焊缝散射对板中超声水平剪切导波直线合成孔径阵列成像的影响

The influence of weld scattering on line synthetic aperture array imaging of ultrasonic shear horizontal guided waves in plate

为探讨焊缝散射与板中超声导波阵列成像之间的关系,提出了将散射渡越时间矩阵作为分析工具用来开展焊缝散射对板中超声水平剪切(Shear horizontal,SH)导波直线合成孔径阵列成像影响的研究。运用散射因子和散射渡越时间矩阵描述焊缝散射,结合分析超声SH导波直线阵列信号所特有的圆锥曲线特征和合成孔径成像算法,从导波阵列信号和阵列成像机理出发,重点研究了焊缝散射因子和散射渡越时间矩阵在阵列成像中的作用。结果显示,焊缝散射易造成同一成像散射体反射声波的阵列信号形成"多峰",焊缝散射因子随之同步变大,散射渡越时间矩阵的秩随之成倍数关系增大,导致导波图像相应出现对应倍数的"条带"伪像,图像椭圆簇轨迹特征复杂化,特别是图像背景噪声增幅可达50%,图像信噪比减小幅度可达10%。成像实验验证了理论分析的有效性,表明散射渡越时间矩阵是研究焊缝散射对超声导波阵列成像影响规律的有力工具,该影响规律的揭示可为深入开展焊接板结构超声导波阵列图像处理和图像识别提供基础。

The matrix of scattering time of flight （MSTF） was proposed to line synthetic aperture array imaging of ultrasonic shear horizontal guided discuss the influence of weld scattering on （SH） waves in plate, which could be used into explicating the relation between the weld scattering and the array imaging of ultrasonic guided waves. The weld scattering factor （WSF） and the MSTF have been used into describing the weld scattering, the cone characteristic of line array signals and the ultrasonic SH guided waves imaging theory of line synthetic aperture array with MSTF were all researched. After that, with the help of the array signals and the array imaging theory, the roles of the WSF and MSTF in array imaging of ultrasonic SH guided waves were emphasized. The result shows that, the weld scattering may cause ＂multi-peaks＂ of array signals for the same defects, then the WSF become larger synchronously. Because of which, the rank of MSTF would become larger by multiple times of WSF that lead to pseudo strip-shaped shadows with the same degree, and the characteristic of elliptical cluster tracks of array image become more complicated, especially the background noise of image may increase 50% and signal-nose ratio may decrease 10%. The imaging experiment verify the validity of the theory analyze proposed, and which indicate that the MSTF may be a forceful analysis tool that may be used into researching the influence of weld scattering on line synthetic aperture array imaging of ultrasonic SH waves in plate, which could provide support for array image processing and array image recognition of ultrasonic guided waves in plates with welded structure.