Effects of Stiffener/Rib Separation on Damage Growth and Residual Strength

Two existing composite aircraft structures were used to evaluate the effects of skin/stiffener separation on the residual strength of the structures. These structures are basically compression dominated upper wing structures designed to comply with the impact damage tolerance requirements. The severity of impact damage and delaminations were analytically compared with that of skin/stiffener disbond. Critical disbond sizes were determined so the residual strengths of the structures are comparable to those obtained from impact damage tolerance designs. A damage tolerance certification approach based on the results of this study was recommended. The approach is to prevent local buckling in the disbond region under the applied load that governs the damage tolerance design for impact damage and delaminations. This would lead to a critical disbond length for the structure that has the same residual strength capability as in the case of impact damage and delamination. (Document in MS WORD format)