Quantitative Monitoring Method Of Crack Damage In Metal Structures By Ultrasonic Guided Waves

Metal structure as an irreplaceable and important structural element in actual engineering,crack damage in structure will bring significant safety hazards and economic losses to the engineering,so crack monitoring of metal structures has important research significance.In the field of structural health monitoring,the crack monitoring based on active Lamb waves can locate cracks by using the propagation characteristics of Lamb waves in the structure.However,influenced by the change of crack state,the current research on Lamb wave-based crack monitoring still has shortcomings in the monitoring and evaluation of cracks.Therefore,in this paper,we use active Lamb wave RAPID imaging technique to quantitatively monitor crack damage in metal structures under different states in real time.Specifically,this paper firstly sets up different monitoring means to detect cracks comprehensively for different current states of cracks.Secondly,by analyzing the mechanism of the crack damage in the structure to the signal direct wave,the cross-scan method and the localization method are set up to determine the crack direction.Finally,by correcting the SDC values on the crack direction path,the path direction information is enhanced,so as to complete the image reconstruction and quantitative evaluation.The content of the study are as follows:(1)The harmfulness of cracks in metal structures is briefly described,and the research background and status quo of Structural health monitoring are introduced.The basic methods of several Structural health monitoring technologies commonly used for crack monitoring are analyzed,and the advantages and disadvantages of several technologies are compared.Then,briefly describe the research status of active Lamb wave crack monitoring technology.(2)The basic theory of Lamb wave is studied.Aiming at the propagation characteristics and dispersion characteristics of Lamb wave propagation,the excitation conditions of Lamb wave in metal plate structure are proposed.Conduct research on signal excitation methods,sensor array layout,and imaging methods.(3)Briefly describe the process of crack formation,and based on the process of crack formation,obtain the possible formation of single cracks and folded cracks at different stages.Through simulation analysis,establish a plate structure model,and analyze the law of signal direct waves affected by single cracks and folded cracks.(4)Analyzing the characteristics of single crack,corresponding monitoring method is proposed and the experimental software and hardware system is established.Through practical experiments,it is demonstrated that the influence of crack damage on signal direct waves is consistent with that in simulation analysis.The position,direction,size,and other information of a single crack in the metal structure at the initiation state are monitored through experiments.Comparative experiments are set up to analyze cracks of different sizes and directions,and the reliability of the experimental method is verified.(5)Research and analysis were conducted on the folded cracks caused by cracks in metal structures in the extended state.A new sensor array was proposed,and the Fan-shaped region local localization method is used to preliminary determine the position and direction of cracks.The path affected by crack folding was corrected,Then,crack monitoring is achieved through the cross-scanning method.Experiments have shown that damage location can be located through Lamb wave monitoring.By using cross scanning method,RAPID imaging,and improving the sensor array,the length and orientation information of single and fold cracks can be reflected,which has broad research prospects.