Investigation of Compressive–Shear Fracture in Rock Considering Flaw Distribution and Interaction via an Improved Energy-Stress-Based Peridynamics Model

True‐triaxial deformation, cracking and strength failure characteristics of chemically corroded flawed sandstone

Fracture behavior and constitutive modeling of rock-concrete contact surfaces with different roughness under freeze–thaw cycles

Research on the Stability of Arc-Fractured Rock–Concrete Composites: Mechanical Response and Energy Evolution

To mitigate the violent movement of overlying strata in goaf areas, rock–concrete composite support systems are widely utilized. However, the mechanical behavior of such systems under the influence of complex pre-existing defects, such as arc-shaped fractures, remains insufficiently understood. This study aims to clarify the failure mechanisms and the evolution of stability in these composites by evaluating the influence of fracture inclination angles. A synergistic methodology was adopted, combining laboratory uniaxial compression tests with discrete-element method simulations. Based on energy dissipation theory and the strain equivalence hypothesis, a statistical damage constitutive model was established to bridge the gap between microscopic damage and macroscopic mechanical response. The results demonstrate that fracture inclination significantly dictates the energy partitioning and crack propagation patterns within the composite. The established constitutive model, validated by numerical results ( R 2 > 0.999), effectively quantifies how increasing inclination angles enhance energy absorption efficiency and retard structural damage progression. Due to the high toughness of the concrete component, the composite maintains substantial residual bearing capacity, preventing instantaneous failure. These findings provide a robust theoretical framework and practical guidance for optimizing support designs in deep underground excavations with intricate geological defects.

Micro‐Macro Fracture Mechanism, Energy Evolution and Damage Constitutive Model of Rock‐Like Materials With Heterogeneous Parallel Double Flaws Under Triaxial Compression

To investigate the effects of flaw geometric heterogeneity on the mechanical behavior of rock under triaxial compression, this study examines sandstone‐like specimens containing parallel double flaws, systematically evaluating the coupled effects of multiple parameters including flaw spacing and the apertures of primary/secondary flaws (considering non‐uniform configurations). Through triaxial compression tests and numerical modeling using the Particle Flow Code (PFC2D) for energy evolution analysis, a damage constitutive model incorporating microcrack event counts is developed, which accounts for the aperture ratio between primary and secondary flaws ( λ = a / c ) and flaw spacing ( b ). The results indicate that increasing flaw spacing significantly enhances both the strength and integrity of the specimen, whereas increasing the aperture of the primary flaw markedly reduces strength. Under non‐uniform flaw aperture conditions ( λ ≠ 1), a decrease in the aperture of the secondary flaw improves compressive strength but also induces a more complex crack network and more concentrated microcrack activity near the peak stress. Energy evolution is significantly governed by flaw geometry, with non‐uniform aperture conditions fundamentally altering energy accumulation efficiency and instability modes. The developed constitutive model accurately characterizes ( R 2 ≥0.96) these complex mechanical responses, demonstrating that geometric heterogeneity in parallel double flaws is a key factor controlling rock mass stability, thereby providing important theoretical support for hazard prevention in underground engineering.

Numerical Investigation of Mixed Mode I-III Fracture Behavior in Sandstone Under Static and Dynamic Loading

Mixed mode I–III fracture commonly occurs in rock masses under complex three-dimensional stress states, yet the combined effects of loading conditions and fracture mode remain unclear. In this study, a heterogeneous sandstone disc model is developed in ABAQUS by coupling the Drucker–Prager elastoplastic model, an equivalent-strain damage model, and cohesive elements. The model is validated against static Brazilian splitting tests and dynamic SHPB tests. ENDB specimens are then employed to investigate mode I, mode III, and mixed mode I–III fracture under static and dynamic loading with offset angles ranging from 0° to 62.5°. As the offset angle increases, crack propagation evolves from straight tensile extension to deflected, twisted, and fragmented patterns dominated by anti-plane shear. Dynamic loading intensifies crack segmentation, localized damage, and transient instability while increasing the peak load, fracture toughness, and fracture energy. In contrast, the effective fracture toughness and fracture energy decrease monotonically with increasing offset angle under both loading conditions. A linear trend consistent with R2 > 0.99 is observed between the mode I–III mixing coefficient and the effective fracture toughness based on single-realization simulations, the effective fracture toughness under dynamic loading is approximately 2.22 times that under static loading based on direct comparison of calculated values. These findings improve the understanding of loading-dependent mixed mode I–III fracture in sandstone and provide guidance for rock mass stability assessment.

Competitive Meso-Damage Model Dependent on Stress State for Advanced High-Strength Steels

Advanced High-Strength Steel (AHSS) exhibits stress-state-dependent competing shear–tensile fracture modes that limit the applicability of conventional ductile fracture criteria based solely on equivalent plastic strain accumulation, such as the Forming Limit Diagram (FLD) approach and the classical Gurson–Tvergaard–Needleman (GTN) model. This paper proposes an extended GTN damage model incorporating Hill’48 anisotropy and the Nahshon–Hutchinson shear mechanism, regulated by a stress-state-dependent weighting function. The experimental program comprised uniaxial tension tests for constitutive calibration, notched plate specimens with shear angles ranging from 0° to 90° (spanning pure shear to tensile–shear stress states), and tension-bending tests. The fracture initiation point was identified from the abrupt load drop on the experimental force–displacement curve and further located in the finite element simulation to extract the corresponding stress-state history. SEM fractography was employed to characterize the microscopic damage mechanisms, revealing a continuous transition from shear-dominated to void-dominated damage at a critical stress triaxiality of approximately 0.35. A weighting function dependent on both stress triaxiality and the normalized Lode angle was formulated to couple void evolution with shear band localization. Following calibration via finite element inverse fitting, the model, implemented as an ABAQUS VUMAT subroutine, successfully reproduced fracture strains and crack paths across stress states ranging from pure shear to high hydrostatic tension. Comparative simulations indicate that this approach yields improved prediction accuracy over the classical GTN model, particularly under mixed-mode conditions, thereby offering a practical numerical tool for analyzing AHSS formability.