Research On Interaction Of Lamb Waves And Typical Defects In Plate-like Structures

All kinds of defects(e.g.holes,cracks,lamination,etc.)will inevitably appear in plate-like structures such as aircraft skins,hulls,bridge support plates and pressure vessels during structure making and using.The expansion of these defects will lead to destructive accidents.Therefore,the research on the health monitoring technology of plate-like structures has great value and theoretical significance.Using Lamb waves,we can realize rapid,accurate and large-scale structural health monitoring of large plate-like structures.In this paper,we combined the scattering coefficient matrix with artificial bee colony algorithm to study the interaction of Lamb waves with typical defects in plate-like structures based on the three-dimensional finite element simulation.The main research contents of this article are as follows:(1)Firstly,an improved artificial bee colony(MABC)algorithm is proposed in Gaussian ultrasonic guided wave model for the sake of parameters estimation and mode separation.We improved the artificial bee colony(ABC)algorithm by means of modifying boundary conditions of food source and enlarging changing elements of parameter vector for onlooker bees.A single ultrasonic waveform was tested to evaluate the parameter estimation performance of ABC,MABC and ABC with improved dimensions.It has been shown that MABC leaves a better impact on the ultrasonic guided wave model in all cases.Then,we apply MABC to the Lamb wave detection signal,extracted from the finite element simulation experiment,achieving accurate parameter estimation and modal separation of Lamb wave signals.(2)Second,according to the elastic theory,we established an ultrasonic Lamb wave 3D finite element simulation model for isotropic and anisotropic media,respectively.One is an aluminum plate,the other is a carbon fiber composite plate with one single layer.Due to the multi-mode characteristics and noise corruption of Lamb waves,we used MABC to evaluate parameter estimation and modal separation of Lamb wave signals received by all sensors in the plate.Then,combining the pre-processed signal with the scattering parameter matrix theory,we identified and measured the features of the roundhole defects in the plate.(3)Finally,we have analyzed the attenuation characteristics of ultrasonic Lamb waves in the plate and derived the attenuation equation of ultrasonic Lamb waves in an isotropic media plate.In view of the limitations of traditional sparse sensor arrays,a scattering coefficient displacement compensation algorithm based on ultrasonic attenuation coefficient was proposed.We can use the ultrasonic attenuation coefficient to compensate the scattering coefficient obtained from the random sparse sensor array to the defect-centered unit circle.Through the research above,we have obtained the following research results: Firstly,an improved artificial bee colony algorithm(MABC)was applied to the study of Lamb wave parameter estimation and modal separation.In this way,we can achieve the pretreatment of the Lamb detection signal,which sets up the basis on later research.Then,to identify and measure the characteristics of defects in the plate,we combined MABC with the scattering parameter matrix to study the interaction between ultrasonic Lamb waves and the typical defects in a plate.Finally,a scattering coefficient displacement compensation algorithm based on ultrasonic attenuation coefficient is proposed,which realizes the detection of defect features in the plate by a random sensor array.The three parts above constitute a complete scheme for studying the interaction of Lamb waves with typical defects in plate-like structures.