Determination of the constants of material models at high strain rates and elevated temperatures using shot impact test

Abstract

Material models are widely used in finite element codes for analysis of material deformations particularly at high strain rates and elevated temperatures. The problems such as necking and bulging limit the conventional test techniques to measure the stress–strain curves only up to small strains. This is while in some deformation processes, the strain can be greater than 1. In this study, steel shots of 6 mm in diameter are impacted on specimens at high impact velocities and at elevated temperatures using shot impact test. Strains up to 1.6 and strain rates up to about 4 × 106 s−1 are achieved in this study. The geometry of the crater created by the shot impact on the specimen is used for determination of the constants of Johnson–Cook material model. A combined experimental, numerical and optimization approach is used for determination of the constants. The experimental and numerical crater geometries coincide when the constants of material are chosen correctly. The selection of the constants is performed using an optimization technique such as genetic algorithm. The computed constants are verified by quasi-static tests. With this new technique, stress–strain curves are no longer needed to be obtained by experiment at high strain rates and elevated temperatures.