Etude du comportement de céramiques à blindage sous chargement de compression haute-vitesse par essais d’impact de plaque plan ou sans choc

Ceramic materials are widely used in armour or protective structures providing weight savings for equivalent performance compared to their steel counterparts. In these conditions, they experience extreme damage, micro-plasticity and fragmentation mechanisms. To fully understand these behaviours, characterization under high-strain-rate compression needs to be conducted. Several experimental techniques, such as the plate-impact test, are used to investigate the dynamic behaviour of ceramic under high compressive loading. During this experiment, a flyer plate (often made of a metallic material) strikes the target, and some mechanical properties such as the HEL (Hugoniot Elastic Limit) as well as the Hugoniot curve of the material can be deduced from the rear side velocity measured at the back of the target. Nevertheless, this test do not provide a controllable loading-rate in the target and the hardening behaviour cannot be directly deduced.One of the aims of this thesis was to develop and implement an experimental shockless plate-impact configuration enabling Lagrangian Analysis. The various experimental campaigns were carried out using the 3SR laboratory launcher. The use of wavy flyer plates to generate a loading ramp was validated using tests on 316L steel, which has the asset of not changing phase in the range of studied stresses. Two ceramics, F99.7 alumina and Forceram SiC, were then studied in this configuration. These tests coupled with Lagrangian analysis enable to obtain the curve of axial stress as a function of axial strain beyond the HEL.At the same time, some other plate impact configurations were developed to characterise the temporal profiles of axial and radial stresses in the ceramic. This configuration is based on the use of Manganin piezoresistive gauges. These tests were carried out on steel and alumina targets. The results were compared with the ones obtained by rear side velocity measurements during the same tests.The experimental results from the thesis were compared with numerical finite element simulations based on a JH2-type (Johnson–Holmquist) plasticity model. These calculations were used to identify the parameters of the ceramic behaviour model thanks to an inverse approach. It helps providing a better understanding of the mechanical behaviour of these materials under such loading conditions. Nevertheless, other tests, in particular triaxial tests, could be further considered in order to complete the identification of a constitutive model for these microstructures under intermediate confinement pressures.