A Method for Predicting Fatigue in Notches Utilizing CAE and the Theory of Critical Distances

Abstract

When performing fatigue evaluations, the most critical areas governing the fatigue life of a component are geometrical discontinuities such as notches or sharp corners. Thus, accurate modelling of the geometric discontinuities and their effects is of highest importance to avoid catastrophic failures or overdimensioned components. Today, fatigue evaluations are done mainly utilizing CAE tools, such as FEA, to allow for more precise and complex calculations. Generally in fatigue design, the guideline is to avoid sharp corners and notches and thereby create robust designs. The first choice of FEA based fatigue evaluation typically overestimates the severity of notches, leading to conservative fatigue predictions. This has the consequence of some design ideas not meeting the fatigue requirements when they in reality might do. The authors therefore investigated methodologies for incorporating FEA with different approaches to fatigue in notches with the aim of producing a less conservative method. In this report, a methodology for predicting fatigue in sharp corners and notches has been developed. The proposed methodology stems from the Theory of Critical Distances and was verified against available fatigue test data, gathered from four different articles, with good correlation. The methodology was also expanded to allow for fatigue predictions of more complex geometries using virtual test specimen. Based on the results gained from the method validation it is clear that utilizing the proposed methodology and concepts would decrease the overestimation of notch severity. This allows for an enhanced ability to more accurately assess design ideas.