Fatigue life prediction and modal analysis of carbon fiber reinforced composites

Abstract

Fiber reinforced composite materials are finding increasing applications in aerospace structures, naval industry, military and automotive industry, because of their high specific stiffness and strength. The fatigue of composite materials is not completely understood which is quite different from metal fatigue. The objective of research is to apply modal testing for the fatigue life prediction of Carbon Fiber Reinforced Plastic laminate in plane bending with different fiber orientations. CFRP laminates with three fiber orientations as 0°, 45° and 90° are applied to fatigue loading in plane bending with R = -1 and S-Nf. curves are plotted and power equations are determined. For modal testing of the laminates the specimens previously undergone fatigue loading are tested at specific intervals to determine the effect of modal characteristics on fatigue life of these laminates. The modal characteristics are determined by using FFT analyzer and the frequency effect on fatigue life is determined. Results are plotted between the fatigue life ratio and the natural frequency and empirical equations are generated for predication of fatigue life prediction. From the results it is concluded that the modal testing is an effective nondestructive testing method that can be applied for estimating the fatigue life of composite laminates