Quantification of Geometry and Material Mismatch Constraint in Steel Weldments with Fusion Line Cracks

Abstract

Finite element analyses of an idealised steel weldment show that the constraint caused by geometry and material mismatch can be separated in a Modified Boundary Layer (MBL) model. The MBL model was loaded by a KI+T displacement field. Analyses of four fracture mechanics specimens revealed that the loss of constraint in the investigated weldments was different from the corresponding loss of constraint in a homogeneous reference case. Therefore, it was not possible to use the homogeneous reference to predict the development of constraint in the investigated weldments. In the fracture mechanics specimens the analyses show that the mismatch constraint is slightly reduced together with the loss of geometry constraint as large scale yielding develops in the specimens. By using the mismatch constraint determined from the MBL model, good predictions of the constraint in the specimens were obtained. In order to predict the fracture toughness in steel weldments with varying material mismatch and geometry constraint, three failure criteria have been compared. The results show that the RKR failure criterion by Ritchie et al. (1973) is applicable to the inhomogeneous material in this study. The study reveals that the mismatch effect on the failure predictions is influenced by the critical threshold stress used in the failure criteria. For all the investigated criteria, the mismatch effect on the predicted toughness was amplified by an elevation of the threshold stress. The constraint description has been used together with the RKR failure criterion to predict the required toughness (Jref) as a function of J for all the investigated geometries and mismatch cases.