Though advanced composites with embedded actuator materials such as shape memory alloys and piezo ceramics have been developed as active materials, another one by making use of thermal deformation of composites was proposed and an active laminate was prepared as an example by hot-pressing of aluminum plate as material of high coef®cient of thermal expansion (CTE), uni-directional carbon ®ber reinforced plastics (CFRP) prepreg as low CTE material and electric resistance heater, polymer adhesive ®lm as insulator between them, and copper foils as electrodes. Actuation of this laminate is different from that of bimetal because CTE of the CFRP layer is strongly anisotropic due to directionality of its reinforcement ®ber. As CTEs of the CFRP layer and the aluminum plate in the ®ber direction are quite different from each other though they are close to each other in the transverse direction, smooth and uni-directional actuation becomes possible. In this study, its fundamental performances such as shape change and output force were observed and evaluated, and after establishment of its fabrication, an optical loss type sensor was formed in the active composite, by embedding multiply pre-notched optical ®ber in the CFRP layer and breaking it at the pre-notches under bending, followed by lamination on aluminum plate with adhesive. As the sensing part can be formed inside the matrix without any complicated processes, a robust and low cost sensor is obtained. From the results, it becomes clear that: (1) curvature of the active composite linearly changes as a function of temperature between room temperature and its hot pressing temperature by electric resistance heating of the CFRP layer and cooling, (2) its output force against a ®xed punch during heating from room temperature up to around glass transition temperature of the resin phase almost linearly increases with increasing temperature, (3) the multiply pre-notched, embedded and fractured optical ®ber works as a sensitive sensor for monitoring the curvature of the active composite.

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This article describes the formation of strain sensors embedded in a matrix material by breaking a notched optical fiber in the matrix. When a specimen with an embedded optical fiber with a notch is tensile tested, fracture of the fiber at the notch occurs, producing an optical interference type strain sensor. During the formation process optical transmission loss is recorded. The case of multiply notched optical fibers is also considered and it is shown that the optical loss of the embedded optical fiber during tensile test increases with the number of breaks. Using bending, instead of tension, to form the sensor, allows a reduction of break pitch and consequently improves the local nature of the sensor. The multiple fractured type optical fiber sensor has also been used on an active laminate to monitor its curvature change during actuation.KEY WORDS: smart material, optical fiber, composite, strain sensor, active material.

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