CURRENT EFFORTS IN SIMULATING THE INJECTION MOLDING OF SHORT AND LONG GLASS FIBER COMPOSITES

摘要

The properties of fiber-filled composites are strongly influenced by the orientation of the fibersrnwithin the composite structure. A popular way to reinforce composite materials cheaply isrnthrough the introduction of both short glass fibers (SGF) and long glass fibers (LGF) into thernpolymer matrix. This allows current industrial molding techniques to be utilized with little or nornmodification while significantly increasing the molded part’s properties. Traditionally thernFolgar-Tucker model, with the addition of a delay parameter, has been employed to predict fiberrnorientation in injection molded parts and has attained wide success when the fibers are shortrn(L/d < 20). Commercial software aiming to predict short fiber orientation use various simplifyingrnassumptions such as Hele-Shaw flow that discards the effects of the advancing front and thernfountain flow behind it. Fountain flow plays a significant role in orientation of fibers, especiallyrnnear the walls. The pseudo-concentration method is utilized to account for the fountain flowrnphenomena in our simulations of SGF systems and is compared to experimental data.rnIn suspensions where the glass fibers can be considered long (L/d > 50), bending of fibers hasrnbeen seen as a consequence of complex flow fields which arise in injection molding. Thernmodified Folgar-Tucker model becomes less accurate as the flexibility of fibers increases.rnHence, the “Bead-Rod” model, where the semi-flexible fiber is represented as two rodsrnconnected by a hinge, is proposed as an alternative to the modified Folgar-Tucker model inrnmodeling LGF orientation. The Folgar-Tucker and Bead-Rod models are used to predict fiberrnorientation in center-gated and end-gated test geometries for LGF systems. Predictions for bothrnmodels are compared to experimentally obtained data of long fiber orientation. The Bead-Rodrnmodel is observed to agree more closely with experimentally observed LGF orientation than thernmodified Folgar-Tucker model at a number of sampling points through the mold cavity.