Tensile and Lap-Splice Shear Strength Properties of CFRP Composites at High Temperatures

Carbon fiber–reinforced polymer (CFRP) composites are used to retrofit or reinforce existing civil infrastructure. When a new combination of carbon fiber/epoxy system is to be implemented, elevated temperature requirements must be evaluated to determine performance in fire or hot climates. This article presents experimental results conducted on small-scale CFRP laminates produced by the hand layup technique to determine tensile strength and single lap-splice shear strength at temperatures from 23 to 200°C. Two curing regimes were evaluated: room temperature (23°C) and elevated temperature (120°C). The dynamic mechanical analyzer was used to determine the glass transition values from each curing regime. Strength tests were performed at steady-state (heat, then load to failure) and transient (hold load, increase temperature to failure) temperatures. Loss of tensile strength and modulus at elevated temperature is thought to be due to polymer resin matrix softening and loss of load transfer capability from fiber to fiber, whereas failure of the tensile bond strength between the two laminates is believed to be due to the degradation of the polymer resin matrix material. Analysis of variance (ANOVA) one-way statistical analysis has shown that CFRP composite specimens have a statistically significant loss in tensile strength, stiffness, and bond strength as the test temperature was increased but are not statistically significant when grouped above and below the glass transition temperature.