基于激光空化强化提升铸铁材料抗空蚀性能研究

发布时间：2018-03-09 05:12

本文选题：激光空化　切入点：微射流　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：空化是一种常见于水力设备中的流体现象,而空化引起的空蚀破坏问题则严重影响着水力机械等部件的安全性能。本文主要以水泵中最为常见的铸铁材料为研究基体,利用ANSYS软件中流固耦合模块对激光诱导空泡溃灭时产生的高速微射流速度及其对材料的冲击压力进行了模拟研究,分析不同激光参数下空化作用对铸铁材料基体形变、应力分布等影响;同时搭建了激光空化实验平台,研究激光空化作用对铸铁试样性能的影响,并通过超声波空蚀试验,对比分析了激光空化作用前后材料在不同空蚀时间段内的空蚀行为。主要的研究内容及结果如下:(1)在ANSYS仿真软件中采用流固耦合方法,结合VOF多相流模型、激光热效应公式等仿真变量对近壁面空泡溃灭时产生的微射流速度大小及冲击作用压力等现象进行探讨,发现随着离焦量H的不断增加,空泡溃灭微射流的速度及其形成的冲击压力值呈现出先增大后急剧减小的变化趋势,并在H=1mm时达到最大值;同时将流体域中高速微射流等计算结果引入固体域仿真中,计算分析不同参数下激光空化作用对铸铁材料形变、应力分布等性能的影响,研究表明激光空化作用后铸铁材料中的残余压应力最终呈半球状分布,而试样中的最大残余压应力值则出现在作用区域的亚表层。(2)采用激光空化实验方法,探讨不同激光能量、离焦量参数条件下的激光空化作用对铸铁表面三维形貌及残余应力分布的影响,研究表明随着能量的增加,铸铁试样表面作用区域的最大深度及残余压应力值也随之增大;而随着离焦量H的增加,作用区域的残余压应力则呈现出先增大后减小的规律,并在离焦量H=1mm时达到峰值,同时归纳总结出激光空化对铸铁试样作用机制的三个阶段,并验证了模拟结果的正确性和流固耦合仿真方法的可行性。(3)分析铸铁基体在空蚀破坏作用下微观形貌、空蚀失重等参数的影响关系,详细阐述了铸铁基体表面在不同阶段所对应的裂纹萌生、裂纹扩展、塑性变形堆积、表层材料剥落等空蚀机制;同时对激光空化作用区域在空蚀不同时间段内的形貌及硬度变化的原因进行分析,阐述了不同激光能量参数对铸铁试样抗空蚀性能的影响以及激光空化作用区域变形破坏的空蚀机制,研究表明随着激光能量的增加,作用区域的硬度提升也越明显,对铸铁材料进行空蚀破坏时,试样表面会出现一定的塑性变形和加工硬化现象,硬度也呈现出先增大后减小的变化趋势,而随着离焦量H的增加,铸铁表面作用区域面积的缩减量以及缩减速率都呈现出先减小后增大的变化关系,并当H=1mm时达到最小值。
[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.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG143;TG665

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