Keep in mind that there is considerable scatter in the data used to derive the estimated endurance limit given previously, so a larger factor of safety should be used. The endurance limit is generally associated with 1 million (1E6) to 10 million cycles (1E7) for steel. All calculated stresses are multiplied by Kf.) Methods for estimating the strength of fretting. (The strength is accompanied by the number of cycles).Fatigue Strength (fixed number of cycles) Sn. (Kf in Nastran is more like a stress concentration factor. This concentration of stress can be calculated using the finite element method. The fatigue strength is the maximum completely reversed stress under which a material will fail after it has experienced the stress for a specified number of cycles. Note: the input of Kf in Inventor Nastran's material properties is not the same as any of the correction factors discussed here. Depending on the software being used, the correction factors either need to be applied to the rotating specimen endurance limit (Inventor Nastran), or entered into the software (Simulation Mechanical). These factors are beyond the scope of this article and are best determined by consulting a text book. Additional corrections or factors are necessary for surface finish (ka), size (kb), loading (kc), temperature (kd), reliability (ke), and miscellaneous effect (kf) for the real part. The previous calculation for the endurance limit is for a rotating test specimen. Keith Nisbett, 8th edition, 2008, page 274). Shigley's Mechanical Engineering Design, Richard G.
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