中文摘要：

将超声衍射时差法（超声TOFD）应用于奥氏体不锈钢焊缝的无损检测中，分析了焊缝组织对超声TOFD检测信号的影响；基于小波包分解技术的时频分析特性，对检测信号进行三层分解，并获得了适用于灰度成像的分解信号。结果显示：受焊缝组织结构的超声散射影响，检测图像不但存在相当程度的波纹干扰，而且其缺陷特征图像也出现了较严重的形状扭曲；选择合适的小波包分解信号可在保持时间分辨率的同时抑制噪声，基于重构信号进行灰度成像能够提高检测图像的质量并避免缺陷图像的扭曲。

英文摘要：

Ultrasonic Time of Flight Diffraction method （U TOFD） is adopted in testing the defects of austenitic stainless steel weld, and the influences caused by the weld structure are analyzed. Besides, the testing signal is decomposed by wavelet packed method （WPT） and the decomposed signal that fits for gray imaging is obtained. The results indicate that there are amount of noise stripes and shape torsion in the gray imagery because of the ultrasonic scattering caused by the column grain in weld, the noise level can be restrained without destroying the time resolution through choosing suitable decomposed signal. Eventually, gray imaging based on the decomposed signal is beneficial for improving the quality of testing signal and avoiding the torsion of the defect＇s imagery.