On Intelligent Structures Using Optical Fiber. I. On Intelligent Structures Using Optical Fiber. Crack Sensing with Optical Fiber.

Recently, many attentions have been paid to an optical fiber as a sensor for intelligent structures. In present study, the optical fiber is used as a crack sensor for mortar beam. The sensing properties have been investigated by three-point bending test. Fresnel reflection of four optical fibers, which have been stuck on the surface of mortar beam with epoxy resin, is observed with OTDR (Optical Time Domain Reflectmeter). When progression of a crack occurs in the mortar, the crack or the crack propagation breaks the optical fiber. Therefore, the cracking point can be measured by Fresnel reflection. In addition, the crack propagation in the mortar beam can be also measured by the breaking sequence of four optical fibers. Hence, it has been recognized that an optical fiber by using OTDR is very useful as a crack sensor for intelligent structures.