Mechanism Research And Design Of Weld Defect Detection Transducer Based On The Feature Guided Waves

Weld structures are important connection parts of large equipment such as pressure vessels and marine ships,which have been widely used in industrial production and social lives.However,the presence of defects in the weld would greatly reduce its safety and reliability,even lead to major accidents.Thus,it is necessary to undertaken regular weld inspections to keep its health in the industry.Weld defect detection based on ultrasonic guided waves is a new method in the field of weld nondestructive testing,compared with traditional detection methods,it has a series of advantages such as long distance inspection,high efficiency and no harm to humans,it can measure all defects in and out of the structure by only one scan,and realize defects localization and quantification at the same time.However,this technology is developing that some theories are not mature.Studying the excitation and receiving method of guided waves,and exploring its interaction with defects is of great importance.This paper combined numerical simulation with experimental research,analyzed the influence of excitation conditions on the propagation characteristics of guided waves,studied its interaction with typical weld defects,and designed piezoelectric chips and array.Some conclusions have been obtained as follows:?1?The excitation methods and propagation characteristics of S_w0 and SH_w0mode in the butt weld were studied based on the 3D finite element model,the influence of excitation parameters including frequency and array on the dispersion and attenuation characteristics was analyzed.According to wave structure loading method,S_w0 and SH_w0 mode were excited respectively,by comparing their scattered map and propagation waveform,it was found that:S_w0 mode has complex modes and attenuation in the propagation process,while SH_w0 mode is the opposite,SH_w0 mode is more concentrated in the weld.After a comprehensive consideration of dispersion,energy and width of waveform,the optimal excitation frequency of two modes was determined,and got higher energy without dispersion.The relationship between excitation unit and energy under different arrays was studied,it was found that the effect was the best with simultaneous excitation of vertical array.?2?The interaction between S_w0?SH_w0 mode and two typical defects?hole?crack?on the surface or internal of the weld was investigated.Based on the piezoelectric theory,the core component of weld detection sensor—piezoelectric unit and its detection array was designed.It is found that the scattering field of S_w0mode is complex with low reflection waves,which is easy to be submerged by noise signals.SH_w0 mode is the opposite because of simple vibration and no modal conversion.In addition,two piezoelectric chips were designed according to material,vibration and dimension,which have the same vibration forms with two modes and can excite longitudinal and transverse waves propagating along the length.The relationship between excitation unit and energy of vertical array was also verified.?3?The experimental system for weld defect detection was set up,a series of verification experiments were carried out including modal verification,wave excitation and reception,and defect detection.Firstly,wave of S_w0 and SH_w0 mode were excited by piezoelectric chips and verified,the“Energy Trapping Effect”was proved.Secondly,the energy and attenuation characteristics of two modes were verified by receiving signals at different distances.Finally,three defects of hole,vertical and axial cracks in the weld were detected,the defect detection rate and positioning accuracy of two modes are all high and SH_w0 mode has more obvious echoes.It is also pointed out that the abilities of guided waves to detect different defects are various due to their difference in vibration forms.Weld defect detection technology based on feature guided waves has broad application prospect,which has become the focus of research recently.The research of this paper provides a new method for weld detection,as well as useful reference for the development of specialized weld detection sensors and instruments.