| Self-sensing was attained in lightweight structural composite materials, including those with polymer (epoxy), carbon and ceramic (Si3N 4) matrices. Either a volume of the composite or the interlaminar interface in the composite was used as the sensor.; The use of the interlaminar interface as a sensor is a new approach, which was found to be effective in continuous carbon fiber epoxy-matrix composites for sensing temperature, moisture and damage. In case of temperature sensing, the interlaminar interface functioned as either a thermistor or a thermocouple junction. The thermocouple approach required the fibers in the contacting laminae to be dissimilar, whereas the thermistor approach did not. By using two crossply laminae, a two-dimensional array of sensors was attained and demonstrated to be effective for temperature distribution sensing. By measuring the contact electrical resistivity of the interlaminar interface during shear, the interlaminar shear process was monitored in real time. Study of the electrical conduction across the interlaminar interface led to the observation of apparent negative electrical resistance, which could be controlled by composite design.; The use of a volume of a structural composite as the sensor and measurement of the volume electrical resistivity of the volume showed that continuous carbon fiber epoxy-matrix and carbon-matrix composites were effective for the self-sensing of strain and damage, whereas the SiC whisker Si3N 4-matrix composite was effective for the self-sensing of strain only. For the case of the epoxy-matrix composite, it was found that the four-probe method of resistance measurement was effective, whereas the two-probe method was not; it was also found that the though-thickness resistance was a sensitive indicator of matrix damage, while the longitudinal resistance was a less sensitive indicator. Polycrystalline β-SiC fiber without a carbon core was found to be a piezoresistive strain sensor, but that with a carbon core was not.; The consolidation of carbon fiber epoxy-matrix laminae during composite fabrication by lamination was monitored in real time by measurement of the through-thickness electrical resistivity. The consolidation was thus found to be hastened and to occur to a greater extent by increasing the pressure. The consequence of better consolidation remained after curing and subsequent cooling. |
