Evaluation of welded joint cracks by damping analysis in an eddy current testing system

Eddy current testing (ECT) has become state-of-the-art among other modern and classic non-destructive tests. It works by monitoring the change in impedance when cracks are present in conductive materials. The injection, detection and target components make up the ECT system. They wirelessly exchange power via resonating frequencies, allowing for mutual inductance that depends on impedance consisting of inductance, capacitance and resistance (LCR), which in turn determines the damping coefficient of the oscillation in the frequency domain. This study proposes a novel method for crack detection through damping analysis, which evaluates the damping effect on power transmission between the ECT components. Three identical arc-welded joints on high-strength steel specimens with various crack depths (1 mm, 2 mm and 3 mm) were made to be tested. A coaxial helix probe was used for probing purposes. This work successfully determined the presence of cracks through the damping analysis. The damping data was then used to reconstruct the power exchange’s damping distribution in the specimens. Comparisons with standard ECT experimental data show good agreement, explaining the correlation between crack occurrence and amplitude increase and revealing a robust relationship between impedance and damping.