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

$KIA$ 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.