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A Fast Method for Evaluating Effects of Process Parameters on Morphology of Semi-Crystalline Thermoplastic Composites



Semi-crystalline thermoplastics such as PEEK have microstructures that are influenced by process parameters like temperature cycle, humidity, and oxygen levels. Inclusions such as carbon fibers lead to heterogenous crystal nucleation. Further, manufacturing uncertainties involved with techniques such as automated fiber placement, compression molding, or induction welding influence the microstructure of thermoplastic composites. These contributing factors impact type (e.g., spherulitic, cross-linked, transcrystalline, and needle-like), size and distribution of morphologies in the material. Even with similar degrees of crystallinities, these differences affect mechanical properties and overall performance of composite parts. In this study, an experimental method has been developed that allows for fast evaluation of morphology as a function of process parameters in semi-crystalline thermoplastic composites. A compression fixture in a Dynamic Mechanical Analyzer (DMA) is used to process thin films of thermoplastics with embedded carbon fibers, sandwiched between thin glass covers, while carefully controlling processing conditions including temperature, pressure, and strain rate. The sample morphology is then analyzed using through transmission Polarizing Light Microscopy (PLM). Samples can be reprocessed using DMA several times to analyze changes in microstructure. This experimental approach allows for fast exploration of timetemperature- transformation relationships and their effects on morphology. This can be used to enhance our understanding of the material microstructure and develop more accurate process simulation tools, leading to optimization of processing parameters.


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