulation serves as the key factor in generating additional strengthening and work hardening. By utilizing a multi-mechanism strain gradient model, a quantitative analysis of the contributions made by Hall–Petch, Taylor, and back stress strengthening was conducted. Furthermore, effects of each domain volume fraction on the GND density at the boundaries between heterogeneous domains were carefully and extensively investigated and compared. It is found that the strengthening effect of back stress significantly surpasses that of the Hall–Petch and Taylor strengthening accounting. Compared to BGS composites, the TGS composites are more effective in facilitating strain hardening and reducing strain/stress concentrations, which may lead to a better balance between strength and ductility. Full article

Strong mine pressure often emerges when the working face of the lower coal seam in a closely spaced coal seam system passes through the remaining coal pillar in the overlying goaf. This study investigates the law of overburden movement and the manifestation of mine pressure during mining under the remaining coal pillar. A physical model measuring 2.5 × 0.2 × 1.503 m is constructed. Fiber Bragg grating sensing technology (FBG) and Brillouin optical time domain analysis technology (BOTDA) are employed in the physical model experiment to monitor the internal strain of the overlying rock as the working face advances. This study determines the laws of overlying rock fracture and working face pressure while mining coal seams beneath the remaining coal pillar. It analyzes the relationship between the pressure at the working face and the strain characteristics of the horizontally distributed optical fiber. A fiber grating characterization method is established for the stress evolution law of overlying rock while passing the remaining coal pillar. The experimental results indicated that the fracture angle of overlying rock gradually decreases during the mining stage through and after the coal pillar. In the mining stage through the coal pillar, the cycle pressure step distance of the working face is reduced by 33.3% compared to the stage after mining through the coal pillar. Initially, the strain pattern of the horizontal optical fiber is unimodal when pressure is first applied to the working face, and it transitions from unimodal to bimodal during periodic pressure. The peak value of fiber Bragg grating compressive strain and the range of influence of advanced support pressure are 3.6 times and 4.8 times, respectively, before passing through the remaining coal pillar. Finally, the accuracy of the FBG characterization method is verified by comparing it to the monitoring curve of the coal seam floor pressure sensor. The research results contribute to applying fiber optic sensing technology in mining physical model experiments. Full article

Heterostructured materials consist of heterogeneous zones with dramatic variations in mechanical properties, and have attracted extensive attention due to their superior performance. Various heterostructured materials have been widely investigated in recent years. In the present study, a combination of two different types of heterogeneous structures, a surface bimodal structure and gradient structure, was designed using the traditional surface mechanical attrition treatment (SMAT) method in pure copper, and the mechanical properties and microstructural evolution of dual-heterostructure Cu were studied in depth. In total, 100 stainless steel balls with a diameter of 6 mm were utilized to impact the specimen surface at room temperature for a short period of time. In this work, the sample surface was divided into hard areas and soft areas, along with a roughly 90 μm gradient structure in the cross-sectional direction after 30 s of SMAT processing. After the partial SMAT processing, lasting 30 s, the strength increased to 158.0 MPa and a considerable ductility of 25.7% was sustained, which overcomes the strength–ductility trade-off. The loading–unloading–reloading (LUR) test was utilized to measure the HDI stress, and the result showed that the HDI stress of the partial SMAT sample was much higher than the annealed one, especially for the Cu-SMAT-30S specimen, the strength of which increased from 80.4 MPa to 153.8 MPa during the tensile test. An in situ digital image correlation (DIC) investigation demonstrated that the strain developed stably in the Cu-SMAT-10S specimen. Furthermore, electron backscatter diffraction (EBSD) was carried out to study the microstructural evolution after partial SMAT processing; the KAM value increased to 0.34 for the Cu-SMAT-10S specimen. This research provides insights for the effective combination of superior strength and good ductility in dual-heterostructure materials. Full article

This study presents the development of a highly robust, pressureless, and void-free silver sinter-bonding technology for power semiconductor packaging. A bimodal silver paste containing silver nanoparticles and sub-micron particles was used, with polymethyl methacrylate (PMMA) as an additive to provide additional thermal energy during sintering. This enabled rapid sintering and the formation of a dense, void-free bonding joint. The effects of sintering temperature and PMMA content on shear strength and microstructure were systematically investigated. The results showed that the shear strength increased with rising sintering temperatures, achieving a maximum of 41 MPa at 300 °C, with minimal void formation due to enhanced particle necking facilitated by PMMA combustion. However, at 350 °C, the shear strength decreased to 35 MPa due to cracks and voids at the copper substrate–copper oxide interface caused by thermal expansion mismatch. The optimal PMMA content was found to be 5 wt.%, balancing sufficient thermal energy and void reduction. This pressureless sintering technology demonstrates significant potential for high-reliability applications in power semiconductor modules operating under high-temperature and high-stress conditions. Full article