The Bauschinger effect's influence on the SIFs of multiple longitudinal coplanar cracks in autofrettaged pressurized cylinders

The influence of the Bauschinger effect (BE) on the three-dimensional, Mode I, stress intensity factor (SIF) distributions for arrays of longitudinal coplanar, surface cracks emanating from the bore of a fully or partially autofrettaged thick-walled cylinder is investigated. The SIFs for both "realistic" - Bauschinger effect dependent autofrettage (BEDA) and "ideal" - Bauschinger effect independent autofrettage (BEIA) are obtained and compared. The 3D analysis is performed via the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. Both autofrettage residual stress fields, BEDA and BEIA, are simulated using an equivalent temperature field. The Bauschinger effect (BE) is found to significantly lower the beneficial stress intensity factor due to autofrettage, K_IA, by up to 52%, as compared to the "ideal" autofrettage case. The reduction in K_IA varies along the crack front with the maximum determined by the crack ellipticity, crack depth and crack separation distance. The detrimental influence of the BE increases as the crack density decreases and as crack depth decreases. For a partially autofrettaged cylinder, the influence of the BE is considerably reduced as the level of overstrain becomes smaller. Furthermore, the results indicate that in certain situations crack density and crack ellipticity have opposing effects on the autofrettage SIF.