Damage assessment during ultrasonic fatigue testing of a CF-PEKK composite using self-heating phenomenon

Abstract

The knowledge and experience with the very high cycle fatigue (VHCF) behavior are limited compared to the low cycle and high cycle fatigue behavior of fiber-reinforced composite materials. Accelerated cyclic loading using an ultrasonic fatigue testing system is one potential solution to evaluate the longevity of composite materials within a reasonable time. Insufficient sampling rates and the inherent inaccuracies of non-contact measurement devices pose critical challenges in the adaptation of accelerated fatigue experiments. This study aims to overcome these challenges by combining the temperature response of the composite specimen and the input parameters for the dynamic response of the in-house developed ultrasonic fatigue testing system to detect damage before failure. Increasing- and constant-amplitude fatigue experiments were conducted on a carbon fiber satin fabric-reinforced poly-ether-ketone-ketone (CF-PEKK) composite material. These experiments were carried out under three-point bending loading conditions at a cyclic frequency of about 20 kHz. Various parameters, such as the surface temperature, the cyclic displacement, and the input resonance parameters of the ultrasonic generator, were recorded during these experiments. The VHCF behavior of the CF-PEKK material system was characterized based on these results and through digital light optical microscopy.