关于微动磨损与微动疲劳的研究

微动磨损与微动疲劳是２种主要的微动模式,造成的损伤在工业中相当普遍,并可能引发灾难性的后果。主要研究了们移幅度、压力和疲劳应力３个基本微动参数,并以获得的微动区域、微动图为基础,分析了微动磨损与微动疲劳的运行机制和破坏规律。为更好地了解微动磨损与微动疲劳之间的内在联系,进一步探讨了接触磨损与局部疲劳、局部疲劳与整体疲劳之间的竞争机制。     

Mo离子注入提高TC4合金微动磨损抗力的研究

对TC4合金进行了Mo离子注入表面改性处理,利用摩擦磨损试验机进行了点接触微动磨损试验,借助读数显微镜和表面粗糙度仪测量出有关参数,计算出试样的微动磨损体积。结果表明,Mo离子注入使试样表面硬度提高,微动磨损体积明显降低。在微动磨损初期,Mo离子注入具有较好的减摩效果。Mo离子注入带来的表面强化效应是基体合金的微动磨损抗力得以提高的主要原因。     

变桨轴承微动磨损分析与沟道参数确定

在交变和振动载荷的作用下,风力发电机组变桨轴承的主要失效形式为钢球和沟道之间的微动磨损。分析了变桨轴承微动磨损产生的原因、损伤形式及微动运行模式,为降低变桨轴承的微动磨损,通过试验对其沟道参数的取值进行了研究。结果表明:变桨轴承的沟道曲率半径系数为0.53左右,初始接触角为45°左右时,可提高变桨轴承的抗微动磨损能力,减缓沟道微动磨损损伤。     

滚动轴承微动模拟试验装置

分析了滚动轴承微动的运行模式,设计了一台新型微动磨损试验装置。通过驱动单个滚子在轴承滚道上运动,能够模拟滚动轴承发生微动磨损的运动形态;并且可以通过调整载荷、运动速度和运动幅度等参数,满足多种条件下进行滚动轴承微动磨损试验的要求。     

微动疲劳参数对钢丝微动疲劳磨损演化的影响*

微动疲劳易引起钢丝表面磨损和横截面积损失,进而造成钢丝断裂失效并缩短钢丝绳使用寿命。不同微动疲劳参数（接触载荷、疲劳载荷、钢丝直径和交叉角度）引起差异的钢丝微动疲劳磨损特性,故研究微动疲劳参数对钢丝微动疲劳磨损演化规律影响至关重要。基于摩擦学理论和Marc仿真软件构建钢丝微动疲劳磨损模型,探究接触载荷、疲劳载荷、交叉角度和钢丝直径对钢丝微动疲劳磨损演化的影响规律。结果表明：钢丝微动疲劳磨损体积主要与接触载荷和疲劳载荷有关;疲劳钢丝的磨损深度、磨损率及磨损体积随着接触载荷的增加而增大,且不同接触载荷下疲劳钢丝磨损体积均随着循环次数的增加而呈线性增加;随疲劳载荷幅值的增加,疲劳钢丝的磨损深度、磨损率及磨损体积均呈增加趋势;在不同疲劳载荷范围下疲劳钢丝的磨损体积均随着循环次数的增加而呈线性增加;当接触载荷、疲劳载荷及钢丝间摩擦因数相同时,不同交叉角度和不同加载钢丝直径下疲劳钢丝的磨损体积相同。     

某大型柴油机连杆大头轴瓦微动磨损分析

通过使用AVL Excite PU软件和Abaqus软件的联合仿真,在大型V18柴油发电机上进行连杆大头轴瓦微动磨损分析,通过计算微动磨损指示参数(FIP)研究不同装配条件下轴瓦是否会产生微动磨损现象。结果表明:按照当前的装配条件,有可能会产生微动磨损,对于该大型发电机来讲小量级的轴瓦过盈量差别对于微动磨损的影响很小,并且如果螺栓预紧力施加小于设计所要求的力,产生微动磨损的可能性将增大。除此以外,本文对于连杆瓦座余高、连杆瓦座尺寸的上下偏差进行了不同的案例研究。     

基于新型试验装置的TC_4钛合金面接触微动磨损行为研究

自主设计了一套微动磨损夹具装置,可以更好地实现线/面、面/面接触。设置一组喷丸强度梯度处理Ti-6Al-4V合金试样,并与未喷丸磨光态试样进行对比试验分析。探讨喷丸处理对Ti-6Al-4V合金试样面/面接触形式微动磨损性能改善效果。试验结果表明,喷丸强化影响效果随喷丸强度参数变化而波动,其中,0. 20mmA喷丸强度处理在所有喷丸参数中表现最优。微动参数倾向于大滑移状态时,0. 20mmA喷丸强度处理试样较未喷丸磨光试样表现出一定的抗面/面接触形式微动磨损性能;在微动参数倾向于黏着状态时,0. 20mmA喷丸强度处理试样并未表现出良好的微动磨损抗性。     

钢丝微动疲劳裂纹萌生寿命预测研究*

钢丝微动疲劳过程中,钢丝裂纹萌生特性直接影响其裂纹扩展特性,进而制约钢丝微动疲劳寿命,因此开展钢丝微动疲劳裂纹萌生寿命预测研究具有重要意义。基于有限元法、摩擦学理论和断裂力学理论,运用Smith-Watson-Topper（SWT）多轴疲劳寿命准则建立考虑磨损的钢丝微动疲劳裂纹萌生寿命预测模型,基于多种不同的钢丝疲劳参数估算方法对钢丝的微动疲劳裂纹萌生寿命进行了预测,并探究接触载荷、疲劳载荷、交叉角度及钢丝直径等微动疲劳参数对钢丝微动疲劳裂纹萌生寿命的影响规律。结果表明：基于中值法的预测结果最接近实际值;在微动疲劳过程中,钢丝微动疲劳裂纹萌生寿命主要与接触载荷和疲劳载荷相关。通过引入微动损伤参数建立简化的适用于钢丝绳的钢丝微动疲劳裂纹萌生寿命预测模型,通过与考虑磨损的预测模型计算结果进行对比验证了该模型的准确性。     

硬度对钢蜗轮副用材料微动磨损特性的影响

通过调整40CrNiMoA钢的热处理工艺参数获得了4种不同硬度的试样,在无润滑、室温条件下,在SRV Ⅳ微动磨损试验机上研究了硬度对40CrNiMoA钢-18Cr2Ni4WA钢摩擦副微动磨损量和摩擦因数的影响.结果表明:试验条件下,随着40CrNiMoA钢硬度的增加,其微动磨损体积减小,而较硬的18Cr2Ni4WA钢的微动磨损量变化趋势则与试样的位置等有关,但总存在一个硬度配对使得两摩擦副微动磨损体积相等;摩擦因数在40CrNiMoA钢为上试样时,随时间变化较平稳,波动较小;当40CrNiMoA钢为上试样时,其微动磨损机制主要为黏着磨损,而18Cr2Ni4WA钢的磨损机制以磨粒磨损和黏着磨损为主.     

微动磨损工况下二维柱面对平面磨损形貌的数值计算与分析

基于改进的Archard磨损方程,推导了适应于不同微动振幅下的局部磨损方程,建立了二维刚性柱面-平面的微动磨损数值模型,研究了微动工况、材料参数对平面磨损形貌的影响规律.结果表明,在柱面载荷为20MPa,微动振幅为4μm的工况下,随着柱面半径的增大,平面的磨损宽度逐渐增大,磨损深度逐渐减小;在微动振幅为4μm的工况下,随着施加在柱面上载荷的增大,平面的磨损形貌呈现出变宽变深的趋势;在柱面载荷为20MPa,微动振幅为4μm的工况下,随平面弹性模量的增大,平面的磨损轮廓从宽而浅变化到窄而深.其次,根据Hertz接触理论和Archard磨损方程预测的平面磨损面积与本论文中模型计算的结果进行了对比,结果发现在磨损初期,两者间差别不大,随着微动循环次数的增加,Hertz理论预测结果小于这里模型计算的结果.     

Characterization of friction-induced local convex topography under dual-rotary fretting

Dual-rotary fretting (DRF) is a complex fretting wear mode combining torsional fretting with rotational fretting. Two different typical friction-induced convex topographies (Type I and Type II) in contact area were showed, which are under the control of torsional and rotational fretting components, respectively. To investigate their evolution characteristics and formation mechanism, the convex topographies were analyzed by SEM, XPS, a nano-hardness tester and surface profilometry, etc. The results show that the convex topographies significantly depended on the test parameters and environmental conditions. The initiation and propagation of fretting fatigue cracks were found related with the convex topography under the fretting wear.     

不锈钢焊接区金属微动磨损行为研究

以1Cr18Ni9Ti不锈钢材料为母材,采用焊条电弧焊方法制备焊件。在焊接检验合格的焊态试件上从焊缝区、熔合区和焊接热影响区金属中分别截取并制备微动磨损试验用试样。将制备好的焊接区不同位置金属试样在相同条件下进行微动磨损试验,研究焊接区金属微动磨损行为。研究结果表明,在选定的微动磨损试验参数下,微动处在完全滑移区;焊接区不同部位金属的微动磨痕形貌存在差异,具有不同的微动磨损行为。焊缝区金属磨痕最大深度差异不明显,但磨痕平面投影面积差异显著。焊接热影响区金属磨痕最大深度差异显著,而磨痕平面投影面积差异不明显。     

Research on torsional fretting wear behaviors and damage mechanisms of stranded-wire helical spring

Wear on the local area of steel wires’ surface is attributed to torsional fretting on the working process of stranded-wire helical spring. A mathematical model to calculate normal contact force and angular displacement amplitude among the wires is established first when the spring is impacted. With the experimental parameters obtained from the model, the torsional fretting test, which stimulates torsional fretting among the wires in the working process of the spring, is realized successfully on a newly developed fretting tester. Torsional fretting behaviors are strongly dependent upon normal contact force, angular displacement amplitude, and number of cycles. There are three basic types of T-θ curves (short for torque), angular displacement curves during the process of torsional fretting, namely, parallelogram, elliptic, and linear T-θ curves. To analyze the damage mechanisms, distribution maps of oxygen in the wear scar of spring wires under different working conditions are revealed. The damage gets slight in the partial slip region, mainly with the abrasive wear and the slight oxidative wear, whereas the wear mechanisms are mainly the abrasive wear, the oxidative wear, and the delamination, accompanied with obvious plastic deformation in the mixed fretting and slip regions.

     

Effect of ZDDP on friction in fretting contacts

The effect of ZDDP on fretting wear was investigated in a ball on flat machine. The results confirm previous work that anti-wear agents may reduce friction and wear in fretting contacts. It was further found that temperature, adsorption time, base oil polarity as well as the presence of other surface active additives in the oil were all important parameters affecting the ability of ZDDP to protect the surfaces against fretting wear.     

Friction and Wear Characteristics Due to Stick-Slip under Fretting Conditions

Friction and wear characteristics between two steel surfaces under fretting conditions are investigated experimentally. The fretting damage caused by low-amplitude oscillatory sliding can be classified into three regimes of gross-slip, mixed-slip, and partial-slip due to the stick-slip phenomenon. One of the most important characteristics of fretting wear is the transition from gross-slip to mixed-slip. Several criteria have been introduced for a quantitative determination of the transition between mixed-slip and gross-slip. However, the transition criteria have some problems in determining the regimes because parameters are difficult to calculate or depend on the system. To introduce new transition criteria in this study, the phase difference between friction force and relative displacement is used to determine the transition and predict the fretting wear. It is found that the phase difference with a range of 0° to 90° can predict the onset of fretting conditions.     

Frequency effects in fretting wear

The effect of frequency of vibration on fretting wear has been investigated in the 10 – 1000 Hz range with additional experiments at 20 000 Hz. Fretting tests were performed with two materials, a low carbon steel (AISI 1018) and an austenitic stainless steel (AISI 304). The experiments showed that two cases of fretting contact can be distinguished and related to the displacement amplitude. If the amplitude is low, the contact situation is characterized by partial stick at the interface. At these conditions the wear rate (measured as the volume of material removed per cycle) is little affected by frequency. However, in low amplitude fretting material damage by surface degradation and fatigue crack initiation is usually of more concern than the actual wear itself. Both of these parameters are found to be greatly accelerated by an increase in frequency. In high amplitude fretting, in contrast, gross slip occurs at the interface and wear becomes the dominant damage mode. At these conditions variations in frequency appear to have little effect on fretting wear and related mechanisms. Therefore, in the case of fretting at high displacement amplitudes, it may be possible to apply high frequency fretting to obtain accelerated testing conditions.     

The fretting wear of mild steel from room temperature to 200°C

This paper investigates in detail the fretting wear behaviour of mild steel from room temperature to 200°C. Contact resistance measurements and the scanning electron microscope have been used to interpret the wear mechanism in relation to the observed progress of different wear scar parameters. The fretting apparatus used was specially constructed for elevated temperature work, the wear area concentrated in the form of an annulus. It is found that in the fretting of mild steel, there is an initial stage of adhesion followed by a conditioning period before adhesion zones undergo deterioration and dispersal to form eventual oxide debris. The different stages in this mechanism are dealt with in detail. It is found that with mild steel the fretting damage decreases with increase of temperature in the range considered and reaches a constant value at 200°C, the transition temperature. The possibility of abrasive wear as an influencing factor in fretting is also examined but microfatigue is found to be by far the more important process during the steady state.     

基于双重扩展自适应卡尔曼滤波的汽车状态和参数估计

准确实时地获取行驶过程中的状态信息是汽车动态控制系统研究的关键,为此提出了一种新的汽车状态估计器。建立了包含不准确模型参数和未知时变统计特性噪声的非线性汽车动力学模型,针对该非线性系统提出一种双重扩展自适应卡尔曼滤波算法（DEAKF）。该算法采用两个卡尔曼滤波器并行运算,状态估计和参数估计互相更新,同时将带遗忘因子的噪声统计估值器嵌入到状态校正过程和参数校正过程之间,以解决系统的噪声时变问题。基于ADAMS的虚拟试验和实车试验结果表明,该算法的状态估计精度高于EKF方法和DEKF方法的状态估计精度,同时具有良好的模型参数校正能力,对汽车动态控制系统中估计器的设计具有理论指导意义。
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