Experimental studies on structural load monitoring using piezoelectric transducer based electromechanical impedance method

Abstract

In general aerospace, civil and mechanical (ACM) structures are often subjected to some or the other forms of loading during their service life. It has been reported that about 75% of aerospace structures fail due to fatigue cyclic loading. The civil-structural components are subjected to some form of axial and transverse loading which continuously deteriorates the health of the structure. Mechanical components are also subjected to stresses due to contact pressures between several components. Thus for ACM structures, effective monitoring through-out the entire life is required as these often involve public life and huge investments. Owing to such necessity, researchers around the world are continuously working on the development of smart sensor based effective monitoring techniques. Piezo electric (PZT) transducer based electromechanical impedance (EMI) is one such technique which was developed for structural health monitoring (SHM). In this technique, PZT transducers are usually attached to the structure to be monitored and are then subjected to unit sinusoidal electric voltage to generate the electromechanical (EM) admittance signatures when interrogated to the desired frequency range of excitations. These signatures consist of real (conductance) and imaginary (susceptance) parts which serve as indicator to predict the structural health. Any deviations in these signatures during the monitoring period indicate disturbance in the structure. However, the EMI technique was not widely explored for structural load monitoring (such as fatigue cyclic load, monotonous load, axial and transverse load) compared to damage detection. In this paper, systematic experiments were presented on the specimens for axial load variations, transverse load variations, monotonous and fatigue load variation with discussions on boundary effect and buckling effects. For axial, fatigue, monotonic load, the conductance was found to be effective where as for transverse load monitoring susceptance was found to be effective. This paper summarizes different types of loading effects related to EMI.