Study Of The Finite Element Simulation Analysis Of Structural Damage Identification Based On Lamb Waves Method

With the development of modern industry and technology,nondestructive testing technology has become an important means to ensure product quality and safety in machinery,metallurgy,petroleum,chemical engineering,aerospace engineering and other industry sectors.The Lamb waves damage detection technique has been widely used and studied in depth in structural health monitoring.Based on the knowledge of nondestructive testing and Lamb waves theories,the propagation characteristics of Lamb waves the thin plate structures is presented.And as well,the propagation characteristics and the dispersion curves of Lamb waves,and the damage identification of thin plates using Lamb waves are simulated using MATLAB and ABAQUS.First of all,this thesis made an exposition of the current situation at home and abroad of Lamb wave detection.The theory and propagation characteristics of Lamb waves are studied,and the deformation of the Rayleigh-Lamb equation of Lamb waves is derived.And furthermore,the Rayleigh-Lamb equation of Lamb waves is numerically simulate using MATLAB,and the dispersion curves are drawn,and the corresponding relationship between the group velocity and the phase velocity of the A0 and S0 modes with respect to the frequency-thickness products is also established,and the above research is the basis for the structural damage identification using Lamb waves.And then,the excitation signal of Lamb waves including the optimal window function,the optimal center frequency and the wave crest numbers is determined through the theoretical calculation and comparison.The simulation processes of the propagation of Lamb waves in thin plates are stated in detail by using ABAQUS,the excitation signals of Lamb waves are loaded on the model of thin plates,the meshing length of the finite elements is determined.After being solved for the above processes,the propagation of Lamb waves is obtained.Finally,through the two-dimension finite element modeling,the propagation simulation processes are furtherly presented.The group velocities and phase velocities of the A0 and S0 modes,which are obtained through the numerical simulation,are calculated,and the calculation results are compared with the group velocities and phase velocities which are obtained through the dispersive curves drawn by MATLAB,and therefore the validity of calculating the group velocities and phase velocities of Lamb waves by finite element simulation is verified.And then,the propagation processes of Lamb waves in the defective thin plates structures are simulated,and the simulation results are compared with those which are obtained in the health thin plates.The propagation variation in the defective thin plates is analyzed,and the positions of the defects are confirmed by means of the reflection echoes of Lamb waves which encounter the defects.The influence of the different defective cracks with different depth on the finite element simulation results is also discussed.Finally,through the two-dimensional finite element modeling,the propagation characteristics of Lamb wave in cracked aluminum plate are analyzed,and the propagation characteristics of healthy aluminum plate are compared.The finite element simulation of A0 mode and S0 modal group velocity and phase And then the finite element simulation of the defective plate structure is carried out.The defective and defect-free models are compared respectively,and the defects are analyzed for the finite element simulation.The finite element simulation of the finite element simulation is carried out.The influence of the results of the Lamb wave on the reflection of the defect in the aluminum plate is determined by the reflection echo of the aluminum plate,and the influence of the crack at different depths on the finite element simulation results is analyzed.