Numerical and experimental failure analysis of rifle extractor

Abstract The purpose of this article is to present a research methodology used to determine the causes of mechanical damage of a cartridge case extractor in a newly designed 5.56 mm assault rifle. It combines numerical analyses and materials science research. Based on the results obtained through simulation studies utilizing the Finite Element Method, values of local stress concentrations in the case extractor were identified. The paper provides detailed information on the used numerical models and adopted initial-boundary conditions required to carry out computer simulations. Based on the obtained values of maximal principal stress, the authors decided to carry out additional experimental research in order to reveal the cause of extractor damage. An adopted approach was consisted of micro hardness and metallographic analysis of the images depicting the microstructure of the extractor material. There were not observed any negative effects of an extractor heat treatment process on mechanical properties of the extractor material. Additional metallographic tests revealed that the main reasons of extractor failures were structural defects of material used in the manufacturing process of the extractor.