Comparison of three thermographic post processing methods for the assessment of a repaired aluminum plate with composite patch

Composite patches are widely used to repair damaged metal structures, especially in aerospace industry. Perfect patch and bonding are necessary to achieve an effective repair. Various thermographic methods such as step heating thermography are commonly applied to inspect repaired structures. Since accurate determination of defect features are admirable, some techniques are used to process the thermal films. In this study, three common post processing techniques of thermography (namely, principle component analysis (PCA), pulse phase thermography (PPT) and thermal signal reconstruction (TSR)) have been utilized to inspect an aluminum plate repaired with carbon/epoxy patches. Several delaminations with various sizes and locations along with some disbond defects were artificially embedded in five samples of composite patches to experimentally investigate the performance of the three techniques for post-processing of the step heating thermography data. Furthermore, the outputs of the mentioned processing techniques were quantitatively compared to find the most effective one. Based on the comparison results, it was demonstrated that, TSR outputs leads to the more accurate defect sizing.