An experimental study of the electromechanical impedance method for sensors embedded in a 3D printed plate employing capacitance as structural health sensitive feature

Abstract

The growth of additive manufacturing requires methods to assess the structural condition of the 3D printed structural parts. This research focuses on the electromechanical impedance method that proved its effectiveness in damage assessment of structures made of metals and fibre reinforced polymers. This work investigates a square plate with four piezoelectric sensors for EMI measurements. Three sensors were embedded in the material and one was surface bonded. The laser vibrometer was used to assess the sensors excitation range. The vibrometer study indicate high attenuation of the material and allowed us to determine that the EMI investigations should be made for frequencies up to 100 kHz. The capacitance of a piezoelectric sensor is proposed as a structural health sensitive feature. The mean value of capacitance allowed to separate the responses from individual sensors but failed to give information about the structural condition. The relation between the depth of sensor embedding and capacitance mean value was established. The work proposes a new 3-step approach for damage assessment: 1. polynomial fitting of capacitance spectra, 2. principal component analysis 3. Euclidean distance-based damage index. The approach showed sensitivity to a mass placed at three distances from the sensors and to the through thickness drilled hole of four diameters. The results indicated that the structural damage assessment can be realized in a relatively low frequency range (below 100 kHz). Structural health assessment using electromechanical impedance can be realized by embedded sensors but their sensitivity is lower than for the surface bonded sensor.