Stress intensity factor interaction between two semi-elliptical cracks in thin-walled cylinder

Stress intensity factor interaction between two semi-elliptical cracks on the internal surface of internally pressurized cylinder has been examined in Ansys Workbench. A wide range of cracks with different configurations were considered and their interaction effect on each other was investigated. Results show that, when two cracks approach, stress intensity factor increases dramatically along the crack front, especially on surface points. Since, surface points are critical in semi-elliptical surface cracks, interaction between surface defects can cause unexpected fracture. Besides, as far as the distance between cracks is more than the cylinder’s thickness (d> t) or exceeds two times the crack length (d> 2c), interaction between flaws can be ignored and two cracks have no influence on each other. Furthermore, two interacting deep cracks create more severe condition than two surface cracks. This means that a larger a/t exacerbates the interaction effect between cracks and results in higher stress intensity factor interaction. Stress corrosion cracking (SCC) and fatigue loading (whether thermal or mechanical) that are inevitable in pressure vessels create such deep cracks. This means that deep adjacent cracks are more probable in pressure vessels and should be considered in order to prevent failure.

Keywords:

Semi-elliptical crack , Stress intensity factor , thin-walled cylindrical vessel , Stress intensity factor interaction , Finite element