Approximation of a lightning test by a mechanical impact one: from equivalence criterion based on deflection to mechanical modelling of core damage and delamination

Lightning strike threats are well accounted for by aircraft manufacturers, through rigorous procedures acknowledged by airworthiness authorities, but there still remains a significant potential for mass optimization of protections, especially regarding features adopted for composite structures. In a first paper we presented a method to design mechanical impact tests representative of lightning ones in the sense that strains and stresses applied to the material in both situations are comparable. The strategy is based on a decomposition hypothesis of surface and core phenomena. Here we complete our approach by designing a 3D damaging numerical model representing the mechanical impacts, in order to predict the experimental mechanical damage and evaluate the ability of the model to predict lightning strikes damage. The numerical model reproduces quite well the area and depth distribution of delamination measured after mechanical impacts. The ability of the numerical model to estimate accurate predictions of delaminated surfaces from lightning strikes is strongly related to its ability to predict the peak value of the central rear face displacement, thus validating the equivalent mechanical impact strategy presented in the first paper. Discrepancies between models and lightning measures are mostly due to inadequacies of the projectile to smoothen the impulse, and in a more general way of the mechanical impact to represent the feedback between the paint preservation or erosion and the composite plate damage.