Short-carbon-fiber-reinforced epoxy as a piezoresistive strain sensor

Epoxy containing 5.5 vol.% short carbon fibers was found to be piezoresistive strain sensor, such that the magnitude of the reversible fractional increase in electrical resistance per unit strain was 6-23 under tension and 29-31 under compression. These values are much higher than those of previously reported composite piezoresistive materials. The reversible fractional increase in resistance was positive under tension and negative under compression, but the irreversible fractional increase in resistance was positive under both tension and compression. Both reversible and irreversible fractional increases in resistance increased in magnitude with increasing stress/strain amplitude. The reversible portion was due to piezoresistivity, while the irreversible portion was due to damage.