Comparison of recent fiber orientation models in injection molding simulation of fiber-reinforced composites

In the structural analysis of automotive products made of lightweight fiber-reinforced thermoplastics (FRT), the primary mechanical requirement is their relation to the orientation states of fibers. The famous Folgar-Tucker equation of fiber orientation has hitherto been used to predict the skin-shell-core structure of fiber orientation patterns for injection-molded fiber composites. However, this model results in inaccurate predictions regarding the thinner core width. To enhance the reliability of fiber orientation predictions, Tucker and coworkers rigorously derived the reduced strain closure and anisotropic rotary diffusion (ARD) models in relation to the theoretical rheology of fiber suspension. More recently, the improved ARD and retarding principal rate model and the Moldflow rotational diffusion model were developed and made available in the industry dealing with the state-of-the-art software of injection molding simulation. A deep understanding of these fiber models is important for achieving successful FRT structural analysis. In this work, we therefore investigate the accuracy of these fiber orientation models, as well as the changes in fiber orientation distribution related to model parameters and model objectivity.