Damage state model for fatigue of CFRP

Fatigue is the major failure mode for any structure under cyclic loading. In particular, composite materials exhibit highly complex damage mechanisms and are often overdesigned due to lack of understanding under cyclic loading. Many papers have been written on the modelling of fatigue in fiber reinforced composites. All such models they assumed some internal damage parameter which themselves defined by the mechanical property. However, the growth of these damage parameters are themselves defined by the mechanical property degradation. Hence these fatigue models do not give actual stiffness degradation. In this study, actual 3D microstructural damage in CFRP under cyclic loading was quantitatively measured. Damage micromechanisms viz., fiber breakage, matrix microcracking, debonding, and fiber pull-out were estimated and a model to predict the property degradation with these damage mechanisms (parameters) was developed. Thus, the property degradation in CFRP under cyclic loading was modelled with independently measured damage parameters.