Rheological measurements and rheological shell model Considering the compressible behavior of long fiber reinforced sheet molding compound (SMC)

For a realistic process simulation of sheet molding compound (SMC), comprehensive and reliable viscosity data are essential. As the fiber-length in SMC is as long as the sample size of shear or rotation rheometers, an alternative rheology tool method was developed. To improve the quality of this method, a molding tool was equipped with seven pressure sensors. By means of this tool, compressibility of a semi-structural SMC was observed during the molding process. To consider this behavior, an empirical approach is proposed to describe the material compressibility in terms of relative volume change. By adding this approach to the rheological shell-model proposed by Dumont, good agreement with experimental measurements is achieved.With the new tool design, a single molding trial is sufficient to generate a series of pressure data over the flow length. This leads to an improved quality of viscosity-data and to faster results due to fewer molding trials.