Inherent relationship between process parameters, crystallization and mechanical properties of continuous carbon fiber reinforced PEEK composites

High-performance thermoplastic composites have been developed as significant structural materials for cutting-edge equipment in the aerospace and defence fields. However, the internal mechanism of processing parameters on mechanical properties in the manufacturing process of thermoplastic composite structures is still a serious challenge. The purpose of this study is to investigate the process/crystallization/property relationships for continuous carbon fiber (CF) reinforced polyether-ether-ketone (PEEK) composites. The composite laminates are fabricated according to orthogonal experiments via the thermoforming method. The mechanical performance is investigated in terms of crystallization properties and fracture morphology characterizations. Experimental results show that the mechanical performance and crystallization properties of thermoplastic composites are significantly affected by the coupling of processing parameters. The increased molding temperature, pressure, and holding time improve the degree of fiber/matrix infiltration and affect the crystallinity and crystalline morphology of the matrix, which further influences the mechanical properties of the composites. This is reflected in the test results that crystallinity has an approximately linear effect on mode-I interlaminar fracture toughness and transverse flexural modulus. As well as the higher molding temperature can destroy the pre-existent crystals to improve the toughness of the matrix, and the well-defined crystalline structures can be observed when fabricated at higher temperatures and longer periods of holding time.