Hydrostatically extruded glass fiber reinforced polyoxymethylene. II: Modeling the elastic properties

This paper describes an investigation into modeling the elastic properties of hydrostatically extruded short glass fiber reinforced polyoxymethylene (POM). The starting material for the extrusion was randomly arranged short glass fibers (25 wt%, average length 150 μm) in an isotropic POM matrix. Extrusion was carried out through a reducing conical die at 15°C below the melting point of the matrix phase (hence the composite was extruded in the solid state), such that after extrusion, preferential alignment along the extrusion direction was developed for both the fibers and for the crystalline fraction of the polymer matrix. The elastic properties of samples, made over a range of extrusion ratios, were measured using the ultrasonic immersion method, a technique that allows a complete set of elastic constants to be determined for a composite. Theoretical predictions for the elastic properties of the oriented extrudates were generated by combining a modification to the theory of Wilczynski to allow for the fibers' being surrounded by an oriented matrix phase, together with the aggregate model of Ward to model the effects of partial orientation of the fiber oriented matrix units.