EXPERIMENTAL EVALUATION OF THE ORIENTATION OF LONG , SEMI-FLEXIBLE GLASS FIBERS IN COMPLEX 3-DIMENSIONAL FLOW

The experimental orientation of long, semi-flexible glass fibers has been evaluated in complex 3-dimensional flow. The system selected for this study consisted of a polypropylene matrix and long glass fibers with an average post-processing length and aspect ratio of approximately 3.9 mm and 300, respectively. Preliminary experimental values of long fiber orientation were obtained within injection molded end-gated plaques at multiple percentages of plaque length and width, including the areas of complex flow near the mold side walls. Additionally, experimental values of orientation were obtained within the sprue and gate region of the injection molded parts. Unlike in the axisymmetric center-gated disc, the end-gated plaque features a fully 3-dimensional velocity profile, resulting in complex fiber orientation behavior and increased curvature near the mold side walls as well as near the gate region. Modification of the experimental method for measuring fiber orientation in these regions due to the increased length and flexibility of long fibers is included. Background The use of glass fibers as reinforcing agents in polymer composites has been the focus of research for several decades. The addition of reinforcing fibers to a polymer matrix has resulted in improved mechanical properties, including an increase in stiffness, fracture toughness, and strength-to-weight ratio [1-3]. The mechanical properties of a part are dependent on final length and orientation of the fibers within the polymer matrix, with longer fibers generally leading to a greater enhancement in mechanical properties [3-5]. Glass fiber suspensions, however, maintain the benefit of being melt processable and can thus be processed via injection or compression molding. Glass fibers are commonly segmented into two separate categories based upon average, post-processing fiber length [6]. Short glass fibers composites have an average fiber length, l, of less than 1 mm, with typical values observed commercially of approximately 0.3 mm. Short glass fibers (SGF) are assumed to behave as rigid rods in flow and thus during processing, and a number of recent studies have focused on the evaluation of the predicted and experimental orientation evolution [7-9]. Long glass fibers (LGF), however, have average lengths in excess of 1 mm, and may exhibit flexibility and curvature during flow, and thus during processing such as the filling of an injection mold. The added complexities of LGF may result in increased difficulty not only in the prediction of fiber orientation evolution during flow and processing but also in the determination of the experimental fiber orientation distribution (FOD), particularly within complex geometries which exhibit a fully 3-dimensional filling profile [10]. The goal of this paper is to evaluate the experimental fiber orientation distribution of long, semi-flexible fibers within the end-gated plaque (EGP), a geometry which exhibits a fully 3dimensional flow field and is thus significantly more complex than the previously studied center-