Residual strength of sandwich panels with hail damage

Hail strikes, possibly exceeding an energy level of 50 J, may cause damage to thin-gauged composite airplane structures in the form of an indentation or puncture of the top facesheet. If not repaired properly, they may trigger extensive damage to airplane structures and disruptions to airline operations, therefore posing a major maintenance and repair concern for the airlines. It is important that both the original equipment manufacturer and the airlines be able to classify the hail strike damage in order to establish appropriate repair procedures. This study presents a methodology to assist engineers in the classification of the repair type for hail strike damage through the determination of allowable damage size. The methodology involves an accurate prediction of stress and strain fields and residual strength prediction. The stress analysis is performed by utilizing a plate element based on a higher-order single-layer theory. The damage zone model, previously used for notched panels, has been employed to predict the residual strength of sandwich panels with indented facesheets subjected to tensile load. The failure load is established when crack propagation in the facesheet becomes unstable.