Influence of different mineral grain sizes on AE source and rock mechanical properties: an example of non-homogeneous modeling

Acoustic emission statistical characteristics and fracture evolution of sandstones with different grain sizes

This study investigates the effects of grain size on the acoustic emission (AE) statistical characteristics and fracture evolution of fine-, medium-, and coarse-grained sandstones. Uniaxial compression tests with real-time AE monitoring were conducted, integrated with avalanche dynamics, fractal theory, RA-AF crack classification, and scanning electron microscopy fracture surface observations. Results show that all three sandstones exhibit four typical loading stages (compaction, elasticity, crack propagation, and post-peak instability), with uniaxial compressive strength decreasing as grain size increases. The probability density of AE absolute energy, Omori aftershock decay, and waiting-time distributions all follow power-law behavior, and their exponents increase synchronously with grain size, indicating a transition in fracture energy release from high-energy concentrated events to multi-source, small- to medium-scale events, accompanied by enhanced short-term clustering and local abruptness. Macroscopic fractures are predominantly tensile, with the tensile crack proportion rising with grain size. The microscopic failure mechanism shifts from relatively continuous intergranular propagation in fine-grained sandstone to a composite mode involving intergranular cracking, transgranular cracking, interface debonding, and grain pull-out in coarse-grained sandstone. The correlation dimension exhibits a fluctuating increase during loading, a pre-peak decline, and low values at instability, reflecting a progressive scaling process from dispersed microcrack development to localized coalescence of major macrocracks. These findings provide a statistical physics basis for understanding fracture evolution in heterogeneous rocks and offer reference value for rock engineering stability assessment.

Effects of thermal treatment and grain size on the basic friction angle of granite rocks

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

Experimental and Numerical Study of Water Effects on Mechanical and Fracture Behavior of Sandstone: A Case Study

Water significantly modifies rock mechanical performance and fracture characteristics through water content and water distribution. Nevertheless, the evolution laws of rock mechanical properties and underlying fracture mechanisms under variable water conditions remain incompletely clarified. In this study, uniaxial compression tests were carried out on sandstone samples with diverse water immersion durations. Experimental observations reveal that the uniaxial compressive strength (UCS) and elastic modulus of sandstone follow negative exponential attenuation with prolonged immersion time, with maximum reductions of 50.1% and 25.6%, respectively. Under equivalent water contents, samples featuring dry exteriors and wet interiors possess lower strength than those with wet exteriors and dry interiors. A self-developed numerical code incorporating humidity diffusion effects was subsequently adopted to interpret water-controlled sandstone fracture behaviors. Numerical outputs verify that water-induced softening and heterogeneous water distribution exacerbate rock material heterogeneity and internal stress non-uniformity, triggering tensile microcracks along dry–wet interfaces. As the immersion duration rises, the rock failure mode transitions from shear-dominated mixed failure to tension-dominated failure, and finally reverts to shear-dominated mixed failure. Macroscopic rupture is predominantly governed by the gradual coalescence of tension-generated microcracks. This study offers a theoretical foundation to advance the understanding of water-triggered mechanical degradation and fracture mechanisms in sandstone.

Microstructural Evolution Study Under Shear Loading: A Combined CPFFT Simulation and EBSD Investigation

Metals and alloys exhibit scale‐dependent mechanical behavior governed by crystallographic slip, requiring explicit consideration of slip systems in microscale simulations of polycrystals. Crystal plasticity (CP) theory addresses this by explicitly modeling anisotropy and slip‐system interactions. In this study, the texture evolution of an aluminum wire under shear was investigated using the spectral solver of the crystal plasticity fast Fourier transform (CPFFT) method on a 100‐grain representative volume element (RVE). An initial non‐random ⟨100⟩ fiber texture was assigned based on electron backscatter diffraction (EBSD) measurements, and the accuracy of the CPFFT predictions was validated against experimental EBSD results. Pole figure and ODF analyses of the deformed sample confirmed the partial development of FCC simple‐shear‐related texture components, indicating a shear‐induced modification of the inherited wire‐drawing texture rather than a complete replacement by a fully developed shear texture. EBSD misorientation analysis showed an increase in the high‐angle grain‐boundary fraction from 28.52% to 46.05% and an increase in the average misorientation angle from 11.86° to 20.39° after half‐turn torsion, indicating enhanced torsion‐induced misorientation development. Both experimental and simulated inverse pole figures exhibited an intensified [001] || SD fiber after shear. Furthermore, the sensitivity of the simulations to grain number and grid resolution was examined as a numerical verification step. Increasing the number of grains from 10 to 100 and 500 improved predictive accuracy, while variations in grid resolution had minor effects. The yield strength increased from 80 to 92.3 MPa, and the average hardness increased from 53.06 to 57.46 HV after deformation.

Grain breakage_induced evolution of grain size distribution, pore structure, and permeability of sands under high oedometric stress

Grain breakage under high stress conditions can significantly affect the hydro-mechanical behavior of granular materials by altering grain size distribution, pore structure, porosity, and permeability. This study investigates these coupled effects in two sands with contrasting mineralogical characteristics, namely Hostun silica sand and carbonate sand, subjected to high oedometric stresses up to 105 MPa. High-pressure oedometer tests were performed on dense specimens prepared at a relative density of approximately 0.9. Grain size distribution was determined by post-loading sieve analysis, while permeability was measured at different stress levels using a constant-head system connected to the oedometer cell. Pore-access size distribution was characterized using two complementary techniques depending on material response and stress level: the tensiometric method, based on drying-path water retention measurements and the Young–Laplace law, and mercury intrusion porosimetry for carbonate sand specimens that developed sufficient cohesion after high-stress loading. The results show that increasing stress induces progressive grain fragmentation, leading to an evolution of the grain size distribution toward an ultimate grading state, together with reductions in pore size and porosity. The crushing threshold was identified at approximately 12.5 MPa for Hostun sand and 3 MPa for carbonate sand, indicating the strong influence of mineralogical composition on breakage resistance. Permeability decreased markedly with stress, with a reduction of about 50 % for Hostun sand and more than 70 % for carbonate sand. This stronger reduction in carbonate sand is associated with more pronounced particle breakage, pore structure modification, fines production, and reduced pore connectivity. The experimental results were interpreted using the Continuum Breakage Mechanics framework, and a power-law relationship between permeability and porosity was calibrated for both sands. The analysis indicates that grain rearrangement and grain breakage jointly control porosity and permeability reduction, with the influence of grain breakage becoming increasingly significant at higher stress levels, particularly for carbonate sand.These findings provide an experimental and modeling basis for understanding the coupled effects of high stress, grain breakage, pore structure evolution, and permeability reduction in sands, with implications for geotechnical, geomechanical, and petroleum reservoir engineering applications..