Predictive Thermal Modeling and Characterization of Ultrasonic Consolidation Process for Thermoplastic Composites

Ultrasonic consolidation (USC) of thermoplastic composites is a highly attractive and promising method to manufacture high-performance composites. This work focuses on USC of dry carbon fiber (CF) fabrics with high-temperature polyphenylene sulfide (PPS) films. Experimental trials to assess feasibility of the process are time-consuming. Conse-quently, a predictive thermal model would facilitate process parameters selection to reduce expensive trial-and-error approaches. This paper presents a 2D finite element model of samples under consolidation, incorporating equations for viscoelastic heating, matrix phase change, and material properties. Theoretical temperature profiles for nodes of interest were compared to the corresponding experimental temperature curves for various control parameters (i.e., weld time and vertical displacement of sonotrode) and showed good agreement during heating phase. It was found that welding time values below 1750 ms were insufficient to reach melting temperature, whereas weld times above 3000 ms led to the lowest average void content (2.43 +/- 0.81%). More specifically, the time the material spent above melting temperature, i.e., residence time, was established as a parameter that could estimate cases resulting in better consolidation and lower void content (time above 2600 ms for void content below 2.5%). X-ray diffraction (XRD) char-acterization revealed that the USC process led to mostly amorphous PPS, due to the high cooling rates (70 degrees C/s to 108 degrees C/s). Overall, the thermal model and micro-structural out-comes confirmed the feasibility of the USC process for layered composites made from dry fabric and high-temperature thermoplastic films.

Automated summary

Ultrasonic consolidation (USC) is a promising method for manufacturing high-performance composites. This study focuses on USC of dry carbon fiber fabrics with high-temperature polyphenylene sulfide films. A 2D finite element model was developed to predict the thermal behavior during consolidation, and it showed good agreement with experimental results. The study also identified optimal welding time values and highlighted the importance of residence time in achieving better consolidation. X-ray diffraction characterization revealed that the USC process resulted in mostly amorphous PPS due to high cooling rates. Overall, the study confirms the feasibility of USC for layered composites.