AbstractAxial fatigue of two, commercial, talc‐filled polypropylenes was studied. A significant result of our investigation was the identification and characterization of the failure mechanisms and the effects of frequency and hysteretic heating. Frequency was found to be important to the fatigue response of the polymers. At low frequency, fatigue failure appeared to be a process of crack initiation and growth with very little dissipative heating. At high frequency, the fatigue process was dominated by dissipative heating resulting in significant creep and modulus loss, and failure was much accelerated and due mainly to material softening and melting. Correlation of temperature rise with on‐line energy loss in selected experiments enabled us to extract information from the fatigue process. The results provided some quantitative understanding of the different fatigue failure mechanisms at low and high frequenc