Search Results (843)

Existing methods for assessing the stability of deep tunnel face rarely account for the weakening effect of rock mass parameters caused by excavation disturbance. This paper employs a vertical discretization method to divide the rigid failure body into vertical strip elements with fixed horizontal widths. By considering the weakening effect of rock mass parameters, a stability analysis model for the tunnel face is established. The equivalent cohesion and internal friction angle of the rock mass are obtained using the Hoek–Brown criterion and the equivalent Mohr–Coulomb transformation. Combined with the disturbance weakening factor, these yield the equivalent rock mass parameters after disturbance. Stability is solved using limit analysis and the principle of virtual power. The accuracy of the established model is verified through numerical simulation, demonstrating that the proposed analytical approach requires only about 90 s per run compared to approximately 7 h for 3D numerical models. The results indicate that the importance of parameters, in descending order under the specified reference conditions for deep-buried tunnels, is GSI > D_r > h₁ > m_i, where GSI play a dominant role. Excavation disturbance significantly reduces rock mass strength numerically. Assessing GSI and controlling the blasting disturbance are key to ensuring the stability of deep tunnels. Full article

Rabbit manure with high-moisture content exhibits complex adhesive and flow behaviors, which make accurate parameterization in discrete element method (DEM) simulations difficult. To improve the reliability of DEM modeling for rabbit manure composting processes, this study calibrated the contact parameters of rabbit manure at 65% moisture content using the angle of repose as the target response. A physical angle of repose test was first conducted using the cylindrical lifting method, yielding a measured value of 38.77°. The Hertz–Mindlin with Johnson–Kendall–Roberts (JKR) contact model was then adopted to represent the adhesive behavior of the material, and a three-stage optimization strategy consisting of a Plackett–Burman screening test, a steepest ascent test, and a Box–Behnken design was applied to identify and optimize the key parameters. The results showed that the particle restitution coefficient, rabbit manure–PLA rolling friction coefficient, and surface energy were the dominant factors affecting the angle of repose. The optimal parameter combination was a particle restitution coefficient of 0.56, a rabbit manure–PLA rolling friction coefficient of 0.375, and a surface energy of 0.243 J/m². Under these conditions, the simulated angle of repose was 39.21°, with a relative error of 1.13%. These calibrated parameters provide a reliable basis for DEM simulation and engineering optimization of rabbit manure composting equipment. Full article

Stepped bonded repair is widely used to restore load-carrying capacity in damaged composite structures, yet conventional circular-patch configurations require repair footprints that are frequently prohibited by spatial and geometric constraints in service environments. This study proposes an elliptical stepped repair strategy in which the patch axes are independently sized to accommodate directional space restrictions while preserving effective load transfer. A parametric three-dimensional finite element framework incorporating a Hashin-based progressive damage model and a cohesive-zone traction–separation law is developed and validated against both in-house lap-joint tests and an independent stepped-repair benchmark from the literature (discrepancy < 10%). Systematic variation in the elliptical geometry reveals that the major axis—oriented along the loading direction—is the dominant geometric parameter controlling strength recovery and failure mode: insufficient major-axis length results in premature adhesive debonding, whereas an appropriately sized major axis shifts failure to parent-laminate fracture and raises the ultimate load by up to 20% relative to a circular repair of equal minor-axis dimension. The minor axis plays a secondary but non-trivial role, and a synergistic optimum is identified at the 40–90 mm (minor–major) configuration. Regarding step partitioning, a four-step arrangement consistently maximizes ultimate load across all tested geometries due to the competition between transition-gradient smoothness and step-edge stress concentration density. Finally, an external woven overlay is shown to both improve and equalize strength across geometrically distinct repairs by suppressing interfacial stress concentration and engaging a global cooperative failure mode. These findings establish design guidelines for elliptical stepped repairs under engineering space constraints. Full article

The service behavior of polyurea used for joint sealing and seepage control in concrete arch dams is governed by complex material, geometric, and interfacial nonlinearities. This study developed a generalized interface element model incorporating damage evolution based on the nonlinear Ogden constitutive theory of polyurea materials. Using the Xiaowan Arch Dam as the engineering case, a multiple-nonlinearity coupled numerical model was established, covering the construction period, impoundment period, and temperature cycles during the operation period. The mechanical responses of surface polyurea at different locations and under varying material parameters were systematically investigated. Results show that the proposed coupled model accurately captures nonlinear contact behavior. Governed by the structural stress pattern of the arch dam, the impermeable coating is predominantly subjected to compression, while regions of high tensile stress are confined to the bottom joint areas. In seepage-control design, the coating’s restraining effect on macroscopic dam deformation can be neglected; however, dam deformation must be treated as the primary boundary condition. It is recommended that polyurea with an elastic modulus of 50 MPa and a 3 mm thickness be adopted. Blindly increasing coating thickness or stiffness may instead significantly elevate the risk of internal tensile stress. Full article

Quasi-brittle structures modeled with softening constitutive laws may lose the uniqueness of equilibrium, producing bifurcation and multiple admissible crack evolutions even under symmetric loading. This paper develops a stability test and a constructive multiplicity procedure for finite element cracking analyses formulated as a Parametric Linear Complementarity Problem (PLCP) solved in tableau form. The approach exploits the pivot sequence of a complementary tableau to monitor stability by tracking the positive definiteness of the reduced active-mode Hessian $\widehat{\mathbf{A}}$ through a complement condition, without eigenvalue computations. A direct relationship between loss of positive definiteness and the sign of the incremental load factor $\Delta \dot{\mathsf{\alpha }}$ is established, providing an intrinsic indicator of transition to descending response. When degeneracy occurs, a “void pivot” mechanism is introduced to generate an alternative admissible tableau, enabling a systematic construction of multiple isolated solutions associated with competing crack patterns. The method is demonstrated on a two-notched direct tension specimen with cohesive softening, where symmetric and antisymmetric paths emerge at a critical step. The implementation is compatible with parallelized matrix operations and remains effective in the presence of non-holonomic constraints. Full article

The near-surface mounted (NSM) technique with carbon fibre-reinforced polymer (CFRP) composites has been proven to be one of the most effective alternatives for the flexural strengthening of existing reinforced concrete (RC) members. However, several issues remain unresolved, including the effects of elevated temperatures on the performance of these strengthened RC elements. This study experimentally investigates the mechanical performance of RC slabs strengthened with NSM-CFRP systems under elevated temperatures, using both (i) steady-state and (ii) transient heating under applied loads. The steady-state tests were conducted at 20, 40, 50, 70, and 80 °C, while the transient tests were performed at 20 and 80 °C. Deflections, strains, temperatures and loads were registered during the heating phase and during the flexural tests up to failure. These measurements were used to analyse the system response in terms of load–deflection curves, evolution of concrete and CFRP strains, and bond stresses between the epoxy adhesive and CFRP. At 80 °C, the NSM-CFRP-strengthened RC slabs exhibited an average reduction of 12.1% (steady-state) and 2.3% (transient) in ultimate strength. Moreover, the concrete crushing failure mode governed up to 70 °C, despite passing the epoxy’s glass transition temperature (54 °C), while cohesive failure of the adhesive governed the failure at 80 °C. Full article

Repeated impact loading can induce progressive fatigue delamination in composite laminates, in which both damage accumulation and strain-rate sensitivity of the interlaminar interface play important roles. In this work, an adopted rate-dependent fatigue cohesive formulation is extended to a three-dimensional framework for simulating interlaminar delamination in composite laminates subjected to repeated impact. The constitutive formulation incorporates separation-rate-dependent critical tractions and fracture toughness together with cumulative fatigue damage, enabling a unified description of dynamic rate effects and progressive interface degradation. A time-incremental algorithm is developed and implemented in ABAQUS 2020/Explicit through a user-defined cohesive element subroutine (VUEL). The cohesive formulation is further coupled with the Hashin intralaminar failure criterion to represent the interaction between interlaminar delamination and intralaminar damage. Numerical simulations are conducted for composite laminates with three structural configurations—conventional, drop-off, and wrapped drop-off—to systematically examine the influence of rate dependence on fatigue delamination under repeated impact. The results show that the developed framework captures the progressive evolution of delamination and impact response under repeated impact and indicate that the sensitivity to rate-dependent interlayer properties depends on both laminate configuration and impact velocity. The present study provides a feasible computational framework for the comparative simulation and assessment of fatigue delamination under repeated impact and offers numerical insight into the role of structural configuration and interfacial rate dependence in composite laminates. Full article

The presence of random fissures significantly alters the mechanical properties and failure mechanisms of rocks. To systematically investigate the impact of fissures on the failure behavior of sandstone, a multivariable random fissure numerical model was developed based on the Weibull distribution probability density function, in combination with a random fissure generation algorithm and cohesive element embedding method. This study primarily focuses on analyzing the influence of fissure ratio (R), fissure dip angle interval (A), fissure length interval (L), and fissure width interval (W) on the sandstone failure process. The results show that the failure modes change with variations in R, A, L, and W, specifically manifested as the formation of “X”-shaped, “Y”-shaped, or inverted “Y”-shaped primary cracks; the increase in fissure ratio significantly reduces both peak stress and total damage dissipated energy (ALLDMD), and promotes the propagation of tensile cracks; the increase in L leads to more complex failure patterns, but its effect on peak stress and peak strain fluctuates non-linearly, the ALLDMD remains insensitive to this change, while the number of tensile cracks decreases as L increases; conversely, an increase in W results in a failure mode characterized by a single crack path, the peak stress first increases and then decreases, and the ALLDMD exhibits an “N”-shaped fluctuation, though the overall variation is limited. Full article

Existing studies have extensively investigated sand-rich shallow-water deltas. However, the sedimentary characteristics and internal architecture of mud-rich deltas remain poorly understood. In this study, two comparative flume experiments were conducted with sand–mud ratio as the key variable. High-resolution topographic data were acquired using a laser scanner to extract geometric parameters of the architectural elements. Three-dimensional architectural models were established and validated against the Ganjiang Delta (sand-rich) and the Ouchi River Delta (mud-rich) in China. The results reveal contrasting depositional styles: sand-rich deltas develop dense, laterally migrating braided channels with broad fan-shaped morphologies, forming blanket-like geometries that consist of vertically stacked and laterally amalgamated channel complexes with good connectivity; mud-rich deltas are characterized by stable channels with limited bifurcation, forming elongated finger-like morphologies with isolated, ribbon-like channel–mouth bar complexes that exhibit strong lateral heterogeneity and poor connectivity. These contrasting behaviors are governed by sediment cohesion: non-cohesive sands promote channel migration and dispersion, whereas cohesive silt and mud stabilize channels and focus sediment transport along main conduits. The experimental models successfully reproduce natural delta end-members, confirming the universal control of the sand–mud ratio. The established quantitative relationships provide a predictive basis for subsurface reservoir characterization and the formulation of differentiated development strategies. Full article

This research delves into the impact of varying printing angles in the range (0°, 15°, 30°, 45°) on the thermal and mechanical characteristics of carbon fibre–PLA/PHA composites fabricated via fused filament fabrication (FFF). The microstructural arrangement within the 3D-printed PLA/PHA is unveiled through the application of SEM, X-ray microtomography and optical imaging. Tensile loading conditions are employed to extract meaningful mechanical parameters such as Young’s modulus, tensile strength, elongation at break, and mechanical energy, all of which are associated with the printing angle settings. The results indicate that the filaments exhibit a porosity of approximately 3%, while the porosity of the printed structure ranges from 27% to 38%, depending on the printing angle. Tensile modulus in the range 840 to 890 MPa is found not to be highly sensitive to the printing angle. However, tensile strength reaches 37 MPa for a printing angle of 30°. The variations across conditions are limited to approximately 6% in tensile stiffness and 16% in tensile strength. Finite element simulations based on 3D imaging indicate that an effective modulus of the solid phase between 1.6 and 1.8 GPa provides the closest agreement between experimental measurements and numerical predictions. This study presents novel findings concerning the deformation mechanisms associated with different length scales, from filament composite to filament arrangement, in the carbon fibre–PLA/PHA composite. This study highlights that while printing angle has a moderate influence on mechanical response, the overall structural integrity and interlayer cohesion of carbon fibre–PLA/PHA composites remain robust across a wide range of processing parameters, demonstrating their potential for reliable structural applications in additive manufacturing. Full article

The impact of boron (B) on the microstructure evolution and stabilization of mechanical properties in the IN718 superalloy during aging at 680 °C for 3000 h is investigated. The results indicated that B had negligible effects on grain size and the intragranular γ″ phase growth. In contrast, it effectively suppressed the precipitation and growth of the δ phase during long-term aging, which is attributed to grain boundary segregation of B that retards the diffusion of alloying elements. Adding B could improve the impact toughness and stability of the creep properties of the alloy. The primary mechanism is that the addition of B enhances grain boundary cohesion and suppresses the coarsening of the δ phase, while the beneficial effect of B on mechanical stability becomes negligible during the later stages of aging, as the severe coarsening of grain boundary phases offsets the enhanced grain boundary cohesion resulting from B segregation. Furthermore, the presence of slip bands was observed in the creep deformation mechanism of B-added alloys, which is likely attributable to B promoting dislocation slip at grain boundaries. With prolonged aging time, the dominant creep deformation mechanism in the B-modified alloy shifts from being primarily governed by twinning and dislocation slip to a mechanism involving twinning, stacking fault shearing γ″ phase, and dislocation slip. Full article

This study aimed to compare carcass composition and selected meat quality traits of guinea fowl (Numida meleagris) and common pheasant (Phasianus colchicus L.) reared under the production conditions applied in this experiment. The study material consisted of 32 birds, including 16 male common pheasants and 16 male guinea fowl, all slaughtered at 13 weeks of age. The analysis revealed significant differences (p < 0.05) between the two groups in carcass composition and several meat quality parameters. Under the given rearing conditions, guinea fowl were characterized by higher body and carcass weight, as well as weights of individual carcass components, compared to pheasants. They also showed higher carcass yield and greater proportions of certain elements, including leg muscles, skin with subcutaneous fat, and wings, whereas pheasants exhibited a higher proportion of breast muscles and neck. Guinea fowl had higher absolute masses of meat, fat, and bones, but a lower meat-to-fat ratio. No significant differences between groups were observed for the meat-and-fat-to-bone ratio or the meat-to-bone ratio. The highest protein content was recorded in the breast muscles of pheasants (27.1%), while the lowest was found in the leg muscle of guinea fowl (22.1%). Differences between the groups were also observed in intramuscular fat and water content in both breast and leg muscles, as well as in collagen content in the breast muscle. Regardless of group, breast muscles were characterized by higher protein content and lower fat and collagen levels than leg muscles. Differences were further noted in electrical conductivity (EC) and the a* and b* color parameters in both muscle types. Breast muscles exhibited lower pH and a* values but higher EC and L* values than leg muscles in both groups. Textural traits of the breast muscles, including cohesiveness, springiness, and chewiness, were higher in guinea fowl, whereas hardness and Warner–Bratzler shear force (WB) were lower compared to pheasants. However, these differences should be interpreted with caution, as the birds were reared under different feeding and management systems, which may have contributed to the observed variation. Overall, the results provide comparative data on carcass composition and meat quality of guinea fowl and pheasants under the studied production conditions. These findings may serve as a basis for further controlled studies designed to more clearly isolate species effects and to evaluate their potential relevance for poultry production. Full article

To address the complex dynamic mechanisms and lack of static operation data in trench-digging for transverse planting of Salix psammophila sand barriers, a transverse trench-digging device was designed. Based on the discrete element method, the Hertz–Mindlin with JKR Cohesion model was used to simulate sandy soil. The Box–Behnken experiment was adopted to optimize the single auger structure with helix angle and soil-cutting angle as factors and trench depth and working torque as indices, yielding the optimal parameters of 30° soil-cutting angle and 20.37° helix angle (5.52 cm trench depth, 2.6 N·m maximum torque). The optimized auger was integrated into the device, and a further Box–Behnken experiment was conducted under a 20 cm fixed descending depth of the lifting platform. With auger rotation speed, shaft spacing and lifting speed as factors, and trench depth, soil compaction and Salix psammophila insertion depth as indices, the optimal operating parameters were determined as 257.25 r/min, 7 cm and 9 cm/s, corresponding to 6.7 cm trench depth, 33.37 kPa soil compaction and 14.87 cm insertion depth. This study clarifies the effects of auger and operation parameters on trench-digging quality, provides a basis for the design and parameter matching of dynamic continuous operation equipment, and offers a reference for the R&D of mechanized transverse planting equipment for Salix psammophila sand barriers, which is of practical value for reducing sand control costs and improving efficiency. Full article

In the aviation industry the so-called ballistic impact of small accidental or human-made sources on aircraft elements during their service life encompasses several scenarios of practical interest. The experimental assessment of ballistic impact requires dedicated infrastructures (such as the light-gas gun system utilized in this study) and exhibits intrinsic difficulties, mainly concerning the proper acceleration of a projectile and the accurate measurement by a high-speed camera of its (inlet and outlet) velocity. As a first objective, this study aimed at characterizing the dynamic response of fiber metal laminates, manufactured ad hoc by the authors with two different stacking sequences currently not available in commerce. The layups included aluminum 2024 T3 and aramid fiber-reinforced prepregs, leading through specific treatments to excellent specific properties. The collision of the laminate with a 25 g, 9 mm radius steel sphere, traveling at speeds ranging from 90 to 145 m/s, caused a variety of scenarios: partial or complete penetration, with the projectile passing through and continuing its trajectory, remaining stuck in the sample (embedment) or even being bounced back (ricochet). The experimental information led to the estimation, for each typology of sample, of a conventional ballistic limit according to the Lambert-Jonas approximation, as a second objective, these data were utilized to validate an accurate heterogeneous model of the samples developed in the ABAQUS^® platform, discretized by finite elements in explicit dynamics and including geometric nonlinearity and contact. We describe plasticity and damage of the metal layers by the Johnson–Cook phenomenological model, progressive failure in the fiber-reinforced plies through a 2D Hashin criterion with damage evolution, and interlaminar debonding at multiple cohesive interfaces governed by the Benzeggagh–Kenane criterion. The outlet speed of the bullet measured during the experiments was retrieved correctly by this model, and a satisfactory agreement of the finite element predictions was found with the deformation patterns and the damage mechanisms identified by post mortem visual inspection. Finally, several discussion points are raised, concerning the robustness of the numerical analyses, the reliability of the constitutive modeling and the identification of the governing parameters. Full article

Organizations increasingly rely on environmental, social, and governance (ESG) practices as a core element of sustainable management, yet little is known about how ESG affects employees during periods of crisis. Despite the growing ESG literature, limited research has examined how firm-level ESG performance influences employee psychological mechanisms and innovative behavior under crisis conditions through multi-level pathways. Drawing on corporate reputation theory and conservation of resources (COR) theory, this study examines how corporate ESG performance shapes employee experiences and behaviors under crisis conditions. This study conceptualizes ESG performance as a reputation-based organizational resource that buffers employees against psychological stress, thereby enabling innovative behavior that is critical for business sustainability. In addition, team cohesion as a contextual social resource was proposed to strengthen the stress-buffering effect of ESG. Using multi-level data from 980 employees nested within 51 large Korean firms, combined with objective ESG ratings collected prior to the crisis, this study tests the proposed model through multi-level structural equation modeling. The results show that higher corporate ESG performance is associated with lower employee psychological stress, which in turn promotes innovative behavior. Moreover, team cohesion amplifies the negative relationship between ESG performance and employee stress. By revealing a micro-level pathway through which ESG enhances employee well-being and innovation during crises, this study advances research on the economic and business aspects of sustainability. Full article