Integrated failure analysis, defect investigation and prevention of stress corrosion cracking in brass seat ejection cartridges used in defence aircraft escape systems

Abstract This study presents a comprehensive failure investigation of cracked brass cartridge cases used in aircraft seat ejection systems. The objective was to determine the root cause of surface cracking observed in cartridges stored under magazine conditions and to evaluate the influence of the defects on functional performance. The investigation included visual examination, thickness measurement, optical emission spectroscopy (OES), metallographic characterization, Vickers hardness testing, X-ray diffraction (XRD) residual stress analysis, scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM/EDXA), mercurous nitrate, stress corrosion cracking (SCC) testing, and vented vessel performance evaluation under hot and cold environmental conditions. The cartridge material was confirmed as nominal 70Cu–30Zn brass by OES analysis. Metallographic examination revealed elongated grains, slip bands, localized strain accumulation, and secondary microcracks in the vicinity of the crack region. Hardness values were within the specified range of 90–110 HV, indicating that hardening was not the primary cause of failure. XRD analysis identified the presence of tensile residual stresses generated during sheet metal forming operations, while SEM fractography showed surface-originated cracks with branching morphology characteristic of SCC. The mercurous nitrate test further confirmed the SCC susceptibility of the material. Comparative vented vessel testing demonstrated that the cracked cartridges produced p max , TP max , and T½P max values within the specified acceptance limits under both hot and cold conditions, indicating no measurable short-term degradation in ballistic performance. The combined evidence established that the failure resulted from residual-stress-assisted SCC in cold-worked cartridge brass exposed to a corrosive storage environment. The study demonstrates that SCC induced surface cracks may not immediately impair cartridge functioning but represent a significant long-term reliability concern. The findings provide a systematic rootcause analysis methodology and support the implementation of stress-relief treatment, improved manufacturing control and enhanced storage management to mitigate SCC in aerospace seat ejection cartridges.