Mixed-mode Stress Intensity Factors for Tubes under Pure Torsion Loading

Abstract

Although it seems like a common load-geometry configuration, there is neither an analytical nor a numerical solution for Stress Intensity Factors (SIF) in cracked tubes under pure torsion. Standards such as API 579, BS 7910 or handbooks do not present such case. There is plenty of solutions based on FEM or weight functions calculations for an extensive load-geometry combinations, but not for tubes under pure torsion. This paper shows curves of KI, KII, and KIII for through-wall cracks obtained with ANSYS simulations for slim tubes, under pure torsion with a rounded horizontal slit, numerically calculated via J-integral. Additionally KI, KII, and KIII are calculated using relative displacement between two points along the crack lips using Linear Elastic Fracture Mechanics (LEFM) formulations for Crack Tip Opening Displacement (COD) and Crack Tip Sliding Displacement (CTSD). Results are compared with experimentally measured SIF using the Digital Image Correlation (DIC) technique for fatigued-growth cracks reported in literature.