Sonic IR crack size estimation using 2D heat diffusion model with arbitrary heat source function along the crack

Over the past decade, sonic infrared (IR) has been gaining rapid popularity in fatigue crack detection. Accuracy and robustness of crack size estimation using existing temperature-based image processing techniques are rather limited due to the absence of analytical solutions describing the heat diffusion around the crack. In this study, a 2D heat diffusion model with an arbitrary heat source function along a crack line is developed to make the technique more practical and capture the random nature of heat generation along the crack. The validity of the forward 2D heat diffusion model is established in close comparison with 2D finite element (FE) results. The validated analytical solution is used as a basis for best-fit analysis to retrieve the arbitrary heat source functions along the crack, which are used to estimate crack sizes. Using the 2D FE simulations with and without random temperature uncertainties, the proposed method delivers high accuracy in estimating crack sizes. Moreover, the accuracy in estimating crack sizes is validated using experimental sonic IR data. This makes it a practical approach to unlock the potential capabilities and limitations of sonic IR inspection technology.