Search Results (10,000)

Plasticized polyvinyl chloride (PVC-P) geomembranes (GMBs) are widely used in cold regions as impervious barriers, facing combined low-temperature and variable loading effects. However, design specifications rely on room-temperature tests at fixed rates, not reflecting actual conditions. This study systematically investigates the axial tensile properties of a 1.5 mm thick PVC-P GMB across eight temperatures (−40 °C to 20 °C) and five tensile rates (1–100 mm/min). A total of 211 uniaxial tensile tests were conducted using a low-temperature system with a servo-hydraulic machine and DIC extensometer. Nominal and true stress–strain curves were analyzed. Results show that fracture strength, fracture strain, and elastic modulus are highly sensitive to temperature and tensile rate, with a pronounced coupling effect between these two factors. Lower temperatures increase fracture strength and elastic modulus but reduce fracture strain, leading to brittle transition at −40 °C, especially at high rates. The fracture strength, fracture strain, and elastic modulus all increased with tensile rates at low tensile rates (1–20 mm/min). However, negligible difference in these parameters at high rates (20–100 mm/min) was observed. Elastic modulus follows a Boltzmann function with temperature, and fracture strain linearly correlates with temperature (R² > 0.93). The mechanical properties measured at room temperature overestimate the deformability at low-temperature and hence underestimate the brittle failure risk. Therefore, future cold-region testing should adopt tensile rates of 10 or 20 mm/min, and temperature-rate coupled constitutive models should be developed. These findings provide essential data and guidance for material selection, design, and standard revision for PVC-P GMBs in cold-region applications. Full article

This study addresses the production of 3D printing filament by extrusion from acrylonitrile butadiene styrene blends containing virgin and recycled material. The effect of recycled acrylonitrile butadiene styrene content on selected quality indicators was investigated, with particular emphasis on mechanical response and filament diameter stability. Dimensional stability was considered a critical quality parameter, as diameter fluctuations directly affect material flow consistency during subsequent FFF/FDM processing and may contribute to extrusion-related defects. The fracture surface morphology of the tested filaments was evaluated by optical microscopy. Based on experimental measurements and data analysis, recommendations are proposed to improve the stability of the filament extrusion process when processing ABS blends containing recycled material. Full article

The reciprocating cutterbar is evolving from a conventional harvesting mechanism into an intelligent end-effector for crop harvesting, mechanical weeding, and selective cutting. However, plant anisotropy, moisture-dependent fracture, root-soil constraints, vibration, and wear still hinder low-energy cutting, long service life, and robust control. This review integrates harvesting and mechanical weeding within a unified analysis of reciprocating cutterbar technologies. It first links plant tissue structure and dynamic fracture to blade penetration, fiber stretching, crack propagation, and energy dissipation. It then examines how cutting speed, sliding-cut angle, blade clearance, and root-soil anchorage jointly affect performance. Advanced testing, response surface methodology, discrete element method, finite element method, and multiphysics simulations are compared for failure analysis, parameter optimization, and contact modeling. The review further assesses bionic blade design, surface strengthening, composite coatings, novel transmissions, multisource perception, and adaptive control. Key barriers include inconsistent plant-mechanics datasets, computationally intensive models, limited field robustness, and conflicts among performance objectives. We therefore identify digital twins, modular electric cutterbars, and closed-loop control as priorities for translating mechanistic insight into reliable field performance. Full article

Owing to its unique pyramid-shaped stacked abrasive structure, the pyramid belt pro-vides fine and uniform grinding performance, making it increasingly attractive for precision grinding applications. However, the wear evolution behavior of such belts during the grinding of GH4169 superalloy has not yet been systematically understood. In this study, a full-life-cycle pyramid belt wear experiment in grinding of GH4169 was conducted under fixed conditions. Three monitoring points were arranged along the belt length, and the same abrasive agglomerate arrays were repeatedly tracked using a digital microscope and optical profilometer, while a scanning electron microscope was used to identify the wear mechanisms. The results show that the main wear modes include agglomerate flat wear, fracture, pull-out, and metal adhesion, with flat wear dominating throughout most of the belt life. Across the belt width, the wear height exhibits an approximately symmetric distribution, with more severe wear in the central region. Temporally, the wear process comprises an initial rapid-wear stage followed by a steady-wear stage. In addition, belt wear evolution significantly affects the ground surface roughness, which first decreases and then increases with wear progression. These findings clarify the material-specific wear characteristics of the pyramid belt during GH4169 grinding and reveal the spatial and temporal characteristics of its wear evolution. Full article

Localized densification of nanoporous silica under combined mechanical compression and elevated temperature involves coupled pore collapse, skeletal rearrangement, and thermally activated sintering. Clarifying how local pre-compression regulates these processes is important for understanding the surface and near-surface densification of nanoporous silica and related porous materials. In this study, the microscopic sintering behavior of a silica-inspired aerogel-like nanoporous model under the coupling of non-uniform local stress and high-temperature fields (indentation depths of 50–150 Å and temperatures of 298–1800 K) was systematically investigated using molecular dynamics simulations combined with a three-dimensional (3D) topological recognition algorithm (probe sphere method and DBSCAN clustering). The results indicate that the sintering densification of the silica-inspired aerogel model exhibits significant pore-size dependence and a “depth-temperature inverse relationship”: the local pre-compression induced by the 150 Å indentation facilitates thermally activated atomic rearrangement and shifts the onset of densification to a lower temperature, leading to an early bimodal splitting of the pore size distribution at 1300 K, accompanied by a significant jump in the elastic modulus from 3.0 to 10.07 GPa. In contrast, the 50 Å shallow region requires heating to 1800 K to achieve an equivalent densification effect. Furthermore, topological analysis quantitatively reveals the phase transition process of the pore network from connected to isolated: taking 1300 K as an example, the number of connected pore clusters decreases from the initial 86 to 70 (at 1000 ps), marking the fracture of the connected network; subsequently, the number of isolated pores surges to 4861, and the residual connected framework is severely fragmented into 136 micro-clusters. Based on the above microstructural and topological evolution data, a four-stage thermo-mechanical synergistic evolution process of the silica-inspired aerogel model is summarized. These findings provide quantitative fundamental data that conceptually supports the design of functional gradient structures with alternating “dense-thermally-conductive” and “porous-thermally-insulating” layers within a single continuous aerogel matrix; such structures may be realized in the future through strategies such as arrayed nanoindentation combined with high-temperature sintering. Full article

Primary hyperparathyroidism (PHPT) and vitamin D deficiency (VD) are two frequent medical conditions in the Western world. Purely by dint of their prevalence, these conditions are commonly comorbid. Moreover, they can interact with one another: VD may stimulate PTH secretion, while PHPT may lead to unregulated vitamin D activation from 25-hydroxyvitamin D (25OHD) to 1,25-dihydroxyvitamin D (1,25OH2D), thereby lowering 25OHD levels and further exacerbating VD. Thus, a real conundrum arises: should the careful clinician replete VD in PHPT or not? On the one hand, both conditions could lead to bone mineral density (BMD) loss if untreated, ultimately resulting in osteoporosis and fragility fractures; on the other hand, vitamin D supplementation could lead to further worsening of hypercalcemia and its dreaded complications. To complicate matters, patients undergoing parathyroidectomy (PTX) after long-standing PHPT can also suffer from postoperative hungry-bone syndrome and symptomatic hypocalcemia, which may be further exacerbated by VD. This narrative review aims to summarize the relevant pathophysiological mechanisms underlying these two diseases and their complex interactions. The latest evidence regarding thresholds and targets for vitamin D supplementation in PHPT will be discussed, with a focus on the balance between benefits and risks. Full article

During the operation of large reservoirs, slope rock masses at different elevations are subjected to confining pressure variation and alternating wet–dry cycles induced by water-level fluctuations, resulting in the evolution of their mechanical properties. To investigate this issue, conventional triaxial compression tests were conducted on limestone from Badong County in the Three Gorges Reservoir area under confining pressures of 5–20 MPa and 0–50 wet–dry cycles. The results show that confining pressure significantly enhances limestone strength, whereas wet–dry cycles induce a progressive deterioration in mechanical properties. Under the same confining pressure, the deterioration exhibits a staged characteristic, with a rapid decrease at the early stage followed by a slower decline. Higher confining pressure effectively suppresses crack propagation and mitigates the degradation caused by wet–dry cycling. Meanwhile, wet–dry cycles promote the transition of the failure mode from single-fracture failure to multi-fracture fragmentation. The elastic modulus, cohesion, and internal friction angle all decrease exponentially with increasing wet–dry cycles. Based on damage mechanics theory, a constitutive relationship considering wet–dry cycle effects was established to characterize rock stiffness degradation and its influence on the overall mechanical response. The proposed model effectively describes the evolution of mechanical parameters and deformation characteristics under wet–dry cycling conditions. This study provides an experimental and theoretical basis for evaluating the long-term stability of reservoir slopes. Full article

Background: The aim of this study was to investigate the association between glenoid anatomy and proximal humeral fracture geometry and to identify radiographic parameters associated with multi-segment and articular fractures. Methods: In this retrospective observational study, 113 patients treated for proximal humeral fractures between 2016 and 2019, regardless of treatment modality, were included. Demographic characteristics, injury mechanisms, and fracture classifications were recorded. Fracture geometry and complexity were evaluated using the Neer and AO/OTA classification systems. Glenoid anatomy was assessed by measuring the Critical Shoulder Angle (CSA), glenoid inclination, and glenoid version on radiographs. Multivariable ordinal logistic regression was performed to adjust for age, sex, and injury mechanism. Results: Older age was correlated with higher Neer and AO/OTA types (p = 0.031, r = 0.176; p = 0.013, r = 0.208, respectively). Glenoid inclination was correlated with fracture geometry and fragmentation according to the Neer classification (p = 0.007, r = 0.228), while glenoid inclination and version were correlated with the AO/OTA classification (p = 0.028, r = 0.181; p = 0.014, r = −0.207, respectively). However, these associations were not independently associated with fracture configuration after multivariable adjustment, whereas older age remained independently associated with higher AO/OTA classification. Conclusions: Glenoid morphometric parameters showed weak univariate associations with proximal humeral fracture configuration but were not independent predictors after adjustment for age, sex, and injury mechanism. These findings suggest that glenoid morphology is only one of several factors contributing to fracture configuration and warrants further investigation in larger prospective studies. Full article

This study systematically investigates the effects of gold tailings (GT) sand substitution levels and particle fineness on the rheological behavior, mechanical properties, and microstructural characteristics of Engineered Cementitious Composites (ECC). The results demonstrate that incorporating moderate amounts of GT sand (≤75%) effectively enhances both the compressive strength and fracture toughness of the composite. However, complete substitution (100% GT) significantly increases matrix porosity, leading to a consequent reduction in comprehensive mechanical strength. A critical size-dependent decoupling effect was observed: while the full replacement of fine aggregates with coarse GT severely degrades compressive strength due to excessive void formation, it unexpectedly increases the matrix fracture toughness by inducing significant crack deflection and tortuosity. Conversely, the incorporation of fine GT optimizes the distribution of matrix flaws and fosters a stable fiber pull-out mechanism. Consequently, despite a reduced pseudo-strain hardening (PSH) index, the fine GT-blended ECC achieves a remarkable tensile ductility of up to 3.0% by satisfying the fundamental multiple-cracking energy criteria while maximizing frictional energy dissipation. Furthermore, substituting natural silica sand with GT yields a highly sustainable composite, reducing carbon dioxide emissions by 41% and material costs by 20% without compromising core mechanical performance. Full article

Geohazards in rock mass are essentially results of fracturing evolution. Regarding deeper exploration, to better contribute to evaluating and predicting instability, Particle Flow Code (PFC) has gained increasing popularity because of its logical resemblance in simulating rock composition and cracking processes. However, micro-parameter calibrations in PFC mainly focus on both the peak strength and macroscopic cracks in many previous, as well as current, studies, resulting in the existence of two widely used yet distinct strategies in stiffness calibration. The first is to ensure the consistency of the elastic modulus, and the second is to ensure the deformation consistency at peak-stress states. Do these two stiffness calibrations have a strength equivalence? To explore it, several rock mechanical tests—with and without confining pressures and a pre-existing flaw—were numerically conducted using PFC for two materials produced by these two distinct stiffness-calibration strategies. The results demonstrate that the two stiffness calibrations can yield equivalent strength parameters, including tensile strength, cohesion, and internal friction angle. This strength equivalence could be attributed to the evolutionary process of micro-crack initiation, accumulation, nucleation, and global failure (coalescence). Fracture mechanics analysis demonstrates that crack initiation is independent of the elastic modulus and marginally influenced by Poisson’s ratio, leading to a negligible impact of stiffness-calibration distinction on crack-initiation stress. Subsequent micro-crack accumulation follows a nearly identical non-linear increasing trend, with a high consistency of spatial distributions in stress concentration, displacement gradient, and strain localization. As a result, the near-identical structural logic in micro-crack nucleation results in failure-pattern consensus and governs the macro-scale strength equivalence of these two distinct stiffness-calibration strategies. These findings could help us to better comprehend those previous, as well as current, research results based on the two stiffness-calibration strategies. Full article

Reservoir-triggered seismicity (RTS) is commonly associated with stress perturbations induced by reservoir loading and pore-pressure diffusion within fractured rock masses. Shortly after the initial impoundment of the Irapé Hydropower Plant (Minas Gerais, Brazil), a sequence of induced earthquakes was recorded, providing an opportunity to investigate the compatibility between reservoir loading and the observed seismic response. This study presents a first-order hydromechanical assessment integrating finite element modelling, analytical elasticity solutions, and pore-pressure diffusion theory to evaluate the spatial distribution of stress perturbations and the characteristic diffusion times associated with reservoir impoundment. A two-dimensional elastic model was developed to simulate stress redistribution induced by the maximum reservoir load, while a parametric diffusion analysis was performed for representative hydraulic diffusivities and hypocentral depth scenarios between 1 and 6 km. Numerical results showed excellent agreement with the analytical elasticity solution (RMSE = 14.36 kPa, MAE = 11.08 kPa, mean relative error = 1.38%, and R² = 0.999), supporting the reliability of the numerical model. The simulations indicate that vertical stress perturbations decrease from approximately 1.8–2.0 MPa immediately beneath the reservoir to about 0.01–0.1 MPa at kilometer-scale depths, where the recorded seismicity is presumed to occur. The diffusion analysis indicates that pore-pressure propagation to these depths generally requires substantially longer times than the interval between reservoir filling and the onset of seismic activity. Nevertheless, owing to uncertainties in hydraulic diffusivity, fracture connectivity, and hypocentral depth estimates, the diffusion results are interpreted as a first-order sensitivity analysis rather than a site-specific prediction. Overall, the results support the temporal compatibility and physical plausibility of rapid elastic stress redistribution as a potential triggering mechanism, while recognizing that the available geological and seismological data are insufficient to establish a direct causal relationship or demonstrate fault reactivation. Full article

Si₃N₄ ceramics with a YF₃-MgSiN₂ binary additive system were fabricated by hot pressing (HP) and spark plasma sintering (SPS) at 1500–1700 °C, followed by annealing at 1850 °C for 6 h. The effects of sintering route and temperature on phase transformation, microstructure evolution, thermal conductivity, and mechanical properties were systematically investigated. SPS significantly accelerated the α→β phase transformation compared with HP, and the β-Si₃N₄ content in SPS samples exceeded 94% at 1600 °C. After annealing, all samples were completely transformed into β-Si₃N₄, accompanied by obvious grain growth. Thermal conductivity was closely related to both grain size and relative density. Grain growth reduced grain-boundary phonon scattering, whereas density loss and residual porosity deteriorated heat transport. The mechanical properties were jointly governed by β-Si₃N₄ content, grain morphology, and porosity. Elongated β-Si₃N₄ grains promoted crack deflection and crack bridging, thereby improving fracture toughness, while excessive porosity reduced flexural strength. These results demonstrate that optimizing the balance between phase transformation, grain growth, and densification is essential for tailoring the thermal and mechanical performance of Si₃N₄ ceramics containing non-oxide sintering additives. Full article

In order to verify the reliability and engineering applicability of the AE-CMT welding technology for magnesium alloy joining, AE-CMT welding experiments were conducted at welding speeds ranging from 0.5 to 3.0 m/min on 1.5 mm-thick H24-temper AZ31B magnesium alloy sheets using imported 1.2 mm-diameter WE-33M welding wire. Within the welding speed range of 0.5–3.0 m/min, increasing the welding speed progressively reduces heat input, thereby refining grains and homogenizing the microstructure. The welding heat input of the AE-CMT process ranges from 0.47 KJ/mm to 1.07 KJ/mm, and the grain sizes of the weld zone and HAZ are 9.61–14.18 μm and 6.35–12.22 μm, respectively. In the range of 0.5–2.0 m/min welding speed, increasing welding speed progressively enhances the tensile strength of the welded joint. Notably, joints fabricated at a welding speed of 2.0 m/min deliver the maximum tensile strength, equivalent to 98.0% of the base metal. Well-defined dimples are also detected on the corresponding fracture surfaces. A further increase in welding speed leads to a gradual reduction in the tensile strength of the welded joint. It is demonstrated that welding speed acts as a critical process parameter for tailoring the microstructure and mechanical properties of AE-CMT-welded AZ31B magnesium alloy joints. Full article

Reservoir stimulation is essential in enhanced geothermal systems and unconventional reservoirs where low permeability, inadequate fracture connectivity, or near-wellbore damage restricts commercial injection or production. This review evaluates hydraulic fracturing, thermal stimulation, plasma-pulse stimulation, and selected dynamic stimulation technologies. It compares their physical mechanisms, fracture-network development, reservoir applications, permeability enhancement, operational maturity, deployment challenges, and future perspectives. Hydraulic fracturing remains the most mature method for reservoir-scale fracture creation, fracture conductivity, and reservoir connectivity. In enhanced geothermal systems, however, performance depends on the heat-exchange area, distributed flow, thermal sweep, long-term energy recovery, and induced-seismicity control rather than permeability enhancement alone. Thermal stimulation is integral to geothermal reservoir development. Cold-fluid injection generates thermoelastic stress redistribution, enlarges the fracture aperture, activates natural fractures, promotes thermally assisted fracture propagation, and influences thermal breakthrough. Plasma-pulse stimulation, also termed pulsed-power plasma, electrohydraulic, or shock-wave stimulation, provides a low-water method for near-wellbore permeability enhancement, damage bypass, fracture reactivation, and restimulation. Its broader deployment remains constrained by the limited treatment radius, scale-up uncertainty, energy-transfer efficiency, tool durability, completion integrity, and insufficient field validation. Liquid CO₂ phase-transition, propellant, and explosive stimulation provide additional dynamic-loading options with distinct fracture responses, controllability, safety, and technology readiness. Stimulation technologies should therefore be selected according to the dominant reservoir limitation and evaluated using sustained injectivity or productivity, effective reservoir contact, distributed flow, delayed thermal breakthrough, treatment durability, wellbore integrity, and a controlled geomechanical response. Future progress requires hybrid stimulation, coupled thermal–hydraulic–mechanical–chemical (THMC) modeling, integrated monitoring, adaptive control, physics-informed artificial intelligence, digital twins, standardized field validation, and techno-economic and life-cycle assessments. Full article

To address the severe threats posed by stay cable fractures, this study investigates a fatigue fracture of a fork-eye anchor head induced by excessive cable vibrations on a landscape cable-stayed bridge. A comprehensive methodology integrating field monitoring, theoretical analysis, and finite element simulation is employed to reveal the vibration characteristics, fatigue mechanism, and multi-factor coupled effects. Field tests identify wind-induced vibration and parametric resonance as the primary external triggers for fatigue damage. A simplified mechanical model of the fork-eye anchor head is established to evaluate the stress state under combined axial tension and bending moment. Fatigue analysis using the stress–life method elucidates how vibration-induced alternating stress significantly reduces the fatigue life of the connecting screw. The multi-factor coupled fracture mechanism is revealed, and practical mitigation measures including supplementary dampers and regular inspection are proposed. The findings provide a theoretical basis and engineering guidance for the design, maintenance, and safety assessment of similar landscape cable-stayed bridges. Full article