ABSTRACT. This work presents a methodology for fretting fatigue life estimation based on the evaluation of a multiaxial fatigue parameter at a critical distance below the contact surface. The fatigue parameter is defined using the Modified Wöhler Curve Method together with a measure of shear stress amplitude based on the Maximum Rectangular Hull concept. To apply the approach in the medium-cycle fatigue regime, the critical distance is assumed to depend on the fatigue life. Available fretting fatigue experiments conducted on a cylinder-on-flat contact configuration made of Al-4%Cu alloy were used to evaluate the methodology. Most of the fatigue life estimates were within factor-of-two boundaries.
The Smith-Watson-Topper (SWT) criterion, the Fatemi-Socie criterion, and the Jiang criterion were evaluated based on the experimentally observed cracking behavior and fatigue life of an extruded AZ31B magnesium alloy. The fatigue experiments were performed on thin-walled tubular specimens subjected to tension-compression, torsion, and combined axial-torsion loading. The SWT criterion fails to correlate the tension-compression and torsion baseline experiments. The Fatemi-Socie criterion predicts well the fatigue lives for all experiments, but the criterion yields a less satisfactory prediction of the cracking behavior for most of the tests. The difficulty of the SWT and Fatemi-Socie criteria in correlating the observed cracking orientations is attributed to the mixed cracking behavior of the material. The Jiang criterion provides a reasonable description of the cracking behavior and fatigue life predictions. A discussion on the current capability of the critical plane approaches to predict the fatigue behavior of wrought magnesium alloys is presented, and further studies are recommended.
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