A non-local approach to model the combined effects of forging defects and shot-peening on the fatigue strength of a pearlitic steel. (February 2018)

• Record Type: Journal Article
• Authors: Gerin, Benjamin; Pessard, Etienne; Morel, Franck; Verdu, Catherine
• Is Part Of: Theoretical and applied fracture mechanics. Volume 93(2018)
• Page Start: 19
• Page End: 32
• Publication Date: 2018-02
• Subjects: Steel -- Forging -- Shot-peening -- High cycle fatigue -- Surface defects -- Non-local approach; Fracture mechanics -- Periodicals; 620.1126
• DOI: 10.1016/j.tafmec.2017.06.012
• Languages: English
• ISSNs: 0167-8442

Abstract

Highlights: Two approaches to modelling the effect of surface integrity are detailed. The first is a geometrical analysis of defects using ellipsoids to fit their shape. The second uses finite element simulations of the actual geometry of the defects. A non-local model integrating residual stresses is used to predict fatigue strength. Abstract: This study focuses on the influence on fatigue behaviour of the surface integrity of a steel connecting rod. The component is hot-forged and shot-blasted, producing a complex surface state with large surface defects and high residual stresses. In a prior study, the surface was thoroughly characterized and fatigue tests were performed. Several different surface states were analysed in order to quantify the influence of the various surface aspects. These tests showed that the forging defects and the residual stresses are the most influential aspects of the surface. The goal of this paper is to develop an approach capable of taking into account the influence of both these aspects on fatigue behaviour. Two methods were developed. First, using surface scans of the fatigue specimens, the forging defects were fitted with ellipsoids so as to determine their size and shape. This allows to easily compare the numerous defects and test various criteria in order to identify the critical defect of each specimen. The second method used was the finite element simulation of the defects based on real topography scans. Using a non-local approach based on the theory of critical distances, the simulations were used to accurately predict the influence of the defects' geometry. The residual stress profiles were integrated in the simulations using Dang Van's criterion. The predictions are accurate and show the importance of taking into account the real defect geometry when estimating the fatigue strength.