Abstract
An innovative active thermography technique is proposed for the inspection of typical wind blade material. The proposed technique is based on the use of a multifunctional material obtained adding a grid of Shape Memory Alloy wires, which would serve also as a protection against lightning, to a traditional glass fibre composite panel. This technique, called SMArt thermography, which exploits the SMA wires as internal heat sources, has been compared to a traditional pulsed thermography in the case of a representative panel of unidirectional glass fibre and epoxy matrix with embedded SMA wires and artificial defects. The experimental results of the two techniques are reported and compared to the result of a numerical FEM transient model, in order to establish the reliability and the detectability limit of the proposed technique. The FEM model has been proven to be a useful tool for the definition of the multifunctional material at a design stage.
Highlights
Wind energy exploitation is considered one of the most positive developments originated by todays’ storm of uncertainty unleashed as a result of turbulence on oil prices, climate changes, environmental degradation and dependence of foreign energy supplies
The first observation is that traditional thermography is able to find all the defects inserted in the panel, in particular defect d7 and d8 that are characterized by the minimum diameter of 5 mm, according to the prediction of the numerical model
In the case of heating time of 10 s, absolute contrasts are higher, but a preaccumulation of heat during the heating phase was observed. This circumstance is showed by the fact that the curves of the normalized contrast in the case of a heating time of 10 s show a discontinuity in its first derivative (Fig. 13b)
Summary
Wind energy exploitation is considered one of the most positive developments originated by todays’ storm of uncertainty unleashed as a result of turbulence on oil prices, climate changes, environmental degradation and dependence of foreign energy supplies. The success of wind energy is largely due to the fact that the cost of wind energy is comparable to the one of traditional fossil fuels, becoming attractive this form of renewable energy. In order to obtain lower rates of energy cost, larger wind turbines are commonly used. As a consequence of this trend, modern wind turbines are the largest rotating machines on Earth, with the length of one blade exceeding the entire span of an Airbus A380. These large turbines have been called “fatigue machines” and have design lifetime requirements 20 times longer than standard cars. It is clear that design, manufacturing and in-service phases constitute critical issues and an additional effort is required for component optimization and structural integrity assessment
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