EVALUATION OF LOCAL BRITTLE ZONES USING THE FINITE-ELEMENT METHOD

Abstract

The existence of local brittle zone (LBZ) in multipass C-Mn microalloyed steel welds has caused a great deal of concern to the offshore industries. A number of fracture toughness studies revealed the presence oi LBZ in the coarse; grained weld heat-affected zone (HAZ) of multipass welds. Although the HAZ toughness in LBZ can be very low, whether the low value of fracture toughness is detrimental to the structural integrity is not well understood. This paper describes the effect of the LBZ size on the resistance to fracture of the specimen using the elastic-plastic finite element method. The crack tip opening displacement (CTOD) criterion was used to evaluate the crack stability and arrest behaviors. Plastic zones emanating from both crack lip and LBZ interface were plotted for various combinations of base metal (EM) and LBZ sizes in order to characterize the specimen. A threshold LBZ size under which a crack extended initially in the LBZ, but would arrest at the interface of LBZ and BM due to tougher surrounding base metal, was also discussed.