Investigation of Mixed-Mode Crack Propagation Behaviour under Impact Loading

The fractured rock masses are often subject to impact loading, giving rise to complicated mixed-mode cracking. The propagation of the cracks may result in structural instability and project disaster and often cannot be understood by studying only the mode I fracture. Discovering the mixed-mode crack behaviour is of great interest to engineering design. Here, we report on an investigation of mixed-mode crack propagation under impact loading. A Single Cleavage Simi-Ellipse configuration was proposed with different pre-crack dip angles. Split Hopkinson pressure bar impact tests were conducted and a high-speed camera was employed to capture the cracking behaviour. With the experimental-numerical method, the dynamic initial stress intensity factors KI and KII were calculated by the finite element method. The AUTODYN was applied to study mixed-mode crack propagation numerically. The investigation demonstrates that the mixed-mode crack would adjust fracture mode continuously in the whole propagation process companied with several extending decelerations. The crack initiation mode and the dynamic initiation stress intensity factor have a relationship with the impact loading orientation. The AUTODYN can be applied in predicting rock crack propagation, offering new insights into dynamic stability analyses in engineering design.