Multiaxial High Cycle Fretting Fatigue

The aim of this work is to show that multiaxial fatigue can be successfully adpted to model fretting problems. For instance, the paper presents (i) the critical direction method, as an alternative to the critical plane concept, to model the crack initiation path under fretting conditions and (ii) studies on size effects considering the influence of incorporating fretting wear on the life estimation. A wide range of new data generated by a two actuators fretting fatigue rig considering Al 7050-T7451 and of Ti-6Al-4V aeronautical alloys is produced to validate these analyses. It is shown that, the development of appropriate tools and techniques to incorporate the particularities of the fretting phenomenon into the multiaxial fatigue problem allow an accurate estimate of the fretting fatigue resistance/life in the medium high cycle regime. Such tools and techniques can be extended to the design of other mechanical components under similar stress enviroments.

Toward Developing a Probabilistic Methodology for Predicting High-Cycle Fretting Fatigue in Aero-Engines

This paper reports the results of an investigation focused on identifying the necessary steps required to develop a probabilistic fracture mechanics-based methodology for treating high-cycle fretting fatigue in military engine disks. The current methodology based on finite-element method (FEM) modeling, analytical contact stress analysis, and probabilistic fracture mechanics for analyzing low-cycle fretting fatigue is highlighted first. Incorporation of high-frequency vibratory stress cycles into a composite mission profile containing mostly low-cycle stresses requires the use of the Campbell diagram and the need to identify the mode shape, frequency, and forcing function for blade excitation induced by stator wake, flutter or rotating stall. Forced response computation methods for addressing these phenomena in the literature are reviewed to assess their applicability for integration with a contact stress analysis and a probabilistic fracture mechanics life-prediction code. This overview identifies (1) a promising path for combining vibratory stress computation, FEM structural modeling, contact stress analysis, and probabilistic fracture mechanics for treating high-cycle fretting fatigue at the attachment region of engine disks, and (2) a new approach for treating high-cycle fretting fatigue due to vibratory stresses separately from low-cycle fretting fatigue at various positions of a fan-speed profile.