Research On Damage Detection Of CFRP Laminate By Electro-mechanical Impedance Technology

Carbon fibre reinforced polymer(CFRP)is widely used in mechanical engineering,chemical textiles,electronic and electrical and biomedical fields due to their excellent comprehensive properties such as low relative density,high strength and rigidity,and high chemical stability.However,internal damages such as delamination and fiber breakage may occur in composite materials during use.Such damages are not easy to be found,but they pose a serious threat to structural safety.Therefore,it is very necessary to carry out structural health monitoring.In this paper,based on Electro-Mechanical Impedance(EMI)technology,combined with simulation analysis and experimental research,the PZT-metal sensor is used to conduct damage detection and location research on CFRP laminates in the low frequency range.The main research contents are as follows:Firstly,based on the characteristics of piezoelectric materials,the basic relationship of coupling electro-mechanical impedance is deduced,and the relationship between the mechanical impedance of the tested structure and the dynamic mechanical impedance of PZT is obtained,which provides a theoretical basis for damage detection and location of CFRP laminates.Secondly,the finite element models of the PZT-metal sensor and the PZT sensor are established respectively,and the damage detection of the composite laminate structure is simulated and analyzed in the low frequency range.The root mean square deviation(RMSD)value is used as the damage index to quantify the damage degree.The results show that compared with the PZT sensor,the real part of impedance measured by the PZT-metal sensor in the low frequency range contains more resonance peaks,which is more sensitive and effective for damage detection,and is more suitable for damage location research.Thirdly,experimental research is carried out on the interlayer hole damage and crack damage of CFRP laminates.In the experimental research on the damage of the interlayer holes,the results of the experiment and the simulation are consistent,which proves the effectiveness and superiority of the PZT-metal sensor in the detection of damage in the low frequency range.In the experimental study of crack damage,the influence of different degrees of damage on the real part of impedance curves was studied by setting the crack damage of different lengths.The results show that the damage index RMSD value increases with the increase of crack length.Finally,through experiments,the influence of the size of the metal disc on the damage detection sensitivity of the PZT-metal sensor is explored,and the damage of the same through hole is monitored by changing the thickness and diameter of the metal disc of the PZT-metal sensor.The results show that within a certain frequency range,the PZT-metal sensor composed of thinner and larger metal disc has higher damage detection sensitivity.Last,combining piezoelectric impedance technology and probabilistic damage imaging algorithm,the damage location test of carbon fiber composite laminates is carried out,and the value of the sensing area radius r in the probabilistic damage imaging algorithm is explored,and the calculation formula for the r is proposed through experiments in order to reduce the trial and error time of determining the optimal sensing area radius r value.The damage location image shows that in the low frequency range,the combination of the PZT-metal sensor and the RAPID algorithm can greatly improve the accuracy of damage location,providing a new idea and method for damage location of composite.