Experimental determination of critical crack size for an aircraft bulkhead with oversized fastener holes

During aircraft maintenance, oversizing modification has often been undertaken to remove fatigue cracking in fastener holes. In the example considered here, multiple modifications resulted in an oversized fastener hole in a fighter aircraft centre fuselage bulkhead. The short edge distance as a result of the oversized hole may have had an adverse effect on the component's fatigue life. Therefore, there was a need to reassess the fatigue life of the affected bulkhead and to establish the critical crack size for the oversized fastener hole. In this study, an ex-service bulkhead was configured with similar oversized holes as discovered in the fleet, and then was subjected to a residual strength test in accordance with the aircraft certification structural design standard. The test results obtained were essential for the determination of new inspection intervals for fleet structural integrity management for aircraft with a similar configuration.