Abstract
Finite element modeling was used to evaluate the stress triaxiality, the crack driving force (J-integral) and crack extension of shallow and deep surface cracks under bending. Ductile crack extension experiments were also conducted. The results showed non-uniform crack tip stress triaxiality and crack driving forces as well as non-uniform crack growth around the crack front at large loads. Shallow semi-elliptical surface cracks exhibited maximum stress triaxiality at the deepest point, while in deep semi-elliptical surface cracks the maximum stress triaxiality and crack extension were at 45̊-70̊ from the deepest point. The maximum growth at the deepest point at early stages of shallow surface cracks was inhibited when the crack depth reached half thickness and growth occurred beneath surface. The results emphasise that both stress triaxiality and the J-integral have a strong effect on crack growth of elastic-perfectly plastic materials.