Residual stress fields and fatigue analysis of autofrettaged parts

Abstract

Compressive residual stresses improve the fatigue life of cyclically loaded components. Therefore, they are often introduced intentionally, e.g. by rolling, shot peening, proof load tests, or autofrettage. This paper addresses the calculation of residual stresses due to autofrettage and the resulting increase of the endurance limit. The deformation behaviour of materials unloaded from an elastic–plastic state is dependent on the maximum strain. Unloading curves can be determined experimentally using smooth specimens. In inhomogeneously stressed components each material element is subjected to a different maximum strain value. Thus, the unloading stress–strain behaviour is also inhomogeneous. In order to model this effect in finite element (FE) stress analyses a different unloading elastic–plastic material behaviour is attached to each FE depending on its maximum equivalent strain value reached in loading. Residual stress distributions using this procedure are compared to results from application of different methods proposed in the literature. The calculated residual stress field serves as input for calculating the endurance limit of the component. A fatigue crack growth arrest criterion is used for its prediction. The necessary stress intensity factors due to loading and residual stresses are calculated using the weight function method. Experimentally determined and predicted endurance limits are compared.