The Method To Estimate The Thickness And Shear Wave Velocity Of Single-layered Cylindrical Media By SH Guided Waves

With the acceleration of industrial modernization,non-destructive testing technology has attracted more and more attention.Among them,the thickness measurement of materials,parts,and equipment is particularly important in industrial production and transportation.In the manufacture and maintenance of many types of equipment,pipes,and components,the thickness must be measured to confirm the size,corrosion,and wear conditions to ensure product quality and production safety.Among them,pipeline corrosion detection is particularly important in industrial production and transportation.When the pipeline has a long service life,the pipeline may be corroded due to the internal and external environment,resulting in the gradual thinning of the pipeline wall and entering a period of high accidents.Therefore,it is necessary to measure the thickness of the pipeline,determine the corrosion of the pipeline,find the risk in time,and ensure the safety of transportation.With the rapid development of the field of non-destructive testing,a variety of testing methods have emerged,one of the more common is the ultrasonic non-destructive testing.It detects many physical parameters by studying the interaction between ultrasonic guided waves and the detected object.Among them,the SH wave has received extensive attention and research from many scholars in the field of nondestructive testing due to its unique propagation characteristics,and has great application value and prospects.In this paper,the use of multi-order SH guided waves to estimate the thickness and shear wave velocity of single-cylindrical layer media is carried out.First,the wave field of SH waves excited by the annular shear source on the outer wall of the single-cylindrical layer elastic medium is theoretically solved.The numerical solution of the SH guided wave dispersion curve is obtained by Newton's iterative method,and the approximate analytical solution of the dispersion curve is obtained by the approximation method whose inner diameter tends to infinity.Through comparison,the correctness of the approximate analytical solution in the high frequency band is verified.The real-axis integration method is used to carry out the numerical simulation of the full-wave wave train of SH wave in time domain,and the frequency wave number method is selected to obtain the dispersion curve using multi-channel signals.Finally,the three solution results are compared to verify the feasibility of using the frequency wavenumber method to extract the dispersion curve.Secondly,based on the SH guided wave dispersion equation,the formula is derived,and the inversion formula of thickness and shear wave velocity are given.The frequency and velocity points are extracted from the energy map obtained by the frequency wave number method and substituted into the inversion formula for calculation,and the final estimated value is determined by the median value.The optimization strategy is used to determine the order of the extracted dispersion curve using the preliminary inversion results,and the higher order dispersion data with smaller errors are used alone to improve the accuracy of the thickness and sound velocity inversion results.Inversion results of thickness and shear wave velocity,the error can be controlled within 1%.The influence of the center frequency of the sound source,the thickness of the model,the inner diameter of the model,the material of the model,the number of receivers,and the interval of the receivers on the inversion results were investigated respectively,which verified the general applicability of the thickness measurement method in this paper to most situations.Finally,a preliminary investigation was made on the thickness of the single-cylindrical layer porous medium and the inversion of sound velocity.Because the shear wave velocity of the porous medium itself is affected by many factors,by examining the influence of porosity parameters on the inversion results,it is found that the thickness inversion results nearly does not change with the porosity,and there is still a slight error but very small;the error of shear wave velocity inversion results becomes larger as the porosity increases.In practice,it is difficult to obtain the porous parameters of the object to be measured,so it is impossible to use thickness measurement methods with known wave speeds such as ultrasonic thickness measurement.The inversion method in this paper can avoid this problem,and is less affected by the parameters of the porous medium.It can invert the shear wave velocity of the porous medium while measuring the thickness.In short,based on the importance of thickness measurement and the limitations of traditional thickness measurement methods,this paper proposes a new theoretical method for thickness measurement,which uses multi-order SH guided waves to fast estimate the thickness and shear wave velocity of single-layered cylindrical media.In addition to the advantage that no waveform conversion occurs during the measurement process using SH waves,the method proposed in this paper has the characteristics of no need to know the sound velocity of the measured material in advance,metal and non-metallic materials,elastic media and porous media are applicable,the measurable thickness range is large,the accuracy is high and the error is small.