Strain sensing behaviors of GnPs/epoxy sensor and health monitoring for composite materials under monotonic tensile and cyclic deformation

The graphene platelets (GnPs)/epoxy flexible sensor with controllable sensitivity and linearity can be used to monitor the deformation and damage of composite structures. The sensitivity and linearity can be regulated by dispersing different content of GnPs in epoxy and the dispersion was better improved by optimizing ultrasonic time and the ball mill mixing process. The GnPs/epoxy mixture exhibited relatively low percolation threshold of 0.76 vol %. In this paper, GnPs/epoxy mixtures with GnPs loading of 0.84 vol.%, 1.05 vol % and 1.58 vol % were selected as damage detecting and strain sensor, and the characteristics of sensors were demonstrated via various mechanical tests. The monotonic tensile results suggest that there are three different linear change sensing stages, (1-0.2%), (0.2%-0.6%) and (0.6%-1.2%), the linear growth of the electrical response is softened while the linear tendency is enhanced due to increasing GnPs content, and it exhibits relatively high gauge factor of 11.81, 15.25 and 22.54 for 0.84 vol %, 3.63, 8.13, 11.46 for 1.05 vol % and 2.53, 3.77, 4.69 for 1.58 vol % in different sensing stages respectively. The sensor of 0.84 vol % is more reversibility than 1.05 vol % upon cyclic loading-unloading test. The GnPs/epoxy sensor show promising applications for the damage monitoring of structural composite in the field of aerospace.