Micromechanical Analysis of Constraint Effect on Fracture Initiation in Strength Mismatched Welded Joints

Abstract

In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a0/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). Highstrength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored arc-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip.

Computational fracture mechanics: An overview from early efforts to recent achievements

“…121,122 These micromechanical models have been successfully applied to several classes of problems, including pressure vessels, [123][124][125] pipelines, 126,127 and welded joints. 128,129 Modelling of ductile fracture includes void nucleation around inclusions and second-phase particles, followed by their growth and coalescence (Figure 13). Proposed models typically assume that voids nucleate when critical stress within inclusion or at inclusion-matrix interface has been reached.…”

“…On one hand side, it was relatively simple model for brittle fracture, ie, cleavage, whereas more complex mechanisms of ductile fracture were modelled as a process of void nucleation, growth, and coalescence, which is the focus here. In this chapter, numerical methods, used for simulation of ductile fracture process, are presented as a compilation of previously accomplished research, followed by an overview of more recent results …”

“…The more recent methods and approaches are focused to specific problems, including void coalescence criterion, detailed microstructural analysis, and the effect of size, shape, and distribution of voids . These micromechanical models have been successfully applied to several classes of problems, including pressure vessels, pipelines, and welded joints …”

“…Keeping in mind that most metals have very narrow fracture process zone, 3D modelling of the whole specimen using a damage constitutive model is unnecessary and inefficient. Therefore, a single layer of elements with a damage constitutive model was used in front of the crack to simulate the ductile tearing, following procedure described in Rakin et al and Zrilic .…”

Application of Complete Gurson Model for Prediction of Ductile Fracture in Welded Steel Joints

“…Microstructural observation of the materials indicates presence of sulphides, oxides, silicates and complex inclusions. A significant fraction of oxides is observed in the BM and the WM (for details see [19]), and a micrograph with clusters of oxides in the BM is shown in Fig. 1b.…”