Electrical properties of low temperature-sensitive coating sensor for fatigue crack monitoring in steel bridges

Coating sensors are used for high-precision monitoring of fatigue cracks in steel bridges. However, the timevariation temperature has a considerable impact on the monitoring precision of fatigue cracking of steel bridges. This study developed a coating sensor using silver-plated copper powder (conductive filler)/acrylate composites as a sensing layer of a coating sensor to monitor fatigue cracks considering variable ambient temperatures. The synthesis and preparation of the composite were presented, and the microstructures of the coating sensor composites were observed by scanning electron microscopy. The bulk conductivity of the sensing layer at different conductive filler contents was measured by the four-probe method to investigate the effect of the concentration of the conductive filler on the electrical conductivity and temperature sensitivity of the resistivity. Moreover, the fractional change in resistivity (FCR) of the sensing layer was tested over a range of temperatures to investigate the temperature sensitivity of resistivity at different conductive filler contents. Finally, the composite with the lowest temperature sensitivity of resistivity was selected to prepare a coating sensor for fatigue crack monitoring. The composite of the sensing layer with 60 wt% of conductive filler content had the lowest temperature sensitivity of resistivity with a minimum value (5.1%) of FCR. The maximum range of the FCR did not exceed 6.4% under cyclic loading and variation-time ambient temperatures. The temperature variation had minimal effects on the output signal of the coating sensor compared with the output signal variation caused by fatigue cracking. The proposed coating sensor can be used for high-precision monitoring of fatigue cracking in steel bridges under different ambient temperatures.