STRESS INTENSITY, STRESS-CONCENTRATION, AND FATIGUE-CRACK GROWTH ALONG EVACUATOR HOLES OF PRESSURIZED, AUTOFRETTAGED TUBES

The geometry analyzed consists of a thick-walled cylinder having a sma ll-diameter evacuator hole penetrating radially through the wall. The loading involves pressure acting on the i.d, of the tube and all or pa rt of this pressure acting on the evacuator hole. In addition, the tub e may be fully or partially autofrettaged. Total hoop stress concentra tions are determined for a range of radial locations along the evacuat or, as are stress intensity factors along a crack emanating from the e vacuator hole. Fatigue crack growth rates, and hence crack profiles, a re predicted at each of the radial locations. These predictions indica te 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 a pproximately halfway through the wall thickness. Taking account of the influence of stress ratio, sigma(min)/sigma(max), has a significant i nfluence an crack shape in autofrettaged tubes, but a limited effect u pon lifetime. The effect upon fatigue lifetime of axial residual stres ses due to the autofrettage process is described and it is demonstrate d that an insignificant reduction in lifetime results from the presenc e of such stresses. Finally the predicted profiles are compared with e xperimental observations of fatigue cracked evacuator holes and a limi ted comparison of predicted and actual lifetimes is presented. Agreeme nt is considered good.