A new constitutive model for nitrogen austenitic stainless steel

Quasi-static, quasi-dynamic and dynamic compression tests have been performed on a nitrogen alloyed austenitic stainless steel. This alloy achieves a high hardening modulus and a good ductility at all strain rates. In addition, this steel is very sensitive to strain rate. The temperature sensitivity has been determined for temperatures varying between 20°C and 400°C. Microstructural analysis has been performed on samples subjected to different loads in order to relate the microstructure to the material behaviour. Johnson-Cook and Zerilli-Armstrong models have been selected to fit the experimental data into constitutive equations. These models are unable to reproduce the behaviour of this type of steel over the complete range of tests. A new constitutive model that better fits all the experimental data at different strain, strain rate and temperature has been determined. This empirical model supposes that the influence of the main parameters is independent. Single Taylor impact tests have been realized to validate the models. Live observations of the specimen during impact have been achieved using a special CCD camera set-up. The overall profiles at different times were compared to numerical predictions performed with LS-DYNA.