Predicting the Cause of Failure in 120-mm Mortar Fins

Abstract : During 2002, approximately 1500 120-mm mortars were tested at Yuma Proving Grounds, Arizona. Of the 1500 rounds, seven fell short of the 7200-m range requirement. Inspection of the short rounds indicated that short rounds lost one or more fins. This paper describes the structural analysis used to predict two proximal causes of failure. First, unequal pressure on one side of the fin can cause permanent bending, twisting, and breaking of the fin at its root. Second, internal pressure in the mortar tube can result in high hoop stresses where fracture failure can occur. Actual broken parts were consistent with one or the other predicted cause of failure.