Health-monitoring technologies for alumina-fiber-reinforced plastics

Transmitted light could detect matrix cracks that occurred in the early stages of fracture of alumina-fiber-reinforced plastics (alumina-FRPs); these cracks could not be detected by acoustic emission (AE). An optical-fiber Bragg grating (FBG) sensor could detect the matrix cracks but it must be embedded in the FRPs. To determine which wavelength is sensitive to the defects in the FRP, the spectra of the transmitted and reflected light were measured. The intensity of the transmitted light, especially in the visible region (wavelength: 400¯800 nm), decreased as the bending stiffness of the test piece decreased. It is thus concluded that to monitor the decrease in bending stiffness of FRPs, a simple sensor using a visible ray is good enough. And this transmitted-light NDE technique can work in the strong electromagentic field associated with a superconductor. It will therefore be useful for detecting defects in the FRP of the loadsupport system in service