Comparison of the flow and rheological behavior of two semi-structural sheet-molding-compound (SMC) based on a hybrid resin and glass or carbon fibers

For a realistic process simulation of sheet molding compound (SMC), comprehensive and reliable viscosity data are essential. As the mean fiber-length in SMC is similar to the sample size of shear rheometers, an alternative rheology tool and method was developed. Therefore, a molding tool for the compression molding process was equipped with pressure sensors. By means of this tool, the pressure distribution was measured and thus the rheological behavior of two semistructural SMC systems consisting of a hybrid UPPH resin with glass or carbon fibers were estimated. The characterization of the carbon SMC is performed by using a previously developed compressible rheological shell-model [5]. This shell model describes the SMC rheological behavior during 1D flow by considering the elongation flow in the core and the thin resin rich outer lubrication layer. In contrast, the glass fiber SMC shows a significantly different pressure distribution and thus different flow behavior. It shows a significant pressure peak at the flow-front, which decreases after a certain flowlength and then follows the classical SMC pressure behavior. This cannot be modeled by the compressible shell-model, nor any other available SMC related model. Therefore, a new approach has to be developed. By comparing these two SMCs with their different fiber types, concepts to model the flow behavior of the hybrid glass SMC is presented.