Dielectric state variables as qualitative indicators of moisture absorption-caused mechanical property degradation in GFRP composite structures

Abstract

Fiber reinforced polymer (FRP) composites are being used in numerous fields owing to their intrinsic strength to weight ratio and various design benefits. However, these materials are prone to environmental aging, particularly moisture absorption. In essence, absorbed moisture infiltrates the polymer matrix and induces changes in the polymer network through chain scission, plasticization, and other bonding interactions. This causes irreversible damages to the material and significantly decreases mechanical strength. In this study, Broadband Dielectric Spectroscopy (BbDS) has been used to identify the absorption mechanisms in glass fiber reinforced polymer (GFRP) composites by detecting the related polarization mechanisms. Here, results show an increase in the real permittivity and dielectric relaxation strength of the material with moisture absorption and attaining a steady-state once absorption approaches saturation. In this work, moisture-induced degradation of tensile and flexural properties of the material have also been studied and a correlation has been found to exist between the dielectric state variables, absorbed moisture, and the mechanical properties of the material. The correlation resolves the integration of the different material physics involved here and can be used to empirically predict the residual strength of a composite structure using the non-destructive broadband dielectric characterization technique.