Research of oscillation mode in automated pulsed eddy current testing systems

The formation and analysis of eddy current probe signals obtained in pulsed excitation mode is considered. The proposed method of implementing pulsed eddy current testing with the formation of attenuating harmonic oscillations is more resistant to the effects of noise and interference that accompany the process of inspected object parameters evaluation. The equivalent scheme of the system “test object–eddy current probe” is developed and analyzed. The obtained mathematical model of the eddy current probe signals allowed proposing the natural frequency and the attenuation as informative signals parameters, which are determined from signals phase and amplitude characteristics. Developed algorithm and the proposed methodology was implemented for evaluation of eddy current signals parameters and related characteristics of testing objects. This method was experimentally verified on a series of different test specimens. The obtained results confirm the possibility to apply the proposed informative signals to solve some problems concerned with automated eddy current testing. The formation and analysis of eddy current probe signals obtained in pulsed excitation mode are considered. The proposed method of implementing pulsed eddy current testing with the formation of attenuating harmonic oscillations is more resistant to the effects of noise and interference that accompany the process of automated eddy current testing. The equivalent scheme of the system “test object–eddy current probe” is developed and analyzed. The obtained mathematical model of the eddy current probe signals allows proposing the natural frequency and the attenuation as informative signals parameters, which are determined from signal phase and amplitude characteristics. Methods of increasing the accuracy of determining the eddy current probe signals attenuation and frequency using trends of signals phase and amplitude characteristics are considered. The proposed signal processing method was verified by modeling the process of determining the eddy current probe signals attenuation and the frequency from the signal with Gaussian noise. Algorithmic and software were developed based on the simulation results and the proposed improved methodology was implemented for determining signals parameters and related parameters and characteristics of testing objects.

Subsurface Defect Evaluation of Selective-Laser-Melted Inconel 738LC Alloy Using Eddy Current Testing for Additive/Subtractive Hybrid Manufacturing

New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance. This study comprehensively investigated the effect of influencing factors including excitation frequency, lift-off distance, defect depth and size, residual heat, and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting (SLM). The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting subsurface defects by merely analyzing these two key indicators. Overall, this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals, which provided a practical reference on how to quantitively inspect subsurface defects using eddy current testing (ECT) on SLMed parts, and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing (ASHM) for fabricating SLMed parts with enhanced quality and better performance.

Investigation of Rotating Eddy Current Testing Simulation Using Simplified Model

To reduce the time of simulation for rotating Eddy current testing (RECT) technique, a simplified model without modeling probe was proposed previously. However, the applicability of the simplified simulation model was unknown. In this paper, the applicability of the simplified model for the RECT technique was investigated. The application condition of the simplified model was provided by comparing it with the results of the traditional simulation model. The simplified model was suitable for the study of cracks shorter than 70% size of the uniform Eddy current induced by the probe in a traditional model or experiment. The experiment was conducted to validate the simplified model. Moreover, using the simplified model, the effects of crack depth, orientation, and exciting frequency were studied. The deeper the crack depth was, the greater peak value of [Formula: see text] signal was. The crack angle was linear with the phase of signal. The exciting frequency affected the amplitude and phase of the signal at the same time.