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Interface Failure at Ply Drops in CFRP/Sandwich Panels

This paper presents the results of an investigation of delamination failure at "exterior" ply drops in tension loaded sandwich panels with laminated composite face sheets. The thickness of composite laminates used as face sheets of sandwich panels is often increased locally around highly loaded locations such as joints, rivets, bolts or inserts. At the stations where such ply drops are made, the local bending stiffness of the face sheet laminates change discontinuously, thus inducing severe local bending effects. These local bending effects induce severe stress concentrations in the interfaces between the dropped plies/sub-laminates and the remaining face sheet laminates, and this may initiate delamination failure. The present paper suggests a simple approach for stress analysis and a simple "characteristic length" stress criterion for the prediction of delamination failure. An experimental investigation has been carried out, and the measured delamination loads compare well the theoretical predictions.