Influence of pulse duration on the fatigue behavior of a carbon‐fiber‐reinforced composite under cyclic three‐point bending at 20 kHz

Very high cycle fatigue (VHCF) experiments are limited in practice due to their long testing times. In ultrasonic fatigue test (UFT) systems, the cyclic oscillation is applied using resonance at 20 kHz with a pulse and pause sequence. However, determining optimal pulse durations to achieve minimal testing time and avoid thermal‐induced fatigue damage in fiber‐reinforced polymer composites remains a challenge. In this work, several fatigue experiments, temperature analyses, and digital light optical microscopy were carried out to evaluate the influence of pulse duration on the fatigue behavior of a carbon‐fiber fabric reinforced in polyether‐ketone‐ketone (CF‐PEKK) composite. A shorter pulse duration with the same pulse–pause ratio as the longer pulse duration is proposed for higher stress amplitudes to avoid any thermal influence during mechanical fatigue without altering the underlying fatigue damage mechanisms. Highlights The current pulse–pause ratio = 1:6 leads to effective test frequency of ∼3000 Hz. Fatigue strength of the composite is independent of ultrasonic pulse duration. Short pulse duration leads to mechanical fatigue across all cyclic amplitudes.