Modelling micro-crack initiation and propagation of crystal structures with microscopic defects under uni-axial tension by discrete element method

Abstract

This paper investigates mechanical behaviour and failure process of a 3D notched plate subjected to uni-axial tension using the discrete element method (DEM). The 3D notched plate consisted of different crystal structures, such as simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC) and hexagonal close-packed (HCP), where constituent spheres were bonded together by contact bond. The inclination angle of the notch ranged from 0° to 90° with an increment of 15°. The aim of this study is to explore the effects of crystal packing and notch inclination angle on the mechanical responses, crack initiation and propagation, and crack paths. The proposed DEM model was first verified for the pre-cracking behaviour by the corresponding FEM calculation, and was confidently used to study the post-cracking behaviour. Numerical results reveal that the crack initiation and propagation of crystal structures depend on the crystal configuration and notch inclination angle. The loading stiffness of the four crystal structures follows the sequence of HCP>FCC>SC>BCC. The stress concentration factor shows a convex profile against notch inclination angle, with the maximum value at the notch inclination angle of 30° and the minimum value at the notch inclination angle of 90°. The SC and BCC crystal structures show a symmetric feature of crack propagation, whilst the FCC and HCP crystal structures exhibit asymmetric characteristics. In such a loading scenario, the crack initiation and propagation in all the four crystal structures are mainly dominated by the tension failure mode.