Probabilistic Life Analysis Of An F-111 Wing Based On Teardown Data

A wing from the current fleet of F-111 aircraft was removed from RAAF service and fatigue tested to failure under representative spectrum loading at DSTO. The measured fatigue life was inadequate to certify the fatigue safety of the RAAF fleet and led to replacement wings being fitted to the fleet. A detailed teardown inspection was conducted on the test wing, and cracks (including the failure crack) were found to occur in holes, typically where the fastener/hole interference level and the surface roughness were outside tolerance. The replacement wings were built later in the production history and were shown to have a different, and in some regards better, build quality. A Monte Carlo simulation was used to generate hypothetical wings representative of the replacement wings, with interferences and surface roughness attributed to all the holes. This was combined with the stress distribution over the wing to predict crack growth at each hole, with the fastest growing crack determining the wing life