Influences of mechanical contact on damage evaluation with electromechanical impedance technique

Abstract

The mechanical contact during material mechanical damage evaluation with electromechanical impedance technique was investigated, and the influencing factors, such as the times of in situ contact, contact stress, and area, were studied. The resonance frequency shift Δf of electrical impedance signature was regarded as the damage identification index. Results show that the influence of mechanical contact on damage evaluation could not be neglected. With increasing times of in situ contact, the characteristic resonant peak shifted leftward gradually due to the resulted superficial indentations, and the Δf value was in the order of 10−2–10−1 kHz for each mechanical clamping. The evolution direction of the resonance peak with contact stress was reversed, and the Δf value was about 10−1–100 kHz. The order was equal or even more serious against that of the early-stage mechanical damage. The relationship between the Δf value and the contact area, however, was elusive because of the combined effects of indentation damage and the compressive stress. Simulation experiments were conducted accordingly, and the abnormality was discussed. The quantitative results were compared between the steel and the Al alloy, and the variation with material property was demonstrated. Effective precautions to avoid the influence of mechanical contact were proposed.