Frequency modulated thermal wave imaging techniques for non-destructive testing

Active thermal non-destructive testing (TNDT) methods utilise an acquired surface temperature profile over the object and subsequently process the obtained temperature data to detect surface or sub-surface features of the object. Presently, two phase-based conventional active TNDT methods are predominantly in use: pulsed phase thermography (PPT) and modulated lock-in thermography (LT). This paper highlights correlation processing-based detection capabilities of frequency modulated thermal wave imaging techniques through finite element modelling and simulations on a steel sample having flat-bottom blind holes as defects. The present work proposes a finite element-based simulation for comparison of the widely-used conventional thermal imaging methods (PPT and LT) with more recently proposed non-stationary excitation approaches for non-destructive characterisation.