Electro-Mechanical Impedance Technology-based Study Of Debonding Damage In Carbon Fiber Composites

Carbon fiber composites as a new class of materials are gradually replacing traditional materials such as metals with many excellent properties of low cost,high strength and corrosion resistance,and are widely used in defense industry and civil fields.The composite bonding form is widely used in various composite joining structures due to the advantages of good processability and uniform stress.However,in the long-term service process,the glued structure will suffer from alternating impact loads,temperature,fatigue damage and other factors,and inevitably debonding damage will occur,bringing serious threats to structural safety.Therefore,based on the electromechanical impedance technique,this paper combines finite element and experimental research methods to study the debonding damage in composite structures,and the main research contents are as follows.1.Based on the nature of piezoelectric materials,the conductance and impedance equations of piezoelectric coupling models without and with bonded layers are derived,and the similarities and differences between them are analyzed to provide a theoretical basis for the identification and localization of debonding damage in carbon fiber composites.2.The PZT model is established in the finite element software ANSYS,and the modal extraction and static analysis are carried out to clarify that the main deformation mode of PZT is the contraction motion in the radial direction.The finite element models of debonding damage of two different specifications of composite materials are established,and the damage identification study is carried out based on the electromechanical impedance technique.The results show that the debonding region in the structure can be identified within 200-400 k Hz by the following ways:(1)Compared with the non-debonding region,the real part of the impedance curve of the debonding region will be significantly shifted to the left frequency,and the peak of the curve is higher than that of the non-debonding region.(2)In the scatter plot with the root mean square RMS as the horizontal coordinate and the peak corresponding frequency f as the vertical coordinate,the data measured by PZT in the debonded region are always at the lower right of the non-debonded region.3.In the study of debonding damage,it is found that with the increase of plate thickness,the peak frequency of the real part of the impedance curve in the debonding region gradually shifts to the left frequency,and the two changes are linearly correlated.After identifying the debonding damage in the structure by the PZT curve,the current thickness of the structure can be deduced from the peak frequency,so as to predict the debonding depth.4.Carbon fiber composite and aluminum-carbon fiber composite debonding damage tests were completed,and the effects of PZT paste position,sampling frequency band and material type on debonding damage detection were studied.The results show that the PZT piezoelectric ceramic sensor pasted on the metal plate is more sensitive to the damage extension,and the closer the damage location is the better the PZT piezoelectric sensor detection effect,and different sampling frequency bands have significant influence on the damage detection conclusion5.Based on the damage probability imaging algorithm and piezoelectric impedance technique,the debonding damage localization problem in carbon fiber composite specimens is investigated,and the sensing area radius,sampling frequency band and damage indicators that affect the localization accuracy of the damage probability imaging algorithm are analyzed.The research results show that the sensing area radius can be determined by using the method of large interval sampling and then small sampling area;the localization effect of frequency range 50-500 k Hz is better and the localization accuracy is high;the localization effect of damage index RMSD is better than other damage indexes.