Constraint Effect and Crack-Tip Plastic Zone of the Pipe With Internal Inclined Surface Cracks Under External Pressure

To improve the accuracy of reliability assessment, it is essential to conduct a comprehensive investigation into the constraint effect and the characteristics of the crack-tip plastic zone in a pipe with internal inclined surface cracks. We propose a novel analytical solution for the crack-tip plastic zone in a mixed mode I-II-III crack, based on the von Mises yield criterion, which includes stress intensity factors (SIFs) K-II and K-III. We have examined the impact of several factors, including aspect ratio (a/c), crack depth (a/t), crack inclination angle (b), and friction coefficient (l), on the in-plane constraint (T-11), out-of-plane constraint (T-33 and Tz), as well as the unified constraint (h) of a pipe containing internal inclined surface cracks under external pressure. The research reveals that geometrical configurations (aspect ratio and crack depth) have varying effects on the four constraint parameters, depending on their location along the crack front. The influence is relatively minor at the crack surface and the deepest point but becomes most pronounced at the middle point of the crack front. Additionally, the friction factor exclusively impacts the unified constraint parameter. Furthermore, we observed that the crack-tip plastic zone displays a mixed mode II-III crack at the free surface and a pure III mode at the deepest point.