49 Detection and Evaluation of Ondulations in Glass-Fiber Reinforced Materials Wolfgang Holub 1 , Ulf Haßler 1 1 Fraunhofer Institute for Integrated Circuits IIS – Development Center X-ray Technology EZRT, Dr.-Mack-Straße 81, 90762 Fürth, Germany, e-mail: wolfgang.holub@iis.fraunhofer.de, ulf.hassler@iis.fraunhofer.de Abstract One main defect found when examining rotor blades of wind turbines are ondulations within the layers of the composite material. These may result in structural failure of the rotor blade and thus account for extensive cost for repair and downtime of the facility. Within a study, methods are being developed and apparatus investigated to locate such defects by means of thermography, in order to consecutively acquire high-resolution 3-D images thereof by computed tomography and to develop algorithms to automatically evaluate those ondulations. The methods that we are going to demonstrate include detection, segmentation and measurement of length and height of the epoxy forming underneath an ondulation as well as segmentation of single glass-fiber rovings, evaluation of their orientation through the composite material and maps of these artifacts. Modeling of whole rotor blades and simulation of X-ray images along different trajectories is used to evaluate the necessary geometry and acquisition parameters for a concept to be applied both to quality control during the production and as inspection platform in situ. Keywords: glass-fiber composite, GFRP, roving, ondulation, orientation, computed tomography, simulation, wind turbine, rotor blade 1 Background Since the decision to retreat from nuclear energy, power generation in developed countries like e.g. Austria and Germany is being focused towards renewable energies and especially wind energy. Those wind turbines’ rotor blades are heavily loaded due to the high circumference speeds of up to 300 km/h at radii of up to 90 meters. Wind power industry provides both endurable and lightweight constructions for these conditions by employing glass-fiber reinforced composite materials in semi-monocoque construction. However, failure of wind turbines’ rotor blades can often be traced back to defects originating in manual production steps therein. The high monetary causes of such failure demand for the development of non-destructive testing methods applicable both for quality control during production and for inspections in situ to identify and locate those defects. 2 Study’s Aims and Overview Fraunhofer Society’s Wilhelm-Klauditz-Institute for Wood Research (WKI) together with the Development Center X-Ray Technology (EZRT) are expediting a study to allow measurement and evaluation of critical structures within such composite materials during construction as well as at the site of operation. The idea of the study is to combine the expressiveness of IR thermography and X-ray imaging. Thermography is used to identify and locate suspicious regions in the object. X-ray imaging and computed tomography are applied to provide volumetric data sets of these regions of interest allowing deeper inspections, measurement and evaluation of the found defects.