Effect of temperature on the fiber/matrix interfacial strength of carbon fiber reinforced polyamide model composites

Carbon Fiber Reinforced Thermoplastics (CFRTP) have attracted attention in the automotive industry for their productivity and high specific strength and modulus. To guarantee the durability of CFRTP, it is important to understand the mechanical properties of CFRTP under practical service temperature. Since the mechanical properties of CFRTP are affected not only by reinforcement fibers and matrix resins but also by the fiber matrix interface, to reveal the fiber/matrix interface properties is one of the important issues to be solved. Among thermoplastic resins, polyamide (PA) is expected to be used for the matrix of CFRTP, owing to good interfacial adhesion to the carbon fiber, and good moldability. Although tensile tests of CFRTP under the high temperature environment were performed, the effects of temperature on the fiber/matrix interfacial shear strength have not been fully clarified. In this study, in order to evaluate the fiber/matrix interfacial properties at 25 degrees C, 40 degrees C and 80 degrees C, single fiber pull-out tests, measurement of the thermal expansion coefficient of the resin, and analysis of the thermal expansion of the resin were performed. As temperature rose, resin expanded and interfacial shear strength of the CF/PA model composites decreased. This result suggests that the decrease of the interfacial shear strength by temperature rise is caused by the expansion of the resin.