Compressive creep behaviour at elevated temperature of GFRP composite laminates produced by vacuum infusion

The mechanical properties of fibre-reinforced polymer (FRP) composites are temperature- and time-dependent. Exposure to elevated temperatures degrades the matrix of FRPs, reducing their elastic modulus. This results in increased deformability, relevant to service limit states (SLS), and greater buckling susceptibility in compressed members, which may compromise safety at ultimate limit states (ULS). Since FRP composites are viscoelastic materials, temperature also affects their creep rate, which may further contribute to increased deformability. Since SLS typically govern the design of FRP composite structures, a comprehensive understanding of their viscoelastic response is needed, especially when considering their exposure to elevated temperature (ET), which can occur in outdoor applications or under (accidental) fire exposure. This study presents experimental and analytical investigations into the effects of exposure to ET on the short-term compressive creep behaviour of Glass-FRP (GFRP) laminates produced by vacuum infusion. Specimens were exposed to ET (up to 80 °C) until reaching thermal equilibrium and subsequently loaded in compression for 3 h under steady-state conditions. Compressive loads ranged from 15 % to 30 % of their residual strength at each tested temperature. The results showed a significant increase in creep with temperature: compared to room temperature (RT), at 65 °C the creep coefficient increased about nine times. This was attributed to the glass transition process and the inherent increase of the matrix viscous contribution to the response. To describe the short-term viscoelastic behaviour at ET, an existing model (Findley’s Power Law, originally developed for linear creep, long-term and RT conditions) was used. The formulation was validated and calibrated using experimental data, showing to be appropriate for predicting short-term creep at ET. Finally, analytical predictive models were derived to describe the temperature-dependent evolution of the creep power law parameters.