Finite element evaluation of EMI-based structural health monitoring in high frequencies

Structural health monitoring (SHM) is a growing field with many applications in the aerospace, civil, and mining industries. There has been a desire to develop SHM systems to operate in the microsecond timescale during highly dynamic events. Current efforts have focused on creating an impedance measurement system using the electromechanical impedance (EMI) method technique. In order to consider ways to decrease the time required to measure the impedance of a system, researchers have considered taking measurements at higher frequencies. As part of this research, it is important to consider the sensitivities and capabilities of the sensors to detect changes in the structure at higher frequencies (up to MHz). The goal for this study is to evaluate the sensitivity of the EMI method to damage using a PZT disk bonded to a cantilevered aluminum beam using a finite element (FE) model as well as experimental data. Damage was created by adding holes along the length of the beam, incrementally moving closer to the PZT disk. As a result of this study, an FE model has been developed using previously introduced methods to characterize the material properties of a PZT disk with an optimization algorithm. While initial coefficients resulted in a significant deviation of FE resonance peaks from experimental results, when using the optimized parameters the FE model accurately matches the experimental data. Modeling of the PZT when bonded to the aluminum beam showed a similar trend, there is not an exact match between the model and experimental data. This can be attributed to the material properties of the aluminum beam, which are from a general data sheet for the 6061-T6 and not data from the actual beam. In addition, the bonding layer is not modeled in the FE simulation, which can be a cause of the error in the modeling results. In both the model and experimental data, indications of damage from the impedance curves occurred below 600 kHz.