SELF-MONITORING STRUCTURAL-MATERIALS

Self-monitoring (or intrinsically smart) structural materials, includi ng concrete containing short carbon fibers, and polymer-matrix and car bon-matrix composites containing continuous carbon fibers, were review ed. Each material is capable of monitoring its own reversible strain a nd damage through the effects of these on the electrical resistance of the material. This capability is valuable for structural control and structural health monitoring. Among these three materials, the concret e gives the highest strain sensitivity or gage factor (up to 700), whi le the carbon-carbon composite gives the highest damage sensitivity (i .e., sensitivity even to the damage after the first cycle of tensile l oading within the elastic regime). The origin of the self-monitoring a bility differs among the three materials. For the concrete, it is rela ted to slight fiber pull-out during strain and fiber and matrix fractu re during damage. For the polymer-matrix composite: it is related to t he increase in the degree of fiber alignment and reduction of fiber pr e-stress during tension in the fiber direction and to fiber fracture a nd delamination during fatigue. For the carbon-carbon composite, it is related to dimensional changes during strain and fiber and matrix fra cture during damage. (C) 1998 Elsevier Science S.A.