Characterisation of artificial defects in CFRP and GFRP sheets designed for energy applications using active thermography by C. Maierhofer 1 , R. Krankenhagen 1 , M. Röllig 1 , B. Rehmer 1 , M. Gower 2 , G. Baker 2 , M. Lodeiro 2 , A. Aktas 2 , L. Knazovicka 3 , A. Blahut 3 , C. Monte 4 , A. Adibekyan 4 , B. Gutschwager 4 1 Federal Institute for Materials Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany, christiane.maierhofer@bam.de 2 NPL National Physical Laboratory, Materials Division, Hampton Road, Teddington, Middlesex, TW11 0LW, UK, Michael.Gower@npl.co.uk 3 CMI Czech Metrological Institute, ČMI OI Praha, Radiová 3, 102 00 Praha 10, Czech Republic, lknazovicka@cmi.cz 4 PTB Physikalisch Technische Bundesanstalt, Abbestrasse 2 – 12, 10587 Berlin, Germany christian.monte@ptb.de Abstract The increased use of fibre-reinforced plastic (FRP) composites for improved efficiency and reliability in energy related applications e.g. wind and marine turbine blades, nacelles, oil and gas flexible risers, also increases the demand for innovative non-destructive testing technologies. Thus, in order to achieve increased acceptance of suited and optimized non-destructive testing (NDT) methods in industry, the European Metrology Research Programme (EMRP) project ENG57 Validated Inspection Techniques for Composites in Energy Applications (VITCEA) deals with the development and validation of innovative NDT technologies. In this contribution, results concerning thermographic investigations at test specimens during tensile loading and active thermography testing after tensile loading are presented. Additionally, the determination of the optical properties (relative transmittance and directional spectral emissivity) of CFRP and GFRP test specimens is described. 1. Introduction The aim of the EMRP project VITCEA is to encourage industry adoption and the realisation of the most promising novel NDT techniques, such as microwave, active thermography, laser shearography and phased array/air- coupled ultrasonics, thus enabling the increased use of FRPs for energy applications [1]. This will be achieved through the provision of operational procedures that are based on the comprehensive evaluation and development of each technique for detecting typical defects in composites that are used in wind, wave, tidal, oil and gas and transport sectors. For active thermography, experimental investigations using different excitation sources and time/amplitude profiles for a wide range of defects and materials are scheduled. Thermographic investigations of natural defects like delaminations and impact damage are performed during as well as after loading of the test specimens. The results will provide guidance on the most appropriate selection of inspection parameters and the limitations of the technologies. In addition, theoretical anisotropic two dimensional and three dimensional non-steady heat transfer models will be developed based on known and measured thermal and optical properties. This will be combined with appropriate defect and excitation source thermal simulations which will be solved numerically using finite element analysis and validated by comparison with experimental results. The main innovation of these investigations is to obtain defect information with highest accuracy and resolution by considering well known material parameters in combination with optimised data analysis procedures. For obtaining quantitative information about the defect structures using thermographic testing, the optical as well as the thermal properties of the material without defect have to be determined. The optical properties should include information about the emissivity and the transmissivity of the material; thermal properties comprise the thermal conductivity, specific heat capacity and mass density. In this contribution, the determination of the relative transmittance and of the directional spectral emissivity as a function of wavelength is described. The thermographic inspection of CFRP and GFRP test specimens during tensile loading or impact damage can provide information about the types of damage already during the damaging process [2-5]. In [3], thermography was combined with acoustic emission for the investigation of static load in unidirectional carbon fibres laminates subjected to axis and off-axis static tensile loads. Temperature increases could be correlated to acoustic emission signals concerning fibre breaking during loading and disbonding/interface failure when the sample failed. But in [3], no correlation could be found for matrix breaking. In the referred paper, no information was given on the applied load or strain. In [4], microscopic and macroscopic damage evolution was observed during tensile loading using three different full field measurement techniques: digital image correlation, thermography and x-ray tomography. This combination of methods provided information of some damage features like the location and distribution of defects, failure mode and the influence of the initial anisotropy. In [4], 2 mm thick CFRP test samples with dimensions of 250 mm x 25 mm and fibre orientations of [0/90]6 used for axis loading and of [+45/-45]6 for off-axis loading were investigated. For axis loading, a 10.21611/qirt.2016.076 527