Determination of diameter, length and three-dimensional distribution

Short glass-fibre reinforced polymer matrix composites exhibit superior properties compared to traditional materials. Thus, they have found a broad variety of applications in modern industry. For process development and quality control sophisticated methods for non-destructive characterisation are needed. X-ray computed tomography(CT) is a powerful radiographic non-destructive-testing method to locate and size volumetric details in three dimensions. The main advantages of μ-CT systems based on a matrix detector and a micro-focus tube are the reasonable high scanning speed and the high resolution. This paper comprises the characterisation of short glass-fibre reinforced injection moulded parts by μ-CT to measure diameter, length and the three-dimensional orientation of the contained fibres. For this respect μ-CT-measurements with resolutions between 15 μm and 5 μm were done on fibre reinforced polybutylene terephthalate and polypropylene with fibre diameters of about 13 μm. Samples were prepared with fibre loadings between 10 and 30 volume percent and injection flow rates between 5 and 140 cm3/s. For comparison and verification one sample was studied at the European Synchrotron Radiation Facility (ESRF) in Grenoble with a resolution of 0.7 μm. In addition the experimental results were compared to simulation results of the injection moulding process using Moldflow. It is shown that μ-CT is a very powerful method for the characterisation of glassfibre reinforced polymers. The diameter can be determined by μ-CT if the resolution is at least a factor 2 better than the diameter itself. Length and three-dimensional distribution of glass fibres can be determined even at a limited resolution that equals the fibre diameter. The experimental CT-results correspond to the calculated fibre orientation in the injection moulded part quite well. However, the strength of the orientation of the fibres is overestimated by Moldflow as compared to the CT-results.