
Fatigue High Cycles Finite Life For many applications the number of stress cycles experienced by a component during its service life is between 10 ^{3} and 10 ^{6} cycles. For these applications it is economical to use appropriate fatigue strength as opposed to using the endurance limit. The strength value between the low cycle stress value S'_{l} and the endurance limit value S'_{e} can be plotted on a graph of log_{10} Fatigue strength (S) vs log_{10} Number of cycle (N'_{t}) as a straight line following the equation.
b = the slope of the line At the endpoints of the high cycles finite life rang (10^{3})cycles and (10^{6})cycles ... The endurance strength values are subtracting the equation for S'_{e} from S '_{l} results is the following To obtain C it is simply necessary to substitute the above into the equation for S'_{e} Therefore knowing the low level fatigue strength (S'_{l}) for a metal and the endurance strength (S'_{e}) and the number of operating cycles it is possible to obtain the relevant fatigue value using the equation. If the fatigue strength is known and the number of cycles to failure is needed then the following formula applies Example: to determine the strength at 10^{5} cycles when the strength at 10^{3} and 10^{6} are known. 
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