Analysis of bonded repair patches on cracked thin sheets

Young, Andrew (1988) Analysis of bonded repair patches on cracked thin sheets. University of Southampton, Doctoral Thesis.

Abstract

Mathematical models are formulated for the stress analysis of a patch bonded over a crack in a large metallic sheet. The reinforcement structure is assumed to remain plane after deformation and is representative of a sheet patched symmetrically on both sides. Solutions are obtained for the Stress Intensity Factor of the crack and the distributions of stress in the adhesive layer and the patch. Having shown that the solutions are representative of continuously bonded repairs, a typical case of a uniaxially loaded sheet reinforced by a circular patch is considered in detail. It is found that the Stress Intensity Factor is significantly reduced by the repair and is largely independent of crack length when the crack is completely beneath the patch. The influence of individual repair parameters on the stress solution is investigated and it is demonstrated that the important parameters are the flexibility of the adhesive layer and the stiffness and aspect ratio of the patch. For many practical configurations, it is shown that values of Stress Intensity Factor may be approximated to within a few percent using a simple closed-form expression. When the edges of the patch are tapered, high values of shear stress in the adhesive layer near the patch edge may be significantly reduced. The Stress Intensity Factor is found to be largely insensitive to the amount of tapering and it is concluded that very stiff tapered patches may provide effective and reliable repairs. Finally, repairs in which a single patch is bonded to one side of a cracked sheet is briefly considered. The structural imbalance results in out-of-plane bending and the patching models severely underestimate the Stress Intensity Factor of the crack. An approximation to the Stress Intensity Factor for single-sided repairs is derived and compared with experimental results. (D 82634)

This record has no associated files available for download.

Contributors

Download statistics