No abstract

No abstract

This paper describes the determination of fiber and matrix orientation in oriented short‐glass‐fiber‐reinforced polyoxymethylene (POM) composites produced by hydrostatic extrusion. The starting material was random glass fibers (25 wt% and average length 150 μm) in an isotropic POM matrix, and the oriented composites were produced by extrusion through a reducing conical die at 15°C below the polymer melting point: after extrusion the average fiber length was reduced slightly to 133 μm. Fiber orientations were measured using an image analysis method developed at Leeds University, and the matrix orientation was determined using wide angle X‐ray diffraction. The development of fiber orientation with extrusion ratio was found to be close to that predicted by the pseudo‐affine deformation scheme although the fiber orientation was greater than that predicted by the model at low draw ratios and slightly less at the highest draw ratio. The development of the orientation of the crystalline portion of the matrix was found to be always significantly greater than that predicted by the pseudo‐affine scheme.

No abstract

Summary High‐quality data on the three‐dimensional (3‐D) spatial distributions of glass and carbon fibres in fibre‐reinforced polymer composites are important for both process control and the modelling of the mechanical and thermal properties of these composites. The advent of economical, high‐speed, image analyser systems has enabled numerous research groups to measure directional distributions of fibre samples. Specimens are microtomed and polished and, using optical reflection microscopy, thousands of elliptical fibre images may be analysed within a short period of time. From the eccentricity of the fibre images, estimation of the angles (θ, φ) of each fibre relative to the vertical axis and within the measurement plane is deduced. However, this measurement is subject to considerable error. The confocal scanning laser microscope (CSLM), operating in fluorescence mode or reflection mode, is capable of improving the angular resolution (δθ, δφ) for all fibre directions. The ability of the CSLM to optically section glass and carbon fibre‐reinforced polymer composites down to depths of 20 or 30 μm allows the user to determine accurate fibre directions from the apparent movement of fibre profiles. The CSLM has the potential for standardizing measurements of 3‐D fibre directions in polymer composites and providing the quality directional data which are required for the theoretical modelling of composite processing and composite strength.