THE INFLUENCE OF CONSTRAINT ON CRACK-TIP STRESS-FIELDS IN STRENGTH MISMATCHED WELDED-JOINTS

This paper describes the results of a series of two-dimensional, plane strain, finite element analyses which were performed using the modifi ed boundary layer formulation to model two material idealisations of w elded joints containing clacks. The cracks were assumed to be containe d within the weld material and ran parallel to the material interface. The effects of changes in geometrical constraint on the crack tip str ess fields were modelled by varying the magnitude of the T-stress term at the crack tip, and the effects of constraint due to strength misma tching were investigated by changing that-strength of the base materia l outside the weld. The results show that constraint due to material m ismatching depends on the level of strength mismatching, the applied l oad, and the width of the weld material. A normalised load parameter, J/h sigma(Yw), scales the size of the plastic zone with the width of t he weld material, and can be used to quantify the level of constraint for a given degree of mismatching. Any two specimens loaded to the sam e value of this parameter will have the same crack tip stress field, r egardless of the size of weld material. The effect of geometrical cons traint on overmatched welds, applied through the T-stress term was sim ilar to that observed in homogeneous materials. For undermatched speci mens the influence of the T-stress term on the stress field depends on the normalised load parameter. A level of constraint can be obtained in undermatched specimens which is higher than that obtainable in homo geneous laboratory specimens. This paper discusses the implications of this on the fracture resistance of undermatched welds. (C) 1998 Elsev ier Science Ltd. All rights reserved.