Localization of Defects in Wind Turbine Blades and Defect Depth Estimation using Infrared Thermography

Localization of defects and determination of the depth and size using Infrared Thermography is a critical problem in wind turbine blades. Infrared Thermography offers significant advantages over other Nondestructive Testing modalities due to fast, wide-area inspection capabilities. Lock-in Thermography is an ideal method for defect detection due to the presence of deep-lying defects in wind turbine blades, which otherwise go undetected. Multivariate Outlier Analysis is used in conjunction with Lock-in technique to enhance the detectability of the defect. Results are presented on defects present in a 9m CX-100 wind turbine blade that was designed by the Sandia National Laboratory. A defect depth estimation technique based on Pulsed Thermography is also presented. A 3D depth estimation model is presented which aims to address the shortcomings of the classical depth estimation methods that are primarily based on the 1D heat conduction equation. Results are presented on a stainless steel sample with flat-bottom defects at known depths. The results are in excellent agreement with the proposed theory.