Modelling of the dynamical performance of a protective structure ceramic-adhesive-composite: analysis of the adhesive layer functionality

This thesis proposal is part of an upstream project to improve the performance of so-called ‘dual-hardness’ armour, consisting of a ceramic layer (on the front face) and a composite layer (on the back face, known as the backing), as shown in Figure 1. The main function of the ceramic layer is to slow the progress of the impacting projectile by dissipating energy through fragmentation [Rahbek 2017, Shokrieh 2008, Colar 2013, Colar 2015]. The main function of the backing layer is to retain the ceramic fragments (non-perforation criterion) and to limit the penetration of the protection (penetration criterion). An adhesive is used to join these two materials. At present, this adhesive layer is not explicitly functionalised to contribute to the performance of the armour. One of the main objectives of this project is to understand and model the function of this layer to improve the armouring.

While it is essential to understand the modes of fragmentation of the front face under impact and the modes of backing failure, it is also necessary to consider the influence of adhesive strength on these failure modes. It is the breaking strength of the adhesive that provides the system with sufficient flexural rigidity to limit deflection of the rear face and prevent perforation of the backing layer by ceramic fragments. The adhesive also serves to hold the backing in place. It is also likely to be important to use coupled tests and calculations to understand whether the adhesive layer can help to improve the fragmentation of the ceramic layer. Another objective of this project is therefore to capitalise on the developments of the behaviour models developed during the previous AID ‘tri-layer’ project [Essongue 2022] and the DGA/ISL thesis of Tristan Camalet [Camalet 2020, Duplan 2020, Francart 2017], as well as the developments carried out in the partner laboratories concerning the behaviour of bonded interfaces [Lopez-Puente 2005, Lélias 2018, Jaillon 2019a 2019b, Planas 2024],

In addition, in the development of these protections, research into new materials and optimised assemblies to best satisfy the protection criteria (energy absorption, non-perforation of the backing, punching of the backing, reuse, multi-impact protection, recyclability and environment) is necessary. In this context, two identified partners (currently partners of ISAE-SUPAERO) Arkema for adhesives and St Gobain for protective materials (on the front face and for the backing) wish to participate in the project by supplying adhesive materials (Arkema) or new materials (Saint Gobain). This last point constitutes an opening objective of the project concerning the study of new front panel and backing materials.

The thesis work therefore follows on from these research activities in the field (work carried out at ISAE-SUPAERO/ICA in collaboration with ICUBE and ISL since 2017 (Thesis CAMALET / Post Doc ESSONGUE) and is more particularly interested in the influence of the fracture or holding properties of the adhesive on the modification of the fragmentation of the ceramic and the deflection/damage of the backing. The thesis work is also part of a theme concerning the high-speed modelling of the behaviour of materials and composite structures assembled by gluing (and/or bolting).