| China’s economy has developed rapidly in recent years,large infrastructure continues to be built,the demand for steel materials is also increasing.The health of these steel materials plays a vital role in the safety of all kinds of structures.Ultrasonic guided wave detection method is a newly developed subject in the field of nondestructive testing.At present,the longitudinal mode guided wave is mostly used in defect monitoring.Based on this research status,in order to improve the accuracy of defect monitoring and better damage assessment and judgment,a torsional mode guided wave monitoring method is proposed.Combined with the numerical analysis of ABAQUS finite element software modeling,three types of steel materials commonly used in practice,such as steel bars,steel pipes,and steel strands,were selected as research objects,and the monitoring effects of torsional modal guided waves under various defect conditions were analyzed.The main research work is as follows:In the second chapter,through the study of the vibration diagram,dispersion curve and waveform structure diagram of the guided wave,it is found that the torsional guided wave T(0,1)is a non-dispersion symmetric mode,which has the advantages of smaller error and greater accuracy for defect positioning.Only circumferential displacement occurs,and the maximum displacement occurs on the surface,which is more sensitive to medium surface defect monitoring.In the third chapter,taking the steel bar as the research object,a defect model with different depth and length on the inner and outer surface of the steel bar is established and the uniform corrosion on the surface of the steel bar is simulated.The results show that the torsional wave is more sensitive to defect depth monitoring than the traditional longitudinal wave monitoring method.In the case of uniform corrosion of steel bars,the torsional guided wave is more sensitive to the monitoring of minor defects than the longitudinal guided wave,and the analysis of the location of defects is more accurate.In the fourth chapter,the circumferential localization of the groove defects on the pipe surface by the torsional guided wave is analyzed.The research shows that:whether the defect is located in the inside or outside of the pipe or the inside of the pipe wall,the numerical simulation monitoring of the defect circumferential positioning radar images all present the "T" shape,and the defect is located directly above the "T" shape,the circumferential positioning of the pipeline can be analyzed.A comparative analysis of the torsional wave and longitudinal wave on the circumferential positioning of the defect proves that whether it is the result graph displayed from the circumferential positioning radar chart or the magnitude of the echo return of the defect,the torsional guided wave monitoring method is more useful than the longitudinal wave method,show the superiority of torsional guided wave in the measurement of the defect.In the fifth chapter,the monitoring effect of torsional guided wave on steel strand with or without axial tensile stress is analyzed.The results show that,when no prestress is applied,the guided wave energy only propagates in the excitation wire,but not in the rest of the wire.However,when the steel strand is subjected to axial tensile stress(the maximum tensile stress in this chapter is 1200MPa),the guided wave transmission is coupled,that is,the energy of ultrasonic guided wave will continuously transfer from the excited wire to the rest of the wire,resulting in the same displacement response of all wires.By using the coupling effect,if a steel wire is damaged,it is not necessary to apply guided waves to each wire,only one wire can be excited,and the corresponding damage information can be obtained by collecting the displacement response of any wire,so as to reduce the monitoring time.The sixth chapter of the paper summarizes the main research results of this paper,and discusses the current research problems and the next research content... |
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