Volume 8, Issue 3 (May 1980)
Effect of Clamping Pressure on the Fatigue Strength of Dimpled and Undimpled Loaded Holes
The process of dimpling is applied to improve loaded-hole fatigue strength in the presence of surface fretting such as is found in riveted joints. Dimpling introduces residual compressive surface stress into the region of fretting. It is proposed that this compressive stress delays the formation of crack-site pits and reduces the subsequent crack growth rate. An experimental program was carried out to investigate the comparative behavior of dimpled and undimpled loaded-hole connections in the presence of surface fretting. Specimens of 2024-T3 aluminum alloy were loaded as simulated riveted connections at two values of nominal clamping or fretting (rivet-head bearing) pressure. Experimental results indicate that while clamping pressure influences undimpled fatigue strength, it does not significantly affect dimpled fatigue strength. At the higher clamping pressure, the ratio of undimpled to dimpled fatigue strength is 0.95 at 106 cycles to failure. However, at the lower pressure, and at the same life, the ratio drops to 0.77.