Ductile Damage and Constraint in Components with Embedded and Surface Semi-Circular Cracks

Abstract
Semi-elliptical surface cracks are among the most common defects in welded components subject to fatigue loading. Embedded cracks are also an important type of defects to be considered in welded structures. Control of the static capacity of structures with such defects is important in order to determine load levels corresponding to crack growth initiation and tearing. In the present investigation, the Gurson model based approach has been applied in studying the ductile crack initiation and constraint effect in tension components with semi-circular surface cracks and embedded circular cracks. 3D models of 3 different crack sizes but with exactly the same crack tip element arrangement have been analyzed using the micromechanical parameters established in an earlier study. The results show that for a relatively large embedded crack, the initiation of crack growth will start at the point with the smallest ligament, however, the largest amount of crack growth will occur at the point with the largest ligament. The initiation and growth of surface cracks are rather consistent, with a distinct "canoeing" effect. The influence of crack size and growth on the ductile fracture behaviour is explained by means of constraint.