基于激光冲击效应的微坑加工方法及其摩擦学性能研究

发布时间：2018-04-09 19:11

本文选题：表面织构　切入点：激光冲击　出处：《上海交通大学》2015年博士论文

【摘要】：摩擦导致的磨损是机械设备失效的最主要原因。因此,控制摩擦、改善润滑与减少磨损已成为节约能源和原材料、综合提高机械系统运转效率和服役寿命的迫切需求。微坑阵列等表面织构能够有效改善摩擦副表面的摩擦学性能,延长摩擦副的使用寿命。基于激光冲击效应的微坑阵列加工方法是一种利用激光冲击力学效应的微坑加工新方法,目前人们对该工艺的工艺方法及所加工微坑阵列的摩擦学性能了解尚不系统和深入。本文以典型金属材料作为研究对象,系统分析了基于激光冲击效应的微坑阵列加工工艺机理、工艺适用性、激光冲击工艺参数对微坑阵列几何物理性能的影响规律以及微坑阵列的摩擦磨损性能,为激光冲击工艺参数选择提供优选策略。主要研究内容包括:一、激光冲击微造型工艺机理与工艺方法研究。结合激光诱导等离子体形成过程分析和高压冲击波作用下材料高应变率动态响应过程仿真建模,揭示了激光冲击微造型工艺机理,并对微坑塑性变形状态及残余应力状态进行了预测。通过考察典型金属材料在激光冲击微造型工艺中所制备微坑几何形貌与尺寸的一致性,发现激光冲击微造型工艺具有良好的工艺稳定性和材料适用性,从而为激光冲击微造型工艺规律分析奠定了重要的前提基础。基于激光冲击微造型工艺过程,提出了一种高应变率条件下材料动态硬度的测试方法。二、激光冲击微造型工艺影响规律研究。通过激光冲击微造型试验,系统研究了激光冲击微造型工艺参数(激光功率密度、光斑直径和重复冲击次数等)对微坑几何特征(直径、深度及深径比等)和微坑表面粗糙度、塑性变形层显微硬度、晶粒尺寸等表面完整性的影响规律。研究发现,随着激光功率密度的增大和激光重复冲击次数的增加,微坑直径、深度、深径比、塑性变形层的硬化程度以及晶粒细化程度均增大,但由于应变硬化作用,会表现出冲击饱和效应。随着激光光斑直径的增大,微坑直径也相应增大,但始终小于光斑直径。在激光单脉冲能量一定的情况下,存在一个激光光斑直径阈值,当光斑直径大于该阈值时,微坑深度、深径比、塑性变形层硬化程度以及晶粒细化程度均随着激光光斑直径的增大而减小。当光斑直径小于该阈值时,在等离子体屏蔽效应的作用下,随着光斑直径的增大,微坑深度、微坑塑性变形层硬化程度以及晶粒细化程度均随之增大,微坑深径比的变化因具体情况而异。激光冲击微造型工艺对微坑表面粗糙度的改变取决于材料的原始表面粗糙度及激光冲击参数。当材料原始表面粗糙度较大,且激光功率密度和重复冲击次数较小时,微坑表面粗糙度小于原始表面粗糙度。反之,则大于原始表面粗糙度。三、动压润滑条件下微坑阵列的摩擦性能研究。在流体动压润滑条件下,通过三维计算流体动力学仿真的方法研究了微坑密度、微坑深径比等微坑设计参数和雷诺数等流体特征参数对油膜的压力分布、无量纲平均油膜承载力、无量纲平均油膜剪切力和动压系数等摩擦性能参数的影响规律。研究发现,在流体动压润滑条件下,微坑提高摩擦副动压性能的机理是微坑楔形效应和涡流效应的综合作用;在本文研究的参数范围内,存在最优的微坑密度和微坑深径比使油膜具有最佳的动压性能;而且随着雷诺数的增大,最优微坑深径比呈逐渐减小的趋势,而最优微坑密度保持不变。四、贫油润滑条件下微坑阵列的摩擦学性能研究。在贫油润滑条件下,通过设计合理的摩擦学试验并建立摩擦性能评价方法,系统研究了不同转速和载荷等工况条件下不同密度和深度微坑阵列的摩擦磨损性能。研究发现,随着微坑密度的增大,摩擦副的摩擦系数、最大承载力及失效时间等摩擦性能呈现先提高后降低的趋势,说明存在一个最佳微坑密度范围使摩擦性能达到最优,其机理是由于固-固接触区域接触比压及固-液接触区域润滑作用的双重效应;随着微坑深度的增加,摩擦性能呈现逐渐提高的趋势;同时,通过对磨损表面形貌和能量谱图的分析发现,激光冲击微坑造型能够有效降低摩擦副表面的磨粒磨损和粘着磨损。综上所述,本文结合激光冲击效应形成过程分析和激光冲击压力作用下金属高应变率弹塑性动态响应过程仿真研究,分析了激光冲击微造型的工艺过程与机理。通过激光冲击微造型工艺试验,研究了激光冲击微造型工艺的适用性和激光工艺参数对微坑几何形貌、物理性能的影响规律。通过三维计算流体动力学数值仿真和摩擦学性能试验的方法,研究了流体动压润滑和贫油润滑条件下微坑阵列的摩擦磨损性能,为激光冲击微坑阵列参数的主动优化设计奠定了研究基础。
[Abstract]:Wear caused by friction is the main reason for mechanical equipment failure. Therefore, the control of friction, improve the lubrication and reduce wear has become save energy and raw materials, improve the comprehensive demand of mechanical system operation efficiency and service life. The micro surface texture pit array can improve the tribological properties of the friction surface of the friction, prolong service life. Based on laser shock effect of micro pit array processing method is a kind of micro pits by laser shock mechanical effect of new processing method, the tribological properties of understanding the current process and the process of machining micro pits array is not systematic and in-depth. Based on the typical metal materials as the research object, system analysis micro pits array processing mechanism based on the effect of laser shock process, the applicability of laser shock parameters influence on physical properties of micro pits array geometry. The friction and wear properties of law and the micro pit array, providing optimal strategy choice for laser shock parameters. The main research contents include: first, research on micro molding process and the mechanism of laser shock process. Combined with the analysis of the forming process of laser induced plasma shock wave and high pressure for materials under high strain rate dynamic process simulation modeling, reveals laser shock micro molding process and mechanism of micro pit plastic deformation stress state and residual state were predicted. By examining the consistency of typical metal materials produced in the molding process in the preparation of micro laser shock crater geometric morphology and size, it is found that the laser shock micro molding process has the process of stability and good applicability, which laid the foundation for the premise of laser shock analysis of micro molding process of laser shock. Micro molding process based on a high Test method of material dynamic hardness variation conditions. Two, the study on the micro molding process of laser shock. By laser shock texturing test system of laser shock micro molding process parameters (laser power density, beam diameter and number of repeated impact of micro pits etc.) geometric characteristics (diameter, depth and aspect ratio etc.) and micro hole surface roughness, the plastic deformation layer microhardness, influence of grain size and surface integrity. The study found that with the increase of laser power density and laser repetition times of shock, crater diameter, depth, aspect ratio, degree of hardening plastic deformation layer and grain refinement increased, but due to the strain hardening effect, will show the impact saturation effect. With increasing the laser spot diameter, micro pit diameter also increases, but is always less than the spot diameter. In a single pulse laser energy Under the condition of the existence of a laser spot diameter threshold, when the spot diameter is greater than the threshold value, the crater depth, aspect ratio, plastic deformation hardening degree and grain refinement were decreased with increasing the laser spot diameter. When the spot diameter is less than the threshold value, the plasma shielding effect. With the increase of spot diameter, the depth of micro hole, micro hole plastic deformation hardening degree and grain size are increased, the micro pit depth diameter ratio variation due to laser shock varies according to the specific situation. The original surface texturing process of micro hole surface roughness change depends on the material roughness and laser shock parameters. When the original material surface roughness is larger, and the laser power density and the number of repeated impact is small, micro hole surface roughness is smaller than the original surface roughness. On the other hand, is greater than the original surface roughness. Three, hydrodynamic lubrication Study on friction properties of micro pits array conditions. In hydrodynamic lubrication conditions, through the method of three-dimensional computational fluid dynamics simulation of micro pit density, micro pit depth to diameter ratio of micro pit design parameters and Reynolds number fluid flow parameters on the oil film pressure distribution, the dimensionless average oil film bearing capacity. The dimensionless average oil film shear force and dynamic friction parameters of pressure coefficient are analyzed. The study found that in hydrodynamic lubrication conditions, improve the dynamic mechanism of micro pit friction pressure performance is the comprehensive effect of micro pit wedge effect and eddy current effect; the parameters in this paper, the existence of micro pit density the optimal and micro pit depth diameter ratio of the oil film dynamic pressure has the best performance; and with the increase of Reynolds number, the optimal crater depth diameter ratio decreases, and the optimal crater density remained unchanged. In four, poor lubrication conditions of micro pits Study on the tribological properties of array. In poor lubrication condition, the tribological experiment design and to establish a reasonable performance evaluation method of friction, friction and wear properties of the system were studied in different depth and density of different speed and load conditions of micro pits array. The study found that with the increase of micro pit density, friction coefficient. The maximum bearing capacity and the failure time of the friction performance increases at first and then decreased, indicating the existence of an optimum crater density range of the friction to achieve optimal performance, its mechanism is due to the dual effects of the solid solid contact area contact pressure and contact area of solid liquid lubrication; with the increase of micro hole depth, friction the performance showed a gradual increasing trend; at the same time, through the analysis of wear surface morphology and energy spectrum of the laser impact crater shape can effectively reduce the friction on the surface of abrasive grains Wear and adhesive wear. In conclusion, this paper combined with the effect of laser shock forming process analysis and laser shock metal pressure high strain plastic dynamic response simulation of elastic ratio, analysis of the laser shock process and micro molding mechanism. By making the micro laser shock process test, applicability and laser parameters of laser the impact of micro molding process of micro pit geometry, influence of physical properties. Through the method of three-dimensional computational fluid dynamics numerical simulation and experimental study of tribological properties, friction and wear properties of fluid lubrication and poor lubrication condition of micro pit array, active optimization for laser shock micro pit array parameter design for the basis of the research.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG665;TH117.1

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