Pipeline Defects Detection And Study Of Giant Magnetostrictive Guided Wave Transducer Based On Terfenol-D

Compared with traditional piezoelectric materials,giant magnetostrictive materials have higher electromechanical coupling coefficient and energy conversion efficiency.The development of the giant magnetostrictive guided wave transducer will inevitably improve the efficiency and accuracy of pipeline guided wave detection,which is beneficial to the development of the guided wave nondestructive detection.In this dissertation,the internal components of giant magnetostrictive pipeline guided wave transducer were designed by the combination of theory and experiment.The influence of component parameters on the excitation and reception performance of transducer was studied.The detection performance of giant magnetostrictive sensor was verified by detecting pipelines with different types of defects.The research work and results of this dissertation mainly include the following contents:(1)Based on the requirements of the experiment,a pipeline guided wave detection system was established.The excitation guided wave mode of giant magnetostrictive transducer was determined.The excitation signal of transducer was slected and the evaluation standards for the transducer performance were formulated.In order to enable the giant magnetostrictive transducer to detect any surface of pipeline,a TerfenolElastic based compound oscillator structure was designed.According to the resonance formula,the basic size of Terfenol oscillator was calculated.The optimum size and material of the elastic base in the composite structure were determined by experiments.(2)The biased magnetic fields of different structures were analyzed by experiments.It was found that the experimental echo coefficients of the biased magnetic field of the symmetrical structure were higher than those of the asymmetrical structure.The influence of biased magnetic field with different number of permanent magnets on the performance of transducer was studied.It was found that when the number of permanent magnets reached a certain level,the growth rate of weld echo coefficient slowed down obviously.Through the analysis of the field strength formula of the alternating coil,it was found that the parameters of the alternating coil,such as the diameter,turns and fill factor,affected the strength of the alternating magnetic field.The influence of various parameters on the performance of the transducer was studied experimentally.The results showed that the larger the filling factor of the alternating coil was,the higher the echo coefficient was.When the coil reached a certain number of turns,the echo coefficient no longer increased significantly,and the echo coefficient increased firstly and then decreased with the increase of the diameter of the coil.(3)Four kinds of backing layer materials were prepared by mixing polysulfide rubber,silicon carbide,tungsten powder and epoxy resin according to different proportions.The acoustic impedance values were determined by pulse echo method.The effects of different acoustic impedance backing materials on the detection echo coefficient,signal-to-noise ratio and dead time performance of giant magnetostrictive transducers were investigated.The experimental results showed that as the acoustic impedance of the backing layer material increased,the echo coefficient decreased while the signal-to-noise ratio(SNR)increased,but the blind area time did not change significantly..It also could be found that the appropriate proportion of polysulfide rubber could improve the SNR of the echo signal and reduce the blind area time.(4)The excitation and reception performance experiments of different types of artificial prefabricated defects for the developed giant magnetostrictive transducer were carried out,and the performance comparison experiment between the giant magnetostrictive transducer and the traditional PZT-5 piezoelectric transducer was investigated.The test results confirmed that the giant magnetostrictive transducer had a good detection rate for cracks,holes and corrosion defects,and the axial positioning accuracy of the defects was above 96%,and maintained a good echo signal-to-noise ratio.When the excitation mode was L(0,2),the cross-sectional area of the defect in the pipeline determined the echo coefficient,and it was superior to PZT-5 type piezoelectric transducer in excitation and reception of defect detection performance parameters.The experiments and analysis results showed that the giant magnetostrictive transducer could effectively detect different types of defects in pipelines and surpassed the piezoelectric guided wave transducer in many detection performances.