tailieunhanh - High Cycle Fatigue: A Mechanics of Materials Perspective part 32

High Cycle Fatigue: A Mechanics of Materials Perspective part 32. 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. | 296 Effects of Damage on HCF Properties or near the edge of contact where stresses are normally at a maximum. Because of the steep stress gradients that are present in a contact region parameters that are used for notch fatigue see Chapter 5 should also have merit in fretting-fatigue life prediction. Parameters used for notches such as a modified SWT Walker equivalent stress modified shear stress range or Findley parameter have been tried in an attempt to consolidate data from different fretting-fatigue experiments or from a range of conditions in a single experiment. These parameters are either unidirectional representing a maximum stress in a direction normally parallel to the contact surface or take into account the stresses in different orientations with respect to the contact plane and require consideration of values on all planes in order to find the maximum value. Naboulsi and Mall 38 investigated three critical-plane-based parameters for crack initiation by computing their values over a process volume and compared the results with those obtained by averaging stress or strain over some region and then computing the parameter based on the average value. They used a modified SWT parameter on a plane where the value is maximum. The parameter proposed in 21 had the form SWT maxea where ama is the maximum normal stress and ea is the normal strain range. A second parameter the Shear Stress Range SSR proposed in 39 has the form SSR At Tmax 1 - Rgm where Tmax is the maximum shear stress on the critical plane where At is maximum R is the shear stress ratio on the critical plane and m a fitting parameter obtained from smooth bar fatigue data. The third parameter used is that of Findley 40 in the form FP At kapx where At is the shear stress amplitude on a critical plane a 1 is the maximum stress normal to the maximum shear plane and k is a fitting parameter. Numerical results were obtained based on averaging the parameter over a critical process zone and