Search Results (349)

The dip angle and thickness of coal seams are key geological determinants in mine system engineering. Roadways excavated in steeply inclined or thick coal seams typically exhibit significant deformation, with the combined geological configuration of steeply inclined thick seams thus presenting heightened support demands. Therefore, taking the 1502 level roadway in the Dayuan Coal Industry—situated in a steeply inclined thick coal seam—as an engineering case, mechanical models of roadways with different cross-sectional shapes are established, and the deformation and failure mechanisms of surrounding rock under different coal seam dip angles are analyzed. Based on this analysis, an asymmetric support technology scheme is proposed, followed by surrounding rock deformation monitoring and a support effectiveness evaluation. Key findings include the following: (1) in steeply inclined thick coal seam roadways with different cross-sectional shapes, the stress distribution and plastic zone development of surrounding rock follow a descending sequence, inclined roof trapezoidal section > rectangular section > arched section. Among these, the arched section is identified as the optimal roadway cross-sectional shape for this engineering context. (2) The stress-concentration area in the arch roadway aligns with the inclined direction of the coal seam, forming asymmetric stress concentration patterns. Specifically, as the coal seam dip angle increases, stress increases at the arch shoulder of the upper sidewall and the wall foundation of the lower sidewall. Concurrently, such stress concentration induces shear failure in the surrounding rock, which serves as the primary mechanism causing asymmetric deformation and failure in steeply inclined thick coal seam roadways. (3) In the 1502 level roadway, the asymmetric support technology with dip-oriented reinforcement was implemented. Compared to the original support scheme, roof deformation and sidewall convergence decreased by 46.17% and 46.8%, respectively. The revealed failure mechanisms of steeply inclined thick coal seam roadways and the proposed asymmetric support technology provide technical and engineering references for roadway support in similar mining conditions. Full article

Freeze-thaw (F-T) cycle tests and triaxial shear tests are conducted under varying freezing ambient temperatures and different F-T cycles for remolded loess. The results indicate that nearly all stress–strain curves of remolded loess exhibit strain-hardening behavior under varying freezing ambient temperatures and different F-T cycles. A decrease in freezing temperature alters the yield strain of loess and diminishes its resistance to deformation. As the freezing temperature decreases and the number of F-T cycles increases, the failure deviatoric stress of loess initially decreases, then increases, and eventually stabilizes. The most detrimental freezing temperature is −12 °C, which significantly exacerbates the adverse effects of F-T cycles on failure deviatoric stress. The strength indices initially decrease and then increase with decreasing freezing temperatures, while they first decrease and then stabilize with an increasing number of F-T cycles. Notably, the deterioration of cohesion is significantly greater than that of the internal friction angle. A quantitative analysis is conducted to examine the relationship between failure deviatoric stress, shear strength index, temperature, and freeze-thaw cycles. The fitting results effectively quantify the influence of different variables on the strength characteristics of loess. The findings of this research have significant theoretical implications for practical engineering applications in the northwest loess region. Full article

The structure, strength, and deformation characteristics of artificial structural loess can be manually controlled, which has significant advantages in scientific research on loess. By preparing and testing artificial structured loess, the natural properties of structured loess can be better investigated and studied. In this paper, the influence of varying moisture contents and additive dosages on artificial structured loess strength characteristics through triaxial shear tests were analyzed. The moisture content and additive dosage reflecting the structural properties of natural loess were obtained. Based on the microscopic test results, the mineral components, micromorphology, and pore characteristics of artificial structural loess were analyzed, and the mechanism of the structural evolution of loess under mechanical action was revealed. The results show that the minimum differences in the peak strength between W₁₆-Y_2.0C_2.0 and undisturbed soil under confining pressures of 50, 100, and 200 kPa are 6.481 kPa, 7.676 kPa, and 4.912 kPa, respectively. The minimum differences in the cohesion and inner friction angle between W₁₆-Y_2.0C_2.0 and undisturbed soil are 2 kPa and 0.2°, respectively, indicating that W₁₆-Y_2.0C_2.0 is the optimal structural soil with a structural strength closest to that of undisturbed soil. Compared with the undisturbed loess, the content of calcite in the artificial structure loess increases from 9.8% to 11.2%, the proportion of plagioclase decreases from 20.5% to 17.4%, amphibole is consumed completely, and 2.1% of halite is generated. Furthermore, the pores of structured soil exhibit a three-peak distribution and are divided into four types, including micropores (≤0.02 μm), small pores (0.02~0.21 μm), medium pores (0.21~13.5 μm), and large pores (≥13.5 μm). When the pressure increases from 50 kPa to 200 kPa, micropores increase by 4.67%, small pores increase by 4.97%, medium pores decrease by 2.4%, and large pores decrease by 7.24%. The trend of pore structure changes in W₁₆-Y_2.0C_2.0 is similar to that of undisturbed loess. The research results provide a reference for preparing and applying artificial structural loess. Full article

This study investigated the effects of electron beam radiation on the room-temperature and high-temperature mechanical properties of two ethylene-vinyl acetate (EVA) copolymers, designated EVA 206 and EVA 212. These copolymers had varying vinyl acetate (VA) contents (6 wt.% and 12 wt.%), with the same melt flow index of 2.0 g/10 min. Samples were irradiated at doses ranging from 60 to 180 kGy. The impact of electron beam irradiation on the creep, frequency sweep, and stress–strain behaviors of the ethylene-vinyl acetate copolymers was evaluated using a dynamical mechanical analyzer (DMA). Crystallinity was measured using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Creep compliance was quantitatively analyzed using four-parameter and six-parameter models. While crosslinking had minimal influence on the room-temperature properties, it significantly affected the behavior at 150 °C. With increasing irradiation dose, creep compliance decreased, while the shear modulus, viscosity, and shear stress at a strain of 0.03 increased, indicating enhanced resistance to deformation. Crosslink density also increased with irradiation dose. EVA 212 with a higher vinyl acetate content exhibited a higher resistance to creep and better high-temperature mechanical properties across all measurements. Full article

Expansive soils have significant characteristics of expansion by water absorption, contraction by water loss. Under the freeze–thaw (F-T) cycles, the engineering diseases are more significant, and the serious geotechnical engineering incidents are induced extremely easily. The aim is to investigate the mechanical response characteristics of geogrid-reinforced expansive soils (GRES) under F-T cycles. Based on a series of large-scale temperature-controlled triaxial tests, influencing factors were considered, such as the number of F-T cycles, the geogrid layers, and the confining pressure. The results showed that: (1) Friction between the expansive soil and geogrid and the geogrid’s embedded locking effect indirectly provided additional pressure, limited shear deformation. With the increase in reinforced layers, the stress–strain curve changed from a strain-softening to a strain-hardening type. (2) Elastic modulus, cohesion, and friction angle decreased significantly with increasing number of F-T cycles, whereas dynamic equilibrium was reached after six F-T cycles. (3) The three-layer reinforced specimens showed the best performance of F-T resistance, compared to the plain soil, the elastic modulus reduction amount decreases from 35.7% to 18.3%, cohesion from 24.5% to 14.3%, and friction angle from 7.6% to 4.5%. (4) A modified Duncan–Zhang model with the confining pressure, the F-T cycles, and the geogrid layers was proposed; the predicted values agreed with the measured values by more than 90%, which can be used as a prediction formula for the stress–strain characteristics of GRES under freeze–thaw cycling conditions. The research results can provide important theoretical support for the practical engineering design of GRES in cold regions. Full article

In nature, many brittle materials contain natural defects such as microcracks or joints, for example, rocks. Under water-saturated conditions, the strength of defective materials undergoes varying degrees of attenuation, leading to material failure and even structural instability in engineering contexts. Moreover, the deformation and failure of defective brittle materials are essentially the result of the accumulation and dissipation of energy. Studying the energy evolution of defective brittle materials under load is more conducive to reflecting the intrinsic characteristics of strength changes and overall failure of brittle materials under external loading. Natural defective brittle rock materials were firstly water saturated and triaxial compression tests were performed to determine the mechanical properties of water-saturated materials. The energy evolution patterns of water-saturated materials under varying confining pressures were also obtained. Using the discrete element method, the macro- and micro-failure characteristics of water-saturated materials were investigated, revealing the mesoscopic mechanisms of deformation and failure evolution in these materials. The results indicate that confining pressure significantly enhances the peak compressive strength and elastic modulus of water-saturated defective materials. When the confining pressure increased from 0 MPa to 20 MPa, the peak strength and elastic modulus of the water-saturated materials increased by 126.8% and 91.9%, respectively. Confining pressure restricts the radial deformation of water-saturated materials and dominates the failure mode. As confining pressure increases, the failure mode transitions from tensile splitting (at 0 MPa confining pressure) to shear failure (at confining pressures ≥ 10 MPa), with the failure plane angle gradually decreasing as confining pressure rises. Confining pressure significantly alters the energy storage–release mechanism of water-saturated defective brittle materials. At peak load, the total energy, elastic energy, and dissipated energy increased by 347%, 321%, and 1028%, respectively. The ratio of elastic energy storage to peak strain ratio shows a positive correlation, and the elastic storage ratio of water-saturated defective brittle materials under confining pressure is always higher than that without confining pressure. When the strain ratio exceeds 0.94, a negative correlation between confining pressure and the rate of elastic storage ratio is observed. From the perspective of mesoscopic fracture evolution in water-saturated defective brittle materials, the crack propagation path shifts from the periphery to the center of the material, and the fracture angle decreases linearly from 89° to 58° as confining pressure increases. The dominant direction of crack development is concentrated within the 45–135° range. The findings elucidate the mechanisms by which water saturation and confining pressure influence the strength degradation of natural defective brittle materials from both mesoscopic and energy perspectives, providing theoretical support for the stability control of related engineering structures. Full article

Due to the widespread prevalence of respiratory diseases such as COVID-19 and H1N1, the use of disposable masks has increased significantly. Consequently, the environmental issues arising from their accumulation have become increasingly severe. This study, therefore, aims to investigate the potential of using masks as soil reinforcement materials. This study conducted triaxial and seepage tests on mask–calcareous sand mixtures with varying ratios to examine the effects of mask content on the strength, modulus, particle fragmentation, and permeability coefficient of calcareous sand, as well as the influence of different mask sizes on shear strength and shear dilation. The results demonstrate that with an increase in mask content, the peak stress ratio of the mask–calcareous sand mixture increases by 4% per level, and the internal friction angle rises by approximately 1.6% per level. Conversely, water permeability and shear swelling are reduced, and particle loss decreases by over 70%. The reinforcing effect of the mask is attributed to the high friction between the mask and the calcareous sand at the contact interface, which restricts the movement of soil particles during deformation, thereby enhancing the overall strength of the mixture. Among the three mask sizes, the smallest mask–calcareous sand mixture exhibited the greatest improvement in shear strength, and the shear shrinkage effect was more pronounced. This indicates that particle size also significantly influences the mechanical properties of the mixtures. The reinforcing effect of the mask on the soil results from the high friction at the interface between the mask and the calcareous sand. When the soil deforms, the mask enhances the overall strength of the mixture by restricting the movement of soil particles. Considering the impact of masks on the performance of calcareous sand, it can be concluded that the optimal mass content of masks is 0.3%. This study offers a new perspective on the reuse of discarded masks in civil engineering applications. Full article

A solid/liquid continuous composite casting technology was developed to produce brass-clad copper stranded wire billets efficiently with continuous casting speeds ranging from 200 mm/min to 1000 mm/min. As the casting speed increased, the microstructure of the brass cladding transformed at an angle to the radial direction. The wire billet prepared at a casting speed of 600 mm/min was then subjected to drawing. As the percentage reduction in area of the billet increased from 11.9 to 81.5% during the drawing process, the tensile strength improved from 336 MPa to 534 MPa, while the elongation after fracture decreased from 30.1 to 4.7%. Meanwhile, dislocation, dislocation cells, and microbands successively formed in the pure copper strand wires, while twins, shear bands, dislocation pile-ups, and secondary twins gradually formed in the brass cladding. During the drawing process, the interface between copper and brass remained metallurgically bonded, exhibiting coordinated deformation behavior. This paper clarified the evolution of microstructure and mechanical properties of brass-clad copper stranded wires in high-speed solid/liquid continuous composite casting and drawing, which could provide important reference for industrial production. Full article

Calcareous sand, a critical construction material in reef engineering and building foundations, possesses unique internal microstructures and inherent mechanical properties. Given these characteristics, it is essential to thoroughly evaluate its strength under various loading conditions to ensure its reliability in building applications. This study examines the strength, deformation, and failure characteristics of calcareous sand through consolidated drained shear failure tests using a GDS stress path triaxial apparatus. The effects of shear rate, particle gradation, and compactness are systematically investigated to assess their impact on structural stability in building foundations and load-bearing applications. The results indicate that at low confining pressures, calcareous sand exhibits strain softening, whereas at higher confining pressures, strain hardening is observed. For samples with the same gradation, both peak deviatoric stress and failure strain increase linearly with confining pressure. The volume strain evolution during shear follows three stages: shear shrinkage, shear dilatancy, and stabilization. At low confining pressures, dilatancy is favored, while high confining pressures promote shrinkage. Additionally, under constant confining pressure, peak strength increases and failure strain decreases linearly with compactness. Increasing the loading rate from 0.01 to 0.1 mm/min results in a slight increase in the friction angle, with minimal impact on cohesion. Particle gradation plays a significant role in determining the shear strength of calcareous sand, as its effects vary depending on the combination of compactness and gradation. These findings provide valuable insights for the design and construction of stable building foundations, roadbeds, and other load-bearing structures in reef engineering and coastal developments, where calcareous sand is widely used. Full article

The glass–glass interfaces (GGIs) play an important role during the plastic deformation of metallic nano-glasses (NGs) such as Sc-Fe NGs. In this work, Co-P nano-glasses are synthesized by pulse electrodeposition. Their mechanical properties are characterized by micro-pillar compression and compared to those obtained by molecular dynamics (MD) simulation. The MD simulation reveals that the GGIs with a particular incline angle (about 50.0°) in the direction of applied uniaxial strain is preferable for the accommodation of localized plastic deformation in NGs. The results are consistent with those obtained by spherical aberration-corrected transmission electron microscopy, which reveals that most of shear bands form an angle of about 58.7° to the direction of compressive strain applied on the Co-P micro-pillar. The phenomena are explained with the differences in chemical composition and atom diffusion in the glassy grain interiors and in the GGI regions. This work sheds some light on the deformation mechanisms of NGs and provides guidelines for designing NGs with improved mechanical properties. Full article

This research explores the dynamic characteristics of composite nano-beams with a hybrid cellular structure (HCS) core, composed of two segments with distinct unit cell configurations, and face sheets reinforced with carbon nanotube (CNT) composites. By considering three-layered sandwich beams with aluminum cores of varying unit cell angles, the study explores a broad spectrum of achievable Poisson’s ratios. The top and bottom face sheets incorporate CNTs, distributed either uniformly or in a functionally graded manner. The governing equations are derived using Eringen’s nonlocal elasticity framework and the modified theory of shear deformation, with solutions obtained via the Galerkin method. A detailed parametric analysis is conducted to evaluate the effects of CNT content, arrangement configurations, hybrid core cellular angles, nonlocal parameters, and slenderness ratio (L/h) on the dimensionless natural frequencies of sandwich nanobeams with hybrid cellular cores. A key contribution of this study is the presentation of natural frequencies for nanobeams with hybrid cellular cores and composite face sheets reinforced with functionally graded CNTs, derived from advanced theoretical formulations. These findings offer new insights into design optimization and highlight the potential applications of hybrid cellular sandwich nanobeams in cutting-edge engineering systems. Full article

This research is based on the frequency response of angle-ply laminated cylindrical shells under higher-order shear deformation theory. The higher-order shear deformation theory is used to model the displacement and rotational functions, which are approximated by cubic and quintic splines. The eigenvalue problem is obtained with the simply supported boundary condition. The frequency of cylindrical shells is analyzed by varying the circumferential node number, length, number of layers, and layer alignment. The competence of the formulation is verified by comparing it with the available results of higher-order zigzag theory. Full article

Current deep excavation applications, which pose risks for constructing high-rise buildings and infrastructures, are increasing. Therefore, the increasing urbanization, underground infrastructure requirements, and time and cost constraints in construction projects have led to a growing demand for rapid, economical, and safe deep excavation designs. Although numerical modeling tools enable rapid analyses, the reliability of soil engineering parameters remains a challenge due to natural variability, sample disturbances, and differences between laboratory and field test conditions. In this study, PLAXIS 2D (Version 24) was used to model a deep excavation, allowing for the assessment of soil–structure interaction and excavation-induced deformations. The objectives are to compare field data with the numerical model and identify which soil parameters are critical for excavation. Through the sensitivity analysis, the study highlighted that the variations in shear strength parameters, such as cohesion and internal friction angle, are crucial and shall be precisely determined. The performed analyses revealed that even minor changes in the internal friction angle can dramatically impact displacements by doubling them and highlight the significant disparity between the minimum and maximum margins. The numerical analysis underscores the need for precise parameter measurement and careful analysis to achieve reliable results and ensure safer, more effective designs. The comparison of numerical results with field measurements confirmed the model’s accuracy. Full article

Steel-lattice transmission towers require efficient and reliable connection designs to ensure structural safety and cost-effectiveness. While traditional gusset plate connections increase their complexity and structural weight, direct bolted connections offer a simpler and lighter alternative. However, the adoption of staggered bolt arrangements, necessitated by the geometric constraints of chord angle members, challenges the applicability of existing design standards—particularly regarding block shear and net section failure modes. This study explores the structural behavior of staggered two-bolt angle connections through a combination of experimental testing and numerical modeling. Twelve full-scale specimens were subjected to axial tension to investigate the effects of key geometric parameters, including end distance, edge distance, and bolt stagger. Finite element analyses, which incorporate material nonlinearity and fracture criteria, delve deeper into the stress distribution and failure mechanisms. The results demonstrate significant deviations in failure modes compared with conventional parallel bolt arrangements, underscoring the limitations of current design standards (DL/T 5486, ASCE 10-15, and EN 1993-1-8) in accurately predicting the capacity of staggered connections. Based on the identified failure modes of staggered two-bolt connections, this study proposes an enhanced design methodology for member fracture capacity, incorporating block shear calculation models from the three aforementioned standards. Comparative analysis demonstrates that the ASCE standard provides superior predictive accuracy, with experimental validation exceeding 95% agreement. The study culminates in specific design recommendations for staggered two-bolt connections, offering critical insights into stress redistribution mechanisms, material behavior, and deformation-induced failure patterns. These findings contribute to the development of more accurate and safer design guidelines for bolted connections in steel transmission towers. Full article

In this study, finite element numerical simulations were used to investigate the deformation of critical vehicle components and the damage characteristics of the retaining wall at the end of the emergency escape ramp after the impact of a Ford 800 truck on the retaining wall of the refuge lane. A finite element model of the reinforced concrete retaining wall of the truck was created using the LS-DYNA (R11.0) program and the correctness of the constructed finite element model was confirmed by tests. The parameters of the reinforced concrete retaining wall were determined using orthogonal tests. Finite element numerical simulations of vehicle impact on the retaining wall were carried out, and the results showed that two stages of deformation occurred at the front and rear sides of the cockpit during the impact process, and the damage of the retaining wall increased with the increase in the vehicle speed, the impact angle, and the bumper stiffness. Punching shear damage occurred in the impact region of the wall and shear damage occurred at the corners of the wall. Full article