Research On Damage Identification Based On PVDF Piezoelectric Film Sensor

Marine engineering structures such as ships have served in the marine environment for a long time,and the working environment is complex and harsh.The safety of ships during operation has always been a hot spot of concern.Structural health monitoring technology(Structural Health Monitoring,SHM)can monitor the operating status of the structure during the service period,and identify the existence of damage in the early stage of damage to the structure,which can save a lot of manpower and material resources and avoid major economic and property losses.Therefore,in recent years,the structural health monitoring technology of marine engineering such as ships has been studied by many scholars.Structural damage identification level is the research focus of structural health monitoring technology.The method of identifying structural damage by obtaining structural vibration response signals has attracted widespread attention.The structural curvature mode has been widely used in the field of structural health monitoring because of its high sensitivity to local changes and accurate damage location.Based on the measurement characteristics of the piezoelectric film sensor,this research designed and produced a combined piezoelectric film sensor.The designed sensor can directly measure the strain difference response signal at a certain part of the structure.According to the central difference principle,the measured value is derived and calculated to obtain the local strain curvature of the structure.And combined with the modal identification method to identify the structural strain curvature modal parameters.The effectiveness of the monitoring method in this paper is verified by the damage identification experiment of the cantilever beam and stiffened plate structure.The main research contents of this paper are:(1)Based on the theory of strain mode analysis,this paper derives the corresponding variable curvature mode,analyzes the vibration differential equation of the multi-degree-of-freedom structure,and obtains the mathematical expression of the strain curvature mode.Two methods for calculating structural curvature modes are introduced in detail,which are the calculation method based on the mode shape difference and the calculation method based on the transformation of the strain mode.(2)Based on the basic theory of piezoelectric materials,this paper expounds the measurement characteristics of piezoelectric film sensors in detail,and proposes a combined piezoelectric film sensor measurement method based on the principle of curvature difference calculation.This is the innovation of this thesis.In this paper,a combined piezoelectric film sensor is designed and manufactured,and the strain difference response signal is obtained through the combined piezoelectric film sensor,and then the modal parameters of the structural strain difference curvature are obtained.Analyze the parallel connection mode of piezoelectric thin-film sensors,and compare the damage identification of piezoelectric thin-film single-chip sensors and parallel sensors.(3)This paper designs the modal parameter identification experiment and damage identification experiment of the cantilever beam structure.In the experiment,the environmental excitation is simulated by hammering,and the method of adding mass near the sensor simulates the structural damage.The inherent modal parameters of the cantilever beam structure are obtained through the modal parameter identification method,which is consistent with the numerical calculation results.In the cantilever beam damage identification experiment,the monitoring methods of the combined piezoelectric film sensor and the ordinary sensor are compared and analyzed,and the effectiveness of the strain difference signal monitoring method of the combined piezoelectric film sensor proposed in this paper is verified.(4)In this paper,the damage identification experiment of rigid stiffened plate is designed.In the experiment,the damage recognition effect of the piezoelectric film sensor in the stiffened plate structure is further discussed.In the stiffened plate damage recognition experiment,the piezoelectric film sensor is attached to the plate structure,the web structure and the panel structure.For the same damage location,the sensitivity of sensors at different locations to damage identification is studied.According to the measurement characteristics of the piezoelectric film sensor,the damage recognition effect of the parallel connection of the sensor is studied in the experiment of the stiffened plate,and the recognition result is compared with that of the monolithic piezoelectric film sensor.The damage recognition effect is good.