Search Results (103)

The deformation control of surrounding rock in the combustion air zone is crucial for the safety and efficiency of underground coal gasification (UCG) projects. Coal-bearing sandstone, a common surrounding rock in UCG chambers, features a brittle structure composed mainly of quartz, feldspar, and clay minerals. Its mechanical behavior under high-temperature and dynamic loading is complex and significantly affects rock stability. To investigate the deformation and failure mechanisms under thermal–dynamic coupling, this study conducted uniaxial impact compression tests using a high-temperature split Hopkinson pressure bar (HT-SHPB) system. The focus was on analyzing mechanical response, energy dissipation, and fragmentation characteristics under varying temperature and strain rate conditions. The results show that the dynamic elastic modulus, compressive strength, fractal dimension of fragments, energy dissipation density, and energy consumption rate all increase initially with temperature and then decrease, with inflection points observed at 400 °C. Conversely, dynamic peak strain first decreases and then increases with rising temperature, also showing a turning point at 400 °C. This indicates a shift in the deformation and failure mode of the material. The findings provide critical insights into the thermo-mechanical behavior of coal-bearing sandstone under extreme conditions and offer a theoretical basis for designing effective deformation control strategies in underground coal gasification projects. Full article

In response to the high cost and environmental impact of backfill materials in Xinjiang mines, an eco-friendly, large-volume composite was developed by bonding desert-sand mortar to waste concrete. A rock-filled concrete process produced a highly flowable mortar from desert sand, cement, and fly ash. Waste concrete blocks served as coarse aggregate. Specimens were cured for 28 days, then subjected to uniaxial compression tests on a mining rock-mechanics system using water-to-binder ratios of 0.30, 0.35, and 0.40 and aggregate sizes of 30–40 mm, 40–50 mm, and 50–60 mm. Mechanical performance—failure modes, stress–strain response, and related properties—was systematically evaluated. Crack propagation was tracked via digital image correlation (DIC) and acoustic emission (AE) techniques. Failure patterns indicated that the pure-mortar specimens exhibited classic brittle fractures with through-going cracks. Aggregate-containing specimens showed mixed-mode failure, with cracks flowing around aggregates and secondary branches forming non-through-going damage networks. Optimization identified a 0.30 water-to-binder ratio (Groups 3 and 6) as optimal, yielding an average strength of 25 MPa. Among the aggregate sizes, 40–50 mm (Group 7) performed best, with 22.58 MPa. The AE data revealed a three-stage evolution—linear-elastic, nonlinear crack growth, and critical failure—with signal density positively correlating to fracture energy. DIC maps showed unidirectional energy release in pure-mortar specimens, whereas aggregate-containing specimens displayed chaotic energy patterns. This confirms that aggregates alter stress fields at crack tips and redirect energy-dissipation paths, shifting failure from single-crack propagation to a multi-scale damage network. These results provide a theoretical basis and technical support for the resource-efficient use of mining waste and advance green backfill technology, thereby contributing to the sustainable development of mining operations. Full article

Exhaust manifolds accumulate creep and fatigue damage under cyclic thermal loading, leading to localized failure. Understanding a material’s mechanical behavior is crucial for accurate life assessment. This study systematically investigated the low-cycle fatigue (LCF) and creep–fatigue interaction behaviors of medium-silicon molybdenum ductile iron. It was found that QTRSi4Mo exhibited cyclic hardening at room temperature and 400 °C, whereas it exhibited cyclic softening at 600 °C and 700 °C for low-cycle stress–strain responses. During creep–fatigue tests with hold time, variations in the strain amplitude did not alter the hysteresis loop shape or the hardening/softening characteristics of the material. They only induced a slight upward shift in the yield center. Additionally, stress relaxation primarily occurred in the initial phase of the hold period, so the hold duration had little effect on the final stress value. The investigation of creep–fatigue life models highlighted that accurately characterizing the damage induced by stress relaxation during the hold stage is critical for creep damage evaluation. The calculated creep damage results differed greatly from the experimental results of the time fraction model (TF). A combined approach using the strain energy density dissipation model (T-SEDE) and the Ostergren method demonstrated excellent predictive capability for creep–fatigue life. Full article

Energetic structural materials (ESMs) are widely studied due to their high energy density, which enhances their potential in various industrial and engineering applications, such as in energy absorption systems, safety devices, and structural components that need to withstand dynamic loading. A high-strength WMoZrNiFe energetic structural material was prepared, and its mechanical properties and ignition behavior under dynamic loading were studied. Using the split-Hopkinson pressure bar (SHPB) experimental device, samples with different initial tilt angles of 0°, 30°, and 45° were dynamically loaded. The influence of the sample tilt angle on the ignition threshold was analyzed. The dynamic mechanical properties, failure modes, and ignition threshold based on the energy absorption of the WMoZrNiFe energetic structural material during the dynamic loading process were obtained. The results show that the material has a strain rate effect in the range of 1000 s⁻¹~3000 s⁻¹. The yield strength of the sample with a tilt angle of 0° increased from 1468 MPa to 1837 MPa, that of the sample with a tilt angle of 30° increased from 982 MPa to 1053 MPa, and that of the sample with an inclination angle of 45° increased from 420 MPa to 812 MPa. Through EDS elemental analysis, the ignition reaction mechanism of the WMoZrNiFe energetic structural material under dynamic compression was obtained. The violent reaction of the material occurred after the material fractured, and the active elements reacted with oxygen in the air. Full article

In complex geological environments, the discontinuous dynamic response behavior of jointed rock masses under the coupled effects of in situ stress and transient dynamic disturbances significantly exacerbates the risk of surrounding rock instability. This study establishes three-dimensional numerical models of various jointed rocks under uniaxial–biaxial–triaxial split Hopkinson pressure bar (SHPB) experimental systems through the coupling of the finite difference method (FDM) and discrete element method (DEM). The models adhere to the one-dimensional stress wave propagation assumption and satisfy the dynamic stress equilibrium requirements, demonstrating dynamic mechanical responses consistent with physical experiments. The results reveal that the synergistic–competitive effects between joint configuration and initial pre-compression jointly dominate the dynamic mechanical response of rocks. Multiaxial pre-compression promotes the development of secondary force chain networks, enhances rock impact resistance through multi-path stress transfer mechanisms, significantly improves strain energy storage density during peak stages, and drives failure modes to evolve from macroscopic through-going fractures to localized crushing zones. The spatial heterogeneity of joint configurations induces anisotropic characteristics in principal stress fabric. Single joint systems maintain structural integrity due to restricted weak plane propagation, while cross/parallel joints exhibit geometrically induced synergistic propagation effects, forming differentiated crack propagation paths that intensify frictional and kinetic energy dissipation. Through cross-scale numerical model comparisons, the evolution of force chain fabric, particle displacement distribution, microcrack propagation, and energy dissipation mechanisms were analyzed, unveiling the synergistic regulatory effects of the stress state and joint configuration on the rock dynamic response. This provides a theoretical basis for impact-resistant structure optimization and dynamic instability early warning in deep engineering projects involving jointed surrounding rock. 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

The effects of laser powder bed fusion (LPBF) parameters, such as power (200 to 350 W) and scan speeds (from 200 to 2000 mm/s), on the microstructure and mechanical properties of high-strength, low-alloy (HSLA) AISI 4340 steel were examined. A wide range of volumetric energy density (VED) between 93 and 162 J/mm³ produced samples with relative densities greater than 99.8%. The optimal parameter set was identified with laser power = 200 W, scan speed = 600 mm/s, hatch spacing = 0.12 mm, and slice thickness = 0.03, corresponding to VED = 92.6 J/mm³. Scanning electron microscopy revealed a predominantly martensitic microstructure for all processing parameters examined, although X-ray diffraction revealed the minor presence of retained austenite within the as-fabricated 4340 steel. Using the optimized LPBF parameters, the as-fabricated 4340 steel exhibited a yield strength of 1317 MPa ± 16 MPa, ultimate tensile strength of 1538 MPa ± 22 MPa, and 18.6 ± 1% strain at failure. These are similar to wrought 4340 steel quenched and tempered between 400 and 600 °C. Full article

Engineering structures, including rock slopes and embankments, are vulnerable to wetting–drying cycles caused by tidal shifts and rainfall, which exacerbate mechanical degradation in hole-fissured sandstone. This study investigated the effects of 0, 10, and 20 wetting–drying cycles on sandstone samples using uniaxial compression tests combined with digital image correlation (DIC), computed tomography (CT), and scanning electron microscopy (SEM). The results revealed that wetting–drying cycles progressively reduced peak strength and the elastic modulus while increasing macroscopic crack quantity and width. Internal crack networks simplified, transitioning from tensile-dominated to combined tensile–shear and shear failure modes. An energy analysis showed diminished energy storage capacity—both the total energy density at peak stress and elastic strain energy density declined with increasing cycle numbers, whereas dissipated energy density decreased initially before rising. SEM observations indicated that wetting–drying cycles enhanced the surface roughness of the sandstone, characterized by a scaly texture, thereby compromising its structural integrity. This study provides a theoretical basis for stability and safety assessments of protective engineering systems. Full article

The reliability of GaN-based devices operating under high temperatures is crucial for their application in extreme environments. To identify the fundamental mechanisms behind high-temperature degradation, we investigated GaN-on-sapphire Schottky barrier diodes (SBDs) under simultaneous heating and electrical biasing. We observed the degradation mechanisms in situ inside a transmission electron microscope (TEM) using a custom-fabricated chip for simultaneous thermal and electrical control. The pristine device exhibited a high density of extended defects, primarily due to lattice mismatch and thermal expansion differences between the GaN and sapphire. TEM and STEM imaging, coupled with energy-dispersive X-ray spectroscopy (EDS), revealed the progressive degradation of the diode with increasing bias and temperature. At higher bias levels (4–5 V) and elevated temperatures (300–455 °C), the interdiffusion and alloying of the Au/Pd Schottky metal stack with GaN, along with defect generation near the interface, resulted in Schottky contact failure and catastrophic device degradation. A geometric phase analysis further identified strain localization and lattice distortions induced by thermal and electrical stresses, which facilitated diffusion pathways for rapid metal atom migration. These findings highlight that defect-mediated electrothermal degradation and interfacial chemical reactions are critical elements in the high-temperature failure physics of GaN Schottky diodes. Full article

Indoor direct shear tests under different stress levels were conducted on sandstone–concrete samples to investigate the rock–concrete interfaces’ shear energy evolution features and fracture behaviors under different normal stresses, combined with acoustic emission (AE) and digital image correlation (DIC) techniques. The research results show that the growth of normal stress restricts the coalescence and failure of micro-cracks inside the sample and improves the bearing capacity. The shear strength of the sandstone–concrete cemented interface increases by 12.3–34.34% with increasing normal stress. The evolution behaviors of the total input energy, elastic strain energy and dissipated energy density are similar under different normal stress conditions, and the increase in normal stress raises the energy storage capacity of the sample, as well as the input external energy required for a sample’s failure, thereby enhancing the bearing capability of the sample. In addition, the AE count and b value characteristics indicate that crack propagation shows a three-stage variation trend. It can be seen from the RA (rise time/amplitude)-AF (AE count/duration time) curves that as the normal stress increases, the proportion of shear cracks in the sample progressively increases. When the final overall failure of the sample is imminent, the high-energy level fracture type changes from tensile fracture to shear fracture with increased normal stress, leading to an increasing percentage of shear fracture. Finally, the speckle results indicate that the nucleation and coalescence of tensile wing-shaped cracks are the main causes of sample failure. Under relatively high normal stress conditions, the damage degree of the serrated interface increases and the crack morphology becomes more intricate. Full article

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature–stress relationship curve of the additive manufacturing sample enters the “brittleness temperature zone”, leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition. Full article

Foamed concrete is increasingly utilized in protection engineering because it offers a high energy absorption ratio and a relatively low construction cost. To investigate the dynamic properties of foamed concrete, a series of dynamic compression tests are carried out on high-density foamed concrete with densities of 800 kg/m³, 1000 kg/m³, and 1100 kg/m³ under a strain rate range of 59.05 s⁻¹~302.17 s⁻¹ by using a Φ-100 mm split Hopkinson pressure bar (SHPB) device. The effects of strain rate on the stress–strain relationship, dynamic compressive strength, and dynamic increase factor of foamed concrete are discussed in detail. The results show that the dynamic mechanical characteristics of foamed concrete with different densities exhibit a significant strain rate enhancement effect. Additionally, the energy absorption characteristics of foamed concrete are investigated, demonstrating that it can effectively prevent the transmission of incident energy and that its energy absorption efficiency declines as the strain rate increases. A high-speed camera was also employed to capture the failure process of foamed concrete. The results exhibit that fracture production and development induce the failure of foamed concrete, the failure process of foamed concrete advances as the strain rate increases, and the failure mode becomes increasingly severe. Full article

In engineering practice, layered rock masses often display obvious anisotropy while deforming and failing, and the failure mode directly impacts the engineering construction stability. In this study, the fracture failure load, fracture toughness, crack deflection angle, and failure mode of a layered rock mass under different fracture modes were analyzed by utilizing improved asymmetric semi-circular disc specimens. According to the constitutive model of transversely isotropic materials, the maximum tensile stress (MTS), maximum energy release rate (MERR), and maximum strain energy density (MSED) calculation formulas were modified, and the calculation formulas of the three prediction criteria under anisotropic materials were derived. The calculation results were compared with the experimental results. The results show that the fracture toughness and crack deflection angle were significantly affected by the weak bedding plane. As a result of applying the MTS criterion, the results are closer to the experimental results, providing a solid foundation for engineering deformation, failure, and fracture analyses. Full article

Wind turbines (WT) are a clean renewable energy source that have gained popularity in recent years. Gearboxes are complex, expensive, and critical components of WT, which are subject to high maintenance costs and several stresses, including high loads and harsh environments, that can lead to failure with significant downtime and financial losses. This paper focuses on the development of a digital twin-based approach for the modelling and simulation of WT gearboxes with the aim to improve their design, diagnosis, operation, and maintenance by providing insights into their behavior under different operating conditions. Powerful commercial computer-aided design tools (CAD) and computer-aided engineering (CAE) software are embedded into a computationally efficient multi-objective optimization framework (modeFrontier) with the purpose of maximizing the power density, compactness, performance, and reliability of the WT gearbox. High-fidelity models are used to minimize the WT weight, volume, and maximum stresses and strains achieved without compromising its efficiency. The 3D CAD model of the WT gearbox is carried out using SolidWorks (version 2023 SP5.0), the Finite Element Analysis (FEA) is used to obtain the stresses and strains, fields are modelled using Ansys Workbench (version 2024R1), while the multibody kinematic and dynamic system is analyzed using Adams Machinery (version 2023.3, Hexagon). The method has been successfully applied to different case studies to find the optimal design and analyze the performance of the WT gearboxes. The simulation results can be used to determine safety factors, predict fatigue life, identify potential failure modes, and extend service life and reliability, thereby ensuring proper operation over its lifetime and reducing maintenance costs. Full article

Shale is a common rock type that is associated with underground engineering projects, and several important factors, such as bedding structure, confining pressure, and the loading and unloading path, significantly influence the anisotropy of shale. Triaxial monotonic loading tests and triaxial incremental cyclic loading and unloading tests of shale under three kinds of confining pressures and five types of bedding inclination angles (θ) were thus performed to investigate the anisotropy of shale in terms of mechanical behavior, acoustic emission (AE), and energy evolution, and reveal the mechanism by which shale anisotropy is weakened. The results show that (1) the compressive strength and elastic modulus of shale decrease and then increase as the θ increases, and that both σ₃ and incremental cyclic loading and unloading reduce the anisotropy in terms of the compressive strength and elastic modulus of shale, with the ratio of plastic strain to total strain reaching its maximum at a θ of 60° during each loading and unloading cycle. (2) The failure modes of shale with θ of 0°, 30°, and 90° under triaxial monotonic loading are similar to the counterparts under triaxial incremental cyclic loading and unloading, while the failure modes of shale with θ of 45° and 60° differ significantly under the two loading conditions, and interestingly, the degree to which the bedding plane participates in shale crack evolution under incremental cyclic loading and unloading is considerably lower than that under triaxial monotonic loading. (3) The cumulative AE count and AE b-value of shale first decrease and then increase as the θ increases, while the Felicity ratio decreases as the number of cycles increases. (4) As the θ increases, the total energy density U₀ and the parameter m, which reflects the accumulation rate of elastic energy, first decrease and then increase, with both reaching a minimum at a θ of 60°. (5) The mode by which cyclic loading and unloading leads to failure in shale with a θ of 60° is similar to that at a θ of 0° and is the main mechanism by which shale anisotropy weakening occurs as a result of cyclic loading and unloading. The results provide experimental support and a theoretical basis for safer and more efficient underground engineering projects that involve shale. Full article