Experimental investigation and probabilistic models for residual mechanical properties of GFRP pultruded profiles exposed to elevated temperatures

Here, we investigate the influence of elevated temperatures with negligible ambient oxygen on mechanical properties of various embedded glass fiber reinforced polymer (GFRP) profiles, as well as the application of a predictive Bayesian model for predicting these properties. Both the flexural and compressive properties of FRP profiles were investigated through the tests of I-shaped and box-shaped profiles. To determine the impact of low and high elevated temperature, the profiles were exposed to a wide range of temperatures (i.e., 25–550 °C); effects of the exposure time were also investigated. Experiments showed that specimens exposed to higher elevated temperatures for longer time periods lose more of their mechanical properties. We used profiles in a simulated embedded environment to prevent combustion and charring, thus reducing fire vulnerability of the GFRP material at high elevated temperatures. We found that elevated temperature for 15 min produces slight strength deterioration in the embedded FRP profiles. Also, exposure to a high elevated temperature for 45 min reduced the maximum loads by up to 30%. Next, we performed a filled emission scanning electronic microscopy (FE-SEM) study before and after the mechanical tests to examine both the control specimens and conditioned specimens that were exposed to elevated temperatures. This approach allowed us to investigate the microscale effect of the elevated temperatures as well as the failure mode mechanisms of FRP profiles under flexure and compression. The micrographs revealed that a glut of small cracks formed in FRP profiles exposed to high elevated temperatures, leading to sole resin failure in the mechanical tests. Finally, Bayesian linear regression was applied to the laboratory test results, which led to a predictive model for mechanical properties of FRP profiles exposed to elevated temperatures.