Impact of soft minerals on crack propagation in crystalline rocks under uniaxial compression: A grain-based numerical investigation

Varying external conditions in the metallogenetic process of crystalline rocks contribute to the complex mineral and textural characteristics, rendering the mechanical properties highly heterogeneous at the mineral scale. This research focused on the influences of minerals with relatively low strength and stiffness (soft minerals) in crystalline rocks on their cracking behavior. A particle-based discrete element method (DEM) was first employed to establish random grain-based models (GBM) of crystalline rocks containing soft minerals with different contents, strengths, and stiffnesses. On this basis, responses of the mechanical properties and crack propagation to these parameters were systematically investigated and an optimized micro-parameter calibration method for real CT (computed-tomography) -based GBM was then proposed considering the characteristics of soft minerals. The results demonstrate that with the decrease of the strength of soft mica, the intragranular cracks are prone to initiate and propagate inside the soft minerals and lead to the final crack coalescence. The decrease in the stiffness of soft minerals enhances their controlling effects on the cracking propagation. Based on the CT-based granite model, it was found that a heterogeneous stress field is produced due to the spatial distribution of the soft (mica) and hard (quartz and feldspar) minerals, and the mica minerals tend to terminate cracks or force cracks to deflect or bypass individual grains during crack propagation. This study sheds light on the damage and failure processes of crystalline rocks with contrast mineral components.