Colloquia

Samenvatting

Thermoplastic composites (TPCs) find increasing application in areas such as aerospace and automotive due to their excellent mechanical properties and rapid manufacturing techniques. Hot press forming is such a rapid manufacturing process, and involves the forming of a pre-heated flat laminate into a three-dimensional curved part. To achieve the goal of first-time right production of TPC parts, accurate forming simulation software is required to optimize the process and predict and prevent the formation of defects. An important material behaviour to characterize for these simulations is the ply-ply friction in melt. High ply-ply friction may lead to defects that compromise mechanical performance of the formed part. This research expands on previous work by investigating the effect of fiber orientation on the ply-ply friction during processing conditions.

Friction tests of various specimen layups of unidirectional carbon fiber-reinforced low-melting polyaryletherketone (C/LM-PAEK)  plies were performed over a range of pressures and sliding rates using a newly developed friction tester. The resulting shear stress responses showed a low standard deviation and specimen integrity was well retained, demonstrating the reliability and validity of the results. Specimens with aligned fibers showed the highest friction due to nesting of the fibers reducing the matrix interlayer thickness, a phenomenon impossible for plies with relative orientations. Significant differences in friction were observed between specimens with parallel plies and those with different relative orientations, confirming fiber angle as a key factor in frictional behaviour.

Models in MatLab and COMSOL were created to gain insight in the driving mechanisms behind the shear stress responses. The models shed light on the matrix interlayer thickness distribution and matrix flow dynamics and their effect on the friction response of various fiber orientations. Observations from these models confirmed the effect of fiber nesting on friction, and revealed the complex matrix flow behaviour in oriented specimen layups. The obtained knowledge and characterized data will support the accuracy of forming simulations, contributing to more reliable predictions of defect generation in TPC part production.