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Polymer failures

Stress corrosion cracking of nylon 6,6 - Page 4

Forensic conclusions


The most likely explanation of the accident was as follows. A small leak of battery acid occurred, with acid falling onto the nylon junction immediately below the battery. Chemical erosion of the edge led to stress cracking of the junction. One crack grew radially across the section, major growth occurring at engine start-up. The seven such major crack arrest lines represent seven engine start-ups from cold. Since garage vehicles are generally kept running through the day, each crack arrest front represents growth in one day, so the total sequence lasted about a week. Diesel fuel would have leaked slowly down the chassis , and have been visible to a vigilant driver. Diesel fuel leaves a very slippery deposit on the driving surface, equivalent to black ice. It caused four accidents, the most serious being that experienced by the claimant in this action. Liability was not accepted by the insurers for the garage who owned the vehicle, but the injured driver received substantial damages for their very serious injuries.

 

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ed: PRL 21/6/02

 
 
© 2005 Materials Engineering - Page last modified 18-Dec-2007