Space-time Local/adaptive - Global/fixed coupling strategy for simulation of impact on composite structures.
Résumé
Current design tools allow to avoid failure of composite structures under dynamic loads using appropriate safety margins. On the other hand, the same tools do not allow to predict residual stiffness of a structure after damaging impacts. In the case of unidirectional multi-layered composites, this damage can specify important delamination in many zones through the thickness, an effect not easily detectable on the external surface. The non-linear context of crack propagation and the multi-scale aspects in space and in time increase the complexity of the problem. Furthermore, a methodology able to run accurate simulations of this phenomenon in large structures and with large delaminated zones is not available today with the computing time required by the industry. This work is a contribution to the development of such methods, that must be implemented in commercial software for the operational design. The starting point of our work is the coupling method between subdomains with incompatible time steps developed and improved by the team of Combescure at INSA de Lyon. Parameters, mesh refinement, local time step, space-time coupling method between global and local models have been adapted for the delamination case. The obtained results show a nearly perfect agreement with a fine 3D analysis applied on the entire structure. A disadvantage of the method based on domain decomposition approaches is that different subdomain meshes involve different time steps. In particular, this method obliges to define a shell structure domain and a 3D finer domain and to couple themselves. This feature of the method is suitable for cases in which domains can be predefined and fixed a priori. In addition, subdomains definitions (as shell model or as 3D model) change in function of delamination propagation and size. As well, we have tried to develop a superposition multi-scale strategy by analogies with nonintrusive methods proposed in non-linear statics. The goal is to use a global shell model on the entire structure and to activate or deactivate 3D patches with a finer model only on limited zones of the same structure. The method is necessarily iterative and needs data transfers form global to local and from local to global. When delamination is well defined on a zone of the structure, the 3D finer model can be deactivated and a new penalised constitutive law can be applied on the interested structural finite elements.