Fully plastic j-integrals for mixed mode fracture induced by inclined surface cracks in pressurized ductile pipes

Surface cracks have been recognized as major causes of their potential failures. This paper intends to determine a normalized fully plastic J-integral solution to mixed-mode fracture caused by inclined surface cracks in pressurized ductile metal pipes. A combined J-integral and finite element method is developed to evaluate the J-integral for inclined surface cracks. A set of predictive formulas for the normalized fully plastic J-integral are developed. It is found in this paper that an increase of strain hardening exponent can increase the difference of normalized fully plastic J-integrals in pipes with different wall thicknesses and the normalized fully plastic J-integral increases with the decrease of crack inclination angle and aspect ratios and the increase of strain hardening exponent. It is also found that the critical locations of crack propagation occur between the surface point and the deepest point of cracks when the inclination angle is relatively small and that the developed formulas can accurately predict the normalized fully plastic J-integrals along the front of inclined surface cracks. The results of this paper enable researchers and practitioners to predict the mixed-mode fracture failure of pressurized pipes subject to inclined surface cracks.