Influence of graphene nanoplatelet concentration on the electrical, mechanical, and piezoresistive properties of glass fiber/epoxy composites

Abstract This paper reports the effect of weight concentration of graphene nanoplatelets (GNPs) on the electrical, mechanical, thermo‐mechanical, and piezoresistive properties of unidirectional glass fiber/epoxy composite laminates. The neat (without GNPs) and multiscale laminates (with GNPs) were fabricated with different GNPs contents (0.25, 0.50, 0.75, and 1.00 wt%) using a simple and feasible process based on spray coating followed by vacuum assisted resin infusion. The morphological analysis on glass fiber surfaces evidenced the presence of an effective GNP network formation which tends to be denser as GNPs content increases. As a result, the electrical conductivity and gauge factor measured on top and bottom surfaces of specimens were greatly increased in laminates. Short beam shear and flexural test results showed that the addition of GNPs to the laminates causes a significant reduction in their interlaminar shear strength, flexural strength, and strain to failure with respect to the neat laminate. However, the flexural modulus of laminates does not suffer any apparent change in its reference value and the glass transition temperature was slightly increased in samples with 1.00 wt% GNPs. The fractographic analysis revealed that delamination was the main damage mechanism detected upon mechanical testing, suggesting that relative high concentrations of GNPs cause that interlaminar regions of laminated composites become weaker. In spite of this, excellent strain self‐sensing capabilities and internal damage detection were observed during flexural electromechanical tests performed in beam‐type specimens with higher GNP content.