Development of estimation method of strain rate dependency of materials based on a high-velocity impingement test with a solid sphere

Abstract

Johnson-Cook (JC) flow stress model is widely used in computer aided engineering (CAE) for simulations of car crash and machining behaviors. The JC parameter C, which is a material constant in the model associated with strain rate dependency, is usually identified by a split-Hopkinson bar method. However, a huge equipment is required for this method to achieve an appropriate test condition. Therefore, the JC parameter C is expected to be estimated by a simpler method. In this study, an estimation method of the JC parameter C based on a high-velocity impingement test with a solid sphere, which is called EJCC, was developed. The fundamental equation in the EJCC was theoretically derived based on the energy conservation during impingement process, which was previously reported by our research group. Using the EJCC, the JC parameter C can be easily estimated with a depth of indentation obtained by the impingement test and the other JC parameters identified by a quasi-static tensile test. The quasi-static tensile test, the high-velocity impingement test and a high-speed tensile test were conducted to identify the JC parameters A, B, n and estimate the JC parameter C on three ductile metallic materials. As a result, the JC parameter C estimated by the EJCC was in good agreement with that obtained by the high-speed tensile test irrespective of materials and impingement velocities. Consequently, it was demonstrated that the EJCC can appropriately estimate the JC parameter C on ductile metallic materials.