Carbon-matrix composites with continuous glass fiber and carbon black for maximum strain sensing

Electrically conductive glass-fiber-reinforced polymer composites have been prepared by adding carbon black, and carbonization processes have been applied to the resulting matrices. The carbonized composites were found to show characteristic changes in resistance during cyclic tensile tests, in which the resistance increased in the loaded state was retained even after unloading. Pyrolysis temperature dependence of the residual phenomena was investigated in order to understand the effects of the carbonized matrix and the carbon black network. The residual behavior became more pronounced with increasing pyrolysis temperature until 500 °C, while that diminished over 600 °C. The thermal decomposition of the matrix was almost completed up to 500 °C, and the shrunk matrix coexisting with glass fibers had a residual tensile stress along the fiber direction. The matrix carbonized at higher than 600 °C showed an increase in conductivity, which disrupted the strain-sensitive percolation network and hence the resistance response. These results showed that irreversible change in the carbon black network under the internal tensile stress provided the residual phenomena.