Abstract:

ESDU 90009 presents the results of over 350 axial load fatigue tests extracted from the literature on the joints under variable amplitude loading (mainly the FALSTAFF loading sequence although the TWIST sequence was used for a few tests). A medium load transfer joint is one in which between 10 and 30 per cent of the axial load is transferred between members, and many chordwise and spanwise joints in aircraft wings fall in that category. Three fastener types are included, assembled with a range of fits from clearance to high interference and with three different interfays. Other factors examined were fastener size, head type (either countersunk or protruding) and material (either titanium alloy or steel). Two plate thicknesses were used. Details of the alloys (DTD 5120, BS L93, 7475-T7351 and 2024-T351) and of the test specimens are included and the influence of the various variables on the fatigue strength is discussed. Included are data for joints manufactured with a corner crack in the fastener hole; these tests were designed to investigate a repair in which the hole was drilled out but insufficiently to eliminate an existing crack. It is noted that, due to the unequal load distribution from the different stiffnesses of the joined members along adjacent parts of their length, the joints were subjected to bending. The values of this secondary bending could not be determined and no account of it could be taken in the analysis and presentation of the data.