Scatter Bands Summarising the Fatigue Strength of Aluminium Alloy Bolted Joints

A large number of geometrical, technological and environmental factors theoretically influence the fatigue behaviour and the failure modes of the bolted joints. In order to make clear the influence of some of such variables, in this work over one hundred aluminium symmetric double butt joints were tested, subdivided into eight series, with the purpose to compare their fatigue properties and display failure mechanisms. All tests have been carried out under load control, taking into account plates in 7020-T6 and 6061-T6 light alloys connected by means of A2-70 stainless bolts or 8.8 high strength bolts, in such a way that failure modes were different. The new results, together with those already presented by one of the authors in a recent contribution (Atzori et al. 'Proceedings of the Sixth International Conference on Aluminium Weldments', Cleveland, OH, 1995, pp. 243-254), in which 2024-T4 aluminium alloy and 10.9 high strength bolts had also been considered, allow both a comparison among the series and their synthesis in a very reduced number of scatter bands which seem to depend, for the three alloys taken into account, mainly on the nominal load ratio R, as soon as different definitions of the nominal stress amplitudes are chosen for friction or bearing-type joints.