Failure of Emergency Batteries for Aircrafts due to Stress-Corrosion Cracking
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Several electrical brass (CuZn37) connector bolts of aircraft batteries failed as a result of stress-corrosion cracking. The batteries are used for emergency supply of the avionics in case of power failure or for complete control in the case of engine failure. For activation, the thermal battery is heated by a pyrotechnic element and then supplies electrical power with 5 A for 20 min up to 240 A for 3 min. For assembly of the batteries, an acetic acid curing silicone resin is used for housing seal on the lid and on the connector bolts. Because of the almost hermetic sealing of the enclosure, the silicone resin cures very slowly and metallic parts are exposed to the acetic acid vapor. So the electrical brass connector showed corrosive attack with the formation of copper acetate (verdigris). Subsequent failure due to stress-corrosion cracking occurred. The failure type and damage mechanisms could be simulated in laboratory experiments.
KeywordsAcetic acid Brass Connecting bolt Silicone resin Stress-corrosion cracking
Dipl.-Ing. P. Schillinger and Mrs. G. Härtl are gratefully acknowledged for the SEM investigations of the connector bolts of the emergency batteries. Additionally, the authors want to thank Mrs. C. Knipf for their support in the SCC tests and Mrs. Kunzelmann for the metallography works.
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