TAILIEUCHUNG - High Cycle Fatigue: A Mechanics of Materials Perspective part 31

High Cycle Fatigue: A Mechanics of Materials Perspective part 31. The nomenclature used in this book may differ somewhat from what is considered standard or common usage. In such instances, this has been noted in a footnote. Additionally, units of measurement are not standard in many cases. While technical publications typically adhere to SI units these days, much of the work published by the engine manufacturers in the United States is presented using English units (pounds, inches, for example), because these are the units used as standard practice in that industry. The graphs and calculations came in those units and no attempt was made to convert. | 286 Effects of Damage on HCF Properties The complete stress distributions for normal stress p x and shear stress q x along the contact boundary can be found in 30 . Of greatest interest in the determination of the FLS for fretting fatigue is the maximum value of the axial stress a at the interface as shown in Figure for example at the edge of contact. Such stress can be used in a fatigue initiation criterion. In Giannakopoulos et al. 31 the value of this stress is taken as the sum of the contributions due to the contact shear load the normal pressure and the bulk applied stress. The endurance limit stress can then be formulated as end R max vQ XX max a where a ld R is the endurance limit stress for a smooth bar at the appropriate stress ratio R. If q x is the shear stress due to a tangential load Q the maximum tension is given in 32 as aQx 2f p dx -b b x For the maximum stress due to the pressure apx numerical results from 31 are plotted in Figure which shows that the value of this stress depends on the ratio of the thickness of the substrate to the width of the contact region t is the half thickness and b is the half width . For the infinite thick substrate the tension stress vanishes. Analytical or semi-analytical solutions have been developed for obtaining fretting-fatigue stress fields for more general contact geometries than a cylinder or flat with rounded corners on a half space. Murthy et al. 33 present details of a computationally efficient mechanics-based approach using discrete Fourier transformations to obtain contact stresses. The approach is based on the solution to singular integral equations that Figure . Normalized maximum tensile stress for different strip thickness 31 . Fretting Fatigue 287 characterize the contact of two surfaces and takes into account the details of the shape of the contact surfaces. Of particular significance is the ability to account for distortion or irregularities in the contact interface from .

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