Process Simulation of Sheet Molding Compound (SMC) using Direct Bundle Simulation

Discontinuously reinforced polymers are widely used in lightweight design, because they can be economically pressed in complex shapes. The manufacturing process induces a re-orientation of fibers during the flow, which is of interest for quality assurance and structural computations. Typically, the re-orientation is described with an evolution equation for the second order fiber orientation tensor, which requires a closure approximation and multiple empirical parameters to describe long fibers. However, we observed in CT scans of SMC microstructures that fiber bundles stay intact during the molding process. Therefore, bundles are directly simulated as 1-D Elements using Stokes’ drag forces on bundle segments and opposing forces on the fluid field. The method is applied to SMC specimens with a double-curved geometry and with different positions of initial charges. The results are compared to conventional approaches employing a fiber orientation tensor and to CT scans of accordingly manufactured SMC specimens.