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

Abstract

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.

Online and Ex Situ Damage Characterization Techniques for Fiber-Reinforced Composites under Ultrasonic Cyclic Three-Point Bending

“…control and record the ultrasonic generator’s input resonance parameters at a sampling rate of 1 kHz [ 38 , 49 ],…”

“…capture the maximum surface temperature on the CF-PEKK specimen at a sampling rate of 32 Hz [ 38 , 45 , 49 ].…”

“…The composite laminates were manufactured by Toray Advanced Composites (Nijverdal, The Netherlands). The physical properties of the CF-PEKK composite laminate provided in Table 1 were already published in [ 38 , 45 ].…”

“…The knowledge and experience on fatigue of composites in the VHCF regime conducted using a UFT system under three-point bending by the authors [ 38 ] as well as others [ 18 , 20 , 21 ] are limited to the surface of the composite specimens. Under a pure bending load case, maximum cyclic compressive stresses occur at the top layer of the composite specimen, and tensile stresses occur at the bottom layer.…”

“…However, since the resonance condition for a three-point bending load case leads to short specimens, typically in the order of 30–35 mm for carbon fiber-reinforced polymer composites, cyclic shear stresses occur in the regions between the loading nose and support units. Light optical or scanning electron microscopy (used in [ 18 , 20 , 21 , 38 ]) can provide excellent results on the state of damage anywhere in the specimen but is limited to only one plane. Specimens have to be physically sliced to acquire information across multiple planes.…”