Study On Phased Array Ultrasonic Rayleigh Wave Total Focusing Method Imaging Of Defects On Metallic Surface

The ultrasonic phased array total focusing method imaging technology has the advantages of dynamic focusing within the imaging range,high imaging accuracy and strong defect characterization ability.It can detect and evaluate metal defects by calculating and processing the echo information received by all array elements.However,the current ultrasonic phased array total focusing method imaging technology is mainly used in transverse and longitudinal wave.When the transverse and longitudinal wave are used to detect the metal surface defect,the defect echo will appear in the near field area and overlap with the boundary echo.But the above problems can be avoided by using surface wave detection.In order to obtain highresolution imaging and to analyze defects quantitatively,in this paper,the ultrasonic phased array surface wave full-focus imaging of metal surface defects is researched when the metal surface defects are taken as the object.The main work of the study is as follows:(1)Ultrasonic phased array surface wave deflection,focus and deflection focusing model were bulit.Derived the ultrasonic phased array surface wave detection model.And combining the detection theory and Fermet principle,ultrasonic propagation path in this model was calculate,and the ultrasonic phased array surface wave total focusing method theory and algorithm was studied.It lay the foundation for ultrasonic phased array surface wave detection and imaging of metal surface defects.(2)A finite element model for of the single element surface wave,traditional phased array surface wave and phased array surface wave total focusing method is established.And the effect of frequency and metal thickness on defection were studied.The proper probe frequency mental thickness were selected to realize the total focusing method image of ultrasonic phased array surface wave.The simulation results show that the higher the frequency of ultrasonic,the shallower the penetration depth of surface wave.And the energy is concentrated on the surface.When the thickness of the metal within 2.5 mm,focus point of energy decrease with the increase of thickness.Especially,Compared with the metal thickness of 0.2 mm,the focal point energy decreases by 58.8%when the metal thickness is 1 mm.When the thickness is greater than 2 mm,the energy change at the focus point is not obvious.Consequently,ultrasonic phased array surface wave has a good efect on detecting the flaw of thin mental.(3)Ultrasonic phased array surface wave detection and imaging experiments were conducted when the material of research objects are 45 steel and aluminum with the defects diameter of 1 mm.The surface defect holes were quantitatively analyzed under the relative positions of the wedge and the defect were different.The experimental results show that ultrasonic phased array surface wave can achieve high-precision imaging of 1 mm surface defects,and the size error of the defects detected is within 0.11 mm,indicating that the best imaging area is within the wedge.(4)In order to reduce the influence of the noise in ultrasonic phased array surface wave total focusing method imaging,Analyze the time and frequency domain of th e signal by using one dimensional continuous wavelet transform.The composition and time-frequency characteristics of ultrasonic phased array surface wave defect echo signal are analyzed,And the principal component analysis method is used to denoise the image.The result show that the defect signal-to-noise ratio is improved and the average size error of defects is reduced.When the energy of defect echo signal is large,the effect of suppressing noise in ultrasonic phased array surface wave signal is more obvious,and the imaging effect is better.