Studies on the effects of lack of penetration and bead profiles

Abstract

This paper reports the fatigue strength of welded aluminum alloys (mainly based on Al-Zn-Mg systems) having weld defects and various bead profiles.The studies were made on (1) The effects of weld defects (mainly lack of penetration) on fatigue strength; (2) The effects of bead profiles on fatigue strength; and others.The results obtained were as follows:(1) In case of welds with bead, lack of penetration, even though the lack was more than a half of the plate thickness, had almost no effects on the fatigue strength under repeated bending stress.(2) In case of welds without bead, cracks originated from the root of lack of penetration under repeated bending fatigue test and the lack of penetration gave remarkable effects on the fatigue strength of welds under repeated bending stress. However, the degree of effects depended upon the material of parent alloy or the combination of the parent alloy with filler wires. The fatigue strength of Al-Mg alloy welds decreased in parabolic curve with the increase of the depth of lack of penetration. However, in Al-Zn-Mg alloys, the fatigue strength did not decrease for the lack of penetration of about 1mm. When Al-Mg alloys were used for filler wires (or about 2.5mm. When Al-Mg-Zn alloys were used for filler wires). When the lack increased more than the above values, the fatigue strength decreased in parabolic curve with the same gradient as that in Al-Mg alloys.The critical range of lack of penetration had no effects on the fatigue strength, but it depended upon the composition of the filler wire.(3) Bead profiles had remarkable effects on fatigue strength; the fatigue strength linearly decreased with the increase of root angle of the bead in the range of 20-50°, but the effects on the strength were very little when the angle was without the above range.