Research On Nonlinear Guided Wave Damage Monitoring Based On Duffing Oscillator

Aiming at the problem of low sensitivity of linear Lamb wave to micro damage,early fatigue and other damage forms,this paper carries out the analysis of nonlinear lamb generation and propagation mechanism,and studies the experimental system,sensor network optimization,nonlinear signal analysis and processing methods,realizes the detection of weak second harmonic signal by Duffing chaotic oscillator,and puts forward a new damage index σ based on the maximum Lyapunov exponent,Based on this,the damage degree and location information of micro damage are judged.This provides a new idea and method for structural health monitoring technology based on nonlinear Lamb wave.The main contents of this paper are as follows:Firstly,the defects of Lamb wave in early micro damage monitoring are analyzed,which leads to the analysis of the generation and propagation mechanism of nonlinear Lamb wave.At the same time,the conditions of cumulative effect are analyzed theoretically.In the aspect of characteristic parameter selection,the common nonlinear parameter β is deduced and their potential unreliability is analyzed,so as to pave the way for the subsequent Duffing chaotic oscillator signal analysis method.Secondly,the nonlinear Lamb wave detection system is designed and studied,including signal excitation,amplification,acquisition and other modules,as well as the selection of sensor network.The main work is to design the charge amplifier,and the system meets the experimental requirements.Thirdly,the research on one-dimensional and two-dimensional micro damage evaluation methods is carried out,including experimental mechanism analysis,research object selection,sensor layout optimization and so on.In addition,the method of damage index σ used for micro damage evaluation and location and the corresponding method between damage index σ and damage degree are introduced.Finally,the hardware system necessary for the experiment is designed.At the same time,the damage evaluation experiment is carried out for early micro damage.The experimental results show that: 1.Nonlinear Lamb waves are very sensitive to the changes of material parameters caused by nonlinear effects.2.The damage index is very sensitive to the change of damage.3.Based on the damage index,the micro damage can be located in two-dimensional plane.The above research results provide a feasible method for the design of on-line monitoring system for early fatigue and micro damage.