Fatigue Strength of As Welded and Improved Joints of 6N01 Aluminium Alloy Extrusions

Abstract

In this paper, the fatigue strength of welded joints of 6N01 aluminium alloy extrusions is studied. Less copper content (Cu_??_0.02%) alloys were chosen, taking corrosion resistance to sea water into consideration. Two series of specimens were prepared. One is non-load carrying transverse fillet welded cruciform joint (T-TYPE), and the other has two longitudinal stiffeners welded on both sides of the main plate (L-TYPE). For L-TYPE, three types of specimens, changed in details of end of longitudinal stiffeners from the conventional corner boxing, were arranged. For some specimens, weld toes were ground with a pencil grinder. Using the specimens, fatigue tests under axial tensile loading (R=0) were carried out.In the fatigue test results, evident differences existed. The fatigue strength of ground T-TYPE specimen was highest, and that of as welded L-TYPE ones was lowest. The fatigue strength of as welded T-TYPE specimens was higher than that of ground L-TYPE ones. These SN data were consolidated and yielded to one SN curve, using the equivalent stress, taking the maximum stress into account. The equivalent stress S_??_ was expressed as follows; where Smax=maximum stress, R=stress ratio, m=constant, S=stress range, K=stress concentration factor, Sn=nominal stress range, and SR=residual stress.In the last part of the paper, some techniques for improving the fatigue strength of corner boxing welds are illustrated.