Optimum design of symmetric composite patch repair to centre cracked metallic sheet

Composite patch repair of cracked metallic aircraft structures has recently been accepted as one of the means of improving fatigue life and attaining better structural integrity. The effectiveness of such patches for cracked sheets can be measured as an achievable reduction in the crack lip stress i ntensity factor (SIF). In this paper, a study has been conducted to get an optimum design of symmetric (balanced) composite patch to a centre cracked metallic sheet. It has been achieved considering the SIF at the crack tip o f the sheet as constraint and the plan-form shape of patch and the thicknes s of patch as design variables. The results of square, circular, elliptical and rectangular patches are presented. The effectiveness of smaller patch length perpendicular to the crack compared to the full-length patch in the same direction has been brought out. A new configuration called skewed patc h is studied. Reduction in weight of the patch due to skewed configuration has been brought out. The effectiveness of patch thickness over the patch p lan-form shape in reducing SIF has been brought out. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.