The use of shear-rate-dependent parameters to improve fiber orientation predictions for injection molded fiber composites

Fiber orientation distribution in injection molded fiber composites has an important shell-core structure. Recently, significant theoretical orientation models, including RSC (Reduced Strain Closure), ARD (Anisotropic Rotary Diffusion), and iARD-RPR (improved ARD and Retarding Principal Rate), have been widely applied in commercial injection molding simulation software. However, there is a long-running problem requiring an urgent solution for the state-of-the-art predictive models: obvious deviation of fiber orientation was found in the core region, although the orientation in the shell layer was predicted well. According to the fiber motions of flow-induced orientation, we therefore aimed to introduce a relationship between the model parameters and the shear rate. As validation, the shear-rate-dependent parameters can effectively enhance the prior orientation results for short-glass-fiber composites and long-carbon-fiber-composites in injection molding simulations, with good agreement between the present predictions and the experimental data obtained thereby.