Recent Advancements for Simulating Long Glass Fiber Composites in Injection Molding Applications

 Recent Advancements for Simulating Long Glass Fiber Suspensions in Injection Molding Applications

Kevin J. Meyer, John T. Hofmann, and Donald G. Baird

            The properties of fiber-filled composites are strongly influenced by the orientation of the fibers within the composite structure. A popular way to reinforce composite materials cheaply is through the introduction of both short glass fibers (SGF) and long glass fibers (LGF) into the polymer matrix. This allows current industrial molding techniques to be utilized with little or no modification while significantly increasing the molded part's properties. Traditionally the Folgar-Tucker model, with the addition of a delay parameter, has been employed to predict fiber orientation in injection molded parts and has attained wide success when the fibers are short . In suspensions where the glass fibers can be considered long  bending of fibers has been seen as a consequence of complex flow fields which arise in injection molding. The modified Folgar-Tucker model becomes less accurate as the flexibility of fibers increases. Hence, the “Bead-Rod” model, where the semi-flexible fiber is represented as two rods connected by a hinge, is proposed as an alternative to the modified Folgar-Tucker model. The Folgar-Tucker and Bead-Rod models are used to predict fiber orientation in center-gated and end-gated test geometries for LGF systems. Predictions for both models are compared to experimentally obtained data of long fiber orientation. The Bead-Rod model is observed to agree more closely with experimentally observed LGF orientation than the modified Folgar-Tucker model at a number of sampling points through the mold cavity.