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The scientific essence of coal dynamic disaster is the damage and fracture dynamic effect under the superposition of dynamic and static loads. Obtaining the damage evolution law in the process of coal failure is the premise to explore its occurrence mechanism. One of the important indicators of coal damage is AE signals, but the accurate measurement of AE signals of coal under dynamic and static combined loading is a complex issue. Based on the triaxial test instrument, an integrated loading cylinder and dynamic sealing piston are developed to realize the accurate measurement of coal AE signal under dynamic and static combined loading and solid–gas coupling environment. Based on the above technique, the damage verification tests of coal under different cyclic dynamic load frequencies are carried out. The test results show that the dynamic-static combined loading technique created in this paper is reliable and the AE monitoring technique is feasible.

Additive manufacturing, particularly Stereolithography (SLA), has gained widespread attention thanks to its ability to produce intricate parts with high precision and customization capacity. Nevertheless, the inherent low mechanical properties of SLA-printed parts limit their use in high-value applications. One approach to enhance these properties involves the incorporation of nanomaterials, with graphene oxide (GO) being a widely studied option. However, the characterization of SLA-printed GO nanocomposites under various stress loadings remains underexplored in the literature, despite being essential for evaluating their mechanical performance in applications. This study aimed to address this gap by synthesizing GO and incorporating it into a commercial SLA resin at different concentrations (0.2, 0.5, and 1 wt.%). Printed specimens were subjected to pure tension, combined stresses, and pure shear stress modes for comprehensive mechanical characterization. Additionally, failure criteria were provided using the Drucker-–Prager model.

The majority of the existing calculation methods for determining the ultimate bearing capacity of steel-pipe piles using Chinese criteria are designed for piles with diameters smaller than 2 m. To investigate the bearing capacity of flexible steel-pipe piles with diameters larger than 2 m under combined loading conditions, reveal nonlinear interactions between vertical and horizontal loads, and propose bearing capacity envelopes, in this paper, a numerical method was used to study the bearing capacity of a flexible pile with a diameter of 2.8 m and an embedment length of 72 m under vertical and horizontal loading conditions. First, a numerical model was developed and calibrated using field test results. Then, the effects of vertical pressure on horizontal capacity and lateral force on vertical capacity and uplift capacity of the pile were analyzed. The results indicate that vertical pressure at the top of the pile can nonlinearly reduce its horizontal capacity, but this pressure initially has a slight positive effect on the horizontal bearing capacity before causing a rapid decrease. Conversely, horizontal force negatively impacts both the compressive and uplift bearing capacities of the pile. Finally, depending on the above results, bearing capacity envelopes for piles subjected to vertical and horizontal loads were proposed.

The traditional Mohr–Coulomb and Hoek–Brown strength criteria exhibit limitations in characterizing the strength behavior of layered sandstone under dynamic loading. Specifically, these criteria fail to adequately account for the coupled effects of confining pressure, bedding angle, and impact pressure on the dynamic evolution of sandstone strength parameters, including the internal friction angle (φ), cohesion (c), and Hoek–Brown parameter (m). To address this issue, this study systematically integrates experimental investigations and theoretical modeling to establish a dynamic strength criterion that incorporates multifactorial coupling effects. Using a modified split Hopkinson pressure bar (SHPB) system, uniaxial dynamic impact tests and three-dimensional dynamic-static combined loading tests were conducted on sandstone specimens with varying bedding angles (0°, 30°, 45°, 60°, 90°), confining pressures (0, 5, 10, 20 MPa), and impact pressures (0.8, 1.2, 1.6 MPa). Key experimental findings include: (1): As the impact pressure increased from 0.8 to 1.6 MPa, the cohesion (c) rose from 65.43 MPa to 80.99 MPa, the internal friction angle (φ) increased from 28.63° to 36.39°, and the Hoek–Brown parameter (m) surged from 5.81 to 12.23. (2): When the bedding angle increased from 0° to 90°, the cohesion (c) nonlinearly decreased from 65.43 MPa to 64.24 MPa, the internal friction angle (φ) declined from 28.63° to 26.01°, and the Hoek–Brown parameter (m) decreased from 5.81 to 5.68. Building on these results, enhanced strength criteria were proposed to explicitly integrate the coupling effects of confining pressure, bedding angle, and impact pressure. Theoretical strength values calculated using the improved criteria were compared with experimental measurements. Validation demonstrated that the modified Mohr–Coulomb criterion achieved an accuracy of 15%, while the refined Hoek–Brown criterion attained an accuracy of 10%. These findings conclusively demonstrate that the proposed criteria effectively describe the dynamic strength characteristics of sandstone under the combined influence of confining pressure, bedding angle, and impact pressure, providing a robust framework for stability analysis in deep rock engineering applications. Article Highlights An improved dynamic Mohr-Coulomb strength criterion under the coupling effects of confining pressure, bedding angle and impact pressure is established. An improved dynamic Hoek-Brown strength criterion under the coupling effects of confining pressure, bedding angle and impact pressure is established. Sandstone cohesion and internal friction angle under the coupling effects of confining pressure, bedding angle and impact pressure is studied

Deep coal‐rock formations are subjected to complex stress environments characterized by high static stresses and dynamic disturbances. To study the damage, fracture, and energy evolution characteristics of coal‐rock under dynamic–static combined loading, a new multiscale constitutive model for coal‐rock under dynamic–static combined loading is proposed based on micromechanics, and it is implemented into the LS‐DYNA solver. A numerical model of coal‐rock Split Hopkinson Pressure Bar under dynamic–static combined loading is established using LS‐DYNA, and research on the mechanical and energy evolution characteristics of coal‐rock under one‐dimensional and three‐dimensional dynamic–static combined loading is conducted. The results show that under one‐dimensional dynamic–static combined loading, with the increase of precompression, the dynamic peak stress linearly decreases while the combined peak stress linearly increases, and the dissipated energy of the specimen shows a decreasing trend. The fracture patterns of the coal‐rock specimen include internal shear fracture and external tensile fracture, and eventually, these two modes of fracture intersect to form macroscopic mesh cracks. As the axial pressure increases, the degree of specimen fragmentation gradually increases. Under three‐dimensional dynamic–static combined loading, with the increase of preconfining pressure, the stress–strain curve of the specimen will transition from “stress drop” to “stress rebound” after the peak. The peak stress increases with the increase of confining pressure, and the energy dissipation density of the specimen increases first and then decreases with the increase of confining pressure. With the increase of confining pressure, the hoop deformation of the specimen plays a constraining role, and the degree of specimen fracture gradually weakens, and the time of fracture occurrence gradually delays. The research results contribute to revealing the mechanical and energy mechanisms of rockburst disasters in deep coal mines. Fracture process of coal‐rock under three‐dimensional dynamic–static combined loading.

Abstract—The reliability of numerical modeling of crack growth in a laminate glass-epoxy composite under combined loading by opening (mode I) and shear (mode II) of an interlaminar crack was assessed. According to experimentally determined standard (DCB and ENF) and nonstandard (SLB and OLB) methods for the values of interlayer crack resistance parameters under individual and combined loading modes I and II, the exponent in the Benzeggagh-Kenane equation was calculated as a material constant of a laminated epoxy glass composite. Using this parameter and using the ANSYS application software package within the framework of linear elastic fracture mechanics and the virtual crack closure method, the numerical finite element modeling of interlaminar crack resistance of SLB and OLB type specimens was carried out under a combined loading mode with a different fraction of modes. With an optimal number of elements in a finite element mesh corresponding to a given length of the crack growth trajectory, the numerical modeling provides sufficient accuracy in calculating the limit load of the beginning of crack growth with a minimum amount of calculations and good agreement between the experimentally determined and calculated crack resistance parameters.

In the design of offshore jack-up rigs, it is commonly assumed that the lattice legs have no effect on the fixity and other foundation behavior of the spudcan, presumably because the opening ratio of lattice legs is typically quite large. This paper describes a centrifuge experimental study to explore the effect of lattice legs on spudcan fixity under cyclic loading. The modeling equipment is first described. A novel feature of this equipment is its ability to maintain a constant holding vertical loading on the spudcan leg while subjecting the latter to rocking over many cycles. The centrifuge model results and discussion presented show that the presence and configuration of the lattice leg has a significant influence on spudcan foundation behavior in several different aspects. The effect is most significantly manifested in the fixity and bending moment. The fixity of the entire spudcan foundation is increased substantially by the presence of the lattice. The bending moment at the spudcan-lattice connection is also reduced by the lattice leg, with the maximum moment occurring slightly above the spudcan. Both of these effects can potentially lead to substantial cost savings in jack-up structures.

Stainless steels have many practical applications requiring various mechanical or chemical demands in the working environment. By optimizing a device used in mechanical experiments for torsional loading, several cylindrical samples were tested (both ends twisted with the same torque value in opposite directions) of 316L stainless steel (SS) to evaluate changes in the structural, chemical, and mechanical characteristics. Initially, the experimental samples were pre-loaded by tension in the elastic range (6%) and then subjected to torsion (772°) at different rates: 5, 10, and 20 mm/min. The experimental sequence consisted of a combined loading protocol with an initial tensile test followed by a subsequent torsional test. Two reference tests were performed by fracturing the samples in both torsion and tension to determine the mechanical strength parameters. The macro- and microstructural evolution of the samples as a function of the torsional degree was followed by scanning electron microscopy. The microhardness modification of the material was observed because of the strain (the microhardness variation from the center of the disk sample to the edge was also monitored). Structurally, all samples showed grain size changes because of torsional/compressive deformation zones and an increase in the degree of grain boundary misorientation. From the tensile and torsional behaviors of 316L SS and the structural results obtained, it was concluded that these materials are suitable for complex stress states in the elasto-plastic range through tensile and torsion. A reduction in Young’s modulus of up to four times the initial value at medium and high stress rates was observed when complex stresses were applied.

In recent times, helical piles have found widespread application for commercial and residential buildings and tower foundations. In order to investigate the lifting and lateral-uplift combined load-bearing characteristics of the helical pile in soft clay, field tests were carried out. Two types of helical piles with single-helix and doublehelix configurations were set up for study. The displacement control effect of the double-helix helical pile is much better than the pile with one helix. When the helix spacing is four times the diameter of the helix, the circumferential shear failure mode occurs. However, under the influence of both uplift and lateral loads, the lateral loadcarrying capacity of helical piles with double helices is significantly larger than that of a single-helix helical pile due to the action of the top helix.

Finite element (FE) model studies have made important contributions to our understanding of functional biomechanics of the lumbar spine. However, if a model is used to answer clinical and biomechanical questions over a certain population, their inherently large inter-subject variability has to be considered. Current FE model studies, however, generally account only for a single distinct spinal geometry with one set of material properties. This raises questions concerning their predictive power, their range of results and on their agreement with in vitro and in vivo values. Eight well-established FE models of the lumbar spine (L1-5) of different research centers around the globe were subjected to pure and combined loading modes and compared to in vitro and in vivo measurements for intervertebral rotations, disc pressures and facet joint forces. Under pure moment loading, the predicted L1-5 rotations of almost all models fell within the reported in vitro ranges, and their median values differed on average by only 2° for flexion-extension, 1° for lateral bending and 5° for axial rotation. Predicted median facet joint forces and disc pressures were also in good agreement with published median in vitro values. However, the ranges of predictions were larger and exceeded those reported in vitro, especially for the facet joint forces. For all combined loading modes, except for flexion, predicted median segmental intervertebral rotations and disc pressures were in good agreement with measured in vivo values. In light of high inter-subject variability, the generalization of results of a single model to a population remains a concern. This study demonstrated that the pooled median of individual model results, similar to a probabilistic approach, can be used as an improved predictive tool in order to estimate the response of the lumbar spine.