Analyse de la réponse sous impact des stratifiés composites par virtual testing : difficultés et influence des effets de vitesse

Composite laminates are, nowadays, largely used in aeronautical structures, for their specific properties and low density. However, the complexity of their response, in particular for impact loadings, leads to a high number of tests required for their certification. In order to minimise the costs of these tests, the concept of virtual testing has become a staple of the validation phase. The challenge of virtual testing is, using models accurately describing the physics, to replace the expensive large scale tests by numerical simulations. However, this strategy is not yet mature, mainly because of the complexity of the phenomena taking place at a small scale (which are difficult to simulate), and, in the case of impact loadings, because of a lack of understanding of strain rate effects in the materials used.The work in this PhD focuses on this issue, by studying different aspects of the modelling of composite laminates under impact loading. First of all, a numerical model capable of predicting the propagation of damage, caused by impact loadings, has been developed. The influence of strain rate effects in the ply behaviour has then been studied under impact loadings of different velocities, and for different layups, highlighting their influence on damage propagation. Because of a lack of consensus in the literature, one aspect, revolving around the influence of the loading speed on delamination propagation, remains open to this day. The work in this PhD focused on two main points. The first one being the correct modelling of strain rate effects, for loadings of variable velocity. The second one being the proposal of a model, based on robust experimental data of delamination propagation. A comparison between simulation and experimental results demonstrated the importance of (i) the modelling of discrete fracture in the plies and (ii) the coupling between the damage in the plies and in the interfaces. Finally, a modelling strategy, allowing the simulation of an impact loading followed by a compression after impact loading in a commercial software has been presented, facilitating the study of the residual strength of composite laminates subjected to impact loadings.