Micro-scale shale fracture wear under normal stress: 3D point cloud-coupled experiments/simulations study

• Rough surfaces exhibit slight relative rotation under normal stress. • The relative height of the fracture surface significantly influences contact wear. • There is a positive correlation between wear amount and normal stress. • The S q value among the geometric parameters of rock cracks effectively explains the variations in contact wear under stress. A comprehensive understanding of frictional interactions and wear mechanisms in rough fractures is critical for advancing research in earthquake dynamics and associated geological hazards. Systematic loading experiments were performed on unconfined shale fractures using a six-dimensional rock pressure detection and displacement monitoring system. High-resolution three-dimensional point cloud datasets of fracture surfaces were acquired via laser profilometry, while pressure-sensitive films were employed to quantitatively map contact behavior under varying normal stresses. Spatial integration of point cloud data with pressure-sensitive film measurements demonstrated that initial contact occurs preferentially at asperities with elevated heights. A wear distribution model was constructed by computationally aligning and subtracting pre- and post-loading topographic datasets. Mesh-based analytical methods identified a robust correspondence between extreme wear loci and regions of concentrated contact stress. The steady-state wear rate of shale fractures followed a power-law relationship with normal stress, consistent with micromechanical wear theories. Statistical evaluation of 3D surface topography parameters revealed that the root-mean-square height ( S q ) displayed significant correlations (Pearson’s r > 0.85, p < 0.01) with mechanical metrics. These findings advocate for S q as a robust 3D geomechanical index for characterizing contact wear evolution in fractured media.