时反导波对管中通透裂纹扩张过程的检测规律研究

Time-reversal Method of Guided Waves for Crack Expanding Inspection in Pipeline

将时间反转方法用于管道缺陷超声导波检测时,可实现导波能量在缺陷处的时间—空间聚焦,但需进一步研究该方法对沿轴向、周向扩张通透裂纹的检测规律.采用数值时反方法观察了管中导波能量聚焦过程,研究了时反前、后缺陷回波反射系数随通透裂纹扩张过程的变化规律.结果表明,当裂纹张角较小时,时反后的缺陷回波反射系数相对于时反前增大较大,随着裂纹张角的扩张,时反前、后缺陷回波反射系数逐渐趋于相等;当裂纹轴向长度从λ/100增大至λ过程中,时反后的缺陷回波反射系数是时反前的5—8倍,且最大、小值出现规律一致.

When time reversal method is used for nondestructive testing of the pipeline with ultrasonic guided wave, the energy can be focused on the defect both in time and spatial domain. But the inspection of defects with different axial length and circumferential angle need to be further studied. Time reversal numerical simulation method was employed to visualize focusing process of guided waves in pipes. The varying of reflection coefficient of through-thickness crack before and after the time reversal method was studied. Results shown that reflection coefficient after time reversal method was much bigger than that before it when circumferential size was smaller, and it tended to be equal when circumferential size increased. When crack axial length increased from A/100 toA ,reflection coefficient after the time reversal method was about 5--8 times of that before it, and both smallest and biggest value was consistent.