| Metallic materials have wide applications in the fields of production and life.However, on the hostile conditions such as high temperature, high voltage, high speedand high loads, materials are easily subjected to different degrees of damages. Also,fatigue damages inside the materials may lead to cracks or complete ruptures, whichcould result in huge losses of property or life. Therefore it is very crucial to conductthe health monitoring for materials.Laser Ultrasonic (LU) testing technology is a non-destructive technology formaterial health monitoring, which is a subject to study the generating mechanism,propagating and receiving of ultrasound waves induced by laser in the materials. Onthe other hand, people have paid much attention on LU for its good features, such asremote distance detection, non-contact, without restriction about the surface andgeometry of materials, wide frequency bandwidth testing, et al.In this paper, iron and aluminum blocks were as samples to conduct LU testing.A Nd: YAG laser was as excitation source and an interferometer as a receiver. Theposition of flaw was determined by using reflected surface acoustic waves. Aftercalculation, the relative error is1.2%.The thickness of an aluminum plate was measured by surface acoustic wave andlongitudinal wave. Compared with the actual value, the relative error is less than0.5%. It is also studied that when the lens (focal length100mm) from the test sampleis about88mm, the effect of the ultrasonic signal received is best.By scanning the surface of an aluminum block with artificial flaws via laser,longitudinal ultrasound waves were excited in the material. Using a Matlab program,the data acquired were processed by wavelet threshold denoising. Then a3D model ofthe aluminum block with artificial defects was reconstructed. Such that，the flaws in the aluminum block can be visualized by LU imaging, including positions and sizes.It is demonstrated that LU imaging is a non-destructive defect testing method formetallic materials. |
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