Crystallization mechanism and mechanical properties of CF/PPS thermoplastic composites manufactured by laser-assisted automated fiber placement

In situ consolidation of the thermoplastic composites can be realized through laser-assisted automated fiber placement technology, and the properties of the composites are significantly affected by the crystallinity. Understanding the complicated crystallization process is very important for controlling the performance of the composites manufactured by automated fiber placement. In this work, the crystallization mechanism of carbon fiber/polyphenylene sulfide composites during the automated fiber placement process and its effect on the mechanical properties were investigated. Crystallization kinetics analysis indicated that the crystallization window of the carbon fiber/polyphenylene sulfide composites was 87–270°C. Furthermore, for carbon fiber/polyphenylene sulfide composites manufactured by automated fiber placement, the crystallinity was influenced by the parameters including laser temperature, placement speed and tool temperature, in which the tool temperature was the main factor. Increasing the tool temperature was an effective method to achieve high crystallinity. Meanwhile, when the tool temperature was in the range of the crystallization window, the composites could experience isothermal crystallization, which could further improve the crystallinity. With the increase of the tool temperature, the flexural strength and interlaminar shear strength were improved due to the enhanced self-adhesion of the matrix, while the Mode І fracture toughness was decreased because of the reduction of the matrix ductility. The combination of the kinetic method and experimental study was conducive to a better understanding of the crystallization mechanism and optimization of the processing conditions.