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Description
Inductive thermography is a non-destructive testing technique widely used for detecting surface and near-surface defects in electrically conductive materials. In ferromagnetic steels, the interaction between electromagnetic induction, material properties, and defect geometry produces localized thermal variations that can be detected by infrared imaging. The characteristics of the thermographic response are influenced by several factors, including defect size, depth, and orientation, as well as by the excitation and measurement conditions.
This work presents an investigation of the influence of crack geometry on the inductive thermography response in ferromagnetic steel, considering both surface and subsurface simulated cracks. Artificial open cracks with controlled geometrical parameters are introduced into steel specimens in order to analyse the effect of variations in length, depth (surface and subsurface), and inclination on the measured thermal signal. Different measurement approaches, namely pulsed and lock-in combined with Fast Fourier Transform (FFT) processing, are adopted to characterize the cracks quantitatively, with particular emphasis on phase information, which is generally less sensitive to non-uniform heating and surface emissivity effects than temperature amplitude.
The experimental configuration is designed to provide stable and repeatable induction heating, enabling a consistent comparison between different crack geometries. Different experimental set-ups, excitation coil geometries, and infrared cameras have been investigated to study the influence of key parameters and to identify the main limitations affecting defect detectability and characterization.
A numerical modelling approach was employed to simulate a broader range of crack geometries and to evaluate the corresponding inductive thermography response, thereby gaining insight into crack behaviour while reducing the amount of experimental data and the number of specimens required for different crack geometries. Experimental measurements were used to support and validate the simulations in different set-up scenarios, showing that inductive thermography enables the detection and characterization of surface and sub-surface simulated cracks, with the phase response exhibiting measurable and repeatable variations as a function of crack geometrical parameters.
Overall, this study highlights the versatility of inductive thermography for assessing surface and sub-surface simulated cracks in ferromagnetic steel. The experimental results serve as the basis for subsequent comparative experimental–numerical investigation, enabling more extensive parametric analyses and supporting an improved probability of detection and crack characterization in different inspection configurations.
