Defect Investigation of Seat Ejection Cartridge for Operating Seat Ejection Mechanism for the Aircraft Applications

This manuscript presents a detailed defect investigation observed in metallic brass cartridge cases used in seat ejection system for fighter aircraft applications. These cartridge cases play a vital role in propelling the ejection seat and pilot safely from a disabled aircraft. The objective of this research study was to identify the underlying factors responsible for occurrence of cracks observed on the cup portion of cartridge cases, particularly those stored under magazine conditions. The findings indicated that the observed defects were primarily associated with factors such as deviation from the prescribed annealing process, elevated zinc content, and excessive hardness. Additionally, the presence of residual stresses induced by cold working was identified as a major contributor, emphasizing the necessity for adequate stress-relief treatment to prevent ageing-induced cracking. The investigation concluded that the failures were attributed to Stress Corrosion Cracking (SCC), a critical degradation mechanism impacting the reliability and safety of brass cartridge cases. The recommendations provided by the technical committee were subsequently incorporated into the engineering drawings and manufacturing specifications to mitigate recurrence. This paper further examines the phenomenon of SCC in brass, highlighting the conditions that promote crack initiation and propagation. It also reviews historical cases, experimental results, and preventive measures, providing insights into the material behavior and environmental factors influencing SCC. Finally, practical solutions for mitigating SCC in seat ejection cartridges are proposed to enhance operational safety and extend service life.