Study Of Health Monitoring Technology Of Metal Structure Based On PVDF Piezoelectric Sensor

Due to the advantage of excellent piezoelectricity and electromechanical coupling,light weight,corrosion resistance,wide frequency response range,stable performance etc,the Polyvinylidene Fluoride（PVDF）piezoelectric film is widely used in structure health monitoring of aerospace engineering and the structure of civil engineering.The system of PVDF for dynamic strain was builded in this experiment.the piezoelectric effect is used to accumulate charge by the top and bottom electrode.Charge amplifier was applied to implement voltage signal output and signal amplification.The data collector was adopted to collect data and record.The computer software was used to display signal waveform and signal processing.Based on building of PVDF piezoelectric film sensor system,this thesis researched the piezoelectric sensing of PVDF film、the dynamic and static behaviors under cyclic load and the behavior of PVDF on health monitoring of metal structural crack damage.The main research contents list as follows:（1）The static bias of the PVDF sensor keeps a significant linear correlation with amplifier gain.Meanwhile,it is also showed that the sensor output can be real and effective by removing the static under the different amplifier gain.Because of insulating layer of PVDF and adhesive layer weaking the external strain environment,there are some deviation between experimental output value and theoretical value.When the deformation direction of the metal sample is consistent with the d₃₁1 direction of the PVDF,the output of the sensor system have a high sensitivity.When cyclic loading in 5 Hz to 25 Hz range,sensitivity increases with the increase of the loading frequency and frequency deviation decreases with the increase of frequency.（2）Comparing the PVDF sensors output signal of the five different crack sample with the results of finite element analysis,it show that sensitivity and accuracy of the sensor system was higher on detect damage monitoring.in five different types of prefabricated crack,there are biggest damage degree on through crack sample and minimum damage degree on not through crack damage sample.In constant strain and low cycle fatigue experiment,in crack initiation stage,the damage identification index of sensor increased due to plastic deformation of metal sample.When cyclic time is in20 to 40 weeks,the damage identification index of PVDF sensor signals are far smaller increase due to plastic deformation tends to saturation.In the stable crack propagation stage,the crack damage index of PVDF piezoelectric sensor signals have a significant linear correlation with crack size.Increase rate of the damage index in crack propagation stage is four times higher than that in crack initiation stage.Damage degree crack propagation stage also is bigger than in crack initiation stage.