Fracture mode transition in expanding ring and cylindrical shell under electromagnetic and explosive loadings

In the present study, we designed the electromagnetic and explosive driving expanding ring/cylinder experiments and investigated the expanding fracture characteristics of oxygen-free high-conductivity copper (OFHC) in consideration of the conception of the reduction of area, the local fracture strain and the average fracture strain. We used a high speed camera to record the fracture process and obtain the fracture strain of the copper cylinder and the Doppler pins system (DPS) to obtain the radial velocity of the specimen in order to achieve the strain rate of the loading. We verified the local fracture strain and the fracture mode by analyzing the soft-recovered fragments of the expanding ring and the cylinder. Based on the experimental results, we found that the average fracture strain and the reduction of the area increases as does the strain rate. Moreover, the fracture mode transition may occur at the strain rate of about 1.0×10⁴ s^-1, and the reduction of the area may increase by an order of magnitude, i.e. from the order of 10⁰ to that of 10³, and the local fracture strain exhibits an obvious subarea.