Abstract
The bending configuration of shrink-fitted connection fretting fatigue tests causes a fluctuation of the contact pressure and in turn a more favourable condition for shear, rather than tensile, crack initiation. According to the classification Type I (shear) and Type II (tensile) fretting cracks, the type II was only observed for the tests with no surface enhancement, which experienced the lowest fretting strength and then a reduced pressure fluctuation effect. The crack initial direction was predicted as the critical plane orientation undergoing the maximum FS stress parameter, for the shallow type I shear cracks. If the critical plane is searched at the fretting hot-spot, the incorrect outward direction is obtained, since the orthogonal direction, with the same shear stress amplitude, experiences a more compressive maximum normal stress. On the contrary, with the application of the Point Method, taking the stress location at half the critical distance and by following the potential critical plane, a higher shear stress along the inward direction is obtained. The more compressive stress below the contact can therefore be compensated, and then the inward shallow direction is correctly predicted.
Highlights
Fretting fatigue damage is experienced by those elements forced to stay in contact with a fluctuating loading, such as blade dovetail connections of compressor rotors, riveted joints, and shrink-fitted shafts, as summarized by BaiettoDubourg and Lindley [1]
Two types of crack initiations were defined: type I and type II, and this distinction was in relation to the crack initial orientation, which in turn suggested the kind of load causing the crack
Giner et al [28] assumed that the observed cracks were type II as evident from their experiment, and they correctly predicted the initial orientation by selecting the angle for which the normal stress amplitude was maximum
Summary
Fretting fatigue damage is experienced by those elements forced to stay in contact with a fluctuating loading, such as blade dovetail connections of compressor rotors, riveted joints, and shrink-fitted shafts, as summarized by BaiettoDubourg and Lindley [1]. Giner et al [28] assumed that the observed cracks were type II (i.e. tensile, in line with the Lamacq and Dubourg’s definition) as evident from their experiment, and they correctly predicted the initial orientation by selecting the angle for which the normal stress amplitude was maximum. After this initiation analysis, the X-FEM technique was again implemented, and the criterion of minimum shear stress range was applied to determine the angle for each step increment of the crack. The observed cracks are clearly oriented with a shallow, or even very shallow, initiation angle towards the inside of the contact obviously type I (shear) cracks
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