Study On The Ultrasounds Stimulated Inside Carbonenhanced Composite Materials By 2 Micrometer Laser

Ultrasonic detection is an advanced way of non-destructive evaluation,which involves the stimulation of the ultrasound,collection of the acoustic signal containing information of the materials,and the analysis and evaluation of the ultrasonic signal.There are several sources of the ultrasound that are used to make the detection,like sounds generated inside the material that is about to detect by electrical stimulation,or heat,or light radiation,ultrasound coming from an outside source like an ultrasonic generator,etc.And this paper is to study on the stimulation of ultrasound with a pulse laser.To be specific,it is to research on and understand how ultrasonic is generated by a 2?m pulse laser in a carbon-enhanced composite material both theoretical and experimentally.To begin with,the background and the meaning of the study is introduced.Also,Descriptions about the history of 2?m actively Q-switched laser,the developments of laser ultrasonic,and its application in the field of composite detection are made.Plus,the theory of the thermos-elastic generation and the characteristics of the generated ultrasound are analyzed.Comsol Multiphysics is utilized here to simulate the generation and propagation of the ultrasonic generated inside the composite material.Three different models are studied to help us understand the whole process.The first one is a model of one layer board made of carbon-enhanced composite materials.The next one is a model of three layers with a layer of epoxy as the connection.The last one is a model used to understand the process of getting a Lamb wave and a Rayleigh with a good orientation.For each model,we analyzed the influence of the materials,the lasers,as well as the defects inside the materials on the output ultrasonic results.Next,the rate equations of both continuous-wave Ho:YAG laser along with the actively Q-switched Ho:YAG laser are set up and analyzed.So are the thermal distribution and thermal lens effects of the crystal.Meanwhile,the Tm:YLF laser as the pump and the actively Q-switched Ho:YAG laser are demonstrated so that a quite satisfying 2?m laser which could be used to stimulate the ultrasound inside the composite materials is prepared.At last,I used the laser setup demonstrated last part and the theoretical knowledge obtained before to experiment on the stimulation of the ultrasonic.Detailed stimulation results are given here as well as the analysis and the comparison of the results.As we can see,the experimental data is a match to the result of comsol simulation.This part will lay a solid ground for further study in the field of thermos-elastic generation and laser ultrasonic.