对脉冲衍射时差法超声探伤技术(TOFD)作了原理探析。在超声A扫描的基础上, 解释了TOFD图像的形成原理。讨论了TOFD技术的两种扫查方式, 即平行扫查和非平行扫查, 并对后者作详细论述。给出了上折射角和下折射角等参数的计算方法, 由此分析了扫查范围。分别给出了有、无缺陷工件的TOFD检测图像, 进一步分析TOFD成像机理, 归纳TOFD检测的特点。最后对TOFD检测盲区作了分析, 给出了上下表面盲区计算方法, 并根据CEN/TS 14751—2004标准给出了五种不同厚度工件的表面盲区。

The principle of ultrasonic time of flight diffraction(TOFD) method was analyzed. Based on ultrasonic A-Scan, the TOFD imaging principle was investigated. Two scan methods of TOFD, as parallel and non-parallel scan methods were discussed, and the second was analyzed in detail. The calculation formulas of up and down refraction angle were given, and then the scan range was analyzed. The TOFD imagines of work piece contained defect or not were given, the TOFD imaging principle was investigated more deeply, and the character of TOFD testing was concluded. Finally, the dead area of TOFD testing was investigated, the calculation formulas of up and down dead area were given, and according to the standard CEN/TS 14751—2004, the dead area of five different thickness work piece was given.