Strength prediction of patch-repaired CFRP laminates loaded in compression

The repair of a composite structure with a composite patch may use mechanical fastening, which often introduces undesirable stress concentrations or adhesive bonding, external or flush patches. In this paper the compressive behaviour of bonded external patch repairs is examined; the compressive loading mode is more severe than the tensile mode owing to the instability of delaminated plies, instability of the patch and skin strength reductions occurring under elevated temperatures and absorbed moisture conditions. By using a non-linear shear-lag analysis [Soutis C, Hu FZ. Design and performance of bonded patch repairs of composite structures. Proc Instn Mech Engrs 1997;211(G):1-9], design guidelines are produced for the selection of patch size, shape and membrane stiffness. A three-dimensional finite-element analysis is then performed to determine the stress field in the optimum repaired configuration and is used with a recently developed cohesive zone model [Soutis C, Fleck NA. Static compression failure of carbon fibre T88/924C composite plate with a single hole. J Compos Mater 1991;24(5):536-58; Soutis C. Damage tolerance of open-hole CFRP laminates loaded in compression. Composites Engineering 1994;4(3):317-27] to estimate the compressive failure load of the repaired laminate. The predicted strength is within 10% of the experimental data. (C) 2000 Elsevier Science Ltd. All rights reserved.