Detection of defects in wind turbine composite blades using statistically enhanced Lock-In Thermography

Delaminations are a common type of defect that occurs in composite structures such as wind turbine blades. In this study, a nondestructive testing technique based on Lock-In Thermography is proposed to detect skin-skin delaminations and skin-core delaminations present in a 9-m CX-100 wind turbine blade. A set of image processing algorithms and multivariate outlier analysis were used in conjunction with the classical Lock-In Thermography technique to counter the blind frequency effects and to improve the defect contrast. Receiver operating characteristic curves were used to quantify the gains obtained by using multivariate outlier analysis. Experiments were performed on a set of 16 defects of various sizes that were incorporated during the construction of the CX-100 wind turbine blade at different locations and depths.