基于激光超声的钛合金裂纹合成孔径组合成像研究

Synthetic aperture combination imaging of cracks in titanium alloy based on laser ultrasonics

针对钛合金内部疲劳裂纹激光超声成像问题,提出了一种基于合成孔径聚焦技术的多模式组合成像方法。采用扫描激光源法,通过提取不同探测位置的时域模式回波信号,根据Bscan图中反射纵波与反射横波的幅值分布,将裂纹回波时域特征进行分区重组,对其进行反演聚焦完成了对内部裂纹的识别及图像重构。使用COMSOL Multiphysics对钛合金板材内部裂纹成像过程进行数值模拟并通过MATLAB图像算法验证了其可行性。与单一模式波成像相比,采用反射纵波与反射横波组合的成像方法有效减少了伪像,实现了对内部裂纹的定位及图像重构,重构裂纹位置X轴与Y轴相对误差均在3以内。

In this paper,a multi modal combination imaging method based on synthetic aperture focusing technique is proposed to address the laser ultrasonic imaging problem of internal fatigue cracks in titanium alloy.The scanning laser source method is employed to extract time domain mode echo signals from different detection positions.By analyzing the amplitude distribution of reflected longitudinal waves and reflected shear waves in the B scan image,the temporal characteristics of crack echo signals are partitioned and recombined.Furthermore,inversion focusing is applied to accomplish the recognition and image reconstruction of internal cracks.The feasibility of this approach is demonstrated by conducting numerical simulations of the internal crack imaging process in titanium alloy plates using COMSOL Multiphysics,and its viability is further validated using MATLAB image algorithms.Compared to single mode wave imaging,the imaging method that combines reflected longitudinal wave and reflected shear waves effectively reduces artifacts,enabling accurate localization and image reconstruction of internal cracks.The relative errors of the reconstructed crack positions in the X axis and Y axis are both within 3%.