The Effects of Residual Tensile Stresses Induced by Cold-Working a Fastener Hole
During a spectrum component fatigue test performed at IAI, a crack initiated at a notched edge near a cold-worked fastener hole, and propagated towards the hole. Fractographic analysis confirmed that the crack initiated at the edge and grew towards the hole. Since the maximum measured stress in the notch was not sufficiently high to explain crack-initiation during the test, it was suspected that the tensile residual stresses at the edge contributed to the cracking. An experimental study was initiated in order to measure the tensile residual stresses induced by cold working at various edges located near cold-worked holes. Tensile residual stresses as high as 35 ksi were measured at an edge near a cold-worked hole. Elastic-Plastic finite-element analysis results (ABAQUS and StressCheck) showed good agreement with the experimental results. Fatigue analysis has shown that when these residual stresses are combined with high cyclic notch stresses that arise from external loading, the fatigue life at the edge can be drastically reduced.
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“At DST Group, we have effectively used StressCheck® over the last 10 years to determine accurate stress intensity factors. The results have been used to improve our residual strength and structural life estimates for aircraft in service with the Royal Australian Airforce, including C-130, P-3C and F/A-18 A/B. We have found it to be extremely easy to use and a very versatile code with which to create parametric models.
We have recently used StressCheck® to obtain improved stress intensity factor solutions (Improved stress intensity factors for selected configurations in cracked plates and Improved stress intensity factors for a single corner crack at a loaded fastener hole) for five key generic configurations. These transferable parametric results have been published externally. One specific example is the non-linear contact analysis of a cracked, filled fastener hole, with both fastener and remote plate loading.”
Dr. Manfred Heller, HeadStructural & Damage Mechanics, DST Group