High-sensitivity rGO/epoxy strain sensor integrated into CFRP composite structures

Carbon fiber-reinforced polymer (CFRP) composites are widely used in aerospace and automotive industries for their superior mechanical properties and lightweight characteristics. However, their complex behavior challenges structural safety, requiring effective online monitoring. Existing sensors lack sufficient sensitivity to detect minor damage, while embedded sensors may compromise the mechanical properties of CFRP, impairing long-term strain monitoring. This study proposes a reduced graphene oxide (rGO)/epoxy strain sensor based on a pre-strain strategy, which achieves anisotropic regulation through the directional alignment of microstructures and effectively preserves both the pre-strained configuration and aligned microstructure using transfer printing technology. The sensor demonstrates a gauge factor of 80.07 under 25 % pre-strain, representing a 9.43-fold enhancement compared to sensors without pre-strain. The underlying mechanism of sensitivity enhancement was revealed using a tunneling theory model. During cyclic tensile testing, the sensor demonstrated excellent stability and repeatability, underscoring its potential for real-time structural health monitoring of CFRP composites. The simulation results demonstrate that when the thickness of the embedded sensor is 20 μm, the maximum relative strain error induced is only 1.220 %, indicating that reducing the sensor thickness is a critical approach to minimizing interference with the strain field of the composite material and preserving its mechanical properties.