SCATTER BANDS SUMMARIZING THE FATIGUE-STRENGTH OF ALUMINUM-ALLOY BOLTED JOINTS

A large number of geometrical, technological and environmental factors theoretically influence the fatigue behaviour and the failure modes o f the bolted joints. In order to make clear the influence of some of s uch variables, in this work over one hundred aluminium symmetric doubl e butt joints were tested, subdivided into eight series, with the purp ose to compare their fatigue properties and display failure mechanisms . All tests have been carried out under load control, taking into acco unt plates in 7020-T6 and 6061-T6 light alloys connected by means of A 2-70 stainless bolts or 8.8 high strength bolts, in such a way that fa ilure modes were different. The new results, together with those alrea dy presented by one of the authors in a recent contribution (Atzori et al. 'Proceedings of the Sixth International Conference on Aluminium W eldments', Cleveland, OH, 1995, pp. 243-254), in which 2024-T4 alumini um alloy and 10.9 high strength bolts had also been considered, allow both a comparison among the series and their synthesis in a very reduc ed 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 dif ferent definitions of the nominal stress amplitudes are chosen for fri ction or bearing-type joints. (C) 1997 Elsevier Science Ltd.