Flaw assessments assume homogeneous material properties, but welds are heterogeneous. A procedure to account for heterogeneity effects on crack driving force (developed at Ghent University and Limerick University) requires strength properties along slip lines originating from the defect tip. For uniaxial tension loading, these lines are assumed straight and oriented 45° to the axis of loading. The presented paper investigates the soundness of this assumption. Clamped single-edge notched tension tests and simulations have been performed on base metal and welded specimens. Extensive deformation analyses reveal the evolution of slip line trajectories as the specimen deforms. Observed slip lines in base metal specimens are initially close to the assumed 45° trajectories, but deviate towards the notch section as deformation is increased. The change in angle is roughly linear as a function of crack tip opening displacement. Deformation analyses of the welded specimens reveal that hard regions can serve as barriers, causing slip lines to deviate from linearity and split into different branches. The implications of these observations on the flaw assessment of heterogeneous welds are investigated in ongoing work.
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