Resonant approach for testing glass-fiber-reinforced composites in the VHCF-regime

Abstract

Numerous applications of composite materials face fatigue lives beyond 10^8 cycles. On the other hand, only few researches have been done to identify the active fatigue mechanisms and the development of fatigue damages. As conservative testing is done at rather low testing frequencies, a concept for high-frequency testing has to be found. This leads to reasonably short testing times for studies in the very-high-cycle-fatigue regime of fiber-reinforced-composites. In this paper a resonant test setup is presented, that contains a two-mass-oscillator. The specimen is a component of the oscillator and one single eigenmode is used to load the specimen at a load ratio of -1. To ensure a single-axle load case, tubular specimens are used, as they suppress subordinated eigenmodes of the oscillator. Furthermore, tubular specimens have no free edges, so no defects originate from free edges. Thus only damage mechanisms are observable that occur inside the laminate. For initial tests tubular specimens with a ±45° layup are made by filament winding as this layup induces a high interlaminar shear stress. Finally, first results are presented and a control circuit is proposed to maintain a constant load at the natural frequency of the resonant system.