Structural Damage Detection Based On Piezoelectric Impedance Method With Far And Near-field Excitations

With the development of practical and efficiently structural health monitoring technology,more and more intelligent materials have been applied in the field of nondestructive detection.In this regard,piezoelectric impedance technique has emerged as one of the most attractive and powerful methods for the nondestructive detection.Through the identifying the variation of the impedance spectrum to demonstrate the expansion of the damage in the structures.However,suffering from the low drive voltage of the piezoelectric sensor,the sensitivity of micro-damage detection is not sufficient for the measurement of mirco-damage in structures.Therefore,a method of piezoelectric impedance with near and far field motivation in the damage detecting process is utilized,compared with the traditional methods,another PZT sensor was installed in the far-end of the prime to PZT sensor to realize the near and far field motivation at the same time.The new method would dramatically upgrade the sensitivity of nondestructive detection.Through analyzing three different kinds of damage models via comsol to verify the feasibility of the method.Initially,the piezoelectric impedance equation of double piezoelectric element simultaneous motivation coupled model was deduced.It was found that the damage would affect the frequency and amplitude of peak value of the impedance spectrum.In order to quantitative analyes the damage of buildings,RMSD index is employed to indicate the damage.Two dimensional piezoelectric coupling beam model was established by the comsol.The corresponding admittance diagram of the single motivation method and the protocol under different damage conditions were obtained.It was found that the admittance diagram peak value of the new method was much higher.Moreover,the admittance diagram indicated the admittance diagram peak frequency would shift to the left and the index of the damage increase obviously and the RMSD data were more distinctly in the strategy.Therefore,these results demonstrated the feasibility of the strategy in the detection of damage expansion and the high sensitivity in the identification of micro damage.Under the corrosion of reinforced concrete beam,debonding of bonding interface between FRP and concrete and steel plate hole damage conditions,the corresponding three dimensional piezoelectric coupling model were established to analyze the influences of the size of damage,frequency segment of detection and the distance between damage and PZT.The results show that method can well identify the three kinds of damage.With the damage propagation,admittance peak frequency shift,the RMSD value increased;Low frequency has poor damage identification ability,high frequency has excellent damage identification ability.When increasing the distance between damage and PZT,the detection capability of single piezoelectric sensors piezoelectric impedance technique decreased obviously,which could apply in the localization of the damage.As for this method,the effective distance of the inspection and the detection sensitivity were much more further.Experimental platform and steel plate damage specimen were built to investigate the influence of detection frequency and constraint condition to impedance spectrum.The admittance spectra of PZT at different distances from damage under different damage conditions were measured.The consequences were in accordance with finite element results which indicated that the new method could overcome the low sensitivity of traditional method and strengthen the the recognition of minor damage in any position.