3-D Stress Intensity Factors for Internal Cracks in an Overstrained Cylindrical Pressure Vessel—Part II: The Combined Effect of Pressure and Autofrettage

Abstract

K IA and KIP stress intensity factors (SIF) for three-dimensional semi-elliptical, surface, radial cracks prevailing in a pressurized or autofrettaged thick-walled cylinder were evaluated and discussed in Part I of this paper and in Perl et al. 1996, “Three-Dimensional Interaction Effects in an Internally Multicracked Pressurized Thick-Walled Cylinder—Part I: Radial Surface Cracks,” AMSE J. Pressure Vessel Technol. 118, pp. 357–363), respectively. These SIFs were calculated for a wide range of configurations: for cracks pertaining to large arrays of up to 180 cracks, with ellipticities of a/c=0.2, 0.5, 1, 1.5, depth ratios of a/t=0.05−0.6, and for various levels of autofrettage. In Part II of this paper, the effect of the combined SIF KIN=KIP+KIA is considered, which enables the prediction of fracture endurance, crack growth rate, and the total fatigue life for a modern gun barrel. The results reconfirm the impact autofrettage has on delaying crack initiation and propagation. This favorable effect is found to be governed by ψ=σ0/p—the ratio of the vessel’s material yield stress to its internal pressure. The higher ψ is, the more effective autofrettage becomes. While KIA and KIP reach their maximum absolute values, usually, for an array of n=2 cracks, the largest combined SIF-KIN occurs for arrays of 2–16 cracks. Finally, the similarity in the behavior of KIA and KIP along the crack front is studied as well as its relation to the respective stress fields.