Analysis of failed combustion chamber bolts of an aircraft

A few fractured bolts recovered from an in flight incident of an aircraft were received for analysis. Examination revealed that all the bolts failed by fatigue. Fatigue cracks were found to have initiated at the thread roots of the bolts in all the cases and propagated progressively to over more than 90% of the cross section before culminating in overload failure. From the nature of striations, fatigue appears to be of high cycle – low stress type and vibration appears to be the most probable causative factor. Since the details of the bolts were not made available, it was not possible to examine whether or not the bolts meet the specification