Effect of Shot Peening and Overload Residual Stresses on EX35 Multi-Lug BreechFatigue Life

摘要

The EX35 multi-lug breech system is designed to replace the conventional breechsystem in order to diffuse the concentrated load at the block-ring interface. This report describes the residual stress effect of shot peening and overload processes on the BX35 multi-lug breech fatigue life. Shot peening of the lugs utilized the inside diameter peening technique, and an overload cold working process was applied using an overload fixture. Residual stress distribution in the lugs was characterized using X-ray diffraction. The magnitude of the maximum compressive stresses induced by the two processes is comparable, while the overload process produces much deeper zones of compressive residual stresses than shot peening. Both shot peening and overload processes retard crack growth and improve fatigue life. Our analysis showed that the thicker layer of compressive residual stress generated by overload compared with the shot peening process improves the fatigue life of the multi-lug breeches by a factor of two.