Online damage identification based on electromechanical impedance and cointegration under varying dynamic loads


The electromechanical (EM) impedance-based structural health monitoring (SHM) technique based on piezoelectric materials is rapidly emerging as a effective technology. In the EM impedance method, piezoceramic (PZT) transducers surface bonded to the host structure act as both sensors and actuators for positive and negative piezoelectric effect. The EM admittance signatures of the PZT transducers related to the mechanical impedance of the structure which is affected by damage serve as indicators to predict the health of the host structure. The damage index is usually introduced to quantify the change of the admittance signal. However, the EM admittance is susceptible to environmental conditions such as loading during structural health monitoring. In order to avoid misdiagnosis of structural health, it is necessary to study the influence of loading on the EM admittance signatures and make further compensation.This paper presents a series of experimental,analytical studies conducted to investigate the effect of varying load on admittance signatures,and statistical correlated coefficient deviation (CCD) index is used for quantification for EM admittance variations involved with damage/stress. The stiffness of the structure is affected by the loading imposed on the structure. Varying dynamic loads cause non-stationary structural characteristics and lead to the change of PZT admittance signal. Co-integration,a tool for the analysis of non-stationary time series,is used to remove the influence of loading that can often mask the signature of structural damage in the presentation.The procedure of the method is presented. At last, the proposed approach is examined with a experiment of loose bolt identification of the aluminum plate which is subjected to varying dynamic loads.