DEVELOPMENT AND APPLICATION OF HIGH-STRAIN RATE CONSTITUTIVE MODELS IN HYDROCODES

A pre-requisite to the numerical modelling of warhead designs and concepts is a basic understanding of how materials behave under various loads, ranging from elastic to plastic through to hydrodynamic. This paper describes the development and application at RARDE of improved high strain rate material models for use in hydrocodes. These physically derived models are capable of describing the observed deformation behaviour and are based on the work of Armstrong and Zerilli. This model has been modified and constants derived for RARDE based material, both unshocked and shocked. The importance of having a physically based constitutive model, as opposed to a purely semi-empirical type model (e.g Johnson-Cook) is illustrated. The novel use of the hydrocodes in the simulation of the experimental material tests is shown to provide an extra insight into the method of analysis used in the derivation of a constitutive model. Results are presented which provide powerful evidence of the validity of the Armstrong-Zerilli model for pure iron in the high strain-rate, strain, and temperature regimes for both unshocked and shocked material. The successful application of this model to explosively formed projectile formation studies is also illustrated.