Impact Damage Detection of CFRP with Michelson Interferometric Fiber-Optic Sensors

Response of a Michelson Interferometric fiber-optic sensor to impact loading was investigated. A Michelson Interferometric fiber-optic sensor was mounted on the surface of unidirectionally aligned carbon fiber-reinforced epoxy composites. Using a Charpy tester, the load was applied to the specimen at two impact energy levels. One was the case where the specimen sustained no damage; another was the case where localized damage occurred in the specimen. Both the optical interference signal and the strain were measured during the impact loadings. The spectrum analysis of the interference signal was performed by the Fast Fourier Transforms. The analytical results were compared with the predicted frequency characteristics from the strain rate. In the case where damage occurred in the specimen, the interference signal recorded before and after the peak in load and during unloading had relatively high intensity in wider frequency range than that predicted from the strain rate. This discrepancy in frequency characteristics is attributed to the vibration induced by fiber breaking or crack closure. The Michelson interferometric fiber-optic sensor proved to be effective for detecting the impact damage of the material studied.