A new approach to improving the fatigue resistance of loaded holes in sheet material is presented. The material is first dimpled centering about the region where the hole is to be made, thus introducing tensile plastic strain. The dimple is then flattened and the hole drilled so that the region around the hole is under residual compressive stress. Zero to tension fatigue tests indicate considerable improvement in the fatigue strength of loaded holes as a result of dimpling. A fatigue strength improvement factor of nearly three for 106 cycles to failure was obtained based on the median lives of nominally 0.050-in. thick 2024-T3 aluminum alloy specimens.

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