Study on mode I dynamic fracture characteristics with a mini three-point bending specimen for the split Hopkinson bar technique

In recent years, dynamic fracture experimental techniques have been developed rapidly in the field of engineering and scientific research. However, there still exist some difficulties in dynamic fracture tests, such as the limitation of loading rate, the accuracy of transmitted wave, the difficulty of crack initiation, and etc. To solve such problems, a novel mode I dynamic fracture experimental technique is proposed in this work, with a mini three-point bending(3PB) specimen and two kinds of fixtures specially designed for the split Hopkinson pressure bar (SHPB) system. In this method, the dynamic stress intensity factor curve (DSIF) is obtained by the experimental-numerical method, and the crack initiation time is determined by the strain gauge method. To verify the feasibility and reliability of the proposed method, the dynamic fracture toughness (DFT) of two kinds of ultra-high-strength steel (UHSS) is determined by this new method and then compared with the results of other methods. Meanwhile, the loading rate effect of fracture toughness, the size effect of crack initiation time and the failure mechanisms of the two materials under mode I fracture are also studied. The results show that fracture toughness depends on the energy consumed to form two types of fracture regions within the fracture initiation time. This work provides a new method for studies of the dynamic fracture behaviors of brittle solids.