MODELING THE EFFECT OF LOCAL BRITTLE ZONES ON DUCTILE TEARING OF A WELD

The effect of the local brittle zone (LBZ) on the critical crack tip d isplacement (CTOD) of a welded joint has been analysed and a theoretic al model is established. It is shown that the CTOD depends not only on the toughness of the LBZ but also on the width and position of the LB Z intersected by the crack front. The CTOD decreases rapidly with incr easing LBZ width and approaches a Limiting value when the LBZ exceeds a critical size. The predicted results by the proposed model are consi stent with those obtained from experiments. In addition, the initiatio n of the macroscopic crack is mainly controlled by the LBZs located in or near the middle of the specimen thickness. The total width of the LBZs as a controlling fracture parameter is of questionable value beca use it ignores the effect of the effective LBZ width and position alon g the crack front.