30CrNiMo8合金钢的弯曲微动疲劳特性

在不同弯曲载荷水平下,对30CrNiMo8合金钢进行了系统的弯曲微动疲劳试验,建立了其微动疲劳S-N曲线,讨论了其弯曲微动疲劳特性及相关规律。结果表明:30CrNiMo8钢弯曲微动疲劳的S-N曲线明显不同于常规疲劳的,呈现"C"曲线特征;随着弯曲载荷的增加,微动依次运行于部分滑移区、混合区和滑移区;在混合区,裂纹最易萌生且微动疲劳寿命最短;微动损伤区的磨损机制主要为磨粒磨损、氧化磨损和剥层;弯曲微动疲劳裂纹的扩展表现为三个不同的阶段,第一阶段裂纹斜向扩展,以接触应力控制为主,第二阶段裂纹转向,受接触应力和弯曲应力共同控制,第三阶段裂纹扩展方向变为垂直方向,以弯曲应力控制为主。     

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。     

Ti-6Al-4V燕尾榫结构微动疲劳裂纹萌生及扩展行为研究

针对Ti-6Al-4V钛合金燕尾榫连接结构在不同载荷下的微动疲劳现象,采用榫形微动疲劳试验进行研究,并对裂纹萌生扩展、微动磨损及断口进行分析。结果表明,微动疲劳使构件疲劳寿命显著降低约70%;疲劳载荷对微动裂纹扩展的影响比对裂纹萌生的影响更大;微动疲劳裂纹起始于接触面边缘,与接触表面约成45°角,裂纹扩展到60~150μm后转向与接触表面垂直;微动疲劳断口形貌表面在微动磨损区具有多个裂纹源点,但只有一个主裂纹形成。     

带有微动磨损缺口钢丝的疲劳特性

在自制的微动磨损试验机上进行钢丝的微动磨损试验,将微动磨损后的钢丝试样在液压伺服疲劳试验机上进行不同应力比和不同应力幅下的疲劳试验。结果表明,钢丝的微动磨损深度随微动时间和接触载荷的增加而增加,磨损缺口处的应力集中使其成为了裂纹萌生源,也使钢丝试样的疲劳寿命大大降低,微动磨损后钢丝试样的疲劳寿命和磨损深度呈反比关系。通过钢丝疲劳断口的SEM形貌分析了其疲劳断裂机制,断口对应不同的疲劳阶段,可分为裂纹萌生区、裂纹扩展区和裂纹瞬断区。     

铁路车轴过盈配合结构微动磨损与微动疲劳研究

采用比例车轴试样进行了微动疲劳试验,试验后观察了车轴微动区的微动磨损与微动疲劳损伤,并测量了车轮、车轴配合面磨损轮廓.试验结果表明,车轴轮座边缘微动区的磨损机理主要是磨粒磨损、剥层和氧化磨损.车轴微动疲劳裂纹萌生于微动区内部,初始裂纹角度与车轴径向方向成29°.随着裂纹的扩展,裂纹角度逐渐减小.此后,基于测量的磨损轮廓...     

基于能量密度法预测微动疲劳寿命

通过接触界面的应力应变场和临界平面法计算了能量密度损伤参数,结合疲劳试验得到了能量密度损伤参数-寿命关系曲线中的材料常数,建立了LZ50钢微动疲劳寿命的预测公式。根据裂纹萌生寿命预测效果,将Chen损伤值作为裂纹萌生控制参数。分析了摩擦因数、微动桥半径、循环载荷和微动桥压力对LZ50车轴钢的Chen损伤值的影响,以及CRH2型动车组空心车轴裂纹萌生的位置及寿命。     

空心轴与实心轴过盈配合结构微动磨损与疲劳的仿真分析

为了分析空心轴与实心轴过盈配合结构微动磨损与疲劳行为的差异,建立了两种过盈配合结构的微动磨损-微动疲劳联合仿真模型。该联合仿真模型基于Archard磨损方程和有限元软件ABAQUS的自适应网格技术实现了循环微动磨损的仿真,基于线性累积损伤理论和修正的SWT临界平面法实现了微动疲劳寿命预测。分析结果表明：空心轴的微动磨损比实心轴严重,微动磨损显著降低了过盈配合边缘附近的应力集中,同时在配合内部引起了新的应力集中,并导致微动裂纹萌生位置出现在配合内部。受到微动磨损的影响,空心轴的微动疲劳寿命仅约为实心轴的40%,但两种结构的微动裂纹萌生位置几乎一致。     

微动疲劳寿命的估算方法研究

着重分析了零构件由于微动磨损而造成的疲劳失效机制 ,说明了在这种微动疲劳模式下疲劳寿命的组成情况 ,用门槛值应力公式估算了当磨蚀坑根部萌生扩展性裂纹时蚀坑的临界深度尺寸 ,并分析了微动裂纹尖端的应力强度因子 ,得出了计算微动裂纹萌生尺寸的表达式 ,最后用上述方法计算了螺纹联接件的微动磨损寿命与裂纹萌生尺寸 ,用局部应力应变法计算了微动裂纹的萌生寿命 ,所得到的估测寿命与试验值相符 ,由此可见 ,该微动疲劳寿命的估测方法是合理的、有效的     

微动疲劳寿命的估算方法研究

着重分析了零构件由于微动磨损而造成的疲劳失效机制,说明了在这种微动疲劳模式下疲劳寿命的组成情况,用门槛值应力公式估算了当磨蚀坑根部萌生扩展性裂纹时蚀坑的临界深度尺寸,并分析了微动裂纹尖端的应力强度因子,得出了计算微动裂纹萌生尺寸的表达式,最后用上述方法计算了螺纹联接件的微动磨损寿命与裂纹萌生尺寸,用局部应力应变法计算了微动裂纹的萌生寿命,所得到的估测寿命与试验值相符,由此可见,该微动疲劳寿命的估测方法是合理的,有效的。     

40CrNi2MoA合金钢的弯曲微动疲劳特性

在不同弯曲载荷下,对40CrNi2MoA合金钢进行弯曲微动疲劳试验,建立其弯曲微动疲劳下的循环次数-应力曲线;通过对微动损伤区的微观分析,研究该合金钢的弯曲微动疲劳特性。结果表明:40CrNi2MoA钢弯曲微动疲劳应力曲线不同于常规疲劳应力曲线,呈现"C"型曲线特征;随着弯曲载荷的增加,微动依次运行于部分滑移区、混合区和滑移区;相对于另外两个区域,混合区试样的裂纹更易萌生、扩展且微动疲劳寿命最短;试样表面的磨损机制主要为磨粒磨损、氧化磨损和剥层;由于接触应力和弯曲应力的影响程度不同,弯曲微动疲劳裂纹的扩展分为三个阶段,即接触应力控制阶段、接触应力与弯曲疲劳应力共同控制阶段和完全受弯曲应力控制阶段。     

Effect of contact load on fretting fatigue behaviour of steel wires

Abstract

The tension–tension fretting fatigue tests of steel wires were performed on a self-made fretting fatigue test equipment under contact loads ranging from 40 to 70 N and a strain ratio of 0·8. The results showed that when the contact load increased, the fretting regime of steel wires transformed from gross slip regime to mixed fretting regime. The fretting fatigue life in the mixed fretting regime was significantly lower than that in the gross slip regime. The main fretting wear mechanisms in the gross slip regime, where there were serious fretting damage and a lot of wear debris, were abrasive wear and fatigue wear. Microcracks were observed in the fretting scar of the mixed fretting regime, and the main fretting wear mechanisms were adhesive and fatigue wears. The fretting wear scar was the fatigue source region, and the fatigue fracture surface could be divided into three regions.     

Behavior of alloy Ti–6Al–4V under pre-fretting and subsequent fatigue conditions

The mechanical behavior and microstructural changes in Ti–6Al–4V were determined in fretting tests, followed by axial fatigue tests. Prior to fatigue testing, specimens were subjected to fretting conditions over a range of contact stresses and fretting displacements. Fretting frequency was 100 Hz. High cycle fatigue (HCF) tests were run at 1000 Hz. The fretting test involved a flat-on-flat, bare Ti–6Al–4V/bare Ti–6Al–4V fretting system. The fretting process typically generated very shallow surface cracks at the ends of the wear scar. Subsequently, these shallow cracks were observed to propagate in axial fatigue tests, reducing the fatigue life significantly. Evidence of frictional heating during fretting was observed in the formation of scale-like oxide in the wear scar. Formation of oxides appeared to increase with increasing contact stress. Increased oxygen content was detected in the near surface regions of specimens. Large near surface deformation was typically observed within the wear scar. The contact geometry and slight tilting of the stationary fretting pad influenced the character of the fretting scar and the fretting-induced cracking. Fracture surfaces exhibited featureless, battered surfaces at the crack origins followed by (a) cleavage-type crack propagation, (b) formation of fatigue striations, and (c) final ductile tearing.     

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。     

Fretting of glass

Fretting damage to a glass surface in contact with a steel ball was investigated. In the initial stage of fretting, severe wear occurred on the steel ball and considerable wear debris was transferred to the glass surface. The coefficient of friction increased during this stage by 80%. Fatigue cracks were observed on the glass surface under conditions of high normal load and tangential force. The mechanism of fretting fatigue and fretting wear is discussed in relation to a brittle material. Finally the effect of thin metal foil inserts in reducing fretting damage is described.     

Effect of contact pressure on fretting fatigue of austenitic stainless steel

The effect of contact pressure on fretting fatigue in solution-treated austenitic stainless steel was studied. With an increase in contact pressure, fretting fatigue life was almost unchanged at low contact pressures, however it decreased drastically at high contact pressures. At low contact pressures, stress concentration due to fretting damage occurred at the middle portion of the fretted area and the main crack responsible for failure was initiated there. At high contact pressures, concavity was formed at the fretted area without accompanying heavy wear. The main crack was initiated at the outer edge corner of the concavity which probably acted as a notch. Plain fatigue prior to the fretting fatigue test increased the fretting fatigue life at high contact pressures since the concavity formation was suppressed by the cyclic strain hardening.     

Interface roughness effect on friction map under fretting contact conditions

In many industrial applications where fretting damage is observed in the contact (e.g. rotor/blade, electrical contacts, assembly joint, axe/wheel, clutch) the external loadings or geometry design cannot be changed. Therefore, the surface preparation and finishing process become essential to control and reduce the damage caused by fretting. In this paper, the authors present the experimental study of the initial surface roughness and machining process influence on fretting conditions in both partial and full sliding regimes. Surfaces prepared by milling and smooth abrasive polishing processes have been analysed. The influence of roughness on sliding behaviour and analysis of friction have been reported. Also, the contact pressure influence and qualitative analysis of fretting wear scar have been presented.     

Finite Element Modeling and Experimental Validation of Fretting Wear Scars in a Press-Fitted Shaft with an Open Zone

A finite element (FE)-based method was developed for simulating the fretting wear scar in a press-fitted shaft with an open zone. The method is based on the energy wear approach and is implemented via the commercial FE code ABAQUS. The effects of open zone, mesh size, cycle jumps technique, and increments per fretting cycle were investigated for optimization of this methodology. The results show that when assuming that the surface profile can be changed only in the open zone, the FE wear model gives a good prediction of the scar width. The mesh size has a great influence on the dimensions and shape of the scar profile; when the mesh size is about 3% of the width of the wear scar for a press-fitted shaft, the best compromise between the wear scar shape and the computational time can be achieved. For the cycle jump ΔN, an optimum value of 3,000 is found; above this value, the depth of the fretting wear scar increases rapidly with increasing ΔN. The impact of increments per fretting cycle on the depth of the predicted wear scar is small by comparison with cycle jump ΔN. The results of the optimized model are validated with respect to the experimental data obtained in the interrupted fretting fatigue tests. The FE wear model can provide an accurate prediction of the maximum wear depth and the width of fretting wear scar. The predicted wear depth inside of the contact is slightly larger than that found experimentally.     

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。     

Characterization of fretting fatigue crack initiation processes in CR Ti–6Al–4V

A study was conducted to quantify fretting fatigue damage and to evaluate the residual fatigue strength of specimens subjected to a range of fretting fatigue test conditions. Flat Ti–6Al–4V specimens were tested against flat Ti–6Al–4V fretting pads with blending radii at the edges of contact. Fretting fatigue damage for two combinations of static average clamping stress and applied axial stress was investigated for two percentages of total life. Accumulated damage was characterized using full field surface roughness evaluation and scanning electron microscopy (SEM). The effect of fretting fatigue on uniaxial fatigue strength was quantified by interrupting fretting fatigue tests, and conducting uniaxial residual fatigue strength tests at R=0.5 at 300 Hz. Results from the residual fatigue strength tests were correlated with characterization results.While surface roughness measurements, evaluated in terms of asperity height and asperity spacing, reflected changes in the specimen surfaces as a result of fretting fatigue cycling, those changes did not correspond to decreases in residual fatigue strength. Neither means of evaluating surface roughness was able to identify cracks observed during SEM characterization. Residual fatigue strength decreased only in the presence of fretting fatigue cracks with surface lengths of 150 μm or greater, regardless of contact condition or number of applied fretting fatigue cycles. No cracks were observed on specimens tested at the lower stress condition. Threshold stress intensity factors were calculated for cracks identified during SEM characterization. The resulting values were consistent with the threshold identified for naturally initiated cracks that were stress relieved to remove load history effects.