Failure Analysis of a Helical Compression Spring
Intertek AIM was contracted to perform an independent analysis to determine the cause of power spring failures used in spring brake chambers and to perform conformance testing on unfailed springs. The spring chambers are utilized on heavy construction equipment and trucks to activate the parking brake. A protective polymer coating is applied to the spring surface.
Results of the laboratory testing identified corrosion fatigue as the failure mechanism. Failure was preceded by mechanical abrasion due to coil clashing along with secondary debris particles. Compression testing confirmed coil clashing during normal, intended operation. Pitting corrosion occurred once the coating had been breached and served as sites for fatigue crack initiation. Testing also revealed the springs had not been shot peened as specified.
Recommended measures included a review of the mechanical design to eliminate coil clashing along with a review of the coating process to insure a properly bonded protective finish.
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