Abstract:

A non-contact ultrasonic testing system using a pulsed laser for ultrasound generation and an EMAT for ultrasound detection were developed for the inner crack inspection. To avoid the laser-induced ablation damage on the specimen, thermo-elastic model was used to excite ultrasound, the EMAT probe was used to receive signals. The EMAT in plane and EMAT out of plane were used to study the transversed wave and longitudinal wave spreading in the half aluminum test block respectively. Finally, combining the shadow method, the test system was used to measure the crack on the back of the specimen, the crack depth and the actual depth are very close. It is shown that, in the thermoelastic mode, the laser excitation, the method for EMAT probe received signals are feasible in the inspection of cracks.

Key words: laser ultrasound, thermo-elastic regime, electromagnetic acoustic transducer（EMAT）, inspection of crack, shadow method

摘要：

为检测内裂纹，建立了一套基于脉冲激光激发、电磁超声探头接收的非接触型超声检测系统。为避免在试件表面产生烧蚀损伤,采用热弹性模式激发超声,采用EMAT探头接收信号。利用出平面EMAT探头和内平面EMAT探头,分别研究了横波与纵波在半圆铝制试块的传播情况。最后,结合阴影法,使用该试验系统测量了试件背面的裂纹，检测得到的裂纹深度与实际深度非常接近。证明在热弹性模式下，激光激发、EMAT探头接收信号的方法对于内裂纹的检测是可行的。

关键词: 激光超声, 热弹性, EMAT, 裂纹检测, 阴影法