| In view of the characteristics of solid-state laser ultrasound detection devices such as large size,high price,and difficult to debug,as well as the visualization method of the ultrasound propagation process and its application in the field of defect detection,this paper combines laser ultrasound and optical fiber sensing technology and proposes A laser ultrasonic detection method based on optical fiber light deflection.A set of allfiber laser ultrasonic detection device is built and applied to a laser ultrasonic detection system to realize the visualization of the ultrasonic propagation process and achieve the purpose of defect detection.The device is composed of optical fibers and optoelectronic devices,and each component is fixedly connected to avoid cumbersome optical path debugging.Compared with traditional detection methods,the system has the advantages of non-contact,wide frequency band,anti-electromagnetic interference,simple structure and easy debugging.In particular,this optical fiber optical deflection detection device can detect light beams deflected in any direction,that is,ultrasonic waves propagating in different directions on the sample surface,while traditional optical deflection technology can only detect sound waves propagating in a single direction.Based on this system,we have studied the characteristics of the surface ultrasonic waves propagating along the metal surface,and scanned the metal surface.Combined with the laser ultrasonic visualization algorithm,the propagation process of surface ultrasonic waves propagating along the sample surface is visualized.The content of the paper is as follows:First of all,this paper proposes and designs an optical deflection detection device based on optical fiber by combining optical fiber sensing technology,introduces the structure of the system in detail,and combines traditional optical deflection detection technology to analyze its detection mechanism from a qualitative and quantitative perspective.,And then analyze the factors that affect the detection capability of the system.Secondly,we built a complete laser ultrasonic visual inspection system,including the use of pulsed laser to excite ultrasound,the use of galvanometers to scan the excitation beam,and the use of the proposed optical fiber optical deflection device to detect ultrasound.Through the experimental device,the time-domain waveform is obtained,and the visualization of the ultrasonic propagation process on the sample surface without defects is realized.Finally,we used the same experimental device to perform a two-dimensional surface scan on the sample surface.The samples contained circular vertical holes and strip-shaped groove defects.In the experiment,different scanning steps are used to analyze the influence of scanning steps on the visualization effect;different scanning methods are used to analyze the influence of scanning methods on the visualization effect.The experimental results show that the smaller the scanning step,the higher the resolution of the ultrasonic propagation process;in addition,because the point source is used to excite the ultrasound with the ablation mechanism,when the scanning area covers the detection point,the excitation light will damage the surface at the detection point location,Resulting in a sharp drop in detection efficiency,so it is necessary to plan the scanning route.Through the visualization results of the ultrasonic propagation process on the sample surface,the tip scattering phenomenon at the defect can be observed,which is consistent with the theoretical analysis.Due to the different shape of the circular defect and the strip defect,the reflection and scattering of the ultrasonic wave propagating to the two types of defects are different.Compared with the reflection phenomenon of the ultrasonic wave caused by the circular vertical hole defect,the ultrasonic wave occurs at the strip groove defect.The reflection phenomenon is more obvious.In this paper,combined with optical fiber sensing technology,the laser ultrasonic detection method is studied,and a new detection method is proposed,which not only avoids the inconvenience of carrying and debugging the space-based detection device,but also provides a new method for detecting laser ultrasonic surface waves.At the same time,combined with visualization technology,it provides a new idea for the research of laser ultrasonic detection of crack defects. |
