Modeling hail ice impacts and predicting impact damage initiation in composite structures

Hail ice impacts are a realistic threat to exposed composite structures such as aircraft fuselage and wing skins, leading-edge and control surfaces, engine nacelles, and fan blades. To shed some tight onto this little-understood land unavoidable) threat, experimental, numerical, and analytical investigations have been conducted. Experiments in which carbon/epoxy composite panels were impacted by ice spheres at high velocity (30-200 m/s) were conducted to measure 1) the impact energy at which damage initiates, 2) the multiple failure modes exhibited by thin composite panels over a range of impact velocity, and 3) tbe elastic response of a composite panel resulting from impact. Subsequent numerical analyses of the last case were performed and were validated through correlation with experimental data. Insights gained from the numerical analyses were used to compose a mechanics-based formula that predicts the initiation of damage formation. This formula, derived using a global energy balance, provides a cost-effective (i.e., lower number of tests needed) means by which the impact damage resistance of composite structures and material types can be established.