Stress Analysis of a Plate Containing a Round Hole with Combined Cold Expansion and Interference Fitting Under F-111C Representative Loading Conditions.
DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)
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This investigation has been undertaken as part of a program of work having the aim of determining a suitable fatigue life enhancement option for the non-circular fuel flow vent hole 13 in the wing pivot fitting of the F-111C aircraft. The stress analysis has been undertaken using two dimensional finite element methods assuming either elastic-perfectly plastic or strain hardening material behaviour models. The effect on critical plate stresses due to enhancement by cold expansion and interference fitting, used separately or together, has been quantified in the presence of representative cold proof test loading and a sample remote spectrum loading. For all enhancement cases considered, irrespective of material model, the stress response during the sample remote loading was linear, with a cyclic stress concentration factor of unity. Enhancement through combined cold expansion and interference fitting was considered a great deal better than interference fitting only. For example, the combined enhancement of 1.5 cold expansion followed by 0.5 interference fitting, as compared to 0.5 interference fitting only, led to a change in critical hoop stress from 350 MPa to -1080 MPa. These favourable results indicate that such an enhancement procedure would potentially be suitable for extending the fatigue life of the F-111 13 fuel flow vent hole region, pending the results of an investigation on a non-circular hole geometry currently in progress.