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

Steel bar is widely used in machinery,buildings,Bridges and extract oil engineering fields,as the basic unit of large structures.Steel bar will appear crack,corrosion,pits in the work,and proportion of crack damage is the biggest.Long steel bars tend to appear many cracks especially.These cracks cause threat to the safety and reliability of structures and institutions,so the steel rod crack damage research is very important.Now it need a damage sensitive indicators to solve the problems that the long steel bars crack damage is identified position rapidly.In this paper the research object is multiple cracks steel bar.It uses modal analysis and experiment modal analysis,combined with the method of wavelet decomposition analysis to identify cracks location.It seek a more sensitive damage index.At the same time,the index can identify cracks position rapidly for large institutions.Thesis mainly in the following aspects:(1)firstly outlined the structure damage identification research present situation,and this paper introduces the structural damage identification based on the dynamic characteristics about both at home and abroad research situation,elaborated the superiority of the wavelet analysis method,combining with the damage index of the dynamic characteristics.(2)Building steel bar model witch has different depth cracks.The paper use Ansys software to modal analysis for getting the damage index,such as inherent frequency,vibration mode and curvature mode,curvature change rate and so on.Through simulation analysis proves that damage indexes don’t enough sensitive when the crack depth is less than 0.1 mm.These can’t identify the cracks location.(3)Combining wavelet analysis and curvature change rate to structural damage index.The the second order modal curvature change rate is carried out three layers of wavelet decomposition.Through decomposed signal mutation to identify cracks position of the steel bar accurately.(4)The paper use wavelet analysis and curvature change rate as damage indexes to identify the cracks of the same direction and the different spatial location of steel rod.It discusses interference condition among cracks under different conditions,so building the mathematical expression between interference distance and crack depth to diameter ratio.(5)Building the vibration test bench.It uses rectangular gap to simulate crack of steel bar for vibration experiment and derives from experimental data for modal analysis.From the angle of the experiment shows that wavelet analysis and curvature change rate as damage index of steel bar is more sensitive.This study combines wavelet analysis and curvature change rate as damage index to defect steel rod crack damages from the perspective of theory and experiment.These provide theoretical supports and practical application foundation for NDT of dynamic state and complex structures.