The elastic-plastic fracture behaviour of undermatched double ‘V’ weldments with defects was investigated experimentally. Undermatching occurs when the yield stress of the weld is lower than that of the parent plate. Five notched specimens subjected to tension and four-point bending were tested, and deformation and strains were measured using the moiré fringe technique. Results of the study indicated that the COD in weldments with a large undermatch remained constant for a temporary period, giving a ‘flattening’ effect of the COD curve. This effect arose from the weld being shielded from further deformation by the gradual strain build-up and subsequent yielding of the parent metal.
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