The Temperature And Thermal Stress Analysis Of Metal Target Exchanging Process With The Millisecond Pulsed Laser Shocking

At the end of 20th century, more and more aspects of human life are involved in laser. Using laser shocking, we can synthesize so many new materials, especially in synthesizing the nano-materials. We can also use laser in the material surface process. The interaction between the materials and the laser is a dramatic and unbalanced process. Because of the parameters in the experiment including temperature, laser pressure and thermal stress etc. change dramatically in a very short time. and it is difficult to in-time observe and monitor the certain process in any experiment conditions. Thus, the theory analysis and numerical calculation become an important way that people realize the process of the interaction between the laser and materials.Our research group give a new method of synthesizing the nano-materials which is using millisecond pulsed laser shocked the surface of metal target. We put the titanium target in the deionized water, and use the ND:YAG pulsed laser shocking the target. The power density of laser is P=2100W; the laser facula radius r0=0.3mm,and the diameter and the thickness of the cylinder target are both 0.1cm. At least, we separate and purify the products in order to attain the nano-materials. According to the physical model we established, the problem we researched can be considered as a 2 dimension heating transaction problem. The variation of the temperature leads to the changes of the material's property: when the deformation rate in a high standard, the interaction among of the stress, strain and temperature is very complicated. This dissertation using the thermo-elastic theory analyzes that thermal stress caused by the temperature increasing. In the section 4 of this dissertation, we use the MATLAB to calculate the laser-shocking-target model with the convection-radiation coupled boundary condition, and we use the Galerkin method and variational principle to calculate the thermal stress caused by the temperature increasing.According to the calculation, we can get the temperature variation of the titanium target after a period time of temperature increasing, with lower power density pulsed laser shocking(106W?cm-2). And we can get the temperature distribution along the r axis and z axis directions. at the time of 70ns, the temperature on the surface of titanium target is reaching to the about 4300K. At this time, the convection, thermal radiation and the energy of laser shocking can get to the balance, and thus the temperature is no longer increasing. Accompany with the laser shocking, after the titanium gasification, the target become to a high temperature and high pressure plasma, and this is the basis condition of synthesizing the nano-metal materials.