Investigation of dense suspension rotary diffusion models for fiber orientation predictions during injection molding of short-fiber reinforced polymeric composites.

There is a need for physics-based mathematical models for the design of industrial short-fiber reinforced composites (SFRC) to predict the fiber orientation within the part. Traditional models for fiber interactions use the isotropic rotary diffusion model of Folgar and Tucker, but there is considerable interest to use the Phelps and Tucker anisotropic rotary diffusion model. Both models predict the flow induced orientation, which directly determines the resulting stiffness of an injection molded part. These two models are investigated in the present work. A number of fourth order orientation tensor closure approximations are investigated for both diffusion models, with the goal being to suggest the more effective and efficient closure approximation for a variety of flow conditions. Differences in the resulting elastic properties predicted from the two rotary diffusion models are observed. These observations raise questions as to which diffusion model should be used commercially for injection molded SFRCs.