Residual tensile behavior of carbon fiber/phthalonitrile composites after isothermal and anisothermal heating

The residual mechanical properties of resin-based composite materials exposed to high-temperature environments will significantly decrease. Phthalonitrile has great potential to serve as the matrix for new-generation lightweight resin-based thermal protection composite material, while the residual mechanical properties of phthalonitrile composites after thermal effect have not been fully studied and are pressing. In this study, the residual tensile behavior of unidirectional carbon fiber-reinforced phthalonitrile composites after isothermal and anisothermal heating are investigated. The strength attenuation of carbon fibers in high-temperature environments is the main factor causing the decrease in the tensile strength of carbon fiber reinforced phthalonitrile composites, while the thermal decomposition of phthalonitrile resin has a relatively small impact. The residual tensile strength prediction models with high fitting accuracies based on pyrolysis degree and mass loss are constructed for materials subjected to isothermal and anisothermal heating, respectively. Unidirectional carbon fiber reinforced phthalonitrile composites have higher tensile strength retention after isothermal and anisothermal heating compared to those with quasi-isotropic layup.