Low frequency and boundary condition effects on impedance based damage identification

Details of the investigations on the application of Electro Mechanical Impedance (EMI) technique using smart piezoelectric (PZT) sensors for damage detection of structures are presented in this paper. The behavior and the ability of this method to detect damages, in a homogenous material are studied for its effective utilization in structural health monitoring. Experimental investigations are conducted on a homogenous aluminium plate bonded with PZT patches to study the effects of external low frequency vibrations (mass loading) and boundary condition on EMI signatures and the observations are discussed using RMSD as damage index computed between pristine and damaged states. Effect of low frequency vibration on the resulting EMI signature and the corresponding RMSD is found to be less than 2%. This is the threshold upper control value (UCL) beyond which the change in RMSD shall truly reflect the damage.