The crack nature analysis of primary and secondary cracks: A numerical study based on moment tensors

Abstract

Abstract Cracking processes have been extensively studied in brittle rock and rock-like materials. For a better understanding of failure processes, moment tensor is used to distinguish the nature of primary cracks and secondary cracks in a single-flaw-contained specimen based on the bonded-particle model, which can indicate the force applying on the failure source. The results reveal that the primary cracks solely consist of micro-tensile cracks and the failure nature is tensile, while the secondary cracks are composed of both micro-shear cracks and micro-tensile cracks and the failure mechanisms are complicated. The failure mechanisms of acoustic emission (AE) events of the first part of secondary cracks, which initiate from the tips of the pre-existing flaw, are mainly “implosional” and “shear”, implying that the unbalance forces applied on the failure source are predominately implosional and shear components after breakage. As the secondary cracks propagate farther, the failure nature of AE event changes to “tensile” mode finally.