Automated measurement of 3-D fiber orientation distribution in injection-molded composites

In order to model short fiber composites adequately it is essential to have an accurate measure of the distribution of fiber orientation within the material. Unfortunately, short fiber composites often possess complex three-dimensional distributions which are very difficult to measure. Current surface-analysis based techniques have limited ability to measure orientation components which are perpendicular to the cutting plane, and are incapable of measuring fiber length, which is essential for a correct representation of the fiber orientation distribution. Hence, there is relatively little known about flow-induced fiber orientation and the relationships between fiber orientation and material properties.;A new technique which overcomes these problems is based on optical microscopic sectioning of transparent composites with opaque tracer fibers. With this method a complete 3-D description of the material structure is obtained, from which the fiber orientation distribution is determined by 3-D image analysis. The results from transparent systems can be generalized to more common opaque systems through non-dimensional analysis.;An experimental injection molding apparatus and an imaging system were developed to manufacture and analyze sample materials. Calibration tests demonstrated the ability of the system to measure the orientations of individual fibers 600 ;The potential of this approach has been demonstrated by investigating the influence of a cylindrical obstacle in the gate of an injection mold on the material properties and flow-induced fiber orientation of rectangular coupons.;The present method is compared quantitatively with published fiber orientation distribution results obtained with a standard surface analysis method and found to be at least as accurate and several times faster when specimen preparation time is considered.