Abstract
This study presents a method for monitoring the 3D fatigue damage progression on a micro-structural level in a glass fibre/polymer coupon test specimen by means of laboratory X-ray Computed Tomography (CT). A modified mount and holder made for the standard test samples to fit into the X-ray CT scanner along with a tension clamp solution is presented. Initially, the same location of the test specimen is inspected by ex-situ X-ray CT during the fatigue loading history, which shows the damage progression on a micro-structural level. The openings of individual uni-directional (UD) fibre fractures are seen to generally increase with the number of cycles, and new regions of UD fibre fractures also appear. There are some UD fibre fractures that are difficult to detect since their opening is small. Therefore, the effect of tension on the crack visibility is examined afterwards using a tension clamp solution. With applied tension some additional cracks become visible and the openings of fibre fractures increases, which shows the importance of applied tension during the scan.
Highlights
Wind power turbines are increasingly used in many parts of the world to match the increasing demand for sustainable energy
Slight jumps in the data were observed at each of the interruption points, but since this is due to mounting the extensometers a bit differently every time, the curve sections were off-set to give a continuous curve
Damage was observed in 3D on a micro-structural level including individual fibre fractures and off-axis cracks at four points during the fatigue loading history
Summary
Wind power turbines are increasingly used in many parts of the world to match the increasing demand for sustainable energy. With a life-time in the range of 20-30 years the total number of load cycles sums up to 108-109, which is significantly higher than for e.g. airplanes and cars [2]. It is the degradation of the stiffness rather than the strength which is a concern for wind turbine blades, since the blades might risk hitting the tower. If the damage mechanism was properly understood on a micro-structural level it would be possible to decrease safety factors and make more fatigue resistant wind turbine blade materials. Establishing a method capable of monitoring tension-tension fatigue damage progression in a glass fibre/polymer is the focus of this paper
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