| Cavitation and cavitation erosion is a kind of phenomenon that can not be avoided in hydraulic machinery, and even leads to disaster. Most scholars believe that the jet and the shock wave of bubble is the cause of cavitation erosion. In recent years, scientists began to develop the study of the cavitation peening by using the extreme condition of bubble collapse. Because of good symmetry and control ability, the laser-induced bubble has become an important means to study the bubble jet and the shock wave. In the present paper, put the laser-induced bubble as the research objet, using a combination of simulation and experimental methods to search its effects on 2A02 aluminum alloy. Through change the liquid, the distances between bubble and wall and laser energy to compare the difference of targets under different conditions. Besides, we analyze the mechanism of the bubble jet and shock wave pressure to determine the feasibility of the strengthening mechanism by the jet and the shockwave. Apply reasonable laser cavitation parameters to improve material properties. Some specific research contents are as follows:(1) The finite element model was established for the evolution of cavitation bubble near the wall by FLUENT software. In the simulation, we using the VOF multiphase flow model combined with the cavitation model and N-S equation. Additionally, the laser thermal effect formula was used to transform laser energy into the temperature and pressure of FLUENT software reasonably. The bubble collapse characteristics of differenet liquids and different non dimensional constant?was given by numerical simulation. The results show that the bubble surface is not easy to form pits when non dimensional constant?is to large or small, only when?=1.2,the bubble surface occurred obvious depression. Besides, the liquid viscosity is conducive to maintaining the stability of the bubble compared with the surface tension and saturated pressure of liquid.(2) The result of jet velocity of bubble collapse under different liquid and different non dimensional constant?was investigated by means of numerical simulation. By comparing the result of velocity, the causes of the different was analyzed. Additionally,the yield strength of 2A02 aluminum alloy was compared to the jet impact pressure,which was calculated by water hammer formula, to verify the feasibility of jet impact pressure for material strengthening.(3) Selection of 2A02 aluminum alloy as the experimental target, generate bubble in the vicinity of the target in water, alcohol, silicon by using laser equipment in experiment. Using high speed camera to shoot the whole bubble pulsation process near the target wall and comparing with the results of the bubble oscillation process obtained by simulation to verify the correctness of the simulation. Comparing the surface morphology of target under different liquid and distance between bubble and wall, to analyzes the effect of the jet and shock wave when bubble collapse; While changing the laser energy and the distance between bubble and wall to further discuss its effect on residual stress of target surface, the results show that the bigger laser energy, the greater the residual compressive stress in the target surface, and with the increase of distance the residual stress reduce after the first increase; Comparing three types of liquids in the size of the target residual stress, we can see three types of residual stress are all compressive residual stress, indicating that surface properties of target have a certain upgrade after laser cavitation, the jet pressure and the residual stress values obtained by simulation and experiment were compared and found that the two trends are basically the same, to verify the accuracy of the simulation results. |
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