A new procedure for fatigue life prediction of CFRP relying on the first amplitude harmonic of the temperature signal

The use of thermal indexes assessed by monitoring rapid fatigue tests with infrared detectors as reliable damage parameters to reconstruct S/N curve is a topic still presenting open points. First of all, the selection of the proper thermal index representing damage is a topic to be explored and also the relationship between the damage from rapid stepwise test and constant amplitude test is another a point of discussion. In the present work, we deal with such an issue by investigating the First Amplitude Harmonic (FAH) of thermal signal related to thermoelastic phenomena and dissipative effects too. It has been demonstrated that FAH is related to stiffness degradation and stress induced effects. Moreover, it provides a local analysis of the specific effect related to the material fatigue damage without artifacts. The results show that due to relationship between stiffness degradation and FAH, and specific material properties it is possible to reconstruct S/N curve by carrying out just one constant amplitude test and stepwise rapid tests. Moreover, the capability of temperature FAH to study fatigue behaviour and detect damage during any loading procedure, are also presented.