Search Results (1,162)

Water-retaining roller-compacted concrete (RCC) dams suffer severe deterioration under coupled moisture ingress and freeze–thaw (F-T) cycles. To elucidate the damage mechanisms, this study employed industrial X-ray computed tomography (CT) synchronized with uniaxial compression and acoustic emission (AE) monitoring. The cross-scale damage evolution of RCC was investigated under dry, water-saturated, 25, and 50 F-T cycle conditions. The results indicate the following: (1) Macroscopically, F-T damage causes linear peak stress attenuation, shifting the failure mode from brittle axial splitting to ductile oblique shear. (2) Mesoscopically, frost-heaving stress expands native mesopores (500–2500 μm), increasing their volume fraction from 8.45% to 14.86% and remodeling isolated voids into a 3D interconnected defect network. (3) Microscopically, GMM-based AE clustering reveals a fracture transition. Driven by moisture lubrication and defect propagation, global shear cracks surpass the 50% threshold at 25 cycles (53.5%), reaching 68.6% at 50 cycles. (4) For cross-scale mapping, calibrating the AE b-value via Aki’s method decouples pore-water signal attenuation. Its pre-peak characteristic (an initial decrease followed by a rebound) accurately maps microcracks unstably coalescing along interconnected pores to form macroscopic shear planes. This cross-scale mechanism provides a scientific paradigm for condition monitoring of massive concrete in cold regions. Full article

This study presents a two-stage high shear-strain processing deformation technology, consisting of the intensive plastic deformation method of rotary swaging (RS), in combination with the severe plastic deformation method of continuous equal channel angular pressing (ECAP-Conform). The designed technology is experimentally tested at 25 °C, using a commercially pure titanium. Before each individual processing step, uniaxial compression testing is used to acquire stress–strain datasets to subsequently calculate the Hensel–Spittel rheology laws for both of the processing steps. These rheology models are further used to assemble Finite Element Analyses to numerically examine the stress–strain development within the studied material. The study also investigates and characterizes selected deformation parameters. Further, the predicted results are then put in correlation with the experimentally observed (sub)substructure development. The study documents that pre-processing via two passes of rotary swaging has highly positive effects on the substructure development and microstructure homogenization within the titanium workpiece, when compared to a workpiece subjected to just a single pass of ECAP-Conform. The unprocessed Ti and the Ti subjected to RS and ECAP-Conform exhibited faster work-hardening and higher flow stress than the Ti subjected solely to RS. The results also show that the two-stage high shear-strain processed titanium exhibited significantly higher homogeneity of distribution of the imposed strain than a conventional titanium subjected solely to ECAP-Conform. As confirmed by the numerical analyses, the nature of the material plastic flow during RS affected positively the homogeneity after ECAP-Conform. Full article

Sixteen reinforced concrete beams were tested under symmetric concentrated loading to investigate the mechanical behavior of beams designed using the compressive force path (CFP) method, in comparison with specimens designed according to the Chinese Code for Design of Concrete Structures (GB 50010-2010). The test variables included shear-span ratios (4.0, 3.0, 2.5, and 2.0) and sectional dimensions (150 × 300 mm and 250 × 550 mm). The test process and test results were systematically analyzed. The results show that the stress transmitted along the compressive force path is the main factor governing the shear capacity. The CFP beams achieved peak loads comparable to those of the GB beams while using 5.88–39.99% fewer stirrups, with larger savings observed for smaller shear-span ratios. The CFP method predicted the shear capacity with an error of approximately 10% (ranging from 2.24% to 12.45%). The shear strength of the CFP beams decreased with increasing shear-span ratio and effective depth. Overall, the CFP-designed specimens met the expected mechanical performance requirements, verifying the accuracy and applicability of the CFP method. Full article

Frozen soil on alpine slopes is influenced by inclination and aspect-induced differential solar radiation effects, resulting in non-uniform temperature fields and inclined layered ice lenses that enhance anisotropy and degrade mechanical properties. This study investigates the deformation and strength responses of frozen soil under different temperature-gradient magnitudes and orientations and ice-lens conditions. A stress–strain constitutive model incorporating the magnitude and orientation of the temperature gradient is established. In addition, an equal-scale discrete element model based on the parallel-bond contact model is developed and calibrated against the laboratory results. The numerical specimen is divided into 13 layers, and temperature-dependent interparticle bond properties are assigned layer by layer to reproduce the prescribed magnitude and orientation of the temperature gradient. Results show that the orientation of the temperature gradient significantly alters the mechanical response and failure mode. As the inclination angle increases, the failure mode transitions from compressive dilatancy to combined dilatancy–shear failure and ultimately to shear-dominated failure. At −10 °C, increasing the inclination angle from 0° to 30° reduces the compressive strength by 44.48%. The elastic modulus also decreases with increasing inclination, with a maximum inclination-induced difference of 111.98 kPa. Moreover, the presence of an ice lens further reduces specimen stiffness, and the elastic-modulus difference between ice-lens-bearing and ice-lens-free specimens increases from 5.57 kPa at −1 °C to 75.72 kPa at −10 °C. The DEM results show that particles at the top and bottom of the specimen primarily undergo vertical displacement, whereas particles in the middle region exhibit dominant horizontal displacement, forming an X-shaped shear band. The inclined temperature gradient produces a heterogeneous distribution of interparticle bond strength within each horizontal layer. As inclination increases, the shear band evolves from symmetric to asymmetric; particle displacements on the side toward which the temperature gradient points are larger than those on the opposite side, revealing the microscopic origins of macroscopic mechanical behavior. Full article

Concrete structures are prone to cracking during service, and epoxy grouting is a widely adopted technique for structural intervention. However, the inherent brittleness and poor durability of neat epoxy under complex loading and environmental exposure remain critical challenges. This study systematically evaluates the mechanical performance of epoxy-grouted concrete interlayer systems modified by carbon fiber (CF), glass fiber (GF), and polyethylene microspheres (PE). A comprehensive experimental program was conducted, including compression, three-point bending, and Brazilian splitting tests at three loading angles, combined with digital image correlation for surface strain monitoring. The effects of grout thickness and wet–dry cycles were systematically investigated. Results demonstrate that reinforcement modification helps to improve the performance of grouted concrete, with optimal behavior highly dependent on loading mode. CF-reinforced specimens with strong interfacial bonding exhibit the highest compressive strength, which is 150% higher than the bearing capacity of intact concrete, but are prone to brittle fracture under loading involving tension-shear interaction. GF reinforced specimens with moderate interfacial bonding exhibit better load-bearing capacity under tensile-shear stress interaction, reaching a normalized splitting peak load of 0.95 at a grouting thickness of 5 mm. PE-reinforced specimens with weak interfacial bonding provide relatively extensive energy dissipation. A 3 mm grouting layer shows favorable performance among the tested thicknesses, balancing load transfer enhancement and defect control. A single wet–dry cycle temporarily improves performance, possibly due to epoxy post-curing and pore filling, whereas repeated cycling generates cumulative micro-damage. GF- and CF-reinforced systems demonstrate the most stable resistance to short-term wet–dry conditioning. These findings provide guidance for loading-mode-dependent reinforcement selection in epoxy grouting applications. Full article

This article presents an experimental investigation into the mechanical properties of new laminated bamboo and bamboo–timber hybrid composite materials for construction. A total of thirty-six bamboo and bamboo–timber hybrid composite specimens were manufactured, which include a new configuration that integrates bamboo and pine strips in hybrid bamboo–timber composite members. An interleaved configuration of the hybrid bamboo–timber composites is proposed to enhance stress transfer and interfacial bonding. Such a design can mitigate global hygroscopic and thermal mismatch effects, including composites panel warping and continuous interfacial shear, through redistributing differential strains into small, localized scales. To minimize manufacturing energy demand, cold hydraulic pressing was used to prepare the specimens with bio-epoxy and polyvinyl acetate adhesives (PVAs). The list of experimental tests includes compression parallel to the grain, compression perpendicular to the grain, and flexure. The experimental results revealed that the developed bamboo and bamboo–timber composites outperform the reference materials consisting of commercial engineered bamboo and natural softwood. In particular, the average modulus of elasticity of the hybrid specimens bonded with bio-epoxy adhesive reaches 11.6 GPa (CoV = 13.8%), which is 40 percent greater than that of the tested commercial engineered bamboo specimens (CoV = 15.7%), emphasizing a stiffer and more reliable engineered bamboo. In the case of flexural testing, the hybrid bamboo–timber specimens reach the highest modulus of elasticity, while the engineered bamboo bio-epoxy test series exhibited a modulus of rupture that was 36% higher than that of the commercial engineered bamboo material with a CoV equal to 8%. Full article

Understanding the failure mechanism of soft rock roadways in high-humidity environments, as well as designing appropriate control measures, are critical for ensuring their stability. In this study, swelling and triaxial compression tests on argillaceous sandstone were first performed. Results show that the triaxial compressive strength (TCS), elastic modulus, cohesion, and internal friction angle of argillaceous sandstone are all decreased due to the water weakening effect. Then, a self-developed finite-element-based numerical code was employed to elucidate the role of humidity diffusion in the deformation and failure of soft rock roadways. Simulation results indicate that under the influence of humidity, high stress concentration zones develop, initiating microcracks within these regions. As humidity continues to diffuse, the high stress concentration zones expand and migrate deeper into the surrounding rock, causing microcracks to propagate and accelerating humidity diffusion. This cyclical process repeats, ultimately resulting in macroscopic fracturing. The failure of roadway exhibits a tensile–shear mixed mode during humidity diffusion. A comparative analysis of four control measures reveals that conventional non-waterproof shotcrete primary support is of limited effectiveness in ensuring the stability of high-humidity soft rock roadways. It is essential to promptly establish a closed waterproof support structure. Furthermore, localized support defects significantly impact control effectiveness. Full article

Thin spray-on liner (TSL) technology provides rapid and highly automated surface support for underground coal mine roadways. However, in deep roadways affected by high in situ stress, mining-induced disturbances, and fractured surrounding rock, conventional TSL materials require improved tensile–shear resistance, deformation compatibility, and support adaptability. Although fiber reinforcement is an effective method for enhancing polymer composites, systematic studies on the effects of fiber type and dosage in reactive polymer-based TSL materials remain limited. In this study, a commercially available two-component polyurea-silicate-based TSL matrix was reinforced with polyvinyl alcohol (PVA) fibers, polypropylene mesh fibers, and toughened polypropylene fibers at volume fractions of 0.25–1.50%. A stepwise experimental program, including uniaxial compression, variable-angle shear, tensile, circular-indenter buffered shear, and true triaxial tests, was conducted to evaluate the mechanical behavior and support-related performance of the fiber-reinforced TSL materials. The basic mechanical tests showed that the 0.75% toughened polypropylene fiber group maintained favorable compressive and shear resistance, achieving a cohesion of 8.65 MPa and an internal friction angle of 24.12°. PVA fibers exhibited higher tensile reinforcement efficiency at relatively low contents, with the 0.25% PVA fiber group reaching a peak tensile stress of 13.61 ± 1.00 MPa. The 1.0% PVA fiber group showed good deformation coordination, with a compressive strength of approximately 49.87 MPa. In the circular-indenter buffered shear test, the 1.0% PVA fiber group reached a peak load of 0.636 ± 0.055 kN and an absorbed energy of 3.118 ± 0.832 J at 10 mm displacement. Under true triaxial loading, the 1.0% PVA fiber group absorbed 311.4 J of energy at a displacement of 10 mm, approximately 5.5% higher than that of the 0.75% toughened polypropylene fiber group. Therefore, 1.0% PVA fiber reinforcement is recommended as the optimal reinforcement scheme for polymer-based TSL materials used in deep, fractured, and large-deformation coal mine roadways. Full article

Mesenchymal stem cells (MSCs) have become a focus of regenerative medicine research due to their potential utility in treating a variety of musculoskeletal disorders. Multiple qualities make them an ideal candidate to address musculoskeletal structural degeneration and inflammation, including their multi-lineage differentiation capacity, relative ease of extraction, and paracrine signaling capabilities. This narrative review examines the literature surrounding MSC-related therapies in musculoskeletal disorders, with a particular emphasis on mechanical and cellular factors affecting therapeutic efficacy. Multiple clinical and preclinical studies find that MSCs bolster tissue repair through a combination of extracellular matrix remodeling, inflammatory modulation, and regenerative signaling pathways. In addition, mechanotransduction signaling pathways have been discovered that convert mechanical tensile shear stress, compression, and strain forces into regulatory signals for matrix remodeling and tissue proliferation. Additional studies suggest that MSC efficacy and optimization are greatly influenced by a cell’s mechanical environment within the body. Further understanding of these mechanical factors can greatly bolster emerging regenerative therapies increasingly being utilized for musculoskeletal conditions. Full article

To address the challenge of surrounding rock control in deep gob-side entry driving, the return airway of the 20203 working face of the Dahaize Coal Mine was taken as the engineering background. The stress, deformation and plastic zone evolution characteristics of the surrounding rock of the gob-side entry were studied through theoretical analysis, numerical simulation and field tests, and the surrounding rock control mechanism and the double-layer flexible thick anchor control technology were proposed. The results show that under the influence of the adjacent gob, the peak compressive stress of the gob-side entry is transferred to the solid coal side, and tensile stress areas are generated on the roof; shear failure is the main failure pattern of the surrounding rock in the gob-side entry, which is characterized by significantly asymmetric deformation. Based on the displacement failure characteristics of the surrounding rock zones, a double-layer flexible thick anchorage structure was constructed. The anchorage depth of the first basic support exceeds the critical thickness of the shallow fractured surrounding rock zone, forming a thick load-bearing layer for the roadway surrounding rock; the anchorage depth of the secondary reinforced support extends into the stable rock mass, enhancing the bearing capacity of the anchored body and the roadway surrounding rock. The results of numerical simulation show that after adopting a double-layer flexible thick anchor support, the average deformation of the roof decreases by 48.81%, and the range of the tensile stress zone and plastic zone is significantly reduced. In engineering applications, the average deformation of the roadway roof was 42.58 mm, the two-end convergence was 0–2 mm, the roof separation value was controlled within 0–30 mm, and the rock strata within 0–5.0 m remained intact. This technology effectively suppresses the large deformation of the surrounding rock in deep gob-side entry, providing an innovative strategy for roadway stability control under comparable geological and mining conditions. Full article

This study investigates the flexural performance of prefabricated reinforced concrete (RC) beams with a novel UHPC–cogging–grouted sleeve composite joint. Five beam specimens—one cast-in-place reference and four prefabricated examples—were tested under four-point bending. The key parameters included the presence of interface shear keys and the configuration of middle connecting reinforcement. The results demonstrate that the proposed joint is generally consistent with the “strong joint, weak member” design philosophy. The specimen with shear keys and dedicated connecting bars (W2) achieved the highest peak load of 224 kN, 7.7% higher than the CIP beam, with the joint crack width limited to 0.2 mm at failure. Replacing dedicated bars with two bent-up bottom bars (W4) maintained acceptable performance (219 kN, 5.3% above CIP), while bending up four bars (W5) reduced the capacity to 200 kN, below the CIP level, inducing a near-under-reinforced flexural failure. The UHPC joint and shear keys effectively delayed cracking and suppressed joint damage but shifted the failure mode from flexural to shear-compression. The stress development in the rebars was fully consistent with the failure modes: the midspan rebar dominated in flexure-dominated specimens (580–596 MPa), whereas the loading-point rebar dominated in shear-compression-dominated ones (585–590 MPa). Plane section assumption was validated before cracking. Finite element models developed in ABAQUS reproduced the experimental behavior with deviations within 10%, and the stiffness degradation distributions accurately captured the damage patterns. Preliminary design recommendations are provided, suggesting that the proportion of bent-up bars should be conservatively controlled, subject to further experimental verification. Full article

Predicting compressive–shear fracture in rock masses containing complex flaw distributions remains a major challenge in rock engineering. We propose an improved non-ordinary state-based peridynamics (NOSB-PD) model to simulate rock fracture behavior in this work. A stabilized NOSB-PD formulation is developed by incorporating a bond-level deformation gradient strategy to effectively suppress the zero-energy mode inherent in conventional NOSB-PD formulations, thereby ensuring deformation compatibility and numerical robustness. More importantly, the triple-shear energy criterion is introduced into the PD framework for the first time, enabling a more accurate characterization of shear fracture in rocks under complex stress states. The proposed NOSB-PD model is validated using two examples, demonstrating its excellent capability in suppressing the zero-energy mode and capturing fracture behavior in rock under compressive–shear conditions. Subsequently, the proposed model is used to systematically investigate the influence of flaw distribution on crack propagation and failure modes in rocks. The results indicate that variations in flaw distribution alter the local stress field, leading to a change in the rock fracture mode. Consequently, the rock bridge failure mode transitions from shear-dominated direct coalescence to mixed tensile-shear failure, and finally to tension-dominated indirect failure. The overall rock specimen is more prone to tensile–shear-mixed failure under conditions of shorter rock bridges with larger inclinations, or longer rock bridges with smaller inclinations. These findings provide new insights into the role of flaw distribution on rock fracture behavior. Full article

The exploration of oil and gas resources is shifting toward ultra-deep and extra-deep reservoirs, including in the Tarim Basin, where various types of carbonate rocks are buried. Owing to the extreme burial depths, the mechanical behavior of these rocks under extra-deep conditions differs significantly from that of shallow formations, making it essential to understand their mechanical responses. This study investigated the mechanical properties and failure modes of carbonate rocks, specifically dolomite, argillaceous limestone, and pure limestone. Samples from extra-deep formations were initially analyzed for mineral composition and microstructure, after which uniaxial and triaxial compression tests were conducted to evaluate strength, static elastic modulus, and axial strain at peak stress. The results indicate that dolomite exhibits the highest mechanical strength and stiffness among the three lithologies. Under conditions of a high confining pressure of 100 MPa and a temperature of 160 °C, its elastic modulus and triaxial compressive strength are 65.4 GPa and 611.2 MPa, respectively, compared with 52.8 GPa and 444.2 MPa for limestone. Strength increases with confining pressure for all lithologies, with dolomite showing the most pronounced strengthening response. Although elevated temperature reduces rock strength, its effect is weaker than that of confining pressure. The failure mode is strongly controlled by confining pressure. At low confining pressures, failure is dominated by localized shear bands and brittle fracturing, whereas increasing confining pressure promotes a transition toward quasi-brittle deformation or ductile plastic flow. Dolomite predominantly maintains a quasi-brittle failure mode, argillaceous limestone exhibits a clear brittle-to-ductile transition, and pure limestone shows the greatest tendency to develop ductile plastic flow under high confining pressure conditions. The results further demonstrate that mineral composition and microstructural characteristics play critical roles in controlling the deformation and failure mechanisms of carbonate rocks. High-calcite pure limestone can exhibit ductile-like deformation behavior due to cataclastic processes, allowing significant strain without localization failure. These insights enhance understanding of carbonate rock behavior under extra-deep formations, informing practical applications in geology science. Full article

Developing Cu-based composites with excellent electrical and mechanical properties under multiphysics-coupled service conditions remains challenging. Novel Cu-Nb-Gr composites were fabricated by high-energy ball milling and High-pressure Multi-field Assisted Rapid Sintering. Experiments combined with computational fluid dynamics (CFD) and finite element method (FEM) simulations were used to investigate how Gr regulates material performance. The incorporation of 3 vol.% Gr promoted the formation of a semi-continuous Gr-rich structure coupled with an Nb-rich load-bearing structure. Under arc erosion, the semi-continuous Gr-rich structure provided efficient heat-conduction pathways, reducing the peak temperature and metal-vapor recoil force, while the Nb-rich load-bearing structure suppressed liquid–metal spattering and stabilized the molten pool. Simultaneously, Gr dynamically spread to form a continuous solid-lubricating film during sliding friction, significantly reducing the coefficient of friction and interfacial shear stress. Furthermore, under compressive loading, the semi-continuous Gr-rich structure coupled with the Nb-rich load-bearing structure alleviated interfacial elastic–modulus mismatch and extreme stress concentration, limiting macroscopic plastic deformation of the matrix. Consequently, Cu-Nb-3Gr achieved a favorable balance of arc-erosion resistance, wear resistance, and compressive performance, providing a new strategy for improving conventional Cu-based composites. Full article

Ice lenses in natural frozen soils commonly exhibit inclined and heterogeneous distributions, and their spatial morphology significantly influences the mechanical behavior of frozen soils. To investigate the coupled regulatory mechanism of ice lens inclination angle and thickness on the mechanical properties of frozen silty clay, specimens containing artificial single-layer ice lenses with varying inclination angles (0°, 10°, 20°, 30°) and thicknesses (5 mm, 15 mm) were prepared under constant temperature, water content, and loading rate conditions. Low-temperature uniaxial compression tests were conducted, and the results were systematically analyzed in conjunction with discrete element method (DEM) simulations and a modified Duncan–Chang model. The results indicate that increasing the ice lens inclination angle leads to a nonlinear reduction in the deviatoric stress at 15% axial strain, with the failure mode transitioning from compression-induced bulging to shear sliding dominance. When the ice lens thickness increased from 5 mm to 15 mm, the deviatoric stress at 15% axial strain further decreased across all inclination angles, accompanied by a reduction in the composite modulus. The response surface prediction formulas for parameters a and b, established based on experimental data, effectively describe the stress–strain relationships. DEM simulations reveal, at the mesoscale, the asymmetric displacement field and shear band evolution mechanisms governed by inclined ice layers, with bond breakage accelerating as the inclination angle increases. This study clarifies the coupled effects of ice lens spatial configuration and confining pressure on the mechanical response of frozen soils, providing a theoretical reference for bearing capacity assessment of frozen ground containing inclined ice lenses. Full article