Fatigue Assessment of Carbon Fiber-Reinforced Polyurethane with Regard to Crack Initiation and Propagation

Abstract

Due to their lightweight potential, the use of fiber-reinforced polymers is the current standard for many technical fields of application. Especially, the automotive and aerospace sectors are to be emphasized. This entails a sophisticated knowledge regarding the material properties, since the safety standards applied in these fields are of high importance. To ensure the safety of the components, a detailed mechanical material characterization is indispensable. The aim of this work was to investigate different influencing factors on the fatigue behavior of carbon fiber-reinforced polyurethane, which is to be certified for aviation applications. Tensile tests provided a basic understanding of the material properties, which appeared to be affected by the specimen width, varied from 3 to 25 mm, by up to 30%. Subsequently, the influence of the cutting direction was investigated in the course of the fatigue tests. Thus, the fatigue strength of longitudinally cut specimens was found to be higher than that of transversely cut specimens by 6%. By means of specific measurement technologies, the material responses were associated with crack initiation and propagation during the fatigue lifetime. The material properties, such as the thermoelastic effect, could be examined during the fatigue tests. Furthermore, turning points in the courses of the characteristic values of the material and correlations with local phenomena were identified.