Study On Structural Damage Detecting Method Based On Piezoelectric Sensing Mechanical Impedance

Piezoelectric(PZT)sensor/actuator and structural coupling electromechanical impedance based structural damage detecting method has shown great potential in the field of structural health monitoring,however,in the practical engineering application,the scientific problems of improving the sensitivity of monitor signature,enlarging the monitoring range of PZT sensor,reducing the piezoelectric damage probability,excluding the interference of PZT damage and weakening the impact of environmental factor still needs to be solved.Focusing on these problems,this dissertation systematically investigates and develops piezoelectric sensing mechanical impedance based structural damage detecting method,and the main research and results are as follows:(1)Based on mechanical impedance theory,and through using theoretical and numerical analysis from one dimensional PZT-structure coupling model including bonding layer,admittance characteristics caused by different damages of structure,PZT and bonding layer are obtained.Theoretical validation on the effectiveness of conductance-based PZT damage diagnosis is then conducted and a conductance-based PZT damage diagnosing method is accordingly proposed and applied to a steel beam and concrete tunnel segment structural experimental investigations.Experimental results reveal that the proposed damage diagnosis method can be used for differentiating damages among PZT,bonding layer and structure before and during structural health monitoring process,and it can also diagnose the performance degradation of PZT sensors.(2)Based on the characterizations of conductance and root mean square deviation index,effects on structural damage detetion of PZT damage and environmental temperature are qualitatively and quantitatively investigated in the steel beam and concrete tunnel segment structural experiment,respectively.Through comparion with healthy PZT sensors,it is found that different PZT breakages and debonding both change the resonance features of conductance signature,which also leads to the ability degradation of PZT sensor for detecting structural damage.Long-term monitoring and study of tunnel segment structure indicate that conductance variation caused by PZT degradation and environmental temperature is quite large,hence imposing interference with structural damage detection.(3)Based on two assumptions of mechanical impedance coupling and separation between PZT and structure,united mechanical imepedance of PZT and structure based method is proposed for structural damage detection.United mechanical impedance of PZT and structure and structural mechanical impedance are respectively extracted from one dimensional impedance model.Through comparing with raw admittance signature,sensitivity of three-type signatures is qualitatively and quantitatively evaluated.Application of the method to a steel structural corrosion damage monitoring indicates that mechanical impedance behaves more sensitively to structural damage and possesses larger monitoring range.Comparing with structural mechanical impedance,united mechanical impedance possesses higher sensitivity to structural damage.(4)Based on the effective mechanical impedance theory,a two-dimentional embedded PZT model in which structural mechanical impedance can be extracted for damage evaluation is formulated,and the effective mechanical impedance of the embedded PZT model based structural damage detecting method is accordingly proposed.Analytical calculation,numerical modeling and experimental results are of high coincidence to validate the proposed method.Application to a concrete beam structural impact damage detection and comparison to surface-bonded PZTs shows that the embedded ones are with lower damage probability in the impact damage,and the proposed method can degrade the impact effect on embedded PZT sensors.Comparing with conductance and structural mechanical impedance,the extracted effective mechanical impedance is more accurate in structural damage evaluation.