粗糙表面形貌对电蚀的影响

以名义线接触副轴承和齿轮为研究对象,用分形方法模拟三维粗糙表面,建立由一个粗糙表面与一个光滑刚性平面接触的简单模型和由2个粗糙表面接触的复杂模型,建立粗糙表面的矩形斑点接触电阻计算模型和电流密度计算模型,从接触电阻和电流密度2个角度来考虑粗糙表面形貌对电蚀的影响.分析接触载荷和分形参数对实际接触面积、接触电阻和电流密度的影响;在恒定载荷下,研究接触电阻和电流密度与粗糙度之间的定量关系.结果表明,从接触电阻或电流密度方面,增加轴承和齿轮表面间的接触载荷和减小表面粗糙度可以防止电蚀的发生,因此接触电阻和电流密度一样可以用来作为电蚀发生的判据.在实际应用中,主动设计最佳的接触载荷大小以及最佳的表面粗糙度可以防止电蚀的发生,并且在研究粗糙表面接触问题时应采用复杂的接触模型.所提出的计算方法可以分析表面电蚀失效.

粗糙表面微型气体轴承润滑性能及其转子动力学特性研究

微型气体轴承-转子系统作为微型旋转机械实现功能转换的重要部件,表面粗糙形貌、薄膜润滑性能及转子动力学特性是影响整体设备可靠运转的关键因素.利用Boltzmann稀薄效应模型修正可压缩气体动压润滑Reynolds方程,通过分形理论表征微型轴承表面的粗糙轮廓,研究了气体稀薄效应和表面粗糙度耦合作用下微型轴承的静动态性能.并利用有限元法建立粗糙表面微型气体轴承-转子系统的动力学模型,得到转子系统固有特性和轴心轨迹的变化规律.结果表明:表面粗糙度效应提高了轴承的承载能力和动态刚度系数,在较大轴承数时增加幅度更明显.由于稀薄效应降低了轴承的直接刚度系数,转子振幅随气膜稀薄程度的增加而增大,表面粗糙峰的增加会降低转子系统的固有频率.

2A12铝合金在EXCO溶液中腐蚀损伤形貌演化分析

目的探索2A12铝合金在EXCO溶液中腐蚀损伤形貌的演化规律。方法开展实验室内2A12铝合金的加速腐蚀实验。为实现表面粗糙度与腐蚀损伤相关性的定量研究,首先采用3D扫描成像仪对实验样品进行扫描,取得样品微观几何特征,实现表面粗糙度值的数字化定量表征。观察样品在EXCO溶液中腐蚀损伤的发生发展过程、腐蚀形貌的演化过程,测量腐蚀样品蚀坑深度,并分析表面粗糙度对样品腐蚀损伤的影响。结果当腐蚀时间不超过6h时,2A12铝合金样品在EXCO溶液中的腐蚀类型主要为点蚀,随着时间的延长,将向全面腐蚀发展。粗糙度值高的试件表面有打磨时形成的较深表面纹理,这些纹理制约了点蚀坑的扩展,使蚀坑沿纹理的方向发展,有演化为微裂纹的可能性,蚀坑边界的不规则处也会萌生微裂纹。粗糙度值较小的样品,腐蚀损伤也较小,但粗糙度对腐蚀损伤的影响随时间的延长而减弱。结论常温下,2A12铝合金在EXCO溶液中首先发生点蚀,由于蚀坑向四周扩展的速度快于深度方向,使腐蚀类型从点蚀向全面腐蚀演变。表面粗糙度对2A12铝合金样品腐蚀损伤形貌的演化有重要影响,表面微观几何特征通过制约蚀坑扩展方向的方式来改变样品的腐蚀行为,并造成腐蚀损伤的明显差异。随着腐蚀时间的延长,材料逐渐失去其原有表面微观几何特征,表面粗糙度对腐蚀行为的影响下降。

考虑粗糙表面接触配合的航空发动机多级转子装配误差传递建模

传统的转子系统装配建模方法忽略了转子粗糙表面微观形貌的影响,可能导致装配误差传递建模和优化不精确等问题,在此背景下,提出了一种综合考虑定向误差、定位误差和表面粗糙形貌的航空发动机多级转子装配误差传递分析方法。首先,使用共轭梯度法模拟转子端面的粗糙表面微观形貌,在刚性接触假设下,提出了一种考虑平移、单点和轴线旋转,以及质心作用的接触求解算法,计算两个粗糙表面的装配倾斜角和配合面方程。然后,改进传统基于齐次变换矩阵的装配误差传递模型,建立了考虑粗糙表面接触配合的多级转子装配同轴度误差传递模型。最后,以航空发动机转子模拟件为对象,选取前轴和第一级盘进行实例分析,新模型的同轴度预测精度与传统模型相比提高了11.55%。研究结果表明,所提方法可以提高航空发动机多级转子装配精度预测的准确性,为航空发动机转子系统的精密装配提供了理论依据。

Influence of high-speed milling parameter on 3D surface topography and fatigue behavior of TB6 titanium alloy

High-speed milling of titanium alloys is widely used in aviation and aerospace industries for its high efficiency and good quality.In order to optimize the machining parameters in high-speed milling TB6 titanium alloy,experiments of high-speed milling and fatigue were conducted to investigate the effect of parameters on 3D surface topography and fatigue life.Based on the fatigue fracture,the effect mechanism of surface topography on the fatigue crack initiation was proposed.The experiment results show that when the milling speed ranged from 100 m/min to 140 m/min,and the feed per tooth ranged from 0.02 mm/z to 0.06 mm/z,the obtained surface roughness were within the limit（0.8 μm）.Fatigue life decreased sharply with the increase of surface equivalent stress concentration factor.The average error of fatigue life between the established model and the experimental results was 6.25%.The fatigue cracks nucleated at the intersection edge of machined surface.

汽车水泵轴承密封圈力学分析模型和寿命计算方法

汽车水泵轴承密封圈的密封性能与唇口过盈量密切相关。利用力学知识和Hertz接触理论推导了密封圈与轴表面的接触应力分布计算模型,分析了不同唇口过盈量下接触应力变化规律;采用自适应相关函数模拟轴的微观表面形貌,并计算了由于轴的表面微观不平度导致的轴转动一周时密封圈唇口接触应力的变化规律;根据疲劳理论和雨流法随机计数原理构建了密封圈疲劳寿命预测方法,并预测了密封圈的疲劳寿命随唇口过盈量变化的规律。本文的研究结果可为汽车水泵轴承密封圈技术的进一步研究和应用提供理论帮助。

Effect of hydrogen peroxide concentration on surface properties of Ni-Cr alloys

The effect of concentration of hydrogen peroxide （H2O2） on the surface properties of Ni-Cr alloys was studied. Surface roughness and surface morphology of Ni-Cr alloys were evaluated by surface profiler and scanning electron microscopy after being immersed in different concentrations of H2O2 for 112 h. Surface corrosion products of Ni-Cr alloys were analyzed by photoelectron spectrograph after being immersed in 0% and 30% H2O2. The order of increasing surface roughness of Ni-Cr alloys after being immersed in different concentrations of H2O2 was 0〈3.6%〈10%〈30%. As the concentration of hydrogen peroxide increased, the surface roughness of Ni-Cr alloys increased and the surface morphology showed different degrees of corrosion. According to the XPS results, the corrosion products formed on the outmost surface layer of the studied samples are Ni（OH）2 and BeO.

Wire electric discharge machining characteristics of titanium nickel shape memory alloy

Ti Ni shape memory alloys（SMAs） have been normally used as the competent elements in large part of the industries due to outstanding properties, such as super elasticity and shape memory effects. However, traditional machining of SMAs is quite complex due to these properties. Hence, the wire electric discharge machining（WEDM） characteristics of Ti Ni SMA was studied. The experiments were planned as per L27 orthogonal array to minimize the experiments, each experiment was performed under different conditions of pulse duration, pulse off time, servo voltage, flushing pressure and wire speed. A multi-response optimization method using Taguchi design with utility concept has been proposed for simultaneous optimization. The analysis of means（ANOM） and analysis of variance（ANOVA） on signal to noise（S/N） ratio were performed for determining the optimal parameter levels. Taguchi analysis reveals that a combination of 1 μs pulse duration, 3.8 μs pulse off time, 40 V servo voltage, 1.8×105 Pa flushing pressure and 8 m/min wire speed is beneficial for simultaneously maximizing the material removal rate（MRR） and minimizing the surface roughness. The optimization results of WEDM of Ti Ni SMA also indicate that pulse duration significantly affects the material removal rate and surface roughness. The discharged craters, micro cracks and recast layer were observed on the machined surface at large pulse duration.

Morphology characteristics of joint surface in rock mass

In order to quantify the characteristics of the surface of jointed rock mass,new equipment,the three-dimensional laser surface topography instrument,was used to accurately measure surface morphology of joints.Scan pictures and parameters were obtained to describe the rock joint surface characteristics,for example,the height frequency of surface,and mean square roughness.Using the method of fractal dimension,the values of joint roughness coefficient(JRC) were calculated based on the above parameters.It could access to the joint surface rock sample morphology of the main parameters of characteristic.The maximum peak height is 2.692 mm in the test joint plane.The maximum profile height is 4.408 mm.JRC value is 6.38 by fractal dimension computing.It belongs to the smooth joint surface.The results show that it is a kind of the effective method to quantitatively evaluate the surface topography by the three-dimensional laser surface topography instrument and the fractal dimension method.According to the results,during the process of underground large-scale mining,safe measures to prevent slip failure of the joint plane by controlling surface tension and shear mechanical response were proposed.

Examination and Research of the Surface Topography of Ultrasonic Vibration Honing Nd-Fe-B

The mechanism of ultrasonic vibration honing Nd-Fe-B has been briefly elaborated after the introduction of the strategic significance of processing Nd-Fe-B. Based on the formation principle of Scanning Electrtmic Microscope （SEM）, and at the examination with the aid of SEM to the ultrasonic vibration honing Nd-Fe-B material＇s superficial microscopic topography, the paper discusses the new processing nechanism according to the SEM examination picture. The research indicates that as a result of supersonic high frequency vibration, the path of the abrasion extends at the same time, and the supersonic cavitation effect forms the intense shock-wave, knpacting Nd-Fe-B material＇s intemal surface, providing the supersonic energy for the superticial abrasive dust＇s dimination, which directly explain that the honing processing efficiency is enhanced, and the processing surface roughness is high.

金属封严环泄漏率预测方法

针对金属封严环设计中泄漏率估算问题,综合对密封系统宏观结构和微观表面接触变形的考量,提出一种基于数值计算的泄漏率预测方法。对密封整体结构进行计算,以计算值(接触应力、接触面积)为输入参数,以表面粗糙度为评价指标建立微观粗糙表面,使用有限元法(FEM)进行接触计算后建立泄漏通道模型,在对泄漏缝隙内流体流动特性确定后通过计算流体力学(CFD)方法计算得到泄漏率。使用密封试验台进行泄漏率试验,将计算值与试验结果相比较。研究表明:随着接触应力增加、表面粗糙度值降低以及内外腔压差增长,密封系统泄漏率逐渐减小;所提出的方法极大地摆脱了泄漏率获取对于试验仪器的依赖性,并能够较为有效地预测金属密封结构的泄漏率,对先进的金属封严环的设计和评估具有重要意义。