Theoretical and experimental study of high strain, high strain rate materials viscoplastic behaviour. Application to Mars 190 steel and tantalum

This work enters in the general framework of the study and modelling of metallic materials viscoplastic behaviour in the area of high strain and high strain rate, from 104 to 105 s-1. We define a methodology allowing to describe the behaviour of armor steel Mars 190 and tantalum in the initial area. In a first time, the study of visco-plasticity physical mechanisms shows the necessity to take into account some fundamental processes of the plastic deformation. Then, the examination of various constitutive relations allows to select the Preston-Tonks-Wallace model, that notably reproduce the physical phenomenon of the flow stress saturation. In a second part, a mechanical characterization integrating loading direction, strain rate and temperature effects is conducted on the two materials. Moreover, these experimental results allow to calculate associated constants to Preston-Tonks-Wallace, Zerilli-Armstrong and Johnson-Cook models for each material. In a third time, in order to evaluate and to validate these constitutive laws, we conceive and develop an experimental device open to reach the area of study: the expanding spherical shell test. It concerns to impose a free radial expanding to a thin spherical shell by means a shock wave generated by an explosive. By the radial expanding velocity measure, we can determine stress, strain rate and strain applied on the spherical shell at each time. In a four and last part, we evaluate constitutive models out of their optimization area's. This validation is undertaken by comparisons 'experimental results/calculations' with the help of global experiences like expanding spherical shell test and Taylor test. (author)