In this paper, some research on the Laser Infrared Thermography (LIT) and the Eddy Current Infrared Thermography (ECIT) for quantitative nondestructive testing and evaluation of surface cracks and delamination of multilayer structures are introduced. At first, a Laser Array Spots Thermography (LAST) method for inspection of surface cracks in metallic structures is presented. LAST related measurement and image processing methods for inspection and quantitative evaluation of crack profiles are introduced in detail. Second, LIT technique and numerical analysis methods for detection and sizing of interface delamination of multilayer structures are introduced aiming at application to the in-vessel structures of Tokamak fusion reactors, such as the first wall panels of blanket modules. At last, some studies on the quantitative nondestructive evaluation of delamination of thermal barrier coating system of gas turbine blades with ECIT are given. The numerical methods for forward analysis of heat generation and transfer process of infrared thermography, and for inverse analysis of defect size with infrared thermography signals are emphasized in this paper, in addition with experimental validations of both the numerical methods and the new inspection techniques.
A new infrared preprocessing modality called sequence differential processing is proposed. Different from the cold image subtraction which only decreases the background noise, the proposed modality takes the parallel test into account to preprocess the raw thermal data sequence prior to applying the advanced postprocessing techniques such as principal component thermography and pulsed phase thermography. The results show that the preprocessing method not only effectively reduces the influence of uneven laser energy distribution on detection efficiency but also enhances internal defect information. Moreover, the combination of the proposed preprocessing method with the pulsed phase thermography and principal component analysis algorithms improves the ability of laser infrared thermography to detect defects inside aviation carbon-fiber-reinforced plastics.
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