基于自回归谱外推方法的TOFD检测盲区抑制

结合自回归谱外推方法与超声衍射时差法（Time of flight diffraction，TOFD），抑制直通波脉冲宽度造成的近表面检测盲区。建立碳钢试块模型，并设置上尖端埋深d依次为2.5 mm、3.0 mm、5.0 mm及7.0 mm的底面开口槽，模拟选用中心频率5 MHz、探头中心距34.0 mm的TOFD探头实施检测。利用自回归谱外推方法扩宽傅里叶变换后的混叠信号频带，压缩时域脉冲宽度，分离了混叠的直通波与衍射波，将TOFD检测盲区深度由8.3 mm抑制到2.5 mm以内，实现四个底面开口槽的同时检出与定位。针对碳钢试块中埋深3.0 mm底面开口槽进行试验验证，定位误差为0.30 mm。与常规TOFD和频谱分析方法相比，自回归谱外推方法以高信噪比频带为基础，外推有效频带外的高频与低频范围数据，提高时间分辨率，为TOFD检测盲区内缺陷定位提供了新思路。

Suppressionof Dead Zone in TOFD with Autoregressive#br# Spectral Extrapolation

Combining the autoregressive spectral extrapolation method with the ultrasonic time of flight diffraction method, the near surface detection blind area caused by the pulse width of lateral wave is suppressed. A carbon steel test block model having bottom notches with depth of 2.5 mm, 3 mm, 5 mm and 7 mm is set up. In the simulation, the model is detected using TOFD probes with 5 MHz center frequency and 34.0 mm probe center spacing (PCS). Autoregressive spectral extrapolation method extends the frequency band, compresses time-domain pulse width and separates the overlapping signal. The depth of dead zone is reduced from 8.3 mm to 2.5 mm and four bottom notchesare detected and positioned. Bottom notch having 3.0 mm depth is calculated with the same testing parameters in experiment, and the detected result has an absolute error of 0.30 mm. Compared with conventional TOFD and spectrum analysis methods, autoregressive spectral extrapolation method based on high SNR frequency bands and extrapolate the high frequency and low frequency range data outside the effective band, achieves the goal of improving time resolution and provides a new way for TOFD to detect defects in blind areas.