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-edgeandcontrolsurfaces,enginenacelles,andfanblades.Toshedsomelightontothislittle-understood (and unavoidable ) threat, experimental, numerical, and analytical investigations have been conducted. Experiments in whichcarbon/epoxy compositepanelswereimpacted by icespheresathigh velocity (30‐200m/s)wereconducted 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 ) the 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.

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