Application of Acousto-Ultrasonics in Wind Turbine Blade Inspection
SAMPE Europe 2015, Amiens, France, 15-17 Sep. 2015
L. Zhao , K. Berketis  and Alvaro Garcia Ruiz 
 NDT Department, TWI LTd,
 SpectrumLabs LTd,
 InnotecUK Ltd
This paper presents modelling and experimental results of inspecting Glass Fibre Reinforced Composite (GFRC) wind turbine blades (WTB) with the acousto-ultrasonic (AU) method. The AU responses of micro-porosity and aging-related structural degradation were examined. Such distributed micro-flaws fall below the detection limits of other Non-Destructive Examination (NDE) techniques, until they have coalesced and developed into relatively large scale cracks able to cause catastrophic failure. In order to facilitate the Finite element modelling (FEM) that was performed, each unidirectional GFRC layer was homogenised first. The transversely isotropic fibres and the isotropic resin were homogenised into a single layer with an effective stiffness matrix. The homogenisation was performed with respect to ultrasound propagation in the desired frequency range. Homogenized laminae were then compiled into the multi-ply laminate according to the design of the sample WTB. The propagation and defect interaction of AU waves were then simulated. The simulation established the ways that the AU techniques can be used to detect such flaws at an early stage. Testing was also carried out with GFRC samples, in order to verify the modelling results.
Application of Advanced Acousto-Ultrasonics in Automated Wind Turbine Blade Evaluation
Malaysia International NDT Conference and Exhibition 2015 (MINDTCE-15), November 22 – 24, 2015, Kuala Lumpur, Malaysia
L. Zhao , K. Berketis 
 NDT Department, TWI LTd,
 SpectrumLabs LTd
This paper presented a new inspection method, acousto-ultrasonic (AU), for flaw detection and structural evaluation of wind turbine blade. At the moment, there is no international standard for the inspection of wind turbine blade. Techniques like visual inspection, conventional ultrasound, shearography, tap test and so on can be carried out by various service companies. However, they all have some common limitations in their flaw detection capabilities. For flaws like micro cracks in the matrix, adhesive with regular small spots of unbounding, or structural degradation, none of the current methods is able to detect them. When left un-noticed, such flaws will develop into large scale flaws and lead to catastrophic blade failure. AU method was originally developed by NASA for aerospace inspections, but this paper presents how this method can be adapted for wind turbine blade inspection. Both simulation and experiments were carried out in this work. The blade specifications were mainly obtained from wind turbine blade manufacturers. The finite element model (FEM) was constructed first to understand the flaw responses in the complex composite structure and to help test the signal processing methods. Advanced filtering and signal reconstruction were performed to enhance the detection of flaws and their location. A sample blade obtained from blade manufacture was also used for the experimental validation. A further advantage of this technique is that it can be integrated as part of the automated robotic application. Once automated, it significantly lowers the maintenance inspection cost and improve the inspection reliability. The robotic design is now an on-going part of the project.