Tension-tension fatigue life estimation of CFRP composites by modal testing

Abstract

This study investigates the tension- tension fatigue behavior of carbon/epoxy laminates under constant amplitude loading. Workpieces were prepared as per with fiber orientation of 45˚ were tested at different stress levels, for R = 0.1 with a frequency 5 Hz. The overall stiffness reduction was evaluated in terms of natural frequency by using modal testing. The modal testing was applied at specific intervals by interrupting the fatigue testing. It is shown that modal testing a Nondestructive testing (NDT) method can be applied to the fatigue life stimation of CFRP laminates. Curve fitting technique was used for developing an empirical model for prediction of fatigue life of CFRP components. The experimental results found good agreement with the model results. From the experimental results it was concluded that the modal testing is useful as a NDT for estimation of fatigue life, natural frequency reduction model is capable of representing the overall stiffness reduction due to fatigue. Change in damping ratio (ζ) is more significant than change in natural frequency due to fatigue.