Search Results (789)

The steel frame-shear wall composite system has excellent lateral resistance performance in prefabricated steel structure buildings. However, the traditional steel plate concrete shear wall is prone to early buckling of the steel plate and concentrated interface damage under cyclic loading, which limits its energy dissipation capacity. This study presents a steel plate-enhanced reinforced concrete shear wall (SPRCSW) with an internal corrugated steel plate and double-layer steel mesh working together and conducts a selection study based on finite element analysis. Under the same design conditions, the peak bearing capacity in the positive and reverse directions of the SPRCSW is increased by approximately 55.4% and 46.9%, respectively, compared to the ordinary reinforced concrete shear wall, with a ductility coefficient reaching 6.08. The stiffness decline is mild, and the hysteretic curve is complete. Then, this paper forms an SR-SPRCSW composite structural system by combining the new shear wall with a steel frame using semi-rigid joints. Through the comparison of the finite element analysis and low-cycle reverse loading test results of the SR-SPRCSW structure, it is verified that the overall structural system shows good agreement in hysteretic response, skeleton curve characteristics, and failure mode under both research methods, with the peak shear bearing capacity error of less than 1% and the overall bearing capacity deviation controlled within 8%. On this basis, the key parameters of the semi-rigid joints in the SR-SPRCSW structure are analyzed. The results show that the strengthening of the “top and bottom + double web” angle steel joint can raise the peak bearing capacity of the SR-SPRCSW structure by approximately 26.1% and the yield displacement by approximately 29.5%; increasing the strength grade and diameter of high-strength bolts can heighten the initial stiffness and bearing capacity of the overall structure, but ductility slightly decreases; the thickness of the angle steel has a significant impact on the stiffness and deformation capacity of the structure, and a recommended range of values with better comprehensive performance is provided. The findings offer valuable insights for designing seismic-resistant semi-rigid steel frames with steel plate reinforced concrete shear walls and optimizing their parameters. Full article

Accurately evaluating fracability is crucial for improving shale gas fracturing efficiency. This study proposes a new mechanical deformation modulus to characterize rock fracture modes under coupled effects of stress conditions and mechanical parameters. Combined with tensile strength and fracture toughness, a ternary-index fracability evaluation method is established covering the full process of “fracture initiation–propagation–network formation”. Taking intervals Q1–Q9 of Gulong Shale as the research object, experiments were conducted to classify main intervals into four mechanical models: (1) “low tensile–low toughness–low modulus” (Q2), where fractures crack and grow easily but exhibit small apertures and weak fracture-forming capacity; (2) “low tensile–low toughness–medium modulus” (Q1, Q3, Q6), where fractures crack and grow easily, forming low-angle intersecting fracture networks; (3) “low tensile–low toughness–high modulus” (Q7, Q9), where fractures crack and grow easily, creating large-aperture, high-angle through-going fracture networks; and (4) “high tensile–low toughness–high modulus” (Q4, Q5, Q8), where fractures crack with difficulty but grow easily, developing high-angle through-going shear fractures. The evaluation results are consistent with the actual fracability characteristics of the Gulong Shale. Compared with conventional evaluation methods, the ternary index evaluation method can more clearly reveal the progressive evolution process of fractures from crack to propagation and then to fracture network formation, providing a reliable basis for fracture network prediction and fracturing optimization. Full article

Carbonate reservoirs in the Shunbei area develop pronounced fracture networks after acidized hydraulic fracturing and thus have the potential to be repurposed as underground gas storage (UGS) after hydrocarbon depletion. Characterizing their mechanical behavior is essential for safe UGS operation; however, deep to ultra-deep natural cores are difficult to obtain, and conventional macroscopic tests often cannot provide parameters that meet engineering requirements. To address this issue, nanoindentation combined with QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) was employed to quantify microscale mineral distributions and the mechanical properties of the major constituents. The investigated rock is calcite-dominated (89.62%), with minor quartz (9.89%) and trace feldspar-group minerals (1.89%). Minerals are randomly embedded, and soft–hard phase boundaries are widely distributed. A finite–discrete element method (FDEM) model was then constructed and calibrated in ABAQUS. The discrepancies in uniaxial compressive strength and elastic modulus relative to laboratory results were 6.51% and 9.91%, respectively, indicating good agreement in both mechanical response and failure mode. Parametric analyses using three additional models with different mineral proportions show that damage preferentially initiates at mineral phase boundaries and stress concentration zones induced by end constraints. Microcracks then propagate and coalesce into a dominant compressive–shear band, and final failure is mainly governed by slip along the shear band with localized tensile cracking. With increasing quartz and feldspar contents, enhanced heterogeneity and a higher density of phase boundaries lead to a higher density of crack nucleation sites and increased crack branching, and the failure pattern transitions from a single shear-band–controlled mode to a more network-like fracture system. Moreover, macroscopic strength is not determined solely by the intrinsic strength of individual minerals; heterogeneity and phase-boundary characteristics strongly govern microcrack behavior, such that higher hard-phase contents may result in a lower peak strength. Full article

The long-term stability of embankments is directly influenced by the stress paths associated with river water level fluctuations. To investigate the anisotropic characteristics of slope soil in embankments under such drainage-induced gradual loading conditions, a series of drained directional shear tests was conducted on slope soil to investigate the coupled effects of the principal stress direction angle α and the intermediate principal stress coefficient b on its strength, deformation, and non-coaxial characteristics. Results showed that radial strain exhibited minimal sensitivity to variations in the principal stress direction angle α at the constant principal stress coefficient b. The circumferential and axial strain directions demonstrated symmetry. Specimens initially contracted then dilated during shearing. Octahedral shear strain anisotropy was more significant at b = 0.5 and 1 than at b = 0. For a constant α, the normalized strength at b = 0.5 exceeded that at b = 0 and 1. Strength showed significant anisotropy across angles α at a constant b. Specimens exhibited significant non-coaxial behavior under axial-torsional shear loading. This study offers theoretical insight into embankment slope behavior under anisotropic stress paths. Full article

Granular materials exhibit complex mechanical behaviors during unloading, yet the underlying micro- and meso-scale mechanisms remain unclear. This study employs a discrete element method to simulate a series of triaxial tests on sand and pebble specimens with varying initial densities under different unloading stress paths. While dense specimens demonstrate strain softening and dilatancy, loose samples exhibit shear contraction. To quantify the underlying fabric evolution, persistent homology (PH) theory is adopted to analyze the particle contact force networks. The results reveal that the average strength of this network correlates strongly with the macroscopic stress–strain response. For dense samples, network strength rapidly increases to a peak coinciding with the deviatoric stress maximum, then gradually decreases with further shear. Crucially, this evolution is path-dependent: the average contact force network strength increases approximately 20% more during unloading in the minor principal stress direction compared to unloading in the major principal stress direction. This quantitative analysis of force chain degradation provides a mechanistic explanation for the observed strain softening, highlighting the dominant role of the unloading stress path. In contrast, loose specimens, which initially lack an obvious force chain network, show negligible microstructural evolution during unloading. Full article

The fracturing development of low-permeability and ultra-low-permeability oil and gas reservoirs urgently requires a fracturing fluid that combines high performance and low damage. To overcome this challenge, this study synthesized a novel polyamine boron crosslinker (PBC) suitable for 0.2% guar gum. The molecular structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectroscopy (¹H NMR). Meanwhile, this study introduced the response surface methodology and established a second-order regression model to determine the optimal synthesis conditions (polyetheramine 10.8 g, n-butanol 7.4 g, and ethylene glycol 20.7 g) with a model prediction error of only 0.7%. The results indicated that PBC exhibited excellent performance in 0.2% guar gum. The viscosity of crosslinked gel fracturing fluid remained stable at approximately 100 mPa·s under 60 °C and 100 s⁻¹ shear. The wall forming filtration coefficient was 2.30 × 10⁻⁴ m/s^1/2, and the initial filtration was 1.30 × 10⁻³ m³/m². The static settling rate was 2.4 cm·min⁻¹, demonstrating good suspended sand capacity. Furthermore, the synergistic interaction between borate ester bond and polyetheramine in the PBC conferred dynamic reversible crosslinking and uniform network formation. This enabled high-strength, low-damage crosslinking effects at low concentrations. This study provides an efficient crosslinker solution for 0.2% guar gum, holding both theoretical and engineering significance for advancing the low-cost development of fracturing fluid. Full article

Existing theories leave gaps in explaining the mechanism of concrete cracking. To explain the mechanism of concrete cracking, after considering various methods, this paper finally selects the Particle Flow Code (PFC) based on the discrete element method (DEM) for the research. We selected concrete with single cracks and double cracks as the research object, and constructed a mesoscale model in PFC based on the parameters of the concrete. The model was verified by uniaxial compression tests and published experimental data, with simulated results matching experimental data within an acceptable error range. Simulate the situation of concrete cracking, plot the data into images, and analyze the patterns of the development of concrete cracks. During this process, we set the angle of crack formation and the number of cracks as variables. By analyzing the load–displacement curves and the crack evolution curves, we found that the mode of crack propagation changed from a linear extension to a branched expansion. It is also worth noting that when the inclination angle is 90 degrees, the bearing capacity of the specimen is the best, with its peak strength over 40% higher than that at 0° for single-fissure specimens and over 35% higher for double-fissure specimens, and the initial stiffness also reaches the maximum at this angle. Furthermore, throughout the entire testing process, the PFC based on the discrete element method was able to accurately capture the development process of concrete cracks. This study innovatively quantifies the evolution of tensile and shear cracks with inclination angle, clarifies the nonlinear correlation between peak strength and crack angle, and reveals the unique cracking behavior induced by double fissures, which is insufficiently studied in existing continuum simulations. The above findings not only enhance our understanding of the mechanism of concrete cracks, but also provide a reference for improving the strength of concrete. This study is limited to 2D uniaxial compression simulation, with the concrete microstructure idealized in the numerical model. Full article

Although many studies have focused on the initial adhesion of bacteria, there have been few that looked at responses to changing environmental conditions. To more closely examine the viscoelastic nature of initial adhesion, surface-associated bacteria were quantified and monitored for their Brownian motion vibrations. This study used a flow chamber to observe the surface association of Enterobacter cloacae BS 1037, Staphylococcus aureus ATCC 12600, Klebsiella pneumoniae–1, Acinetobacter baumannii–1, Pseudomonas aeruginosa PA O1, and Enterococcus faecalis 1396 to glass under dynamic shear rates of 7–15–30 s⁻¹, 15–30–60 s⁻¹, and 30–15–7 s⁻¹. Comparing increasing and decreasing shear rates, information about retention and recovery became apparent. Coccoid bacteria primarily reacted to directional changes in shear rates with changes in either surface-associated bacterial densities or surface-associated strength independently. A. baumannii and E. faecalis did not change their associated strength, whereas S. aureus did not change its associated density. Bacillus bacteria demonstrated differences in both associations with directional changes in shear rates. We demonstrate that retention and recovery are different methods of adaptation to environmental conditions utilised by different bacterial species. These adaptations may form the basis of upregulation and downregulation responses used for survival. Full article

A composite meeting the UL94 V-0 rating was produced by adding 30 wt% epoxy silane-modified aluminum trihydrate (EPATH) to a 60/40 epoxy/benzoxazine matrix. Various bimodal and trimodal composites containing 20–40 wt% of three types of ceramic fillers, i.e., aluminum oxide (Al₂O₃), boron nitride (BN), and magnesium oxide (MgO), were prepared to simultaneously achieve flame-retardant and thermal conductive properties. The bimodal composites with 40 wt% of Al₂O₃ and MgO exhibited thermal conductivities of 1.22 W/m∙K and 1.29 W/m∙K, respectively, which were superior to that of the composite containing the same amount of ATH (1.0 W/m∙K). In contrast, both the coefficient of thermal expansion (CTE) and shear strength decreased with increasing ceramic filler content. For agglomerated BN, the filler loading was constrained above 30 wt% because its high specific volume caused a significant rise in the viscosity. In the trimodal composites with a total filler content of 40 wt% of Al₂O₃ and BN, a BN fraction of 7.5 wt% yielded the highest thermal conductivity of 1.64 W/m∙K and the lowest water absorption of 0.69%. When the trimodal composites were exposed to −55 °C and 150 °C for 1000 h, they exhibited a reduction in shear strength of less than 30% compared to their initial values. Full article

This study evaluated the effect of saliva contamination at different stages of application of an acetone-based universal adhesive on dentin bond strength. Seventy-two caries-free third molars were assigned to six groups (n = 12) according to contamination step. Specimens underwent shear bond strength testing. To determine the SBS, each bonded specimen was subjected to an SBS test in a universal testing machine (Shimadzu Autograph AGS-X; Shimadzu Corp., Kyoto, Japan) equipped for operating at a crosshead speed of 1 mm/min. Data were analyzed using one-way analysis of variance (ANOVA) followed by Tamhane’s T2 test for post hoc multiple comparisons with p ˂ 0.05 as the significance level. Saliva contamination significantly affected dentin bond strength (p < 0.001). The highest bond strength was observed in the post-polymerization contamination group with adhesive reapplication (12.32 MPa), whereas the lowest values were recorded when contamination occurred after the initial adhesive application (6.37 MPa). Overall, contamination prior to polymerization resulted in reduced bond strength, while reapplication of adhesive after polymerization improved bonding performance. Within the limitations of this in vitro study, salivary contamination adversely influences the dentin bonding effectiveness of acetone-based universal adhesives, particularly when it occurs before curing. However, adhesive reapplication following post-polymerization contamination may partially compensate for this effect. Full article

Model tests are effective for studying the entire deformation and evolution process of reservoir landslides. The sensitivity of similar materials to seepage effects is crucial to the accuracy of landslide model testing. Based on a fuzzy evaluation of in situ sliding zone soil, this study compared three similar materials, using shear tests and microscopic SEM to assess the similarity. The optimal similar material (sliding zone soil: bentonite: standard sand = 50%: 20%: 30%) with a water content of 13.5% and a permeability coefficient of 3.8 × 10⁻⁶ cm/s was identified, simultaneously matching physical–mechanical properties and seepage effects. When the proportion of in situ sliding zone soil exceeds that of bentonite, the in situ sliding zone soil dominates the strength. Cohesion depends on interparticle cementation force and water film viscosity. Bentonite modifies these forces in stages, leading to a trend where cohesion (c′) first increases and then decreases with rising water content, while the internal friction angle (φ’) decreases continuously. Model test results indicate the failure mode of reservoir landslides is a three-stage traction-braking failure, evolving from initial shallow deformation to deep progressive failure and finally to overall large-scale instability. The proposed similar material exhibits reliable physical–mechanical and seepage similarity and can be directly applied in physical model tests of reservoir-induced landslides to reproduce the hydro-mechanical coupling behavior of sliding zones. Full article

On 8 February 2025, an Mw 7.6 strike-slip earthquake ruptured the Swan Islands Transform Fault in the northern Caribbean near its junction with the Mid-Cayman Spreading Center, providing an important offshore case for investigating rupture dynamics along oceanic transform faults. In this study, we jointly apply teleseismic high-frequency back-projection and low-frequency finite-fault full-waveform inversion to image the multi-scale spatiotemporal evolution of the rupture process. Back-projection results reveal a two-stage rupture characterized by an initial sub-shear propagation lasting approximately 20 s, followed by rapid acceleration to supershear velocities of ~5–6 km/s and westward propagation over ~80–100 km. Finite-fault inversion shows that coseismic slip is primarily concentrated within ~20 km west of the epicenter, with a peak slip of ~5.6 m and an overall rupture duration of ~40 s. Comparison between high-frequency radiation and low-frequency slip indicates that the most seismic moment was released during the early slow rupture stage, whereas the later fast-propagating segment produced enhanced high-frequency energy but relatively small slip. These observations reveal a pronounced along-strike complementary relationship between slip amplitude and rupture speed, suggesting a transition in rupture dynamics controlled by variations in fault strength, fracture energy, and/or geometric complexity. By combining high-frequency back-projection with low-frequency finite-fault inversion, we obtain a more complete view of the rupture process of offshore earthquakes, which helps clarify rupture propagation characteristics, including supershear behavior, along oceanic transform faults. Full article

Adiabatic shear banding (ASB) is a critical failure mechanism in titanium alloys subjected to high-strain-rate deformation, and its initiation is strongly influenced by the initial crystallographic texture. The dynamic response and ASB sensitivity of extruded and annealed Ti-6Al-4V (TC4) alloy rods were investigated under dynamic compression of cubic specimens along the extrusion direction (ED) and the transverse direction (TD) at a strain rate of 2500 s⁻¹. Split Hopkinson pressure bar (SHPB) tests combined with digital image correlation (DIC) were employed to obtain the stress–strain response and the evolution of strain localization. A dislocation density-based crystal plasticity finite element model (CPFEM), incorporating the measured texture, was established to elucidate the correlation between texture and ASB behavior. The experimental results show that TD specimens exhibit a yield strength approximately 100 MPa higher than that of ED specimens, while both orientations display comparable post-yield hardening behavior. ASB initiation occurs earlier in TD (compressive strain ~0.13) than in ED (~0.23), indicating greater ASB sensitivity in the TD orientation. The CPFEM successfully reproduces the directional stress–strain responses and the observed localization morphology, enabling mechanistic interpretation in terms of slip activity and thermomechanical coupling. The simulations indicate that ED loading is dominated by prismatic ⟨a⟩ slip, resulting in lower flow stress and more dispersed strain localization. In contrast, TD loading is governed primarily by pyramidal ⟨c + a⟩ slip, leading to elevated flow stress and intensified localization. The higher ASB sensitivity in the TD orientation is therefore attributed to texture-controlled slip-mode partitioning, enhanced thermomechanical coupling, and a more concentrated crystallographic orientation distribution that facilitates intergranular slip transfer. These findings provide guidance for tailoring microtexture to mitigate dynamic failure in titanium alloys subjected to high-strain-rate loading. Full article

This study aimed to evaluate the individual and combined effects of mechanical, plasma-based, and laser-based surface treatments, along with short- and long-term thermal aging, on the surface morphology, surface energy, and resin cement bond strength of CAD/CAM monolithic zirconia. Significant numerical differences were observed among the treatment groups. Surface roughness increased from 0.22 µm (control) to 0.98 µm after sandblasting, 1.12 µm after sandblasting + plasma, and 1.07 µm after laser treatment, while plasma alone produced a moderate increase (0.31 µm). Wettability improved most notably in the plasma group, where the contact angle decreased to 43.27° compared with 67.00° in the control. The highest shear bond strength after 5000 thermal cycles was recorded in the sandblasting + plasma group (14.80 ± 1.53 MPa), whereas laser treatment demonstrated the best long-term stability, showing no significant decrease after 10,000 cycles (12.48 → 12.02 MPa). From a practical perspective, these findings indicate that sandblasting followed by plasma treatment provides high initial bond strength, making it suitable for clinical situations requiring strong immediate adhesion of zirconia restorations. Conversely, femtosecond laser treatment offers superior resistance to aging-related degradation, suggesting its potential value in cases where long-term durability is critical, such as high-stress posterior restorations or patients with parafunctional habits. Full article

In the long-term operation of canals in loess areas, instability and landslides frequently occur due to the effect of wetting–drying cycles, which severely restricts the long-term safe operation of engineering projects. To reveal the evolution law of loess strength under wetting–drying cycles and establish a strength prediction model, this study conducted wetting–drying cycle tests and direct shear tests, analyzing the effects of different cycle times, dry densities, and initial water contents on the shear strength and its parameters. A combined model of improved adaptive genetic algorithm and backpropagation neural network (IAGA-BP) was adopted for shear strength prediction. An adaptive crossover and mutation operator based on the Sigmoid function, which combines the fitness value with the population iteration number, was proposed. By optimizing the parent selection strategy and the uniform crossover genetic method, the population diversity was effectively maintained, and premature convergence was avoided. The test results show that with the increase in the wetting–drying cycle times, both the shear strength and strength parameters of loess exhibit a trend of gradual attenuation and eventually tend to be stable. The increase in the dry density and initial water content can reduce the degradation amplitude of soil cohesion after five wetting–drying cycles. The model verification results indicate that all evaluation indicators of the IAGA-BP neural network model (MAPE = 3.75%, MAE = 0.95 kPa, MSE = 9 × 10⁻⁴, R² = 0.975) are significantly superior to those of the traditional BP and GA-BP models, with the comprehensive prediction performance improved by 62% and 46%, respectively. This model not only effectively overcomes the defect that traditional models are prone to fall into local extremum but also shows significant advantages in prediction accuracy and convergence speed. This study can provide a theoretical reference for the calculation of loess strength degradation and the prediction of long-term stability under the environment of wetting–drying alternation. Full article