Initial orientation of the fretting fatigue cracks in shrink-fit connection specimens

Abstract

The bending configuration of shrink-fitted connection fretting fatigue tests causes a fluctuation in 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, type II was only observed in the tests with no surface enhancement, which experienced the lowest fretting strength and thus a reduced pressure fluctuation effect. The crack initial direction was predicted as the critical plane orientation undergoing the maximum Fatemi-Socie (FS) stress parameter, for the shallow type I shear cracks. A significant result is that if the critical plane is searched at the fretting hot-spot, an incorrect outward direction is obtained, since the orthogonal direction, with the same shear stress amplitude, experiences a more compressive maximum normal stress. Conversely, 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 consequently the inward shallow direction is correctly predicted.

Statistical properties of threshold and notch derived estimations of the critical distance according to the line method of the theory of critical distances

“…The TCD was combined with a multiaxial fatigue criterion, according to a critical plane approach by Susmel and Taylor [2]. Liao et al [3] recently proposed the orientation of the critical distance length along the critical plane, instead of the notch bisector, and similarly was proposed by Santus [4] for the fretting fatigue application. In this way, more accurate results were obtained suggesting a better matching between the critical distance length and the highest stress path orientation.…”