Failure analysis of a helical compression spring for a heavy vehicle's suspension system

• The concurrent acts of the wear, corrosion together with stress singularities at the edges of the contact zone resulted in fatigue crack initiation.
• The contact pressure and shear stress at the positions of both edges of the contact zone showed severe singularities.
• It is recommended to adopt a non-closed ends design for the suspension spring in order to avoid wear and corrosion and subsequent fatigue failure.

This paper analyzed why a compression coil spring fractured at the transition position from the bearing coil to the first active coil in service, while the nominal stress here should always be much less than that at the inside coil position of a fully active coil. Visual observations indicated that a wear scar was formed on the first active coil and the fracture surface showed radiating ridges emanating from the wear scar. Scanning electron microscopy examination showed crescent shaped region and beach marks, typical of fatigue failure. ZnCaph phosphate layer and painting around the contact zone were worn out due to contact and friction and resulted in corrosion and corrosion pits induced local stress concentration. Stress analysis indicated severe stress singularities at the edges of the contact zone, which facilitated cycle slip and fatigue crack nucleation. Recommendations were also made for improving the fatigue performance of the suspension springs.

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