Detection And Visualization Of Micro Defects Based On Laser Nonlinear Ultrasound

This article is supported by The Ph.D.Programs Foundation of Ministry of Education of China(No.2013142012007)and General Assembly pre research project "XXX damage detection technology".Aiming at the problems of micro defect detection and visualization of laser nonlinear ultrasonic,we expand in-depth research.Around the laser nonlinear ultrasonic detection,the following main research is carried out: starting from the traditional laser ultrasonic testing technology,combined with the nonlinear ultrasonic testing technology,we use laser nonlinear ultrasonic to detect cracks,and focus on the theory and model establishment of laser nonlinear ultrasound.The interaction mechanism of laser ultrasound and micro defect is studied deeply,and the visual image reconstruction of cracks is reconstructed by simulation.The research results in this paper can provide the basic and theoretical basis for the qualitative and quantitative detection of micro defects on the surface of the material,and the main research work and content are as follows.1?Combined with laser ultrasonic testing technology,laser nonlinear ultrasonic detection technology and laser ultrasonic visualization technology,the research progress at home and abroad is introduced in detail,and the source,background and significance of the subject are introduced in detail.2?A laser ultrasonic nonlinear model is established,combined with the characteristics of laser ultrasonic waveform,take the traditional ultrasonic modulation mechanism as the starting point,focusing on the interaction mechanism between laser and ultrasonic crack,combined with cross modulation theory,Two methods for determining are proposed from the aspect of the amplitude modulation index and the energy modulation index.The one to one mapping relationship between the crack depth and the modulation index is obtained;Finally,according to the theory of energy attenuation correlation,the corresponding calculation method of laser nonlinear ultrasonic energy attenuation is proposed.3?The experimental system is designed and built,and four aspects are introduced and explained in detail from the following aspects: laser ultrasonic excitation system,laser ultrasonic signal detection system,laser ultrasonic data acquisition system and sample preparation.According to the experimental system,the related experiments of laser ultrasonic detection are carried out.4?The extraction method of ultrasonic nonlinear coefficient of laser is put forward,using it to process the experimental data,obtained the corresponding characterization results:mapping relationship between the transmitted wave and reflected wave laser ultrasonic nonlinear coefficient,modulation index,energy attenuation value and the crack depth was obtained.The experimental data are processed by the related laser nonlinear ultrasonic algorithm,and the quantitative detection of the crack is realized.5?In this paper,in order to achieve visual simulation of related processes,combined with the K-WAVE toolbox,compiling corresponding programs,The process of ultrasonic propagation,the process of heat propagation and the image reconstruction are preliminarily studied,which lays the foundation for the subsequent research on visualization.