Damage Monitoring of Fiber Metal Laminates by Graphene Nanoplatelets/Epoxy Resin Conductive Matrix

In this study, the real-time monitoring of the internal damage state of fiber metal laminates (FMLs) under quasi-static loading was conducted by measuring the rate of change of resistance using graphene nanoplatelets (GNPs)/epoxy resin conductive matrix. Initially, GNPs/epoxy resin matrices with varying GNPs content were prepared, and their conductivity was measured. A 1.5 vol.% GNPs/epoxy resin mixture was selected as the FMLs matrix. Subsequently, FMLs with 1.5 vol.% GNPs content were fabricated using wet lamination. The resistance changes of the FMLs under three-point bending and stretching loads were tested. The obtained curves confirmed the feasibility of establishing a conductive network in the FMLs matrix by incorporating an appropriate amount of GNPs into the epoxy resin matrix, thereby enabling real-time damage monitoring of FMLs. Experimental results revealed that as the conductive matrix in FMLs was subjected to quasi-static loads and damage occurred at different deformation stages, the resistance of the specimens under three-point bending and tensile loads increased gradually by 5% and 10%, respectively, during the elastic deformation stage, and then increased rapidly to 25% and 50%, respectively, during the plastic deformation stage with the emergence of matrix cracks. Finally, the resistance showed a precipitous increase when the load and deformation reached the damage threshold, indicating a cliff-like rise in the rate of resistance change, which allowed for a more accurate assessment of the damage mode in FMLs.