Failure Analysis of Follower Assembly in the 155mm Artillery Gun

Abstract: The follower assembly is a critical component of the 155mm artillery gun, which acts as a safety lock for the trigger mechanism during firing and releases it effortlessly for recoiling. During the firepower mission, issues arose where the follower assembly part would constantly bend or become crooked. This resulted in the roller detaching itself from the assembly and, therefore, reducing the equipment's effectiveness and negatively disrupting the firepower mission. This failure could have major repercussions for both military operations and national defence capabilities. This study investigates the failures and subjects them to macroscopic inspection, metallographic examination, hardness testing, and fractography analysis. A close look at the microstructure showed the existence of three separate layers: an ultra-fine martensitic layer near the surface, a fine martensitic layer closer to the core, and a normal martensite layer covering the rest of the microstructure. The hardness profile also decreases from the near surface to the core of the follower (part of the follower assembly). An analysis using fractography showed small round or long dimples on the fracture surface. The analysis proved that the follower had an overload ductile fracture. The material of the follower is unknown, and a chemical composition analysis was conducted for re-engineering purposes, showing that its composition closely matches that of AISI 4340. The analysis concludes that the follower is a post-treated ductile material. The authors recommend optimising the heat treatment process to enhance its strength and toughness, along with several suggestions for future studies.