Structural Mechanics Of A Mortar Launched IR Dome: Fid-Bau Portal

Structural Mechanics Of A Mortar Launched IR Dome

Speare, Joel / Belloli, Anthony

This paper presents a case study of the development of a Zinc Sulfide IR dome for a mortar-launched projectile. As a case study, it demonstrates the value of analysis as a means to obtain insight and derive solutions to design problems. It also describes problems solved by a variety of finite element codes: SAAS-3, EPIC-2, and NASTRAN. The paper discusses the determination of inertia loads, joint design, bonding of the dome to the attachment ring, verification testing, mortar test firings, and post test analyses. The paper discusses various FEM analyses performed during the development. Inertia load factors used for design were derived from a transient dynamic response analysis of launch and muzzle exit. Structural integrity of the brittle ceramic dome material was demonstrated by a detailed FEM stress analysis of the joint. This analysis considered modeling techniques for threaded and bonded joints. This FE model was also utilized to define an equivalent proof pressure test to simulate the inertia load. Initial tests resulted in the failure of both the dome and the attachment device of internal ballast. Additional analyses were conducted to evaluate modal response and impact. These analyses established the internal ballast as the cause of failure, and subsequent successful dome test firings validated the analyses.