Relation of damping and fatigue damage of unidirectional fibre composites

For investigation of damage processes by fatigue cycles of unidirectional (UD) fibre composites damping measurement have been applied. UD AS4 carbon fibre reinforced PEEK and epoxy as well as fibreglass reinforced epoxy were considered. A ‘damping plateau’ has been primarily detected from the damping dependence on fatigue cycles in epoxy composites, and the mechanism of the damping plateau is discussed under the assumption of possible energy balance between fatigue load input and damage dissipation. The fatigue life of UD composite with a brittle epoxide matrix is better than that with a ductile thermoplastic matrix by using the same fibre reinforcement. The formation and growth of microcracks in epoxide matrix contributes to the energy dissipation under fatigue load, which seemly improves the fatigue behaviour. Damping is recommended in the evaluation of damage process, which seems more sensitive than stiffness.