Investigation into Strain Sensing with Reduced Graphene Oxide, and Applications in Low-cost Leak Detection and Health Monitoring of Water Equipment

Abstract

Strain gauges are one of the most important transducers that can be used in many applications such as robotics, structural health monitoring, medicine etc. The expensive mass production, as well as lack of high sensitivity, high strain tolerance or high quality can be some of the challenges with the current strain gauges. The reduced graphene oxide possesses many of the excellent properties of graphene while being easy and inexpensive to be mass-produced. However, its electromechanical behavior under strain (especially large strains) has not been well studied. In this dissertation, strain sensing by reduced graphene oxide with Polydimethylsiloxane substrate is investigated and the applications in low-cost leak detection and health monitoring of water equipment is explored.Initial test results showed that with increase in area density of the graphene oxide of the reduced graphene oxide (rGO) sensor, the average strain tolerance of the sensor could be increased. Resistive response of the sensor was tested in the directions aligned with, perpendicular to and at an angle with the direction of applied uniaxial tension up to 20.72% induced strain. The sensor showed mostly linear-nonlinear and increasing behavior in the directions aligned with the direction of applied tension. The linear behavior was consistent with the bulk-like material behavior and the nonlinear behavior was consistent with the percolative like behavior. Mathematical models also matched the increasing linear-nonlinear trend. In the direction perpendicular to the direction of applied tension, sensor showed decreasing trend that could be due to contraction in the rGO caused by the Poisson’s effect in the PDMS substrate. The mathematical model also showed an decreasing trend in the resistive response of the sensor in this direction. In the direction that was at an angle with respect to the direction of the applied tension, sensor showed increasing resistive response similar to that in the aligned direction which was also explained with a mathematical modeling. Cyclic analysis showed that generally the deviation in the resistive response of the sensor in the aligned direction between the first and the second cycles was significant compared to the deviation between other cycles. It could be attributed to the residual microcracks observed in the microscopic images forming after the first cycle of uniaxial tension. Confocal and atomic force microscopic images also suggested the possibility of percolative behavior of rGO in higher strains and accumulation of rGO flakes creating cracks that could be linked to the nonlinear resistive response of the rGO. Furthermore, a novel application of the rGO strain sensor in leak detection and health monitoring of the water equipment was explored and tested under different flowrates. Furthermore, creep, fatigue and high flowrate survival of the sensor were tested.