Research On The Damage Identification Of The Bar's Crack Based On Modal And Wavelet Analysis

Bar structure is widely used in engineering practice, as the basic unit of large structures, many will appear cracks, corrosion, pit injury etc in the work process, and the crack damage is a large proportion, in addition, it is also the defect of the earliest signs of bar structure damage. Due to the early initial crack is not easy to be found, the crack expansion will cause the destruction of the whole structure, and even lead to a major accident, therefore, the research on the cracks of bar is very significant. In this paper, the cracks of the bar are taken as the research object. The identification of crack location and quantitative identification of damage degree are researched by using theoretical modal analysis, experimental modal analysis combine with time-frequency wavelet analysis. The main contents of the paper are as follows:(1) Firstly outlines the research status of structural damage detection, introduced the domestic and foreign research status of structural damage detection based on vibration measurement, the basic theory of the wavelet analysis method for structural damage detection and the model of vibration system of modal analysis, discussed the advantages of the two combination.(2) Built the bar model contained with different depth crack by using Ansys software. Disposed the model by using modal analysis and got the mode parameters. Demonstrated the crack defects will reduce the local unit stiffness, and simulated mathematical expressions of the local elastic modulus and crack depth(3) Disposed the modal shape by using the curvature mode shape analysis and applied the wavelet multi-scale analysis by using Matlab software, established the relationship between wavelet modulus maximum and scale, realized the accurate positioning of the bar crack through the wavelet modulus maximum point.(4) Chose the Lipschitz index as the damage index to evaluate the crack damage information, disposed the bar crack contain with a single crack, oblique crack, multiple cracks by using curvature mode and wavelet analysis of curvature mode, discussed the interaction among multiple cracks. Established the mathematical expression of the degree of damage and the depth of crack, realized the quantification of damage degree.(5) Built the vibration test bench, carried out the vibration experiment of the bar contained rectangular notch crack, derived from experimental data for modal analysis, contrasted the theoretical and experimental modal data, drew similarities and differences between theory and experiment and found the causes of dissimilarity.This study combined theory and experiment to realize the bar crack identification, and provide theoretical supports and practical application foundation for NDT of dynamic state and complex structures.