针对厚钢板内部缺陷的检测问题, 利用合成孔径聚焦技术(SAFT)实现了厚钢板样品内部缺陷的定位及成像。移动脉冲激光线源在样品内激发超声纵波, 利用激光测振仪在固定点探测得到超声时域B扫描信号, 从时域信号中提取缺陷反射的纵波回波, 对样品内部缺陷进行成像。使用有限元方法对该成像过程进行数值模拟, 并通过实验对其进行验证, 所获得的实验结果与数值计算结果一致。采用这一缺陷成像方法可在缺陷回波信噪比较低的情况下实现缺陷检测, 并且过程简便, 在激光超声检测领域具有应用价值。

To deal with the detection of the internal defect in the thick steel plate, we adopt the synthetic aperture focusing technique (SAFT) to locate and image the internal defect of the thick steel plate. The moving pulse laser line source is used to generate the longitudinal ultrasonic waves in the steel sample. The laser vibrometer is applied to obtain the time-domain ultrasound B-scan signals at the fixed point. The longitudinal echo-waves reflected by the defect are extracted from the time-domain signal. And the imaging of the internal defect of the sample is realized. This imaging process is simulated numerically by the finite element method (FEM) and verified in the experiment. The experimental results coincide well with the numerical calculation results. The proposed defect imaging method can realize the defect detection under the circumstance where the defect echo-waves have a low signal-to-noise ratio (SNR). The process of this method is simple and convenient, and the method has practical value in the laser-ultrasonic detection field.