Stress intensity factors for mixed mode fracture induced by inclined cracks in pipes under axial tension and bending

Mixed mode fractures can be triggered by either multi-axial stresses or inclined cracks or both. Little research has been undertaken on stress intensity factors for inclined cracks in pipes under axial tension and bending. This paper intends to determine stress intensity factors for mixed mode fracture induced by inclined external surface cracks in pipes under axial tension and bending, using a combined J integral and 3 dimensional finite element method. Formulae for the influence coefficients of stress intensity factors are developed. To predict the fracture failure of the pipe, the propagation of inclined cracks in pipes is also investigated. From numerical results, it is found in the paper that, for given wall thickness to internal radius ratio and crack depth to half crack length ratio, the absolute values of the influence coefficients of all three modes I, II and III stress intensity factors along the whole crack front increase with the increase of the relative depth for all inclination angles of the surface cracks. It is also found that the crack propagation angles in depth of the inclined cracks increases in magnitude along the whole crack front with the decrease of the crack inclination angle defined as the angle between the crack and pipe axial direction. The results presented in the paper can equip practitioners for more accurate prediction of pipe failures under various loads.