Identification of strain-rate sensitivity parameters of steel sheet by genetic algorithm optimisation

Abstract

The influence of the loading speed on mechanical response of structural materials can be accounted by means of strain-rate sensitivity parameters. The aim of the present work is to show a numerical technique based on an inverse approach to determine strain-rate sensitivity parameters of steels for car body constructions. This technique is based on the numerical simulation of a simple test according to the ASTM D5420/96 standard by means of a finite element explicit code. The test consists of a falling tup with a spherical head impacting on a thin sheet. Some experimental tests are conducted at different speeds, from quasi-static to impact loading conditions, on a specimen made of XE280P steel. A series of simulations are performed, changing the strain-rate sensitivity parameters in each run according to a genetic algorithm strategy. The strain-rate parameters that lead to the best fit of the experimental load-displacement curve with the numerical result are the assumed material characteristic parameters. The Cowper-Symonds and Johnson-Cook strain rate models have been taken into consideration.