Search Results (2,841)

High-entropy perovskite oxides attract considerable attention due to their outstanding properties and extensive applications. In this work, the lattice distortion and the mechanical, thermal and electronic structure properties of high-entropy (Ca_0.2Sr_0.2Ba_0.2La_0.2Pb_0.2)TiO₃ (CSBLPT) are investigated through first-principles calculations. The results suggest that the influence of O atoms on lattice distortion is predominant, and the effect of overall A-site atoms plays a distinctly greater role than that of the B-site atoms. The mechanical results show that the high-entropy CSBLPT has a lower Young’s modulus and higher fracture toughness than ternary SrTiO₃. The Debye temperature also indirectly indicates that the thermal expansion coefficient of the studied high-entropy perovskite is greater than that of SrTiO₃. As for thermal conductivity, the obtained result of CSBLPT is also appreciably lower than that of SrTiO₃, and the lowest thermal conductivity is along the [100] direction. The Fermi level of high-entropy CSBLPT is transferred to the conduction band, exhibiting a degenerate n-type semiconductor behavior with metallic-like characteristics, and the Bader charge values are also related to the local lattice distortion, which may cause differences in thermomechanical properties between high-entropy CSBLPT and SrTiO₃. Above all, high-entropy CSBLPT is a preferable TBC material with excellent performance under working conditions compared to SrTiO₃. Full article

To clarify the migration characteristics of overlying strata during backfill mining of close-distance coal seams, the 3306 working face of Chaili Coal Mine was taken as the engineering background, and similar-material simulation, fracture-fractal analysis, and FLAC3D numerical simulation were carried out under an 85% backfill ratio. The study reveals the coordinated inherited and reactivated evolution of fractures, displacement, and stress in the overlying strata during successive extraction of the upper and lower seams. The results indicate that the movement of the overlying strata shows pronounced stage dependence and inheritance. After extraction of the upper No. 3 coal seam, the response of the overlying strata evolves from local disturbance to overall structural readjustment, with continuous bending subsidence and progressive fracture propagation, and ultimately forms a two-belt structure. During extraction of the lower No. 3 coal seam, the response develops on the basis of the structural state formed after upper-seam mining and is manifested mainly by the reactivation and readjustment of the pre-existing fracture network and displacement field. The fractures undergo a dynamic process of generation, development, closure, redevelopment, and reclosure. Compared with upper-seam mining, lower-seam mining produces a larger vertical displacement and a weaker stress response. The maximum vertical displacement in-creases from 478.85 mm to 1019.76 mm, whereas the stress concentration coefficient of the immediate roof decreases from 2.01–2.03 to 1.93–1.99. Under the geological and mining conditions considered in this study, the 85% backfill ratio maintains overall bending subsidence of the overlying strata and alleviates strata pressure manifestations during lower-seam extraction. These findings provide a reference for strata control under similar backfill mining conditions. Full article

Background/Objectives: The optimal surgical approach for displaced intra-articular calcaneal fractures (DIACFs) remains controversial. While the extensile lateral approach (ELA) has traditionally been preferred for complex fractures, the sinus tarsi approach (STA) has gained popularity due to its potentially lower soft tissue morbidity. However, comparative data focusing on patient-centered outcomes remain limited. This study aimed to compare clinical, radiological, functional, cosmetic, and complication outcomes between STA and ELA in Sanders type II–IV DIACFs. Methods: A retrospective comparative cohort study was conducted including patients treated with open reduction and internal fixation using either STA or ELA between February 2019 and October 2024. Functional outcomes were assessed using the AOFAS Ankle–Hindfoot Score and VAS. Radiological evaluation included Böhler and Gissane angles measured preoperatively, early postoperatively, and at final follow-up. Patient-centered outcomes included time to full weight bearing, return to work, heel width difference, and changes in shoe size. Complications were recorded throughout follow-up. Results: Baseline demographic and fracture characteristics were comparable between groups. Patients treated with STA demonstrated significantly shorter hospital stay, earlier progression to full weight bearing, and earlier return to work (p < 0.001). Functional outcomes favored STA, with significantly lower VAS scores and higher AOFAS scores at final follow-up (p < 0.05). No significant differences were observed between groups regarding Böhler or Gissane angles at any time point (p > 0.05). Wound-related complications were significantly more frequent in the ELA group (p = 0.018), although overall complication rates were comparable. Conclusions: The sinus tarsi approach was associated with comparable radiological restoration to the extensile lateral approach while demonstrating earlier functional recovery and lower wound-related morbidity. Given the retrospective and non-randomized design, these findings should be interpreted as associations rather than causal effects. STA may represent a safe and effective surgical option in appropriately selected Sanders type II–IV intra-articular calcaneal fractures. Full article

Mining coal seams with shallow, thick, and hard roofs often results in extensive roof suspension. This issue poses significant challenges regarding stratum control and mitigation of strong mining pressure, especially within the confined working space of a mining face. This study focuses on the 13101 working face of Shengfu Coal Mine. Through field observations, theoretical analysis, and numerical simulations, the characteristics of support resistance and microseismic activity were investigated. This research elucidates the mechanism behind the strong mining pressure driven by the structural coupling and synergistic breakage of two key strata, highlighting how their interaction dictates weighting intensity. A small-aperture hydraulic fracturing technology, specifically designed for inter-support spaces, was developed. The results indicate that the working face exhibits alternating “minor weighting” and “major weighting” events. Minor weighting occurs at an average interval of 12.38 m with a dynamic load factor of 1.14, while major weighting occurs at 41.07 m with a factor of 1.56. The roof structure was found to form a combination of an “inclined stepped rock beam” and a “voussoir beam.” Field applications demonstrate that the proposed technology reduces the major weighting interval by 41.46% and total microseismic energy release by 35.01%. This study provides a theoretical and technical basis for preventing roof disasters under similar geological conditions. Full article

Carbon fiber-reinforced polymer (CFRP) laminates are susceptible to barely visible impact damage (BVID) under low-energy bird-strike-like conditions. However, in previous studies, most damage evaluations for BVID were limited to a single scale. In this work, a multiscale characterization and evaluation method integrating the analytic hierarchy process (AHP) and the CRITIC weighting method was proposed to investigate the damage evolution of CFRP laminates under low-energy impacts (approximately 12–33 J). Delamination area (S_Da), indentation depth (P_D), surface crack aspect ratio (R_A), energy dissipation, and compression-after-impact (CAI) strength were analyzed based on phased-array ultrasonic C-scanning, 3D optical profilometry, and scanning electron microscopy. The results showed that P_D, S_Da, and energy dissipation increased from 108.73 μm to 213.93 μm, from 228.6 mm² to 695.8 mm², and from 5.96 J to 21.40 J, respectively, with increasing impact energy. Meanwhile, CAI strength decreased from 202.2 MPa to 118.9 MPa, with a maximum degradation rate of 41.16%. A critical transition was observed in the medium-to-high energy range, where delamination growth gradually plateaued, while intralaminar cracking and fiber fracture became increasingly dominant. The proposed framework enables quantitative grading of BVID severity and provides a practical basis for assessing residual damage in impacted CFRP laminates. Full article

Hydraulic fracturing in ultra-deep reservoirs faces significant challenges, including high wellbore friction and inadequate thermal stability of conventional fracturing fluids. To address these issues, we developed a potassium formate-weighted fracturing fluid with delayed crosslinking, excellent friction reduction, and superior temperature resistance, using a hydrophobic associating polymer thickener and a multi-ligand organic zirconium crosslinker. The weighted fracturing fluid has a density of 1.4 g/cm³ and completes crosslinking within 300 s at 90 °C. It achieves a maximum friction reduction rate of 63.2%. Below 60 °C, the system relies on a supramolecular thickener network for low viscosity and friction reduction; above 60 °C, chemical crosslinking between the thickener and zirconium ions creates a dual-network structure that significantly enhances temperature and shear resistance. After 120 min of shearing at 200 °C and 170 s⁻¹, the retained viscosity reaches 75.3 mPa·s. Complete gel breaking is achieved by sodium bromate via an oxidation reaction. This dual-network delayed crosslinking system successfully reconciles the conflict between low wellbore friction and high-temperature proppant-carrying capacity. This work presents a superior weighted fracturing fluid for ultra-deep reservoirs, as well as an innovative technique for their development. Full article

Models are described for calculating the crack initiation times for Alloy 600 and Type 304 SS in PWR and BWR primary coolant circuits, respectively. In PWRs, initiation is defined in terms of the grain boundary oxidation concept of Scott and Le Calvar, whereas in BWRs, cracks are envisioned to nucleate from corrosion pits. In contrast, in BWRs, we envision cracks to nucleate from corrosion pits, with the difference in the two systems being primarily due to electrochemical factors. Thus, in BWR primary coolant and the absence of hydrogen water chemistry (HWC), the oxidizing conditions due to the radiolytic production of H₂O₂ cause the ECP to be significantly more positive than the critical pitting potential. Accordingly, the nucleation and growth of pits due to passivity breakdown and the establishment of differential aeration between the pit nucleus’s internal and external environments, which results in growth of pits to the critical size necessary to satisfy the Kondo criteria for transition of a pit into a crack, is judged to be a realistic scenario. Contrariwise, in PWR primary coolant, the ECP is so negative [≈−1.0 V_she] due to the large amount of pressurizing H₂ present in the circuit [20–60 cm³(STP)/kg H₂O] that the nucleation and growth of pits is not possible. However, Totsuka and Smialowska found that MA Alloy 600 suffers hydrogen-induced cracking (HIC) at an ECP < −0.85 V_she, demonstrating that, in service with a high hydrogen concentration, brittle fractures will occur. The initiation sites were not identified. The crack initiation models for Alloy 600 in PWRs and Type 304 SS in BWRs reproduce the effects of the following independent variables: applied stress, temperature, cold work, grain boundary segregations, water chemistry, pH, and electrochemical potential. The origins of the observed scatter in experimentally measured crack initiation times are discussed, and the challenges of developing a more general crack initiation model (GCIM) are identified. From a mathematical viewpoint, the most significant challenge arises from the nested distributions involving the many parameters and expressions within the GCIM that are either distributed because of an imprecise definition or because some experimentally determined input parameters are experimentally scattered. Additionally, the evolution of semi-elliptical surface cracks resulting from the electrochemical crack length (ECL) being shorter than the classical mechanical crack length (MCL) must be incorporated if the GCIM is to find utility in the water-cooled nuclear power industry where semi-elliptical surface cracks are normally observed. Full article

To address the technical challenge of large-area roof hanging and induced strong strata behaviors in deep mines with hard roof strata, a study on pressure relief using hydraulic fracturing technology was conducted, taking the 1012006 working face in the Yuanzigou Coal Mine as the engineering background. Through geological survey and key stratum theory analysis, a low-position key stratum located 23 m above the roadway roof was identified as the target layer for fracturing. True triaxial hydraulic fracturing experiments coupled with acoustic emission (AE) monitoring revealed a synchronous response characterized by a sudden drop in injection pressure and a rapid increase in AE counts. This established a quantitative correlation between rock mass fracturing and AE characteristics, providing a theoretical basis for field microseismic monitoring. Based on the “dual-borehole synergy” borehole layout principle, a fracturing network comprising 6 drilling fields and 12 directional long boreholes was designed, with a total drilling length of 5727 m and 120 planned fracturing stages. Specialized equipment was selected for implementation. Field monitoring results demonstrated: a maximum fracturing influence radius of 27.8 m; that the average daily frequency and total energy of microseismic events decreased by 50.65% and 27.73%, respectively; and that the stress in the deep part of the roadway decreased by 17.69%. These results confirm the effective improvement of the roof stress environment and the successful achievement of the expected pressure relief and rockburst prevention effect. Full article

Numerical simulation of sequential fracturing in horizontal wells for shale gas and oil extraction requires careful consideration of mechanical interactions between proppant and fracture surfaces—a challenge that remains largely unresolved. This study proposes a novel phase-field model featuring a strain-based formulation and a width-dependent proppant reaction force. Unlike previous studies, we integrate an empirical propped force solution, adapted from established work to account for rock properties and proppant support, to capture nonlinear fracture closure. Results show that reaction stress models significantly dictate propped geometry. The model’s fracture length, width, and closure predictions are validated against theoretical solutions. We conducted a sensitivity analysis to evaluate how fracture deflection angles and widths vary with dimensionless fracture spacing, in situ stress contrast, and proppant strength. Numerical results show that proppants induce pronounced morphological asymmetry and distinct geometric discrepancies. Specifically, the heterogeneous support provided by proppants and the resulting stress redistribution alter fracture propagation paths, leading to an 8% reduction in fracture length and a marked difference in fracture orientation of approximately 80° between supported and unsupported fractures, highlighting the important role of proppants in governing fracture geometry. Both dimensionless fracture spacing and in situ stress contrast strongly influence fracture deflection, with proppant strength also contributing. The propped-force formulation is further extended to nonplanar fractures, enabling application to sequential fracturing with multiple fractures. These results highlight fracture propagation mechanisms and demonstrate the robustness of the proposed phase-field model. Full article

In this study, the microstructure and mechanical properties of ultrasonic welded joints between large-diameter aluminum wire and Cu (Ni-plated copper) terminals were systematically investigated, to reveal the underlying fracture mechanisms. The cross-sectional morphology, interfacial microstructure, and mechanical properties of the two types of welded joints are investigated. The results indicate that ultrasonic welding produces well-structured Al-Cu and Al-Ni joints. Under the same welding process parameters, the Al-Cu joint exhibits many pores, while the Al-Ni joint has no pores in its microstructure. The interfacial region of the Al-Cu joint presents various morphologies, such as flat bonding, interlocking, and eddy current patterns, whereas the Al-Ni joint interface is flat. No significant atomic diffusion phenomenon occurs between the interfaces of the two types of joints. The tensile strength of the Al-Cu joint is 53 MPa, with fracture modes including ductile fracture and brittle fracture, whereas the tensile strength of the Al-Ni joint is 50 MPa, with a failure mode of pull-out fracture. In working conditions requiring ultrasonic welding of aluminum and copper, nickel-plated copper can be used as a substitute for copper to prevent electrochemical corrosion between aluminum and copper. Full article

To address severe strata pressure induced by large end-area hanging spans and poor caving of thick, hard roofs in western coal mines, this study takes the 1302 working face of Zhujiamao Coal Mine as a case study. A multiscale mechanical model is developed to describe the progressive evolution of a stratified hard roof from a continuous beam to a cantilever beam and finally to an arched triangular hanging roof. Limit criteria for the maximum hanging length under bending and shear failure are derived, indicating that bending governs end-area roof instability. The theoretical results show good agreement with field observations and numerical simulations, providing guidance for liquid nitrogen fracturing target selection. Coupled FLAC3D-3DEC simulations reveal the staged deformation of overlying strata and clarify the spatial correspondence between the “O-X” fracture pattern and the arched triangular hanging roof. Based on these findings, a collaborative weakening strategy integrating directional drilling, hydraulic pre-cracking, and deep liquid nitrogen fracturing is proposed. Field observations and comparative tests confirm that this method effectively forms a three-dimensional fracture network, reduces roof stiffness and strength, shortens the caving interval, lowers peak shield resistance, and promotes stable caving of the end-area hanging roof. Full article

In order to verify the feasibility of in situ repair of underwater local dry laser welding (ULDLW) on nuclear power reactor components, this work investigates the microstructure and mechanical properties of 304L austenitic stainless steel repaired by ULDLW using ER308L filler metal. Comprehensive comparison would be made between the ULDLW and conventional in-air laser welding to evaluate their applicability. The results demonstrate that the rapid cooling rate inherent to the underwater environment significantly influences solidification behavior and microstructural evolution. The weld metal (WM) solidifies in the ferritic–austenitic (FA) mode, with an increased proportion of lathy δ-ferrite at the expense of skeletal morphology compared to the in-air welds. Electron backscatter diffraction (EBSD) analysis reveals the substantial grain refinement in underwater welds, with average grain sizes of 39.4 μm versus 47.3 μm for in-air weld bead, accompanied by a higher fraction of low-angle grain boundaries (LAGBs). These microstructural modifications yield superior mechanical properties: underwater weld bead exhibits ultimate tensile strength (UTS) of 685.6 MPa, elongation of 57.5%, and impact toughness of 22.6 J, significantly exceeding the corresponding values for in-air welds (663.9 MPa, 51.8%, and 18.6 J, respectively). Fractographic analysis confirms ductile fracture mechanisms in both conditions. The enhanced performance is attributed to grain refinement strengthening via the Hall–Petch relationship and the increased LAGBs fraction, which impedes dislocation motion and crack propagation. Full article

The multi-cycle high-rate injection and production operations in Underground Gas Storage (UGS) facilities converted from depleted fracture-pore carbonate gas reservoirs induce complex rock–fluid interactions that threaten long-term integrity and performance. This study experimentally investigates the petrophysical responses of the Xiangguosi (XGS) UGS carbonate reservoirs in China using multi-cycle stress sensitivity tests, fines migration experiments, and water evaporation–salt precipitation analyses. SEM observations distinguish the contributions of crack closure and matrix compression to permeability evolution. Results show a sharp contrast in mechanical damage: high-quality rocks present negligible permanent deformation (<8% Young’s modulus reduction), whereas poor-quality rocks suffer catastrophic deterioration (>60%). Fines migration exhibits a three-stage behavior under cyclic flow, with water saturation significantly aggravating permeability impairment. A critical salinity threshold (220,000 ppm) is identified for the transition between drying-enhanced storage and salt plugging. Permeability declines sharply despite a slight porosity increase due to selective salt clogging of key pore throats, revealing a clear porosity–permeability decoupling. Salt deposition under movable water conditions can reduce UGS capacity by up to 1.45%. Reservoir heterogeneity, microfractures, karst structures, and initial petrophysical properties dominate the storage and flow space evolution. This work provides a predictive framework for optimizing injection–production strategies and improving the performance of complex carbonate UGS. Full article

Proppant flowback during the flowback phase after hydraulic fracturing in coal reservoirs critically impacts fracture conductivity and wellbore integrity. However, experimental studies on its critical conditions and controlling mechanisms within coal’s complex fracture networks are scarce compared to sandstone or shale. This study conducted physical simulation experiments using outcrop coal samples from the XD block in China and a modified fracture conductivity system. By establishing a determination method for the critical backflow rate (Q_c), the dynamic evolution process of proppant backflow—characterized by the stages of initial stability, critical instability, severe backflow, and re-equilibration—was revealed. The influences of proppant size, flowback fluid viscosity, proppant concentration, and effective stress on Q_c were systematically analyzed, and the relative weight of each influencing factor was quantified through orthogonal experimental design. Results show that proppant backflow initiates and concentrates preferentially at the fracture outlet region, implying a higher risk of proppant failure in the near-wellbore fracture section. The Q_c decreases with reducing proppant size, increasing flowback fluid viscosity, increasing proppant concentration, and decreasing effective stress, among which effective stress is identified as the dominant controlling factor. Furthermore, no necessary correlation is observed between Q_c and the critical backflow ratio, suggesting that the initiation threshold and post-instability flowback intensity are governed by different mechanisms. This work provides experimental data and a quantitative basis for optimizing flowback strategies in coal reservoir fracturing operations. Full article

Research on the surrounding rock stability and its control during gob-side entry driving with a narrow pillar (GSED-NP) is of critical importance for ensuring safe mining operations and efficient production in underground coal mines. This work proposed a thick anchored dual-layer locking (TADL) supporting technology by analyzing the big and small voussoir beam (BSVB) weighting characteristics in GSED-NP as well as engineering implementation and on-site validation. First, field surveys and numerical simulation show that the 9.60 m and 10.65 m thick medium grained sandstone in the overlying strata were fractured in the coal body of the next face, and formed BSVB structure after rotation, subsidence, and re-hinging. Under the effect of stress transfer of BSVB structure, the lateral abutment pressure distribution is characterized by internal and external stress field (IESF) distribution. Second, numerical calculation was carried out according to the above characteristics. Third, a supporting technical scheme was formulated and implemented, and the field monitoring data proved the ideal outcome. Finally, the influence of the critical fracture location of the main roof on the stress distribution was discussed, and it is thought that the stress distribution is mainly related to the main roof fracture location which has a critical range on the stress transfer. This research can provide a reference for the surrounding roadway control under similar conditions. Full article