Damage detection via electrical resistance in CFRP composites under cyclic loading

Analytical and numerical electro-mechanical models are developed to predict the electrical resistance change due to fatigue damage in unidirectional fiber reinforced composite materials. Fatigue is attributed to underlying fatigue crack growth of pre-existing fiber flaws, and the fiber fatigue model is validated and calibrated by comparison to experimental data on fatigue of dry bundles of T700S carbon fibers. Predictions of fiber damage and resistance change in a carbon fiber reinforced polymer composites (CFRP) during cyclic loading are then made, analytical and numerical models in quantitative agreement over most of the life. The models predict a direct correlation between resistance and stiffness changes, and quantitatively agree with the experimental results for T300/Hexcel 914 system. The effects of single-cycle overloads on the electrical resistance during otherwise fixed-amplitude cyclic loading are studied, showing an influence on life dependent upon both overload amplitude and cycle number. The resistance change is also shown to increase substantially prior to any noticeable change in remaining strength, and to accelerate as the remaining strength decreases. Collectively, the results suggest that electrical resistance can provide insight into the underlying damage evolution and fatigue life of composite systems and serve as the basis for system prognosis or health monitoring.