Failure Analysis of Ribbon Spring Used in Aviation Clutch of a Turbo Starter

The present work details a study performed for determination of the causes of the premature rupture of a spring used in aviation clutch of a turbo starter. The study is based on the general methodology applicable to failure analysis. Fracture surface, mechanical and chemical properties and microstructure of the spring material are analyzed. The results showed that the fracture of the spring was caused by a mechanical fatigue mechanism. The cracks and fracture initiate on the inner surface, and the opening direction of cracks is consistent with the residual tensile stress of the spring inner surface. The fracture of the spring was caused by a mechanical fatigue mechanism whose origin is related to stress concentrations, probably aggravated by oxide inclusions.