Cracking of stainless steel through bulkhead initiators (TBI): A metallurgical investigation

Through Bulkhead Initiators (TBI), fabricated from AISI 302 extruded and cold worked rod, is a shock-based system employing high explosive and pyrotechnic charges. The explosive is press loaded to required densification. TBI is initiated by explosive stimulus generated by mild detonating cord (MDC). This causes detonation of the donor charge explosive, transfers the resulting shock across the bulkhead and gets attenuated. During one of the above tests, the tested unit gave the required pressure output as expected. However the housing developed cracks on the body. Detailed metallurgical analysis indicated that the material yielded and failed in dimple mode of failure during shock transfer. Further, the material had heavy sulfide inclusions, which helped in void formation by de-bonding from the matrix.