Failure analysis of the semi-automatic shotgun locking block

Recently, there have been several occurrences of locking block failure in the semi-automatic shotgun bolts at a shotgun factory in Turkey. The fractured surface and locking block geometry were examined in order to determine failure reasons. The stress distribution of the locking block was performed using ANSYS Workbench 11.0. It was discovered that the reasons for fracture of locking block are: incorrect material selection, incorrect heat treatment, and dimensional geometry problems. For defining best material and heat treatment conditions, AISI 4140 and AISI 4340 steels were used and heat-treated. Tensile, charpy notched-impact and hardness testing were used to fully characterize materials properties. Mechanical test results and fractured surface analysis were analyzed in deciding for proper material. It was concluded that the most convenient material for locking block is AISI 4340 steel and optimum heat treatment parameters for this steel is oil quenching and tempering at 450 C. ANSYS Workbench analysis revealed that overloading has caused plastic deformation in the critical zones of the part