Enhanced 2-D modeling technique for single-sided patch repairs

This paper reviews the current modeling techniques in the literature and proposes a new one to model bonded patch repaired metallic plates by including all known effects on fatigue crack growth rate. The modeling technique makes use of 2-D plate finite elements and takes into account adhesive progressive failure and the secondary bending effect due to the unsymmetrical configuration of single-sided repair patches. First, comparisons between this 2-D model and a 3-D model were carried out to validate the 2-D bending analysis and the calculated crack-tip stress intensity factors. This modeling technique was then implemented into a computer code interfacing with the commercial finite elements package MSC NASTRAN. Calculated crack growth lives were validated by published experimental tests for three different aluminum plates. Second, the computer code was used to conduct a parametric study on the patch geometries for two different substrate thicknesses showing that for a thinner substrate fatigue crack growth life can be improved by a smaller patch. Finally, a design tool has been developed to determine the most effective patch dimensions for a prescribed fatigue life target.