(317a) Insights into Frictional Properties of Carbon Fiber Epoxy Composites Characterized Using Parallel-Plate Rheometry

Composite materials have received much attention as they are widely used in applications where lightweight structures are needed to exhibit superior performance. However, the quality of composite parts manufactured in traditional molding and tape laying processes is influenced by the friction present during the composite forming process. Defects in composite material manufacture include wrinkling and shape distortion, caused by the friction between the tool and laminate surface. Frictional measurements can vary depending on processing parameters, technique, and instruments used. The frictional properties are also dependent on the forming process parameters such as temperature, pressure, and sliding velocity. Therefore, an understanding of the relationship between material properties and the tooling process is of paramount importance in optimizing composite forming processes.

In this work, we develop a rheological approach to characterize tool-ply friction in carbon fiber epoxy prepregs. A commercial rheometer coupled with custom machined parallel plates having annular ring geometry was used to study how processing conditions affect the viscoelastic and frictional sliding properties of a carbon fiber epoxy prepreg system. Rheological measurements suggest that the prepregs exhibit frictional sliding behavior observed in the mixed lubrication regime where there are significant contributions from both Columbic and viscous friction. The effect of sliding rate on the contact between the prepreg and the rheometer plate was monitored by in-situ microscopy. The evolution of contact area during the test significantly affects the frictional response and finding a quantitative estimation will help in interpreting the results from the sliding tests. Surface imaging results using an optical microscope confirmed fiber deformation and distortion in samples tested at higher temperatures. The overall results indicate that the frictional behavior of the thermoset prepreg system is dependent on the contribution of adhesive and load forces, where the frictional sliding behavior between the tool-ply system can be controlled by altering the processing parameters within a design window.