A Numercial And Experimental Study Of The Mechanism Of Miro-nano Manfacture Based On Laser-Induced Cavitation

Laser-induced cavitation is the cavitation phenomenon that laser breakthough the liquid optically.When the high-power laser is on the surface of the liquid or material,if the laser energy density exceeds the breakdown threshold of the material,the optical breakdown and the high-temperature plasma are generated at the same time in the laser action area.Accompanied by the plasma absorbing the subsequent laser energy and shock-wave radiation,laser-induced cavitation bubble also begins to be formed.After cavity formation, under both inside and outside pressuregradients,the bubble can expand and contract with shock wave radiation and micro jet.After several times of pulsation,the bubble will eventually disappear because of all the energy dissipation.The plasma,shock wave and micro jet in the process of cavitation can achieve the micro-nano manufacturing.In this paper, Conducted is the numerical and experimental research on the mechanism of micro-nano manufacturing based on laser-induced cavitation, the detailed research contents are as follows:A simplified model for the micro-nano fabricating based laser-induced cavitation was created,which Illuminated several detailed bubble kinetics which could not be observed by the experimental methods. A mathematical model in light of the potential flow theory was applied to describe the mentioned issue.Considering the influence of fluid compressibility, an approximate perturbation method was developed in terms of the matched asymptotic expansion method.It was concluded that the velocity potential near the bubble surface coincided with Laplace's equation. A dimensionality decrease of the initial 3D potential problem to a ultimate 1D solution was achieved in a cylindrical polar coordinate.It is essential to simplify the fabricating model and treat toroidal bubble accutely. The manufacturing numerical model based on the mixed Eulerian-Lagrangian (MEL) method and the fast multipole boundary elemental method (FMBEM) for bubble dynamics in a weakly compressible liquid near a solid boundary was established.Carried outwere the experimental researches about the mechanisms of some kinds of materials(Al,Silica Gel) micro-nano manufacturing based on laser-induced cavitation.A single cavitation bubble was brought forth with a single pulse Q-switched Nd:YAG laser pulse.The bubble's maximum expansion volume was controlled by the energy of the single incident laser pulse. The incipient position of the single cavitation bubble significantly impacted on the bubble kinetics, which was precisely regulated with a micro-translation stage.A high-speed video camera furnished the real-time and direct monitoring the bubble evolutions. It illustrated detailed deformations of the cavitation during the micro-nano fabrication process including the non-spherical bubble generation proximity to the surface of the materials and the nearly spherical shape during the first expansion phase.a high-speed microjet resulting from the asymmetry of the flow field was used for micro manufacturing and simutaneously a nozzle was directed at precisely controlling shape,Indirect detections of the acoustic signals transmited by the oscillating bubbles and manufacturing process, using a hydrophone system, estimated much more accurately how much the bubble oscillation periods had a influence on the manufacturing process.When the maximum expanded bubble radii were known,the statistics of the non-dimensional bubble oscillation periods could be utilized to approximately forecast the bubble initial positions,which made micro-nano fabrication more precisely.Temporal evolutions of the bubble volume were analyzed in this study by a fresh approach involving the application of CAD. The energy reserved in the bubble was measured using the maximum expanded size after the jet impact.Eventually, the numerical results calculated access to the MEL-FMBEM model were confirmed with previous numerical results and reliable analytical results. Available comparisons were made between the numerical results and the experimental results originated from this study, including those for the evolution of the equivalent bubble radius, the non-spherical bubble shape, and the movement of the bubble cores.An significant benefit of the numerical method were capable of calculating the flow field dynamics near the microjet onto the material surface and the bubble surface. The pressure contours and velocity vectors on the mircrojet contact surface and bubble surface could be simulated under a fixed grid across the liquid field.The jet impact dynamics and the induced hammer pressure that impinged on the materials were calculated and verified access to previous experimental measurements. The formation of the counterjet during micro-nano fabricating was also shed light on with the numerical simulations.Fianally,it presents that water hammer pressure is the main cutting force during the fabrication.