Crack modelling: A technique for the fatigue design of components

Abstract

A new method of fatigue analysis for components is outlined; the novelty of the method is that it uses fracture mechanics concepts without introducing a crack into the component. Stress concentrations are analysed by examining their stress fields and comparing these with the stress fields of cracks of standard geometry. The method was tested by using it to assess three different design conditions for a large cast-iron component. This component suffered fatigue failures from a corner feature which had a sharp fillet radius; it was found in practice that increasing the fillet radius was ineffective, whereas reduction of operating loads eliminated the problem. By estimating the stress intensity range, ΔK, in service and comparing this with the threshold value, ΔK th the in-service observations could be predicted with a good degree of accuracy. The method, which is termed “crack modelling”, appears to have potential for the assessment of design features in components, extending the use of fracture mechanics into industries in which it is currently not used.