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In this paper, we report on optical coherence tomography (OCT) for the investigation of glass–fibre reinforced polymer (GFRP) materials. OCT, a contactless and non-destructive imaging technique, provides depth-resolved information on internal structures within semi-transparent materials. In our study, we apply a highly advanced OCT technique: we use a transversal scanning, ultra-high resolution, polarisation-sensitive (UHR-PS)-OCT for the analysis of various GFRP samples. UHR-imaging with resolution in the micron range is shown to provide information on the scale of single fibres. PS-OCT, an extension of classical OCT, is sensitive to birefringence and consequently to anisotropies and stress within a material. Our system is therefore applied to the investigation of defects located within the fibre layers of loaded and damaged GFRP samples. Imaging of matrix fracture, cracks, and internal stress, demonstrates the high potential of UHR-PS-OCT for the investigation of damage in GFRP materials, with special emphasis on detecting the early stages of defect formation.

Optical coherence tomography (OCT), originally developed and so far nearly exclusively used for biomedical applications (e.g., [1,2]), is a contact-free, non-destructive technique based on low-coherence interferometry to image structures within translucent and turbid materials. Commonly, cross-sectional reflectivity images with a depth-resolution determined by the coherence length of the near-infrared light source are obtained. When OCT is performed in a polarization sensitive way (PS-OCT), additional information about birefringence within a material is obtained by mapping the retardation between ordinary and extraordinary rays [3]. Because birefringence is induced when strain occurs, PS-OCT provides depth resolved information about the internal stress within a sample.

Optical coherence tomography (OCT) is a contactless and non-invasive technique nearly exclusively applied for bio-medical imaging of tissues. Besides the internal structure, additionally strains within the sample can be mapped when OCT is performed in a polarization sensitive (PS) way. In this work, we demonstrate the benefits of PS-OCT imaging for non-biological applications. We have developed the OCT technique beyond the state-of-the-art: based on transversal ultra-high resolution (UHR-)OCT, where an axial resolution below 2 μm within materials is obtained using a femtosecond laser as light source, we have modified the setup for polarization sensitive measurements (transversal UHR-PS-OCT). We perform structural analysis and strain mapping for different types of samples: for a highly strained elastomer specimen we demonstrate the necessity of UHR-imaging. Furthermore, we investigate epoxy waveguide structures, photoresist moulds for the fabrication of micro-electromechanical parts (MEMS), and the glass-fibre composite outer shell of helicopter rotor blades where cracks are present. For these examples, transversal scanning UHR-PS-OCT is shown to provide important information about the structural properties and the strain distribution within the samples.