Failure analysis of a parabolic spring belonging to a railway wagon
V. Infante, M. C. Freitas, Ricardo Baptista
Abstract
This paper describes the study of three fractured parabolic springs belonging to a two-axle wagon suspension system. In order to determine the causes of the failures, a material analysis was performed, followed by a detailed study of the fracture’s surface both visually and using optical and scanning electron microscopy. The observations of fracture surfaces of the three springs revealed that the fractures began in the contact zones between the leaf springs, suggesting a fretting fatigue mechanism. The mechanism of failure of the springs fracture was a fatigue process. The propagation of fatigue cracks is more pronounced and extensive in one of the leaf springs. Finite element analyses were also performed taking into account the service conditions in order to determine the stress and strain distribution along the leaf springs. From the numerical simulations it can be concluded that the maximum stresses occur in two different zones: in the central section of the leaf spring and along the distance to the central section, in the sections where the relationship between the thickness reduction of the leaf spring and the resulting bending moment is most unfavourable. The Goodman's criterion shows a safety factor of approximately 1 and it can be concluded that this value is not enough to prevent the fatigue failure.