Stress Intensity, Stress Concentration, and Fatigue Crack Growth Along Evacuator Holes of Pressurized, Autofrettaged Tubes

Abstract

The geometry analyzed consists of a thick-walled cylinder having a small-diameter evacuator hole penetrating radially through the wall. The loading involves pressure acting on the i.d. of the tube and all or part of this pressure acting on the evacuator hole. In addition, the tube may be fully or partially autofrettaged. Total hoop stress concentrations are determined for a range of radial locations along the evacuator, as are stress intensity factors along a crack emanating from the evacuator hole. Fatigue crack growth rates, and hence crack profiles, are predicted at each of the radial locations. These predictions indicate that the critical location for the crack in a nonautofrettaged tube is at the i.d., whereas in a fully autofrettaged tube it is located approximately halfway through the wall thickness. Taking account of the influence of strees ratio, σmin /σmax , has a significant influence on crack shape in autofrettaged tubes, but a limited effect upon lifetime. The effect upon fatigue lifetime of axialresidual stresses due to the autofrettage process is described and it is demonstrated that an insignificant reduction in lifetime results from the presence of such stresses. Finally, the predicted profiles are compared with experimental observations of fatigue cracked evacuator holes and a limited comparison of predicted and actual lifetimes is presented. Agreement is considered good.