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A method which monitors the changes in electrical resistance in CFGFRP (carbon-fiber-glass-fiber-reinforced plastics) composites was found to be a promising technique for foreseeing fractures and preventing fatal ones. CFGFRP composites containing two types of carbon fibers along with 31.6 vol% glass fibers were used. U-shaped copper electrodes were attached to both ends of the CFGFRP composites, using a conductive adhesive agent, and electrical resistance was measured via a two-thermal dc method. A strain gauge was attached onto a specimen to measure strain. On loading, the changes in electrical resistance increased linearly with increasing strain, and the value reached 38% for the CFGFRP composites containing 0.36 vol% PAN-based high-strength carbon fibers. A tremendous change in electrical resistance was seen for the CFGFRP composites containing 0.38 vol% pitch-based high-property carbon fibers, and the composites could maintain their shape owing to a hybrid effect after the carbon fibers fractured. The change in electrical resistance can be controlled through suitable selection of the type of carbon fibers according to their values of ultimate elongation. Permanent, residual electrical resistance was found to remain, and the changes in resistance were dependent on the maximum previous strain.

Hybrid composites containing both conductive fibres with a small value of ultimate elongation and insulating fibers with a large value of ultimate elongation show promise as intelligent materials with a self-diagnosing function for preventing fatal fracture. Three types of carbon fiber and one type of glass fiber were tested as conductive fibers and insulating fibers. respectively. A tremendous change in electrical resistance was seen at the transition point where the conductive fibers fractured, and this point could be controlled through suitable selection of the type of conductive fiber according to its value of ultimate elongation. Permanent residual electrical resistance was observed even after the removal of load,aand the change was dependent on the maximum strain applied in the past trials, in the application of this method. changes in the electrical resistance of cFww-reinforced concretes were measured during and after loading. A method based on monitoring the changes in t h e electrical resistance is a promising method for improving reliability by self-diagnosis.

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