The performance of fiber reinforced polymer (FRP) composites at high temperatures is a serious concern that needs investigation before the incorporation of these composites into important engineering structures. This article presents an experimental study on the tensile properties of carbon fiber reinforced polymer (CFRP) sheets, hybrid carbon/glass fiber reinforced polymer (C/GFRP) sheets and hybrid carbon/basalt fiber reinforced polymer (C/BFRP) sheets at different temperatures. The specimens of FRP sheets were tested at temperatures ranging from 16 to 200°C, while corresponding dry fiber sheets (without resin impregnation) were tested at 16°C as a reference. The test results show that the tensile strength of carbon fibers in different FRP sheets decreases significantly with increasing temperature, and remains almost stable at an ultimate value (3000 MPa) after the polymer exceeds its glass transition temperature (T g), which is higher than the tensile strength of the non-impregnated fiber sheets at room temperature. At elevated temperatures, the hybridization of fibers can reduce the scatter of the tensile strengths of CFRP composites. Additionally, the tensile strength of CFRP sheets with different dimensions is significantly different, but size dependence is independent of temperature. Furthermore, elevated temperature also influences the failure modes of FRP composites.
To predict temperature-dependent tensile strength of unidirectional CFRP composites, numerical analysis and model simulation were conducted in terms of experimental results. The effect of elevated temperatures on tensile strength of CFRP sheets was evaluated between 20 C and 120 C, and the storage moduli of two types of epoxy resins, with glass transition temperatures (T g ) of 42 C and 45 C, were tested by DMA. The tensile experiments of CFRP sheets show that the tensile strength exhibits stable behavior at the low-temperature range (below glass transition temperature), but drops rapidly during the glass transition region, and then reaches a plateau. Analysis results indicate that the degradation of tensile strength is mainly due to matrix softening and loss of fiber-matrix adhesion, based on which a semi-empirical model is proposed to precisely describe tensile strength reduction as the temperature increases. The parameters of the model consist of the glass transition temperature of polymer matrix, the polymer glass transition region, and the residual strength after the glass transition region. Model prediction of tensile strength vs. temperature shows good agreement with the experimental results.
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