Dynamic fracture behavior and fracture toughness analysis of rock-concrete bi-material with interface crack at different impact angles

Abstract

The crack initiation and propagation behavior of interface crack under impact are of great significance for evaluating the stability of rock-concrete system and other layered structures. Dynamic test using split-Hopkinson pressure bar (SHPB) system was performed on bi-material cracked straight-through Brazilian disc (CSTBD) specimens, and the fracture processes of specimens were monitored by means of a high-speed camera. The effects of the impact angle, concrete strength and strain rate on the dynamic fracture behavior were investigated. The results show that three typical fracture types can be identified: interface fracture, combined fracture (interface/shear and tension fracture) and tensile fracture. The interface fracture appears under small impact angle, while the combined fracture occurs with the further increase of impact angle. The crack initiation time of wing cracks and the number of secondary cracks are mainly affected by the strength of concrete in the bi-material specimen. Crack initiates earlier and more secondary cracks are generated in concrete material (weak material), and the number of secondary cracks increases with increasing strain rate. The dissipated energy increases gradually as the impact angle increases from 0° to 75°, while it decreases when the impact angle exceeds 75°. As the concrete strength increases, the difference in dissipated energy for different impact angles decreases. Furthermore, the effects of impact angle, concrete strength and loading rate on the dynamic fracture toughness for different loading modes are also discussed. The results indicate that the normalized stress intensity factors (SIFs) at the two tips of the interface crack are distinct and the difference increases with increasing crack length-to-diameter ratio. The impact angle, concrete strength and loading rate influence the dynamic fracture toughness significantly.