Damage Identification On Plate Structures Based On Single-mode Lamb Waves

Damage caused during structure service period will endanger the safety of people's lives and property,so it is of great significance to identify structural damage.The structure is composed of several components,and the damage of the components easily causes the whole failure of the structure.In the process of structural health monitoring,it is found that ultrasonic Lamb waves are important for the damage identification of plate structures,but the multimodality and dispersion phenomena of Lamb wave limit its application.In this paper,the damage identification of single-mode Lamb waves for plate structures is studied by means of numerical simulation combined with experimental research.Firstly,based on the theory of elastic dynamics,the dispersion equation of Lamb wave is deduced,and its dispersion characteristics are theoretically analyzed.Taking the plexiglass plate as an example,the method of Matlab programming was used to solve the dispersion equation and to plot the dispersion curve.Reasonable frequency and waveform are selected to build the appropriate excitation signal.The cutoff frequency and other parameters are discussed,which lay the foundation for the selection of frequency in the later damage identification process.Secondly,modeling and calculation of plexiglass plate are based on ABAQUS / Explicit.The model simulates the propagation process and effect of Lamb wave in the whole plate and in the damaged plate,and according to its propagation characteristics,the damage position can be confirmed by ellipse damage localization technique.Elliptic localization requires explicit time parameters,and in the process of signal processing,wavelet transform and Hilbert transform are used to analyze the signal to obtain the required time parameters.A variety of damage conditions are set such as single point of damage,multi-point damage and crack damage.According to the characteristics of symmetry and anti-symmetry modes of Lamb,symmetrical excitation and anti-symmetry excitation are respectively set at the excitation,or a single mode Lamb wave can be obtained by processing the received signal.The single mode Lamb wave can also be used to identify the damage of the structure.The single-mode Lamb wave signal is more clearly analyzed,especially for the multi-damage or crack damage of the plate-like structure.The accuracy of the damage identification method that is based on the ellipse localization satisfies the requirements,but the intersections of multiple ellipses are not all of the points of damage,so the damage location needs further to be confirmed,and the damage location should be visually simulated.The elliptic trajectories formed by each sensor are drawn and discretized to calculate the number of pixels falling in each discrete cell.The damage locations can be visually observed when the path is more enough,and the pseudo-damage points can be removed accordingly.Finally,the experimental platform is established,then the appropriate excitation frequency,excitation voltage and other parameters are made accordingly,then the Lamb wave modal single method,lastly,damage identification on the plexiglass plate is conducted withsingle-mode Lamb wave.The advantages of the single-mode Lamb wave damage identification method are analyzed and compared,and the damage location is obtained more accurately.the influence of damage size on the signal is analyzed.And different length of crack damage are analyzed,if the number of sensors is sufficient,the shape of damage can be acquired.