Failure Analysis of the LAU-7/A Launcher Retention Band Assembly

摘要

The U.S. Army Materials Technology Laboratory (MTL) conducted a comprehensivemetallurgical examination of the launcher retention band assembly to determine the probable cause of failure. The assembly secures the aft end of a nitrogen receiver which is part of the LAU-7/A Guided Missile Launcher located on the F/A-18 Navy Jet. The retention band failed near the weld joint during service. Visual inspection of the assembly revealed areas conducive to crevice corrosion. Deep depressions produced by the spot welding procedure were found on the surface of the base. Wear and galling marks that were caused by fasteners that had bottomed out on surface of the band were observed. Light optical microscopy of the fracture surfaces verified the existence of beach marks. It was determined by metallographic examination that the microstructure of the type 17-4 precipitation hardened (PH) stainless steel retention base was predominately tempered martensite with islands of ferrite while the type 301 stainless steel band showed signs of prior cold working.