Abstract
A set of B × B specimens was taken from homogeneous and heterogeneous welds and tested to obtain fracture behaviour of undermatched welded joints. The critical crack-tip opening displacement (CTOD), as the relevant parameter for safe service of welded structure, was used to evaluate the influence of microstructures. Surface cracks of different depths were positioned in weld metal with fatigue-crack-tip front in different microstructures. It was shown that selection of soft weld consumable (wire) does not guarantee tough root layer in the undermatched weld.

Key words
crack-tip opening displacement (CTOD), CTOD fracture toughness testing, CTOD-R resistance curve, welded joints

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