Mixed-mode fatigue crack propagation in thin T-sections under plane stress

Abstract

Data that can be used in the fatigue analysis of flat T-section bars subjected to axial loading and local restraint are presented. The paper describes how finite element analysis has been used to obtain stress fields in the vicinity of a crack or crack-like flaw introduced into the fillet (i.e. high-stress) region of the component. The effect of both the position and inclination of the crack has been investigated. The inclination of the crack to the transverse direction is varied in such a way that a combination of mode I (tension opening) and mode II (in-plane shear) crack tip conditions are created in the component when subjected to axial loading which is applied to the entire flat shoulder of the projection. Linear elastic fracture mechanics finite element analyses have been performed, and the results are presented in the form of J integrals and notch and crack configuration factors for a wide range of component and crack geometric parameters. These parameters are chosen to be representative of typical practical situations and have been determined from evidence presented in the open literature. The extensive range of notch and crack configuration factors obtained from the analyses are then used to obtain equivalent prediction equations using a statistical multiple non-linear regression model. The accuracy of this model is measured using a multiple coefficient of determination, R2, where 0 < R2 < 1. This coefficient is found to be greater than or equal to 0.98 for all cases considered in this study, demonstrating the quality of the model fit to the data. Predictive equations for stress intensity factors and J-integral values, which are based on the elastic stress concentration factor, are also developed. A crack propagation methodology, based on existing theory coupled with these predictive equations, is then presented for this type of component and loading.