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.

Several research studies aim to employ the electromechanical impedance method (EMI) for effective health monitoring. At the same time, limited studies focused on increasing damage detection efficiency using a combination of sensors under noise and temperature variation. This novel research aims to outperform the temperature compensation algorithm development by using a robust multiple-sensor instrumentational strategy for damage detection in structures. This research combines EMI resistance data in parallel connection for damage detection in the steel beam structure. The resistance parameters based on parallel combinations are studied and compared with the output of single transducers or series connections for the added simulated mass, and simulated cracks with variations of the temperature conditions. The performance comparison has been made in the selected frequency range of 1–100 kHz for the additional mass and 30-80 kHz for the simulated cracked steel beam. The damage sensitivity-based performance comparison has been studied using the root mean square deviation (RMSD) index. The resistance data fusion-based parallel connection has shown a better performance of damage detection capability over a single actuator or a series of connected actuators in varying environmental temperature conditions for the real crack and simulated added mass. The simulated added mass and crack are successfully detected at a higher temperature in the case of the parallel combination of the actuators.

Inspection of composite liquid hydrogen tanks (LH2) for aviation is very challenging using existing non-destructive testing (NDT) technology. This is due to the external insulation layer and limited access to the inside of the tank. New inspection technology is urgently needed for the LH2 tank inspection and maintenance of these LH2 tanks. This work presents the development of a compact high-payload ratio ultrasonic inspection automatic robotic crawler designed for the inspection of the inner curved surfaces of a carbon fiber reinforced polymer (CFRP) composite. The robot is equipped with wheeled locomotion and uses wheel encoders for precise localization on the irregular inner surfaces of the composite LH2 tank. The crawler carries an ultrasonic flaw detector payload housed in a specially designed enclosure, which securely holds a 5 MHz wheel probe for ultrasonic inspection. This study investigates Proportional-Integral-Derivative (PID) tuning for a crawler integrated with an ultrasonic phased array probe, executing straight-line motion on a CFRP composite surface under dynamic conditions at various speeds. The system is designed to operate through tank openings as small as 250-300 mm in diameter, providing a practical solution for challenging inspection scenarios of the LH2 tank.

This research focuses on damage assessment based on the electromechanical impedance (EMI) method. The method uses piezoelectric transducers that excite the investigated structure and sense the response. The damage assessment is based on comparing the electrical spectra gathered for structural parts at different structural conditions. In particular, the unknown case (possibly damaged) is compared with data for known healthy (undamaged) case. In the reported research the EMI method was applied to additively manufactured samples. For several years, additive manufacturing (AM), or 3D printing, has become a popular manufacturing technique that is environmentally friendly by allowing for waste reduction. The structural parts manufactured with AM methods were introduced into the mechanical and aerospace industries. Similar to structures made from traditional metals or polymers, there is a need for structural health monitoring of 3D printed structures. This requires the development of accurate and reliable methods for evaluating and monitoring the structural integrity of such components. Additionally, the AM method gives more freedom in design and also allows for easier sensor integration for structural health monitoring. In this work, the piezoelectric sensors were embedded in a polymer 3D-printed plate and their response was compared with the surface-bonded sensor. In this study, the effective excitability of the sensors was tested with the scanning laser vibrometer. Due to high attenuation, the EMI investigation was limited to 100 kHz. In total four sensors were used for the sample assessment, and the capacitance as a function of frequency was analyzed. Firstly, the structural change was simulated by an additional mass. Secondly, a through-thickness hole was drilled to simulate damage, and the EMI responses were compared for four diameters of this hole. Traditionally, in the EMI approach resistance, conductance, or impedance is studied. However, in this study, promising results were obtained for capacitance that allowed for damage detection and later for severity assessment. The introduced data processing approach based on principal component analysis (PCA) allowed for the differentiation of all the investigated cases and showed good sensitivity to the simulated damage severity.