Development of Self-Compensated Long-Gage Carbon Sensor for Structural Health Monitoring

Abstract

A self-compensated long-gage packaging method of carbon fiber sensor has been developed for solving thermoelectric and moisture influence for assessing the continuous measuring of low-level strains. The continuous measuring of low-level strains is faced with the burden of a complex variety of excitations and an unstable environmental effect. Carbon fiber sensors are ideally suited for static and dynamic strain measurement at low strain levels. However, continuous carbon fibers used as the strain sensing elements in the carbon fiber sensor exhibited an obviously thermoelectric effect. Thus, to reduce the thermally induced resistance change of the carbon sensor to an acceptable level, a novel self-compensation long-gage packaging method was established using carbon sensors placed in series and packaged with low-cost insulating basalt sheets. Experimental verifications of the developed self-compensated long-gage carbon sensor under dry heating and waterbath heating were present. Good agreement of the measured strain results under different moisture condition has been achieved. The packaging method is good to prevent moisture influence and suitable to build up temperature compensation. Furthermore, a long-gage carbon sensor was installed on a tension specimen to provide the continuous monitoring with static loading and impact excitations. The obtained dynamic response is in agreement with the experimental setting. Therefore, the developed long-gage carbon sensor is useful in the identification of excitations under low strain level. Furthermore, with a continuous wavelet transform-based time-frequency analysis, it can be considered the macro strain time histories and frequency identification using the developed long-gage carbon sensor is substantially accurate.