Thèse de Yannick Duplan

Some ceramic grades, such as silicon carbide (SiC) or alumina (Al2O3), are used as ballistic materials thanks to their excellent mechanical performances, such as their hardness, while being light, where weight gain is a major issue for the design of military equipment for personal and vehicle protection. Since the Vietnam War, ceramics have been largely used and integrated as front face in bilayer shielding to stop the threat of AP (Armour Piercing)-type projectiles during a ballistic impact. Nevertheless, the projectile leads to an intense damage in the ceramic due to, amongst other phenomena, a dynamic tensile loading that manifests by multiple cracking, called fragmentation, particularly unfavourable for the integrity of the ballistic protection and its capacity to deal with a second impact. In order to develop a more performing shielding material, it is essential to understand the link between the microstructure of ceramics, the damage generated under impact and their ballistic performances.

This thesis seeks to better understand the dynamic fragmentation phenomenon generated at high strain rates in high fracture-toughness ceramics, including a bio-inspired alumina material mimicking nacre microstructure. This artificial nacre is, a priori, more crack resistant than conventional ceramics as it is characterised by a high static fracture-toughness due to its specific “Brick-and-Mortar” (or BM) microstructure reproduced in the material called here MAINa.

Jury

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Some major results from the PhD: steel core extracted from API-BZ bullet with MAINa microstructure observed in Scanning Electron Microscopy (chapter 2); comparison between the experimental force-displacement response along with the numerical response using the identified experimental law of the steel core (chapter 3); numerical simulation of the penetration process of the steel core (800 m/s) in a SiC ceramic, 56 μs after impact (chapter 4); dynamic cracking of MAINa microstructure, tested in two orientations of platelets during Rockspall tests (chapter 5); multiple fragmentation of MAINa samples (0° orientation) after both Edge-On-Impact test in sarcophagus configuration and tandem test with tomographic segmentation (chapter 6).