Mineral grain-texture model and impact on microcracking and mechanical response of granite

Abstract

Granites are representative of generic crystalline rocks characterized by their complex crystal-grain structure. Variations in the composition, size, shape and orientation of mineral grains result in pronounced heterogeneity and anisotropy at the microscopic scale, significantly influencing mechanical properties as well as the initiation and propagation of microcracks. A grain-texture model (GTM) is used to characterize the microstructural features of porphyritic monzogranite, based on the “templated” − “grain growth” method. This addresses the limitations inherent in Grain-Based Models (GBM) that do not allow for modifications to mineral grain shapes. The accuracy of this novel model was validated through comparisons between numerical and experimental results. Subsequent validations were against granite models with varying biotite contents to examine related mechanical and microcracking response as a result of component mineral properties, shape and orientation. Changes in biotite content influence heterogeneity and consequently both mechanical properties and failure characteristics of the composite granites. As biotite strength decreases, there is an increased likelihood for cracks to initiate and propagate within it; correspondingly, the decrease in stiffness of the biotite has a notable impact on the pattern and path of crack propagation. Alteration in the shape and orientation of mineral grains results in significant changes in the anisotropy of granite through impact on the number and arrangement of grain boundary contacts. When these boundary contact orientations align with fracture directions, rocks exhibit an increased propensity for the evolution of throughgoing fractures and macroscale failure.