13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- value, all predictions are within a factor of two utilizing either averaging method. Figure 12. Correlated nonlocal OD against experimentally determined OP TMF lives using the invariant area surface sweep method. 5. Conclusions For OP TMF 500 950 C C , the 1.3 tk notch represents the lower bound of fatigue notch sensitivity as there is no appreciable knock-down in life relative to the smooth life trend. For 2 tk , the fatigue life is also insensitive to the severity of the notch. The 1.7 tk notch falls in between the 1 tk / 1.3 tk and 2 tk / 3 tk trends. In DS alloys loaded longitudinally, the OP TMF cracks in notched specimens nucleate away from the notch root. The nucleation location approaches the notch root with increasing notch severity and increasing applied force amplitude for a given notch geometry. These trends are captured in a computational stress-strain analysis using either von Mises equivalent stress or the cyclic inelastic equivalent strain range cyclic response parameters. For OP TMF with smaller maximum temperature, 500 750 C C , the 1.3 tk notch exhibits a small knock-down in life relative to the smooth life trend. The 1.7 tk notch falls in between the 1.3 tk and 2 tk / 3 tk life trends. Under IP TMF 500 950 C C , the 1.3 tk notch also follows the smooth specimen life trend similar to OP TMF. Neither local nor critical-domain nonlocal methods adequately collapsed notched and smooth OP TMF 500 950 C C life data. A nonlocal invariant area-averaging method was utilized to collapse all experimental data that included variations in notch severity and force amplitude onto a single trend. Two schemes were implemented to define the invariant area-averaging domain; one based on the maximum value of the generalized damage parameter and a circular sweep of the surrounding domain and another based on the domain around the entire notch surface. Both methods worked reasonably well.
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