3-d stress intensity factors for internal cracks in an overstrained cylindrical pressure vessel-part II: The combined effect of pressure and autofrettage

K_IA and K_IP 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/c50.2, 0.5, 1, 1.5, depth ratios of a/t50.0520.6, and for various levels of autofrettage. In Part II of this paper, the effect of the combined SIF K_IN = K_IP + K_IA 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 c is, the more effective autofrettage becomes. While K_IA and K_IP reach their maximum absolute values, usually, for an array of n52 cracks, the largest combined SIF-K_IN occurs for arrays of 2-16 cracks. Finally, the similarity in the behavior of K_IA and K_IP along the crack front is studied as well as its relation to the respective stress fields.