This work describes the crack tip blunting, initiation and stable crack growth processes of a crack localized in the heat affected zone of a weld. In the first stages of the crack tip blunting process, the same behaviour as that for a crack in a homogeneous medium under mode II was observed. It is also shown that, in the central zone of the thickness, two cracks grow in a stable manner from the blunted crack tip: one in tearing mode and another one in shearing mode. The experimental results were then analysed to discuss the implications for the evaluation of fracture toughness of the weld heat affected zone. © 1991.

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