本文選題：激光空化　切入點：微射流　出處：《江蘇大學》2017年碩士論文　論文類型：學位論文

【摘要】：空化是一種常見于水力設備中的流體現(xiàn)象,而空化引起的空蝕破壞問題則嚴重影響著水力機械等部件的安全性能。本文主要以水泵中最為常見的鑄鐵材料為研究基體,利用ANSYS軟件中流固耦合模塊對激光誘導空泡潰滅時產生的高速微射流速度及其對材料的沖擊壓力進行了模擬研究,分析不同激光參數(shù)下空化作用對鑄鐵材料基體形變、應力分布等影響;同時搭建了激光空化實驗平臺,研究激光空化作用對鑄鐵試樣性能的影響,并通過超聲波空蝕試驗,對比分析了激光空化作用前后材料在不同空蝕時間段內的空蝕行為。主要的研究內容及結果如下:(1)在ANSYS仿真軟件中采用流固耦合方法,結合VOF多相流模型、激光熱效應公式等仿真變量對近壁面空泡潰滅時產生的微射流速度大小及沖擊作用壓力等現(xiàn)象進行探討,發(fā)現(xiàn)隨著離焦量H的不斷增加,空泡潰滅微射流的速度及其形成的沖擊壓力值呈現(xiàn)出先增大后急劇減小的變化趨勢,并在H=1mm時達到最大值;同時將流體域中高速微射流等計算結果引入固體域仿真中,計算分析不同參數(shù)下激光空化作用對鑄鐵材料形變、應力分布等性能的影響,研究表明激光空化作用后鑄鐵材料中的殘余壓應力最終呈半球狀分布,而試樣中的最大殘余壓應力值則出現(xiàn)在作用區(qū)域的亞表層。(2)采用激光空化實驗方法,探討不同激光能量、離焦量參數(shù)條件下的激光空化作用對鑄鐵表面三維形貌及殘余應力分布的影響,研究表明隨著能量的增加,鑄鐵試樣表面作用區(qū)域的最大深度及殘余壓應力值也隨之增大;而隨著離焦量H的增加,作用區(qū)域的殘余壓應力則呈現(xiàn)出先增大后減小的規(guī)律,并在離焦量H=1mm時達到峰值,同時歸納總結出激光空化對鑄鐵試樣作用機制的三個階段,并驗證了模擬結果的正確性和流固耦合仿真方法的可行性。(3)分析鑄鐵基體在空蝕破壞作用下微觀形貌、空蝕失重等參數(shù)的影響關系,詳細闡述了鑄鐵基體表面在不同階段所對應的裂紋萌生、裂紋擴展、塑性變形堆積、表層材料剝落等空蝕機制;同時對激光空化作用區(qū)域在空蝕不同時間段內的形貌及硬度變化的原因進行分析,闡述了不同激光能量參數(shù)對鑄鐵試樣抗空蝕性能的影響以及激光空化作用區(qū)域變形破壞的空蝕機制,研究表明隨著激光能量的增加,作用區(qū)域的硬度提升也越明顯,對鑄鐵材料進行空蝕破壞時,試樣表面會出現(xiàn)一定的塑性變形和加工硬化現(xiàn)象,硬度也呈現(xiàn)出先增大后減小的變化趨勢,而隨著離焦量H的增加,鑄鐵表面作用區(qū)域面積的縮減量以及縮減速率都呈現(xiàn)出先減小后增大的變化關系,并當H=1mm時達到最小值。
[Abstract]:Cavitation is a common fluid phenomenon in hydraulic equipment, and cavitation damage caused by cavitation seriously affects the safety performance of hydraulic machinery and other components. By using fluid-solid coupling module in ANSYS software, the velocity of high speed micro jet and its impact pressure on the material produced by laser induced cavitation collapse are simulated. The deformation of cast iron matrix caused by cavitation under different laser parameters is analyzed. The influence of laser cavitation on the properties of cast iron samples was studied, and the ultrasonic cavitation test was carried out to study the effect of laser cavitation on the properties of cast iron. The cavitation behavior of materials before and after laser cavitation is compared and analyzed in different cavitation time periods. The main research contents and results are as follows: 1) the fluid-solid coupling method is used in ANSYS simulation software, combined with VOF multiphase flow model. Simulation variables such as the formula of laser thermal effect are used to study the phenomena of velocity and impact pressure of micro-jet produced when the cavity collapses near the wall. It is found that with the increasing of defocus H, The velocity of the bubble collapsing and the impingement pressure showed the tendency of increasing first, then decreasing sharply, and reaching the maximum value at H1 mm, and introducing the calculation results of high speed micro jet in the fluid domain into the simulation of the solid domain. The effect of laser cavitation on the deformation and stress distribution of cast iron under different parameters is analyzed. The results show that the residual compressive stress in cast iron is hemispherical after laser cavitation. However, the maximum residual compressive stress in the sample appears in the subsurface layer of the action area. (2) the laser cavitation experiment is used to study the different laser energy. The effect of laser cavitation on the surface morphology and residual stress distribution of cast iron under defocus parameters is studied. The results show that the maximum depth and residual compressive stress of the surface of cast iron specimen increase with the increase of energy. However, with the increase of defocus H, the residual compressive stress in the acting region increases first and then decreases, and reaches the peak value at 1 mm defocus. At the same time, three stages of the mechanism of laser cavitation on cast iron samples are summarized. The correctness of the simulation results and the feasibility of the fluid-solid coupling simulation method are verified. The cavitation erosion mechanisms such as crack initiation, crack propagation, plastic deformation accumulation, surface material exfoliation and so on on the surface of cast iron matrix at different stages are described in detail. At the same time, the morphology and hardness of laser cavitation in different time periods are analyzed. The effect of different laser energy parameters on the cavitation corrosion resistance of cast iron samples and the cavitation mechanism of deformation and failure in the region of laser cavitation are described. The results show that the hardness of the area increases with the increase of laser energy. When the cast iron is destroyed by cavitation erosion, there will be plastic deformation and work hardening on the surface of the cast iron, and the hardness will increase first and then decrease, and with the increase of defocus H, The reduction of the surface area and the reduction rate of cast iron surface showed the relationship of first decreasing and then increasing, and reached the minimum value when H0 was 1 mm.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG143;TG665

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