Strain Sensors Fabricated From Conductive Polymer Composites

Abstract

Strain sensors are vital tools for ensuring the safety, performance, and efficiency of a wide range of systems and structures. There is a need for low cost yet highly sensitive strain sensors, as this is not available in the current commercial market. Conductive Polymer Composites (CPC) have the potential to fulfil this requirement due to their good processability, cost-effectiveness and tunable electrical properties. However, despite significant progress in recent years, there are still areas of CPC-based strain gauges which require further research before they can be used for practical applications. This thesis investigates carbon black and flexible epoxy resin (CB/epoxy) composites
for use as strain sensors. The CB/epoxy composites are fabricated using a method which is low cost and easily scalable, and during environmental testing found to have a Temperature Coefficient of Resistance just three times the magnitude of traditional metallic strain sensors. The CB/epoxy composites are tested under cyclic strain and calculated to have a Gauge Factor (GF) up to eight times that of typical metallic strain gauges. Thin-film metallic
strain gauges are also fabricated, analysed and tested under cyclic strain to provide a reference against conventional strain gauge technology. A design of a Rig for testing strain gauges under cyclic strain is also presented. A model for the electrical properties of the CPCs under strain is developed in order to give insight into the microscopic mechanisms that determine GF, offering a valuable potential tool for optimising CPC compositions to achieve enhanced
performance. Currently few simulations exist for modelling the piezoresistive properties of CPCs. This thesis not only validates the potential of CPCs as a viable alternative to conventional strain gauges, but also lays the groundwork for further innovation in the design of highly-sensitive, cost-effective strain sensors.