A dynamic phase field model for predicting rock fracture diversity under impact loading

Predicting dynamic rock fracture is of great significant in rock engineering. The phase field model (PFM) seems to a suitable numerical tool for simulating dynamic rock fracture. However, dynamic fracture diversity cannot be well reproduced by the existing PFMs. Only tension-induced dynamic fracture can be modeled while the dynamic compressive-shear and mixed-mode fractures are limited. Therefore, this study aims to propose a new phase field model that involves all the commonly seen dynamic fracture mechanisms to reflect dynamic rock diversity under impact loading. A new driving force is used and the hybrid phase field framework is adopted. Our PFM is implemented in the framework of finite element method and a staggered scheme is used to solve the coupled governing equations. Previous numerical and experimental studies are used to initially verify the proposed method. A dynamic mode-II test and a dynamic Brazilian disc test are simulated to show the applicability and feasibility of the proposed PFM and also to investigate the dynamic rock fracture diversity under impact loading. The numerical results indicate that the proposed PFM inherits the advantages of the conventional PFMs. Crack initiation and propagation are automatically characterized by the evolution equations of phase field. The parameters used in our model are more suitable for rocks. The difference between tensile-shear fracture and compressive-shear fracture is well distinguished. Different fracture patterns can be predicted by using different coefficient combinations in the proposed dynamic PFM.