| The multiaxial fatigue behavior of Ti60/TC17 dissimilar EBW(Electron Beam Welding) welded joint is studied in this thesis. Multiaxial fatigue tests for the EBW dissimilar welded specimens and theoretical studies on their fatigue models are carried out. The multiaxial fatigue tests for Ti60/TC17 dissimilar welded joint under different multiaxial loads are performed, in which thin-wall tube specimens are used, to establish the load-life(S-N) curves under different loading modes. The influences of fracture zones on the fatigue life of Ti60/TC17 dissimilar welded joints under different loading modes are also studied.Based on the critical plane theory and fatigue tests results, several fatigue life evaluation models for dissimilar welded joints under multiaxial loading are studied. The applicability of three popular multiaxial fatigue damage criterions are examined and discussed. In considering of the differences of loading models and the influences of material crystal structure, a modified material factor k in the Findley Criterion is proposed, which can be effectively used in the multiaxial fatigue life evaluation of Ti60/TC17 welded joints. Moreover, the fatigue behaviors of Ti60 welded joints, TC17 welded joints and Ti60/TC17 welded joint in different fracture zones have also been discussed. A correction coefficient ‘l’ is proposed for the multiaxial fatigue life evaluation of Ti60, TC17 and Ti60/TC17 welded joints and good expectation results are obtained.Scanning electron microscope(SEM) and general microscope are used to check the macro and micro fracture morphology of dissimilar specimens, in which the extension of fatigue crack in dissimilar welded joints is found in V-shape, the fracture morphology of Ti60 joint is of cleavage type while the one with TC17 joint is of quasi-cleavage type. In general, the crack surface of dissimilar weld seam is of brittle characteristics. |
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