The electro-mechanical (EM) impedance method is gradually emerging as a widely accepted technique for structural health monitoring and systems identification. The method utilizes smart piezoceramic (PZT) transducers intimately bonded to the surface of a structural substrate. Through the unique electro-mechanical properties of the PZT transducers, the presence of damage, as well as the dynamical properties of the host structure are captured and reflected in the electrical admittance response. In the present work, the effect of the bond layer on the electro-mechanical response of a smart system is being studied. Experiments with the EM impedance method were performed on laboratory-sized beams. Consequently, the effects of shear lag due to the finite thickness bond layer were successfully identified. This was followed by the theoretical analysis of shear lag effects. It was found that the induced strain behaviour of the structural specimen in question is inevitably modified by the presence of shear lag between the PZT transducer and the structural substrate. Subsequently, the EM admittance response of the beam specimens were simulated based on the results gathered from the theoretical analysis. Incidentally, it was found that the theoretical model clearly depicts the trends of the measured response.

The in-process changes of weld nugget growth during the Resistance Spot Welding were investigated based on the resistance of input electrical impedance. To compute the time varying resistance of input electrical impedance, the welding voltage and current signals are measured simultaneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying resistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nugget growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions.

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