COMPARISON OF X-RAY COMPUTED TOMOGRAPHY AND OPTICAL COHERENCE TOMOGRAPHY FOR CHARACTERISATION OF GLASS-FIBRE POLYMER MATRIX COMPOSITES J. Kastner 1 , E. Schlotthauer 1 , P. Burgholzer 2 , and D. Stifter 2 1 University of Applied Sciences Upper Austria, Wels, Austria, 2 Upper Austrian Research GmbH, Linz, Austria Abstract: Glass-fibre reinforced polymer matrix composites exhibit superior properties to traditional materials. Thus, they have found a broad variety of applications in modern industry. For process development and quality control of polymer matrix composites sophisticated methods for non- destructive characterisation are needed. Especially for the inspection of complex geometries or critical features located inside the materials, non-destructive testing imaging technologies are of big advantage and often necessary. Optical coherence tomography (OCT) is a novel non-invasive technique, which permits high-resolution cross-sectional imaging. OCT has been originally developed for medical diagnostics, especially for the detection of eye diseases. Just recently the potential of OCT has been discovered also for non- destructive analysis of materials. In this paper we compare OCT with the more traditional method of X- ray micro-3D computed tomography (µ-CT). We outline the advantages and disadvantages of both methods for characterisation of glass fibre epoxy compound material and related composites. OCT does an excellent job of clearly imaging fibre-reinforced composites including detection of voids and heterogeneities (for instance “dry spots”) and fibre structure on micrometer scale. µ-CT is capable of delivering high-resolution 3D images of the reinforcement microstructure of the entire sample and is not limited in depth like OCT. OCT does not work for strongly absorbing materials, whereas CT works for any material. The measurement costs of OCT are much lower than the costs of µ-CT. OCT can be also used for in-line inspection, which is a big advantage for industrial quality control. Introduction: Polymer fibre composites have an increased stiffness and increased strength to weight ratio compared to metallic and other “traditional” materials. Therefore the applications of these materials become more and more important in modern industry [1,2]. Non-destructive and contact-free techniques (NDT) for the characterisation of fibre composites face an increasing demand in process development and production, especially for the inspection of complex geometries and critical features located inside the materials [2-7]. Optical coherence tomography (OCT) permits in a rather simple and fast way high-resolution cross- sectional imaging of turbid and transparent media on micrometer scale. OCT has been originally developed for medical diagnostics. Just recently the potential of OCT has been discovered also for non-destructive analysis of materials, in particular for the characterisation of fibre composites and polymer laminate structures [3,5]. Computed tomography (CT) is a radiographic NDT-method to locate and size volumetric details in three dimensions. A CT-scanner generates a series of X-ray attenuation measurements, which are used to produce computed reconstructed images of an object. In the last years µ-CT systems with a matrix detector and a micro-focus tube become more and more popular. The main advantages of these systems are the reasonable high scanning speed and the high resolution. There are several reports in literature about the application of CT for the characterisation of fibre composites [2,5-9]. Especially in automotive and aerospace industry µ- CT is widely used for non-destructive testing of fibre composites [2,5]. In this paper we outline the advantages and disadvantages of optical coherence tomography and µ- computed tomography for characterisation of glass fibre compound materials and related composites. Experimental: The materials investigated are a liquid moulded glass fibre reinforced epoxy composite (GF-Epoxy) with a fibre diameter of 25-30 µm, a glass fibre epoxy tissue (GF-Tissue) with a fibre diameter of 9-12 µm, and a carbon fibre reinforced polyetheretherketone (CF-PEEK) with a fibre diameter of 5-6 µm. The main data of these materials are summarized in the following table. Material Matrix Matrix-density (g/cm 3 ) Fibre Fibre-diameter (µm) Fibre-density (g/cm 3 )