Fatigue Testing of Carbon Fibre Reinforced Polymers under VHCF Loading

Abstract The rapidly developing market for high strength and high stiffness carbon fibre reinforced polymers (CFRP) among others demands for reliable damage evaluation methods at very high cycle fatigue loading (VHCF). Due to the anisotropic nature of continuous fibre reinforced composites, fatigue damage is initiated in various failure modes. In case of low cycle and high cycle fatigue loading they are well comparable with the failure modes known from static loading. For the analysis of the widely unknown damage behaviour of CFRP at VHCF-loading, specific test principals and a shaker based fatigue test stand are developed. The key aspects in the development are: • high frequency fatigue (f > 150 Hz) without significant warming of the specimen, • homogeneous stress distribution and minor through thickness stress gradients and • adjustable states of stress and mean stresses for the fatigue testing of specific failure modes. Using numerical and experimental investigations, a promising solution for the given problem has been found in form of a shaker based shearing force free bending test stand and a specifically produced specimen. The deformation measurement and specimen observation is performed by a combination of eddy current sensors and digital image processing. With this basis, reliable VHCF-fatigue experiments for CFRPs with and without nanoparticles are performed for the development and validation of damage initiation criteria.