Studies on surface effect and notch effect

Abstract

This paper reports the fatigue strength of welded aluminum alloys, mainly based on Al-Zn-Mg systems.The experiments were conducted on (1) The relation between the method of butt welding and the fatigue strength of parent alloys; (2) The comparison of stress concentration factors between the welds and parent alloys and the study on notch effect; (3) The relation between the cause of large deviations in fatigue strength of welds and surface effect; and others.The results obtained were as follows.(1) The fatigue strength of welds with bead was about 50-60% of that of parent alloys (55-65% in case of one side welds and 50-55% in case of both side welds). However, when the bead was removed, the fatigue strength was about 70-75% of that of parent alloys.(2) The welds can be considered to be notched parent alloys in a broad sense and the reduction factor of fatigue strength of the welds was compared with that of notched parent alloys. Welds without beads corresponded to the notched parent alloy having stress concentration factor of αk=1.68. Welds with beads corresponded to the notched parent alloy having αk=2.10 in case of one side welds or αk=3.10 in case of both side welds.(3) The deviations in fatigue strength of welds had a close relation with the surface roughness of specimens as well as that of parent alloys. When the bead zone or surface of specimen was polished to the smoothness of within 1.0μ, the range of the said deviations markedly decreased accompanied with the increase of fatigue strength.