Proposal of Evaluation for Impact Deformation Properties of High Strength Metallic Materials by Preloading Split-Hopkinson Bar Method

High strength metallic materials have been developed based on various material designs, and investigations of their mechanical properties at high strain rates have been required. Previous studies have shown that the athermal component of flow stress would be the primary cause of increased stress in many high strength metallic materials. As a result, the thermal component of flow stress, which is affected by the strain rate, is relatively small. Therefore, it is difficult to evaluate the thermal component of flow stress with high accuracy in impact deformation test. In this study, a preloading split Hopkinson bar (SHB) method is proposed to establish an impact tensile test method that can evaluate thermal component of flow stress with high accuracy. The preloading applied using a hydraulic jack. Stress, strain, and strain rate were calculated based on the principle of the usual SHB method under preloading effect. The amount of plastic strain to fracture evaluated from the stress-strain relationship was almost identical to the elongation of the specimen optically measured after the test. Therefore, it would be concluded that a highly accurate preloading SHB tensile test apparatus was successfully developed.