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Surface crack detection and sizing is essential for the manufacturing and maintenance of engines, run parts, and other metal elements of aircrafts. Among various non-destructive detection methods, the fully non-contact and non-intrusive technique based on laser-stimulated lock-in thermography (LLT) has recently attracted a lot of attention from the aerospace industry. We propose and demonstrate a system of reconfigurable LLT for three-dimensional surface crack detection in metal alloys. For large area inspection, the multi-spot LLT can speed up the inspection time by a factor of the number of spots. The minimum resolved size of micro-holes is ~50 µm in diameter limited by the magnification of the camera lens. We also study the crack length ranging from 0.8 to 3.4 mm by varying the modulation frequency of LLT. An empirical parameter related to the thermal diffusion length is found to show the linear dependence with the crack length. With the proper calibration, this parameter can be used to predict the sizing of the surface fatigue cracks. Reconfigurable LLT allows us to quickly locate the crack position and accurately measure its dimensions. This method is also applicable to the non-destructive detection of surface or sub-surface defect in other materials used in various industries. [ABSTRACT FROM AUTHOR]

In this investigation, we use pulsed thermography and a multilayer analytical model to critically evaluate the thermal diffusivity and inherent porosity in cold-sprayed Ti-6Al-4V coatings on Al6061-T6 substrates. These coatings are of importance in deploying cold spray as an additive manufacturing technique for the restoration of high-cost alloy components. Our study draws upon experimental data obtained at spray angles from 50°to 90°, illustrating the relationship among the spray angle, porosity within the coating, and the resultant thermal diffusivity. Our results reveal a decrease in porosity and an increase in thermal diffusivity as the spray angle increases from 50°to 90°. In conjunction with our experimental approach, a numerical model was developed, incorporating binary images derived from optical micrographs to simulate transient heat diffusion during pulsed thermography experiments. The congruence between our empirical findings and simulation data affirms the effectiveness of the applied methodology, shedding light on the complex interplay between processing parameters and the resulting thermal properties. This study explores the effects of porosity and thermal gradients introduced during pulsed thermography, providing a profound understanding of the thermal dynamics of cold-sprayed coatings. [Display omitted] • Spray angle affects the porosity and thereby the thermal trait • Microscopic images-based FEM models deepen heat diffusion understanding • Porosity insights enhance cold-sprayed coating thermal dynamics [ABSTRACT FROM AUTHOR]