In this study, discrete element method (DEM) simulations of vibratory peening are combined with a Taguchi L16 screening design, a face-centered central composite design, analysis of variance (ANOVA) and response surface methodology (RSM). The aim is to quantify how vibration amplitude (A = 0.5–2 mm), frequency (f = 20–50 Hz), shot diameter (d = 4–10 mm) and immersion depth (h = 20–50 mm) affect the maximum normal impact velocity of the media on an Almen strip, which is the only response modeled by RSM. The maximum contact force and the impact energy are reported as complementary descriptors of the impact conditions. Amplitude and frequency are the dominant factors, contributing 62.4% and 29.5% of the linear effects, respectively. Their statistically significant interaction shows that high-energy impact regimes are obtained when high amplitude and high frequency act together. Shot diameter and immersion depth act as secondary, dissipative modulators. The reduced quadratic model yields R2 = 91.36%, with R2adj = 89.81% and R2pred = 86.07%. The highest impact velocity (2.184 m/s; composite desirability 0.814) is predicted at A = 2 mm, f = 50 Hz, d = 4 mm and h = 20 mm, i.e. on the boundary of the investigated region. The results provide a simulation-based process map for vibratory peening; experimental validation remains the subject of future work.
Mesoscopic heterogeneity plays a critical role in the brittle instability of crystalline rocks by influencing force transmission, damage accumulation, and fracture localization. However, the three-dimensional relationship among contact-scale heterogeneity, strong-force-chain evolution, and moment-tensor-derived acoustic-emission (AE) characteristics remains insufficiently understood. In this study, uniaxial compression of polymineral granite was simulated using PFC3D-GBM, with intragranular and intergranular contacts explicitly distinguished. Weibull-distributed contact properties were assigned using homogeneity indices of m = 2, 5, 10, and 20, together with a uniform condition, and were analyzed using multilevel force-chain analysis, spatiotemporal microcrack clustering, and moment-tensor calculations. The elastic modulus was nearly insensitive to the heterogeneity, whereas the peak strength increased from 59.81 to 153.81 MPa and the peak strain from 0.296% to 0.696%. Under low-homogeneity conditions, the larger population of weak contacts was associated with early diffuse cracking and disrupted force-transmission paths. With increasing homogeneity, a more continuous intragranular strong-force-chain skeleton developed, enabling greater pre-peak load accumulation and undergoing rapid degradation near the stress peak. At the peak stage, the absolute strong-force-chain load followed the order plagioclase > intergranular structures > quartz > alkali feldspar, whereas the average load per strong-force-chain contact followed quartz > plagioclase > alkali feldspar > intergranular structures. AE activity shifted from sparse, spatially dispersed, low-magnitude events toward denser event clusters with stronger energy release and increasing localization along dominant oblique fracture bands. Overall, the results reveal a consistent multiscale correspondence among contact-scale heterogeneity, strong-force-chain organization and collapse, crack localization, AE-source evolution, and macroscopic brittle instability.
Shaped charge jet formation involves explosive-driven liner collapse, extremely large deformation, high strain-rate plastic flow, strong shock interaction, and localized thermomechanical response. These characteristics pose significant challenges for conventional mesh-based methods because severe material distortion may lead to mesh entanglement and loss of numerical accuracy. To efficiently simulate the axisymmetric jet formation process, this work develops an axisymmetric meshfree method based on the Hot Optimal Transportation Meshfree (HOTM) framework. The proposed formulation extends the updated Lagrangian HOTM method to the axisymmetric r-z coordinate system. The deformation gradient, strain rate, stress update, internal force evaluation, and energy update are reformulated by explicitly incorporating the circumferential deformation and hoop stress contribution. Therefore, a three-dimensional rotationally symmetric problem can be solved using a two-dimensional meridional discretization while preserving the essential axisymmetric kinematics. A regularized near-axis treatment is further introduced to avoid the singular behavior associated with the 1/r terms and to improve numerical stability under strong shock loading. The method is verified and demonstrated through several representative examples, including thin-ring radial vibration, Taylor impact, simultaneous initiation of a cylindrical charge, and shaped charge jet formation. The numerical results demonstrate accurate axisymmetric dynamic and large-deformation responses, while the Taylor-impact simulation reduces the computational time by approximately 94% relative to the three-dimensional reference model. Sensitivity studies show only limited dependence on the near-axis regularization parameters, and comparison with a conventional axisymmetric Lagrangian FEM demonstrates improved robustness under severe mesh distortion. For shaped-charge jet formation, HOTM predicts a jet-tip velocity of approximately 9.4 km/s, compared with 8.8 km/s from the reduced-order PER model, while reproducing the overall decreasing trend of the jet velocity. These results demonstrate that the axisymmetric HOTM method provides an efficient and robust computational framework for explosive-driven large-deformation problems involving strong shock waves and near-axis motion.
Adjacent cavities can reconfigure stress transfer around a straight-wall arched tunnel and alter the load-bearing state of the rock bridges, but a systematic understanding of the relationships among cavity configuration, crack motion, and load-path stability is still lacking. In this study, sixteen single- and paired-cavity configurations were examined with the circular cavity size and minimum cavity–tunnel clear distance held constant. Rock-like straight-wall arched tunnel models were fabricated using sand-based binder-jet 3D printing, and uniaxial compression tests, two-dimensional digital image correlation (2D-DIC) measurements, and simulations using an existing improved smoothed particle hydrodynamics (SPH) formulation were combined to investigate the effects of cavity position and spatial combination on progressive failure. The results show that the peak stresses of the single- and paired-cavity specimens ranged from 2.526 to 3.176 MPa and from 1.940 to 3.218 MPa, respectively. Across the tested configurations, adding a second cavity did not produce a monotonic reduction in peak load-bearing capacity; the observed response instead varied with the relative cavity positions. As the single cavity shifted from directly above the crown toward the shoulder and springline regions, the cavity–tunnel rock bridge changed from near-vertical to inclined or lateral, while the dominant crack kinematics progressively shifted from symmetric opening to asymmetric opening, tensile-shear mixed motion, and localized shear sliding. Under the tested conditions, the paired-cavity configurations showed three recurring interaction patterns: relatively independent disturbance, directional rock-bridge coupling, and bilateral load-path coupling. These patterns corresponded, respectively, to localized damage, stepwise crack connection along a continuous weakening path, and coupled weakening of the load-bearing regions on both sides. These findings provide a mechanical basis for identifying risk-prone cavity–tunnel configurations, critical rock bridges, and priority areas for monitoring, support, and reinforcement around straight-wall arched tunnels in karst regions.
Natural gas wells in coal–gas overlap areas pass through coal seams and overlying strata, and the local surrounding rock conditions vary with the penetrated strata. Mining-induced disturbance further complicates the stress environment around the wellbore, making it necessary to analyze the damage and failure characteristics of surrounding rock–cement sheath–casing composites in different lithological strata. In this study, sandstone, half-coal–half-rock, and coal composite specimens were prepared and tested under uniaxial compression. Acoustic emission monitoring, DIC full-field strain measurement, and macroscopic failure observation were combined with PFC2D simulations of representative sandstone and coal composites to investigate the effects of surrounding rock lithology on bearing response, damage evolution, and failure mode. The results show that the cement sheath–casing structure weakened the overall bearing capacity of the composites. Under the present test conditions, compared with the corresponding intact reference specimens, the peak strengths of the sandstone, half-coal–half-rock, and coal composites decreased by 30.4%, 22.7%, and 19.3%, respectively. Acoustic emission and DIC results indicate that damage in the composites was concentrated around the borehole and bonded interfaces. The sandstone composite mainly showed oblique shear crack propagation, the failure of the half-coal–half-rock composite was jointly controlled by borehole stress disturbance and the coal–rock interface, and the coal composite was dominated by local borehole damage. Macroscopic observations and PFC2D results further show that composite instability was governed by borehole stress concentration, cement sheath damage, interface debonding, and crack propagation in the surrounding rock, accompanied by progressive bond breakage and energy dissipation. These results provide a reference for evaluating local wellbore structural stability and identifying key damaged strata in coal–gas overlap areas.
