A modified fracture-mechanics method for the prediction of fatigue failure from stress concentrations in engineering components

This paper describes a new method, known as 'crack modelling', which is designed for the prediction of fatigue behaviour in components for which elastic stress field data are available through finite element (FE) analysis or similar methods. The approach is based on the well-known result that sharp notches can be modelled as cracks, allowing an equivalent stress-intensity factor to be calculated. The fatigue limit of a sharply-notched specimen is thus found by equating the equivalent stress intensity factor range to the material's threshold value. This approach has been extended notched specimens of standard geometry under simple applied loads to components of arbitrary geometry with complex loading modes. This paper illustrates the application of the method through a number of case studies of components. The reliability of the method is then assessed in two ways. Firstly, the sensitivity of the predictions to errors in the FE: analysis and the processing of FE data is examined. Secondly, the issue of conservatism in the prediction is discussed; predictions suitable for engineering design should ideally be conservative, though the degree of conservatism should not be too great. It is concluded that the method is a robust one which is not strongly dependant on accurate FE meshing and which normally contains a useful degree of conservatism, though further work is needed in the treatment of physically small notches.