Effect of non-metallic inclusions on the fatigue strength of helical spring wire

This work aims to evaluate the effects of the presence of non-metallic inclusions in the early failure of a helical spring subjected to regular design loads during its operation. In order to do so and also to reach a better understanding of the reduction in fatigue strength, an analytical model was used. A two-dimensional (2D) Finite Element Method (FEM) analysis was developed to evaluate the residual stresses originated around an inclusion located near the material surface, by the application of a shot peening process. A three-dimensional (3D) FEM model was developed to study the stress concentration around the inclusion that appears under design loads. This study shows that the analytical model developed by Murakami (2002) [1] provides a valid insight on the fatigue strength reduction and that the FEM model may actually provide good qualitative and quantitative data that can help to obtain a better understanding of the process of early failures of spring wires with non-metallic inclusions.