Research On Coded Ultrasonic 3D Imaging Of Shell Weld Defect

Shell structure is widely used in ship manufacturing process and welding is the most effective way to connect the shell structure.But the weld will inevitably have defects,which will directly affect the quality of the ship and the safety of navigation.Therefore,it is of great significance to research NDT of shell welds,timely to find out dangerous defects,and give quantitative parameters of defects.The traditional ultrasonic array inspection method of weld defects can only get 2D images of defects,which is not conducive to observing the spatial distribution of defects and restricts the accurate quantitative evaluation of defects.In addition,the ultrasonic generally uses pulse excitation.Under the same excitation voltage,the echo signal-to-noise ratio is small,which will affect the imaging resolution of defects and restrict the detection range.In view of the above problems,this thesis studies the 3D imaging method of shell weld defects based on coded ultrasound,which will provide reference and reference for shell weld defect detection.Based on the analysis of the characteristics of shell weld defects,after summarizes the current situation of conventional ultrasonic testing methods and imaging technology of weld defects,this thesis puts forward that get ultrasonic by binary frequency combined coding signal,and obtain the echo signal by part matrix data.The defects information carried in the coded ultrasonic echo signal are extracted after pulse compression information.Calculate the spatial sound field parameters distribution of weld defects through Monte Carlo algorithm,and project the sound field parameters into the shell voxel model to achieve the 3D filling and display of shell weld defects,and obtain the 3D image of defects.In this thesis,this method is applied to the detection of shell weld defect test block,and built test system in the laboratory to detect and image the embedded defects.The results show that this method can effectively detect the five embedded defects in the test block,and the 3D imaging resolution is improved,which effectively reduces the artifacts in the conventional imaging method,so that the inspectors can quickly grasp the defects spatial distribution information.The main research work and conclusions are as follows:1)Based on the analysis of the types and characteristics of the shell weld defects,summarize the current status of the commonly ultrasonic testing methods about weld defects,coded ultrasonic testing technology and ultrasonic imaging.2)This thesis introduces the generation and detection principle of coded ultrasound and the common mathematical model of coded ultrasound.By analyzes the characteristics of its response signal echo signal autocorrelation pulse compression,determines that the coding model of this thesis is binary frequency combination coding.Studies the method of identifying the ultrasonic transmitting array element from the coded echo signal to calculate sound field path in spatial sound field.3)The spatial sound field distribution of ultrasonic sensor array is studied,constructed the echo signal acquisition method based on part matrix data acquisition,and build the rules of part matrix.Three types of part matrix imaging effects are compared by means of sound field simulation.4)Established the spatial voxel model structure of the shell weld.According to the propagation law of the geometric acoustics and the spatial voxel coordinates,the spatial sound field distribution of the measured body is calculated by Monte Carlo algorithm.The sound field parameters are projected on each voxel,which the virtual focus is the geometric center of the voxel and the 3D image of the defect is obtained.The imaging quality is evaluated by API(3D)and T-quantification indexes assessment.5)Through the sound field simulation method,analysis the effect and performance of coded ultrasound 3D imaging which shows that the API(3D)of part matrix ultrasound 3D imaging proposed in this thesis is close to the API(3D)of total matrix 3D imaging,and the number of echo signal receiving channels and the amount of collected data are significantly reduced,moreover computing efficiency is improved by about 35%.6)Ultrasonic testing system was set up in the laboratory to simulate the weld defects of the shell.The defects of the test block were processed according to the standard of?Rules and quality grades of submarine hull structure welding quality inspection?.The sound field parameters calculated from the echo data which obtained form part matrix data under the coded ultrasonic excitation were projected into the space voxel model of the test block.The 3D image of the defects can easily obtain the defect morphology characterization and provide the basis for the quantitative evaluation of defects.