This paper presents the results of an experimental and theoretical analysis of the effect of joint gap on the strength of hybrid laser-MIG welds. The welds were of the partial penetration butt type with various joint gaps but identical weld penetration. Impact testing established that a zero gap gave a weak weld because the weld geometry contained the equivalent of a sharp crack where the unwelded parts met each other.

A small gap between the workpieces improved the weld impact strength as the sharp crack effect became dissipated. Further increases in gap width resulted in a weakening of the joint and this is the subject of a discussion on joint gap optimization.

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