LAUSR

Abstract Anisotropic rotary diffusion (ARD) has proved useful for modeling fiber orientation in molding of discontinuous-fiber composites. A number of ARD models have been proposed, but it has been difficult to compare models or understand the effects of each model’s parameters. We cast the framework laid out by Phelps and Tucker (JNNFM, 2009) into a new form that reveals the scalar magnitude and tensorial “direction” of rotary diffusion for each model. Existing models are compared in this framework. We illustrate the parameter values needed by each model to fit a steady-state orientation in simple shear flow and briefly discuss the behavior of the fitted models in planar elongational flow. The transient overshoot of flow-direction orientation at startup of simple shear varies considerably; however, the transient of the fourth-order component that governs shear stress is very similar among ARD models. Maps of achievable orientation states in steady simple shear are presented; these maps provide first-order estimates of the model parameters needed to fit experimental data.