Research On Propagation Characteristics Of Feature Guided Waves In Butt Welds And Its Interaction Mechanism With Typical Defects

The weld structure,which widely used in industrial production and life,is the key connection part in the ship and other platforms.However,the defects in the weld will greatly reduce the safety and reliability of the equipment.The serious defects will lead to major security accidents and huge losses of personnel and property.The weld inspection must be carried out in the process of shipbuilding and maintenance.Ultrasonic guided wave detection has been developed in recent years as a new method of nondestructive testing(NDT).Compared with traditional weld detection methods,ultrasonic guided wave detection technology has a wide range and high efficiency of detection,and is harmless to human.All defects in the whole thickness range can be detected by once test.The location and scale of defect can also be identified simultaneously.It is of great academic and practical value to study the modal conversions and the mechanism of the interaction between feature guided waves with weld defects.The formation principle and energy decay characteristic of weld feature guided waves have been analyzed.The propagation characteristics of feature guided waves in weld and its interaction with weld defect have also been analyzed based on the combination of numerical simulation and experimental research.Some main conclusions and achievements have been obtained:(1)Based on the basic theory of guided wave in plate,a three-dimensional finite element simulation model of steel butt weld has been established.The relationship between the weld feature guided waves and the parameters of weld structure and material.The simulation results have been obtained,and the following conclusions were drawn.(i)When the weld height increased,the Energy trapping effect of the two feature guided modes in the weld strengthened and the attenuation rate also increased.However the average energy growth rate of SHw0 mode is larger and the attenuation rate is lower.(ii)When the weld width increased,the energy of the Sw0 mode in weld increased gradually and its attenuation rate did not changed.The energy of the SHw0 mode appears at a maximum point where the decay rate is the lowest.(iii)When the Poisson's ratio changed,the energy of two feature guided modes positively correlated with Poisson's ratio.The decay rate of the Sw0 mode is a constant,but the decay rate of the SHw0 modal changes.The energy concentrated in weld of SHw0 mode more than Sw0 mode,and SHw0 mode was more sensitive to the parameters of the weld.(2)The finite element method(FEM)was used to simulate the scattering of two feature guided waves at the weld defects.The interactions between the feature guided waves and the weld defect have been studied,and the relationship between the defect echo wave and the defect type has also been analyzed.The propagation characteristics and defect identification ability of two kinds of weld feature guided modes have been compared.The following conclusions have been gotten.(i)The existence of A0 mode in the scattering field can be used to determine whether the defect is transparent or not.(ii)The same feature guided mode can still generated after the interaction between reflection field and the weld.(iii)The defect echo reflectivity of SHw0 mode is higher and the defect recognition is more convenient.(iv)According to the degree of fracture and the asymmetry of the scattering field after the interaction between SHw0 mode and defect,the severity of the hole defect and the location of the crack can be judged respectively.(3)The nondestructive testing system of weld feature guided wave has been established.The propagation characteristics of two feature guided modes in weld have been studied experimentally,and three typical defects in the weld were detected.The SHw0 mode and the Sw0 mode were excited in the weld successfully.The accuracy of the numerical simulation has been verified by testing the three butt-weld plates with different weld parameters.Three typical kinds of defects in the weld were detected,and it was found that the two weld feature guided modes can recognized the poroid defect effectively.The accuracy positioning of the SHw0 mode is higher than Sw0 mode.Sw0 mode was more sensitive to transverse cracks and difficult to detect the longitudinal cracks in the weld,while the SHw0 mode is the opposite.Weld ultrasonic guided wave detection technology,which has become a popular research topic among many scholars at home and abroad,has broad application prospects.The results of this study provide a reference method for the non-destructive evaluation of butt welds.The simulation results provide a theoretical basis and reference for the further study the propagation characteristics of weld feature guided waves.The experimental results provide a reference for the actual non-destructive testing of welds based on ultrasonic guided waves.