Search Results (294)

This study investigates the impact of mineralogical and petrographic characteristics on the mechanical behavior of granitic and mafic rocks from the Shuangjiangkou (Sichuan Province) and Damiao complexes (Hebei Province) in China. The research methodology combined petrographic investigation, comprising optical microscopy and Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy (SEM-EDS) methods, with methodical geotechnical characterization to establish quantitative relationships between mineralogical composition and engineering properties. The petrographic studies revealed three lithologic groups: fine-to-medium-grained Shuangjiangkou granite (45%–60% feldspar, 27%–35% quartz, 10%–15% mica), plagioclase-rich anorthosite (more than 90% of plagioclase), and intermediate mangerite (40%–50% of plagioclase, 25%–35% of perthite). The uniaxial compressive strength tests showed great variations: granite (127.53 ± 15.07 MPa), anorthosite (167.81 ± 23.45 MPa), and mangerite (205.12 ± 23.87 MPa). Physical properties demonstrated inverse correlations between mechanical strength and both water absorption (granite: 0.25%–0.42%; anorthosite: 0.07%–0.44%; mangerite: 0.10%–0.25%) and apparent porosity (granite: 0.75%–0.92%; anorthosite: 0.20%–1.20%; mangerite: 0.29%–0.69%), with positive correlations to specific gravity (granite: 1.88–3.03; anorthosite: 2.67–2.90; mangerite: 2.43–2.99). Critical petrographic features controlling mechanical behavior include the following: (1) mica content in granite creating anisotropic properties, (2) extensive feldspar alteration through sericitization increasing microporosity and reducing intergranular cohesion, (3) plagioclase micro-fracturing and alteration to clinozoisite–sericite assemblages in anorthosite creating weakness networks, and (4) mangerite’s superior composition of >95% hard minerals with minimal sheet mineral content and limited alteration. Failure mode analysis indicated distinct patterns: granite experiencing shear-dominated failure (30–45° diagonal planes), anorthosite demonstrated tensile fracturing with vertical splitting, and mangerite showed catastrophic brittle failure with extensive fracture networks. These findings provide quantitative frameworks that relate petrographic features to engineering behavior, offering valuable insights for rock mass assessment and engineering design in similar crystalline rock terrains. Full article

Understanding nonlinear fluid flow in fractured rocks is critical for various geoengineering and geosciences. This study investigates the evolution of seepage behavior under varying fracture surface roughness, confining pressures, and shear displacements. A total of four sandstone fracture specimens were prepared using controlled splitting techniques, with surface morphology quantified by Joint Roughness Coefficient (JRC) values ranging from 2.8 to 17.7. Triaxial seepage tests were conducted under four confining pressures (3–9 MPa) and four shear displacements (0–1.5 mm). Experimental results reveal that permeability remains stable under low hydraulic gradients but transitions to nonlinear regimes as the flow rate increases, accompanied by significant energy loss and deviation from the cubic law. The onset of nonlinearity occurs earlier with higher roughness, stress, and displacement. A critical hydraulic gradient Jc was introduced to define the threshold at which inertial effects dominate. Forchheimer’s equation was employed to model nonlinear flow, and empirical regression models were developed to predict coefficients A, B, and Jc using hydraulic aperture and JRC as input variables. These models demonstrated high accuracy (R² > 0.92). This work provides theoretical insights and predictive approaches for assessing nonlinear fluid transport in rock fracture. Future research will address mechanical–hydraulic coupling and incorporate additional factors such as scale effects and flow anisotropy. Full article

Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr–Coulomb criterion were developed to simulate bolt–rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Full article

High concrete gravity dams, particularly Roller-Compacted Concrete (RCC) types, face long-term safety challenges due to weak interlayer formation and crack propagation. This study presented a comprehensive evaluation of safety monitoring indexes for the Guxian high RCC dam (currently under construction) using both numerical and mathematical models. A finite element method (FEM) is employed with a strength reduction approach to assess dam stability considering weak layers. In parallel, a fracture mechanical model is used to investigate the safety of the Guxian dam based on failure assessment diagrams (FADs) for calculating the safety factor and the residual strength curve for calculating critical crack depth for two different crack locations, single-edge and center-through crack, to investigate the high possible risk associated with crack location on the dam safety. Additionally, the Guxian dam’s resistance to hydraulic fracture is assessed under two fracture mechanic failure modes, Mode I (open type) and Mode II (in-plane shear), by computing the ultimate overload coefficient using a proposed novel derived formula. The results show that weak layers reduce the dam’s safety index by approximately 20%, especially in lower sections with extensive interfaces. Single-edge cracks pose greater risk, decreasing the safety factor by 10% and reducing critical crack depth by 40% compared to center cracks. Mode II demonstrates higher resistance to hydraulic fracture due to greater shear strength and fracture energy, whereas Mode I represents the most critical failure scenario. The findings highlight the urgent need to incorporate weak layer behavior and hydraulic fracture mechanisms into dam safety monitoring, and to design regulations for high RCC gravity dams. Full article

Understanding and optimizing the relationship between critical processing parameters (rotational speed and dwell time) and the resulting weld performance is crucial for the effective application of friction stir spot welding (FSSW) in joining aluminum alloys. FSSW is an increasingly important solid-state, clean technology alternative for joining lightweight alloys such as AA5052-H32 in various industries. To optimize this technique for lap joint configurations, the current study examines the influence of rotational speeds (500, 1000, and 1500 rpm) and dwell times (1, 2, and 3 s) on the heat input energy, hardness across weld zones, and tensile/shear load, using a full factorial Design-Expert (DOE) analysis. The FSSW responses of the numerical model were validated using the experimental results for the spot-welded joints. The findings indicate that the dwell time significantly affected the mechanical properties, while the tool rotational speed had a substantial effect on the heat input energy and mechanical properties. Fracture surfaces predominantly exhibited ductile failure with diverse dimple morphologies, consistent with the enhanced tensile properties under optimal parameters. The presence of finer dimples suggests a mixed-mode fracture involving shear. Full article

The dynamic characteristics of fractured coal under cumulative impact are an important basis for evaluating the safety and stability of mining engineering. In order to study the dynamic mechanical properties of fractured coal under cumulative impact, the split-Hopkinson pressure bar (SHPB) device is used to conduct dynamic impact tests on fractured coal under cumulative impact. The wave velocity variation, dynamic compressive strength, fractal characteristics of fragmentation and energy dissipation properties of fractured coal samples under different impact times are analyzed. The results indicate that as the number of cumulative impacts increases, the decreasing trend of wave velocity of the coal samples conforms to the linear change relationship, and the rate of reduction varies with fracture inclination angles, demonstrating an inclination-dependent behavior. The dynamic compressive strength and energy dissipation rate of coal samples continuously decrease with the increase in cumulative impact times. The dynamic strength of the samples decreases approximately 25–40% after five time impacts. Coal samples with a fracture inclination angle of 30° show the largest decrease in dynamic compressive strength and are most prone to failure. As the number of cumulative impacts increases, the fractal dimension of the coal samples gradually increases, and the fragmentation mode transitions from large-size block failure to fine-grain pulverization. The failure mechanism converts from tensile failure to a mixed tensile–shear failure mode. The research findings provide a scientific basis for studying the mechanism of dynamic disasters in fractured coal samples under disturbance impact. Full article

The pre-inserted method for precast shear walls involves casting concealed beams at floor slabs between upper and lower structures, with precast concrete supports spaced at intervals. Vertical rebars at the base of upper walls are pre-inserted and anchored in the beams before slab casting. It offers advantages such as convenient construction without the need for grouting, demonstrating broad application prospects and significant promotional value. To evaluate seismic performance, quasi-static cyclic loading tests were conducted on five specimens: three full-scale pre-inserted precast walls and two cast-in-place counterparts. Under increasing lateral displacement, low axial-load specimens failed via tensile fracture of the outermost rebars, while high axial-load specimens failed by concrete crushing in compression. The test results showed that under identical axial-load ratios, the precast walls exhibited comparable bearing capacity, stiffness degradation, and energy dissipation to cast-in-place walls, but superior deformation ductility. The ultimate drift ratios of pre-inserted walls exceeded those of cast-in-place walls by 16.7% (axial-load ratio 0.2) and 22.2% (axial-load ratio 0.4), demonstrating robust seismic performance. Full article

To overcome the limitation of traditional elastic phase field models that neglect plastic deformation in rock compressive-shear failure, this study developed an elastoplastic phase field fracture model incorporating plastic strain energy and established a coupling framework for plastic deformation and crack evolution. By introducing the non-associated flow rule and plastic damage variable, an energy functional comprising elastic strain energy, plastic work, and crack surface energy was constructed. The phase field governing equation considering plastic-damage coupling was obtained, enabling the simulation of the energy evolution in rock from the elastic stage to plastic damage and unstable failure. Validation was carried out through single-edge notch tension tests and uniaxial compression tests with prefabricated cracks. Results demonstrate that the model accurately captures characteristics such as the linear propagation of tensile cracks, the initiation of wing-like cracks under compressive-shear conditions, and the evolution of mixed-mode failure modes, which are highly consistent with classical experimental observations. Specifically, the model provides a more detailed description of local damage evolution and residual strength caused by stress concentration in compressive-shear scenarios, thereby quantifying the influence of plastic deformation on crack driving force. These findings offer theoretical support for crack propagation analysis in rock engineering applications, including hydraulic fracturing and the construction of underground energy storage caverns. The proposed plastic phase field model can be effectively utilized to simulate rock failure processes under complex stress states. Full article

Snow avalanches occur in snow-covered highland mountains and represent one of the most significant natural hazards pertaining to the field of geoscience. Although some insight into the formation of avalanches has been provided, a comprehensive overview or critical review of the latest research is currently lacking. This paper reviews recent advances on the formation process of dry slab avalanches and provides a guiding framework for further research. The formation of avalanches is the consequence of a series of fracture processes in the snowpack, which is usually induced by the failure of a weak layer underlying a snow slab layer. The parameters at each stage of avalanches’ formation are reviewed from theoretical, experimental and simulation perspectives. In terms of the onset of crack propagation, the understanding of the mechanical process has gone through a transition from shear theory, to the anticrack model and supershear. The critical length shows divergent trends with snowpack parameters and slope angles, and there is a lack of consensus in different models. The specific fracture energy is also an essential component in determining fracture propagation. Within cracks’ dynamic propagation, the crack propagation speed includes both the sub-Rayleigh regime and supershear. The crack speed exceeds the shear wave speed in the supershear mode. When the crack propagation reaches a specific distance, the slab undergoes a tensile fracture and the cracking’s arrest. The numerical simulation allows a complete reproduction of the initial failure, the crack’s dynamic propagation and slab fracture. In the future, a unified model is necessary through refining the formative mechanism and integrating it with the avalanche flow. This work offers a comprehensive understanding of the mechanics of the formation and release of avalanches, useful for both modelers and experimentalists. Full article

In this study, Cantor alloys were prepared via powder metallurgy using spark plasma sintering (SPS) technology. The sintering parameters were systematically controlled, as follows: three temperature gradients (850 °C, 950 °C, and 1050 °C with a fixed holding time of 5 min) and three holding time gradients at 1050 °C (3, 5, and 10 min). The effects of the sintering parameters on the microstructure and mechanical properties were thoroughly analyzed. As the sintering temperature increased, the elemental particle bonding became more uniform, the internal porosity decreased, and densification improved, leading to gradual enhancements in the tensile strength and ductility. Conversely, a prolonged holding time reduced the grain boundary energy and induced grain growth, resulting in improved ductility but decreased strength. The critical shear stress (τ₀) and normal fracture stress (σ₀) were introduced to analyze the influence of the sintering temperature and holding time on the tensile strength and fracture modes. Wear morphology observations revealed scratches and stepped features in all of the samples, indicating that the dominant wear mechanism was adhesive wear. Full article

Thermoplastic fiber metal laminates (FMLs) are hybrid material systems that consist of a thin aluminum alloy sheet bonded to plies of fiber-reinforced adhesive. They provide excellent properties like fatigue strength, damage-tolerant properties, and inherent resistance to corrosion. However, they are still challenging materials in terms of the metal–composite interface, which is the weakest link in this material system. In this paper, an experimental–numerical method for the determination of the fracture stress and energy for metal–composite interlayer is presented and verified. The proposed method utilizes four different experimental tests: DCB test (interface opening—mode I), ENF test (interface shearing—mode II), MMB test (mixed-mode I+II—opening with the shearing of the interface) and three-point bending test (3PB). For each test, digital twin in the form of a numerical model is prepared. The established numerical models for DCB and ENF allowed us to determine fracture stress and energy for mode I and mode II, respectively. On the basis of the numerical and experimental (from the MMB test) data, the B-K exponent is determined. Finally, the developed material model is verified in a three-point bending test, which results in mixed-mode conditions. The research is conducted on the thermoplastic FML made of aluminum alloy sheet and glass fiber reinforced polyamide 6. The research presented is complemented by fundamental mechanical tests, image processing and Scanning Electron Microscopy (SEM) analysis. As an effect, for the tested material, fracture parameters are determined using the described method. Full article

To investigate the performance degradation of emulsified asphalt cold recycled mixtures (CRM) during service, this study selected a 10 km section of the cold recycled layer (CRL) from the Changjiu Expressway reconstruction project as the research subject. The deterioration patterns of key pavement performance indicators—including the Pavement Condition Index (PCI), Riding Quality Index (RQI), Rutting Depth Index (RDI), and Pavement Structure Strength Index (PSSI)—were analyzed in relation to cumulative equivalent axle loads over a 7-year service period. Concurrently, comparative evaluations were conducted on the mechanical properties, water stability, high-temperature performance, low-temperature crack resistance, and fatigue characteristics between in-service and laboratory-prepared emulsified asphalt CRM. The results demonstrate that after seven years of service, the emulsified asphalt cold recycled pavement maintained excellent performance levels, with PCI, RQI, RDI, and PSSI values of 92.6 (excellent), 90.1 (excellent), 88.5 (good), and 93.4 (excellent), respectively. Notably, while the indirect tensile strength and unconfined compressive strength of the CRL increased with prolonged service duration, other performance metrics—including the tensile strength ratio, shear strength, fracture work, and fracture energy—exhibited an initial improvement followed by gradual deterioration. Additionally, increased traffic loading during service led to a reduction in the residual fatigue life of the CRM. Interestingly, the study observed a temporary improvement in the fatigue performance of CRM during the service period. This phenomenon can be attributed to three key mechanisms: (1) continued cement hydration, (2) secondary hot compaction effects, and (3) diffusion and rejuvenation between fresh and aged asphalt binders. These processes collectively contributed to the partial recovery of aged asphalt strength, thereby improving both the mechanical properties and overall road performance of the CRM. The findings confirm that cold recycled pavements exhibit remarkable durability and maintain a high service level over extended periods. 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

Granite is widely used in laboratory rockburst simulations due to its exceptional strength, brittleness, and uniform composition. This study employs a true triaxial loading system to replicate asymmetric stress states near free surfaces, allowing precise control of three-dimensional stresses to simulate strain-mode rockbursts. Advanced monitoring tools, such as acoustic emission (AE) and high-speed imaging, were used to investigate the evolution process, failure mechanisms, and monitoring strategies. The evolution of strain-mode rockbursts is divided into five stages: stress accumulation, crack initiation, critical instability, rockburst occurrence, and residual stress adjustment. Each stage exhibits dynamic responses and progressive energy release. Failure is governed by a tension–shear coexistence mechanism, where vertical splitting and diagonal shear fractures near free surfaces lead to V-shaped craters and violent rock fragment ejection. This reflects the brittle nature of granite under high-stress conditions. The AE monitoring proved highly effective in identifying rockburst precursors, with key indicators including quiet periods of low AE activity and sudden surges in AE counts, coupled with ‘V-shaped’ b-value troughs, offering reliable early warning signals. These findings provide critical insights into strain-mode rockburst dynamics, highlighting the transition from elastic deformation to dynamic failure and the role of energy release mechanisms. Full article

To investigate the effects of impact and static compaction methods on the mechanical properties and crack evolution of rock-like materials with varying particle sizes. Uniaxial compression tests combined with Digital Image Correlation (DIC) technology were conducted on specimens of two aeolian sand gradations (0.075–0.18 mm and 0.22–0.5 mm) and one quartz sand gradation (0.22–0.5 mm). The study focused on elastic modulus, peak strength, stress-strain behavior, failure modes, surface deformation fields, crack propagation paths, and strain evolution at characteristic points under both compaction methods. Finally, the microstructure of specimens was analyzed and compared with natural rock analogs. Key results include: (1) At an identical density of 1.82 g/cm³, static-compacted specimens of fine-grained aeolian sand (0.075–0.18 mm) exhibited higher elastic modulus and peak strength compared to impact-compacted counterparts, whereas inverse trends were observed for coarse-grained aeolian sand (0.22–0.5 mm) and quartz sand specimens; (2) Under equivalent compaction energy (254.8 J), the hierarchy of mechanical performance was: quartz sand > coarse-grained aeolian sand > fine-grained aeolian sand; (3) Static-compacted specimens predominantly failed through tensile splitting, while impact-compacted specimens exhibited shear-dominated failure modes; (4) DIC full-field strain mapping revealed rapid propagation of primary cracks along pre-existing weak planes in static-compacted specimens, forming through-going tensile fractures. In contrast, impact-compacted specimens developed fractal strain field structures with coordinated evolution of shear bands and secondary tensile cracks; (5) Microstructural comparisons showed that static-compacted fine-grained aeolian sand specimens exhibited root-like structures with high porosity, resembling weakly consolidated sedimentary rocks. Impact-compacted coarse-grained aeolian sand specimens displayed stepped structures with dense packing, analogous to strongly cemented sandstones. Full article