| When there is a high power laser irradiating on Aluminum alloy, a kind of shock wave which propagation based on thermal conduction and fluid dynamics will be produced, which is called laser-supported absorption wave(LSAW). The generation procedure of the LSAW is including temperature rise, corrosion, plasma produce and many other physical process.Because each different physical process will affect the generation and propagation, it is important to take consideration on those process when researching on the LSAW. In this dissertation, the whole procedure of LSAW generated by long pulse laser interaction with Aluminum alloy is discussed in both theoretical and experimental aspect.On the theoretical part, it is build a theoretical model of LSAW generated by long pulse laser interaction with Aluminum alloy. For the temperature rise part of the model, solve the phase change problem which after material melting and vaporization by using equivalent specific heat method at first. Then introduced the functions of thermal conductivity and specific heat capacity changing by time, and complete the model modification at last. For the corrosion, it illustrated the phase change of melting and vaporization stages by enthalpy and porosity method and gas dynamics method. Then, there are two difficulties has been solved which are unsmooth phase step of gas-liquid interface and non-conservation of mass during the melting and vaporization process. After that, the trace of gas-liquid interface is finished by improved level set method, following by deducing the rules of the corrosion state changing of Aluminum comparison with laser fluence. At last, it is successfully modified the model which is focusing on he laser fluence distribution after corrosion. For the LSAW part,research on the energy balance process and the plasma shielding phenomenon of inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. Then achieve the changing of laser fluence which irradiating on material surface when the LSAW occurs,leading to the laser fluence modification of the model.On the simulation part, there is a simulation model of LSAW generated by long pulse laser interaction with Aluminum alloy building based on the theoretical model, and complete the simulation research on both single and multiple pulse mode. For the single pulse mode, it is discussed the relationship and causes between laser fluence or pulse length and other parameters, such as material temperature, melting depth, melting radius, plasma density,LSAW threshold and speed. Moreover, turbulence distribution rules of LSAW velocity vector under the focusing beam has been explained, then analysis the energy balance process and mechanism of transmission of LSAW. For the multiple pulse condition, it shows that theinfluence of laser pulse numbers on the material temperature, ablation depth and radius.Furthermore, the generation time of LSAW comparison laser pulse number and frequency has been studied, then analysis the mechanism as well.On the experimental part, it is finished the research on the temperature rise, corrosion,the generation and propagation of LSAW when long pulse laser interaction with Aluminum alloy. On single pulse mode, the relationship between laser parameters and ablation performance has been studied, which including Aluminum alloy material temperature,melting depth, melting radius, plasma density, LSAW threshold and speed. Same as the simulation study, on the multiple pulse mode there is results of the rules for laser pulse number, laser frequency comparison with the generation time of LSAW, material temperature, ablation depth and radius. At the same time, the turbulence distribution of LSAW is achieved by the shadow images as well. At last, compare the simulation and experimental result, it is found that the trend is exactly same, which shows that the model build in this dissertation is able to explain the whole procedure of LSAW generated by long pulse laser interaction with Aluminum alloy successfully. |
PDF Full Text Request