ABSTRACT
Since cycles-to-failure is typically the dependent variable in fatigue crack nucleation testing (and therefore known only after a test has executed), tests specified as a series of discrete strain levels on a material with unknown fatigue behavior can too easily lead to the exhaustion of either 1) available testing time or 2) available test specimens without producing a fully defined material characteristic curve. In order to avoid such operational problems, a fixed test time limit is enforced in the present work by linearly ramping the peak cyclic strain from a minimum initial value to the tensile strain at break over a fixed time period. By running the linear ramp fatigue test for a series of 3 fixed time periods (2 hours, 8 hours and 20 hours), and by analyzing the accumulation of damage as a function of strain and applied cycles, we show that the constant amplitude strain life curve can be recovered within a guaranteed time and specimen budget. The recovered curve is compared to the strain life curve obtained via the classical, direct, open-ended experimental method, demonstrating the accuracy of the method.
