Fatigue life prediction of filled polypropylene based on creep rupture

To predict the fatigue performance of talc-filled polypropylene in engineering applications, a simple relationship using constant stress data to predict the cycles-to-failure (N_f) was developed: where k and n are constants from creep rupture tests, v is the cyclic frequency (≤1 Hz to avoid self-heating), f(n) is a function that accounts for the wave form, and a is the peak cyclic stress with a zero minimum stress. For stress concentrations produced by central holes, σ is taken as the average net section stress and the effect of the stress concentration is ignored. Extensive tests were used to verify this expression for cyclic frequencies of 1.0 and 0.1 Hz, sinusoidal and triangular waveforms, stress concentrations produced by small and large holes, and 20 and 40 percent talc filler content.