Influence of elevated temperatures on the mechanical properties of glass fibre reinforced polymer laminates produced by vacuum infusion

Abstract

One of the main concerns about the use of fibre reinforced polymer (FRP) materials in civil engineering is their behaviour when subjected to elevated temperatures and under fire exposure. In fact, considerable reductions in the mechanical properties of FRP materials have been reported even at moderately elevated temperatures (e.g. 50–150 °C), due to the glass transition of their polymeric matrices. Most previous studies on this topic have focused on the mechanical characterization at elevated temperatures of quasi-unidirectional pultruded FRP composites, namely profiles, rebars and strips; much less data is available about FRP materials produced with different methods with more balanced fibre architectures. This paper aims at contributing to fulfil this knowledge gap by presenting experimental and analytical investigations about the effects of elevated temperatures on the mechanical properties of glass-FRP (GFRP) laminates produced by vacuum infusion, with a balanced fibre architecture, representative of typical GFRP face sheets of sandwich panels used in civil engineering structures. The experimental programme included (i) tensile tests up to 300 °C, (ii) compressive tests up to 250 °C, and (iii) shear tests up to 200 °C, all under steady state conditions, as well as dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The results obtained confirm that the mechanical properties of the GFRP laminates are severely affected by the temperature increase, especially those that are matrix-dependent: compared to room temperature, at 200 °C, the shear modulus was reduced by 88%, whereas the compressive strength and modulus were reduced by 96% and 67%, respectively. The tensile properties (fibre-dominated) were much less affected - at 200 °C, the tensile strength and modulus were reduced by 40% and 48%, respectively. Finally, the suitability of four empirical models and of a design-oriented temperature conversion factor to take into account the variation of the GFRP mechanical properties with temperature was assessed. Overall, the empirical models presented good agreement with the test data, and the temperature conversion factor provided conservative estimates of the material properties, attesting its suitability for design purposes.