Application of EMI technique for crack detection in continuous beams adhesively bonded with multiple piezoelectric patches
Electro-mechanical impedance (EMI) is very effective for detecting the local incipient damages including small cracks in structures and has been validated by many experimental investigations. Meanwhile, some analytical models have been proposed to deal with dynamics of structures for health monitoring. However, there is little analytical work done to relate EMI signatures with crack parameters at ultrasonic frequencies. In this paper, a modified model combining EMI technique and reverberation matrix method (RMM) is proposed to quantitatively correlate crack parameters in continuous beams with high-frequency signatures for structural health monitoring. The model is based on Timoshenko beam theory with the crack treated as a massless rotational spring. The bonded PZT wafers are restricted to one-dimensional axial vibration. A shear lag model is adopted to simulate the interfacial bonding between PZT patches and the host beam. For the first time, an analytical expression of impedance (or admittance) involving information of cracks in this coupled smart structure system is derived. Comparison with existent numerical and experimental results is presented to validate the analysis. Based on this model, EMI signatures extracted from the PZT wafers can be used to identify cracks in a continuous beam.