A compact laser shearography system integrated with robotic climber for on-site inspection of wind turbine blades

Shearography is an optical technique in the field of non-destructive evaluation (NDE) of various materials, with the main advantages of non-contact and relatively large area of coverage in a single inspection. 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. However, the use of shearography to inspect wind turbine blades (WTB) on site a wind tower is not proven, because a WTB is in constant vibration due to wind even when it is parked on a tower at low-speed wind. To address the problem, we aim to attach the shearography sit onto the WTB during inspection when the WTB is parked, the relatively motion between the shearography and the WTB is minimized within the tolerance of the shearography system. The ultimate goal is to develop a robot assisted shearography system able to inspect the WTBs on-site through remote control by operators on the ground (for onshore wind turbines) or on a vessel (for off-shore wind turbines), so that there is no need to send humans to the wind tower via a rope to do the inspections. This paper reports part of our research work surrounding the new shearography that is designed for integration with a robotic climber for on-site WTB inspection. It includes the principle of shearography, comparison of shearography with other NDE technologies, robotic application, experiments validation for fringe patterns, and description of post processing algorithms.