In this study, the effect of pre-fatigue on the impact tensile properties of the laser welded butt joint between three kinds of steel plates, an ordinary steel for vehicles and two high strength steels with the tensile strength level of 590 and 980MPa, were investigated by split Hopkinson bar apparatus. For comparison, quasi-static tensile tests were also performed to examine the effect of strain rate on their strength and elongation. It was found that the effect of pre-fatigue on the tensile strength of welded joints is small. However, the elongation or fracture strain of 980-590 joint specimen subjected to low cycle pre-fatigue was much smaller than that of virgin (not pre-fatigued) joint specimen. These results were observed in both static and impact tensile tests. It was also found that a pre-fatigue parameter, newly introduced here, is useful to indicate a danger of pre-fatigue.
