LOCAL STRAIN COMPUTATION OF CRACK INITIATION LIFE OF AN UNSTIFFENED STEEL TUBULAR T-JOINT

This paper presents the results of the fatigue crack initiation life e stimation for offshore tubular welded joints. The results are obtained by using the fatigue strength exponent, b, and fatigue ductility expo nent, c, computed by a backcalculation procedure from an extensive exp erimental crack initiation estimation of both small scale and medium s cale welded steel tubular joints. A general purpose finite element pac kage, ABAQUS, was used for the stress analysis. This allows for the ac curate determination of the critical location where the crack/cracks i s/are likely to initiate. From the stress analysis, the stress and str ain concentration factors (SCF and SNCF) along the intersection of the tube were obtained. The peak SCF and SNCF were used in modified Neube r's rule and the result introduced into a Manson-Coffin model for crac k initiation life computation. The results obtained were compared with the experimental results previously obtained at the Canadian Cooperat ive Fatigue Studies Program.