Effects of bedding planes on the fracture characteristics of coal under dynamic loading

Abstract

To investigate the influence of bedding planes on its fracture characteristics under dynamic loading, testing and numerical simulations are carried out on semi-circular bend specimens of coal. It is shown that the fracture load and dynamic initiation fracture toughness decrease as the increase of bedding-plane angle. The crack propagation direction is jointly controlled by the maximum principal stress and bedding planes. Based on the digital speckle correlation method, it is found out that, due to stress concentration, strain at the initial loading stage concentrates around crack tip. After crack initiation, there is a specific strain gradient with a candle flame-like shape on the surface of a specimen. The opening displacements at crack tip can be divided into stable and linearly increasing phases. Further, a continuum-based discrete element method is applied to virtually reproduce these fracture characteristics, which are instructive to study dynamic anisotropy in fracture of coal.