Abstract
Shearography is an optical technique in the field of non-destructive evaluation (NDE) of various materials. Its main advantages are that it is non-contact type and can cover a large area in a single inspection. As a result, although it has been widely acknowledged as an effective technique particularly for NDE of composite materials to detect subsurface defects such as delamination, disbond, cracks and impact damages, the use of shearography for on-site inspection of wind turbine blades (WTBs) has not been reported. This is due to wind causing structural vibration in the WTB. The solution in this paper is to make the shearography sit on the WTB during inspection when the WTB is parked, so that the relative motion between the shearography and the WTB is minimized within the tolerance of the shearography system. The ultimate goal of the solution is to enable a robot assisted shearography system to inspect the WTB on-site. This paper presents the research work on a new shearography design for integration with a robotic climber for on-site WTB inspection. The approach is tested and evaluated in experimental settings, and comparative assessment of the approach with other robotic NDE techniques is carried out. The results demonstrate the potential benefits and suitability of the approach for on-site robotic inspection of WTBs.
Highlights
Structural integrity is important for safe operation of engineering structures and industrial facilities
This paper has introduced a compact shearography system for nondestructive evaluation (NDE) monitoring of wind turbine blades (WTBs)
The experimental test has been carried out for its workability on a WTB surface. It could be concluded from the tests that the shearography system is able to inspect the subsurface defect on most of the WTB areas
Summary
Structural integrity is important for safe operation of engineering structures and industrial facilities. Shearography as an optical technique and has the main advantages of noncontact and relatively large area of coverage in a single inspection It was first proposed by Leendertz and Butters in 1973 [2] and was further developed by Hung et al [3]–[5]. Niezrecki et al [8] have given a systematic comparison of five NDE methods based on a CX-100 blade sample for their performance In their tests, shearography has shown better results in terms of full-field identification of flaws and subsurface defects. The ultimate goal is to develop a robot-assisted shearography system which is able to inspect the WTBs on-site with, for example, remote control by operators on the ground (for onshore wind turbines) or on a vessel (for off-shore wind turbines), not requiring human inspectors on the wind tower to do the inspection.
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