Effect of fibre failure on low velocity impact of composite laminate with different stacking sequences
Résumé
During composite structure’s life, low velocity impacts by foreign objects may occur during manufacturing, maintenance, operation… Such impacts can generate damage in the material that significantly reduces the residual strength of the structure even though they can leave only a very little visible mark onto the impacted surface. Composite structures have then to be designed thanks to impact damage tolerance in order to take into account the possible damage. Therefore in order to numerically design this type of structure, a model enabling to take into account the impact damage, the permanent indentation and the residual strength after impact, is necessary. The objective is to be able, thanks to this model, to minimize mass of the composite structure with impact damage tolerance and in particular to study effects of structure parameters, as plate thickness, draping sequence, boundary conditions, impactor shape or impact energy on the impact damage and residual strength. This process remains until now a challenge and a lot of work is necessary to totally design numerically composite structures with impact damage tolerance. This paper deals with model of impact damage enabling the formation of damage developing during a low velocity/low energy impact test on laminate composite panels. The different types of impact damage developing during an impact test, i.e. matrix cracking, fibres failure and interfaces delamination, are simulated. The inter-laminar damage, i.e. interfaces delamination, is classically simulated thanks to interface finite elements based on fracture mechanics. The particularity of this model is to account for the intra-laminar damage, i.e. matrix cracks, thanks to interface finite elements which respect their discontinue character. The fibre failure is also taken into account thanks to failure criterion written inside the volumic elements with criterion based on the fracture mechanics. The effect of draping sequence is more particularly focused and experiments have been simultaneously performed in order to evaluate the model reliability. This experiment/model dialogue allows to better understand the effect of draping sequence on formation of the impact damage and to show the great influence of fibre failures on the force-displacement curves or on the shape of delaminated areas.