Finite element-based three-dimensional stress analysis of composite bonded repairs to metallic aircraft structure

The use of high-modulus composite bonded patches has been shown to be a very useful life extension strategy when used to reinforce damaged or damage-prone aircraft structural components. When applied to aircraft skin panels such as fuselage and wing skins, the patch attracts load up through the thickness of the panel as well as from the wider regions creating a stress concentration on the surface of the panel at the ends of the patch. The main objective of this work is the numerical evaluation of this stress concentration for a single layer patch, a multi-layer equivalent-stiffness patch with uniform taper stepping, and a multi-layer patch with non-uniform taper stepping based on shape optimisation principles. Modelling of the residual thermal effects caused by heat curing of dissimilar materials has been included, as well as comparison of the through-thickness and in-plane 2D results with the 3D results.