摘要
针对超声衍射回波渡越时间（TOFD）法对近表面缺陷不敏感、被测表面以下8mm之内为盲区的现状，提出一种改进的基于衍射和反射回波的渡越时间（TOFDR）的缺陷识别技术。该法不再直接检测缺陷上下端部衍射的信号。通过检测经过底面反射一次的衍射信号，避免了侧向波和衍射波的叠加，将盲区缩减到被测表面以下2mm，且可以实现在线检测。阐述了该法的原理，给出了缺陷参数的计算方法，分析了探头间距和频率的影响。实验表明，该法可以检测到表面下2—35mm内94％的垂直裂缝，实际位置和尺寸同计算结果吻合，精度可达±0．3mm。
According to the time ot flight diffration （TOFD） insensitive to near surface cracks with a blind area from 0-8 nun under the surface,a modified technique based on the time of flight diffraction and reflection （TOFDR） is put forward to identify and size cracks. The modified approach does not receive both tip diffraction signals directly. The overlapping of lateral wave and diffraction waves is avoided skillfully when receiving the diffraction signals after their reflected at the back wall first. The blind area has been curtailed to 0-2 nun under the surface. On-line detection is executable. The TOFDR theory is presented, the expressions denoting the size and location of a crack are deduced, and the influences of the distance and frequency of the probe pairs are discussed. The experiment shows that this approach can detect 94% standard flaws correctly located from 2-35 nun under the surface with an average accuracy of ±0.3mm.
出处
《化工自动化及仪表》
EI
CAS
2006年第4期50-52,60,共4页
Control and Instruments in Chemical Industry
基金
国家"863"计划资助项目(2001AA602021)
