Experimental fatigue behaviour of CFRP composites under vibration and thermal loading

The investigation of the carbon fibre reinforced plastic components under vibration fatigue testing is known to be challenging; as it involves the analyses of both the mechanical response and the inherent self-heating behaviour which emerges due to the high-frequency testing. The paper will firstly address an open question about the so-called critical event, which is a sudden change in one of the dynamic parameters measured during the fatigue test. Past experiments showed that such a change is associated with delamination, but its onset and early growth were not clarified. Therefore, a set of interrupted fatigue tests and CT scan measurements will show the onset of delaminations and how these are correlated with the vibration parameters. The second objective is to investigate the failure behaviour under vibration fatigue and elevated environmental temperatures. The research will present both the experimental set-up for achieving fatigue under environmental conditions and the vibration data obtained from testing samples at many severity levels; both in terms of applied mechanical vibrations and thermal loads. The paper will investigate how the inherent self-heating behaviour and the applied thermal load will affect the time to failure of composites. The relationship between fatigue behaviour and environmental temperature conditions are presented in two forms. The first one is a typical S-N curve, whereas the second one, the relationship between the response phase and hot-spot temperature data. Both relationships will show how relevant is the environmental temperature in terms of fatigue behaviour for the type of components presented in this paper.