High Velocity Hail Impact on Composite Laminates – Modelling and Testing

Abstract

Hail impact on composite structures during flight occurs at high velocities and is a serious concern as it may cause matrix cracking, large internal delaminations, and eventually fibre fracture not visible on the impacted surface. The present paper gives an introduction to hail impact on composite laminates and an overview of experiments and modelling work on this topic, performed during several years at Swerea SICOMP. Ice balls of different sizes and velocities have been shot with an air gun on composite laminates of different thickness and reinforcement architecture. High speed photography and measurement of strain and deflection histories of the laminates have been used to validate the models developed. Models involve dynamic explicit finite element (FE) simulations with cohesive elements to allow for delamination in the laminate, and simplified but fast analytical models. The experimental response has also been compared with predictions from the FE model and the analytical models using various material models of the ice. FE models using a calibrated elastic–plastic ice model are capable of accurately predicting the response and delamination initiation, while the current analytical models are unable to simulate the initial part of the impact. A main conclusion is that delamination occurs at a very early stage of the impact (first 10–50 μs) where three-dimensional wave propagation and the initial elastic–plastic behaviour of the ice are important. Closed form models are capable of predicting the peak contact stresses at the first instance of contact, but further work is required to allow simulation of the decay of contact stresses observed in the FE simulations.