考虑残余应力的螺旋锥齿轮接触疲劳裂纹萌生-扩展寿命计算方法研究

考虑渗碳、磨齿、喷丸等工艺产生的齿面残余应力,建立齿面接触应力与残余应力的复合应力场,提出一种螺旋锥齿轮接触疲劳裂纹萌生-扩展寿命计算方法。构建齿轮有限元接触分析模型,计算多轴交变接触应力场。考虑空间螺旋曲面残余应力分布的复杂性,将变曲率齿面离散为网状节点;测量各节点表面与次表面的残余应力,建立齿面残余应力场。基于Dang Van多轴疲劳准则,构建齿面裂纹萌生模型;计及残余应力与裂纹闭合效应,构建齿面裂纹扩展模型。计算复合应力场下齿轮接触疲劳寿命,研究残余应力对齿面裂纹萌生-扩展寿命的影响规律。结果发现：复杂齿面空间变曲率会影响喷丸等工艺产生的残余应力分布,中心区域的残余压应力高出齿面边缘区域约20%;复合应力场下齿面裂纹萌生位置与寿命主要取决于接触应力,残余应力会改变齿面节点平均应力进而影响疲劳寿命;齿面裂纹扩展寿命约占全寿命的10%,表征齿轮接触疲劳快速失效至迅速断裂。上述研究对于高性能齿轮传动的长寿命、高可靠性设计具有一定的参考价值。     

Analysis of Fretting Fatigue of Cavitation Shotless Peened Ti–6Al–4V

Fretting fatigue behavior of cavitation shotless peened titanium alloy, Ti–6Al–4V coupons was investigated using finite element method and a critical plane-based multi-axial fatigue parameter. Cavitation shotless peening (CSP)-induced compressive residual stress, which was larger at the contact surface than its counterpart from the shot peening (SP). However, compressive residual stress decreased more sharply with distance from the contact surface in CSP than in SP. Analysis using a critical plane-based multi-axial fatigue parameter demonstrated that the crack initiation would occur inside the cavitation shotless peened specimen which matched with the experimental observations. On the other hand, crack initiation would occur on the contact surface in the shot peened specimen which again was in agreement with experiments. The analysis also showed that the crack propagation part of the total fretting fatigue life was longer in the shot peened specimen than in the cavitation shotless peened specimen while the crack initiation part was almost equal from both peening methods. Therefore, CSP could not improve the fretting fatigue life/strength as much as the SP did but it improved relative to the un-peened specimen.     

Rolling contact fatigue life model incorporating residual stress scatter

There has been a considerable body of research concerned with predicting the service life of rolling contact components. It is well known that the prevailing cause of failure in rolling contact components is fatigue crack. Although the trend has been toward the use of surface integrity in fatigue life prediction, one aspect missing in most models has been a consideration of the residual stress scatter in the subsurface. Since the fatigue life of a manufactured component depends on its weakest point, the local extreme is most relevant for the fatigue life prediction. This study thus incorporates the residual stress scatter into the rolling contact fatigue life model to predict the fatigue life closer to the experimental life. It is noted that residual stresses vary significantly at the same depth. After the residual stress scatter is incorporated into the model, the predictions agree well with the experimental lives.     

FE-simulation of the effects of machining-induced residual stress profile on rolling contact of hard machined components

Compared with grinding, hard turning may induce a relatively deep compressive residual stress. However, the interactions between the residual stress profile and applied load and their effects on rolling contact stresses and strains are poorly understood, and are difficult to measure using the current experimental techniques due to the small-scale of the phenomena. A new 2-D finite element simulation model of bearing rolling contact has been developed, for the first time, to incorporate the machining-induced residual stress profile instead of only surface residual stresses. Three cases using the simulation model were assessed: (a) measured residual stress by hard turning, (b) measured residual stress by grinding, and (c) free of residual stress. It was found that distinct residual stress patterns hardly affect neither the magnitudes nor the locations of peak stresses and strains below the surface. However, they have a significant influence on surface deformations. The slope and depth of a compressive residual stress profile are key factors for rolling contact fatigue damage, which was substantiated by the available experimental data. Equivalent plastic strain could be a parameter to characterize the relative fatigue damage. The magnitudes of machining-induced residual stress are reduced in rolling contact. The predicted residual stress pattern and magnitude agree with the test data in general. In addition, rolling contact is more sensitive to normal load and residual stress pattern than tangential load.     

Initiation and propagation of surface cracks in rolling fatigue of high hardness steel

Surface cracks initiating flaking failure observed by Sugino in rolling fatigue were further studied.Surface crack initiation was influenced by either running or material conditions, affecting the residual tensile stress just below the rolling contact surface. The fatigue crack is thought to initiate very near the surface by the stress cycle of small tensile residual stress and large compressive contact stress. The amount and direction of the tensile residual stress due to rolling contact varies with the contact geometry, which probably determines the direction of the surface crack and the appearance of flaking. The transition from the surface crack to flaking failure or complete section fracture is material and running condition dependent and is explained by a fracture mechanics concept.     

预滚压对含缺陷轮轨材料滚动接触疲劳性能的影响

对含缺陷的未预滚压和预滚压车轮钢试样分别进行滚动接触疲劳试验,观察表面缺陷的形貌变化过程,分析预滚压和缺陷尺寸对轮轨材料滚动接触疲劳性能的影响。通过有限元方法分析缺陷附近材料的应力状态,通过多轴疲劳模型分析缺陷尺寸对滚动接触疲劳裂纹萌生规律的影响。试验结果表明:由于表层材料的塑性变形,未滚压车轮试样的缺陷尺寸随滚动周次的增加而减小;超过一定周次后,由于塑性变形不再累积,缺陷尺寸基本保持不变;预滚压处理通过减小表层材料的塑性变形,可抑制缺陷尺寸的减小,从而降低车轮试样的疲劳寿命;缺陷尺寸的增加会进一步降低预滚压试样的疲劳寿命;在油润滑条件下,预滚压和表面缺陷对车轮材料摩擦磨损性能没有显著影响。仿真结果表明,当缺陷尺寸从200μm增加至400μm,最大剪应力幅值从缺陷底部转移至缺陷中部,疲劳裂纹萌生位置也随之改变。     

研磨加工层对高碳铬轴承钢超长寿命疲劳行为的影响

为了阐明磨石研磨加工层对高碳铬轴承钢JIS SUJ2超长寿命疲劳行为的影响,分别使用经砂纸研磨和电解研磨的砂漏形试样,在室温空气环境下进行旋转弯曲疲劳试验.砂纸研磨试样被除去部分磨石研磨层,电解研磨试样被除去了全部的磨石研磨层.结果表明,两种试样的S-N曲线由位于短寿命区的表面破坏模式和位于长寿命区的内部破坏模式的两条组成,表面破坏模式的S-N曲线受表面粗糙度和表面压缩残余应力的影响.内部破坏模式的S-N曲线不受表面条件的影响,是材料固有的特性.砂纸研磨试样表面破坏模式的疲劳极限最高,是电解研磨试样1.11倍和磨石研磨的1.20倍.表面压缩残余应力对表面破坏模式疲劳极限的影响可以用修正Goodman图表示.还讨论裂纹的萌生和扩展条件,推定超长寿命的疲劳极限.     

高碳贝氏体轴承钢滚动接触疲劳性能的研究

以GCr15Si1Mo贝氏体轴承钢为研究对象,在油润滑条件和无润滑条件下,对不同初始碳化物体积分数的试样进行滚动接触疲劳试验,采用扫描电镜观察试验前后试样的表面形貌和碳化物分布,并通过Weibull曲线确定试样滚动接触疲劳性能的优劣性。结果表明,在无润滑条件下,碳化物体积分数为1.9%的试样滚动接触疲劳性能优于碳化物体积分数为5.1%的试样。在油润滑条件下,贝氏体轴承钢的滚动接触疲劳性能的优劣性依次为：无初始碳化物试样、碳化物体积分数为5.1%试样、碳化物体积分数为1.9%试样。碳化物作为基体的硬质相,很容易成为疲劳源,无初始碳化物的贝氏体轴承钢的滚动接触疲劳性能优于有碳化物的贝氏体轴承钢;碳化物脱落后的凹坑增大了润滑油和试样表面的粘着力,有利于增加油膜厚度,从而提高滚动接触疲劳寿命。     

On the prediction of fatigue crack initiation in rolling/sliding contacts with provision for loading sequence effect

The principles of continuum damage mechanics are applied to predict the rolling/sliding contact fatigue crack initiation. The approach involves evaluating the subsurface stresses as well as the state of damage within the contact region. It is shown that the fatigue crack initiation life can be related to the scalar damage parameter D, which is a measure of micro-crack and voids density in the material. Comparison of the predicted results with the available experimental work shows good agreement. The effect of variable loading on the fatigue behavior of rolling contact with provision for non-linear damage evolution is also investigated.     

A Critique of Rolling Contact Fatigue Criteria for Bearing Rings with Hoop Stresses

Tensile residual and interference fit stresses not treated in classical bearing formulations are known to reduce bearing rolling contact fatigue (RCF) life. Recent modifications of such theory to account for these stresses have simply included them in the computation of a single yield stress type criterion—either maximum shear or equivalent stress. An alternative modification is proposed and demonstrated for fatigue crack initiation that recognizes the primary influence of the maximum range of shear stress but includes the effect of normal stress on the critical planes, as in other successful bulk fatigue criteria for multiaxial nonproportional stress cycle fatigue.     

含夹杂物轴承钢中裂纹的萌生与扩展

针对轴承钢中夹杂物周围应力集中导致的疲劳剥落,建立了一种结合连续损伤力学的内聚力模型,用于模拟滚动接触循环加载下的裂纹萌生与扩展。基于内聚力模型的损伤起始准则和损伤演化规律,利用VUMAT子程序结合连续损伤力学构造了新的损伤演化方式,实现循环加载下的损伤累积,建立了基于内聚力模型的疲劳损伤累积失效模型,对含夹杂物模型的疲劳裂纹萌生与扩展进行了模拟,并研究了载荷条件和接触区摩擦因数对裂纹萌生与扩展以及疲劳寿命的影响。研究结果揭示了微观裂纹的萌生与扩展过程,为认识滚动接触疲劳提供了基础。     

Service Loading of Rolling Bearings in Wind Turbine Gearboxes: X-ray Diffraction Material Response Analysis of White Etching Crack Premature Failures

Rolling bearings in wind turbine gearboxes occasionally fail prematurely due to white etching cracks. The appearance of preparatively opened fracture faces indicates damage initiation from the surface in most cases due to brittle spontaneous tensile stress–induced cracking. Under the influence of decomposition products of the penetrating lubricant, branching crack growth is subsequently driven by corrosion fatigue. The material response analysis of rolling bearings from all gearbox locations, based on X-ray diffraction residual stress measurements, reveals vibrations in service as the root cause of surface crack initiation. The occurrence of high local friction coefficients in the rolling contact is described by a tribological model. Depth profiles of the equivalent shear and normal stresses are respectively compared with the measured residual stress patterns and a relevant fracture strength. White etching crack failures are experimentally reproduced on a rolling contact fatigue test rig under increased mixed friction. Causative vibration loading is evident from material response analysis. The generation of compressive residual stresses by cold-working the surface is proven to be an effective countermeasure.     

Evaluation of non-metallic inclusions of steels used for rolling bearings from fracture surface by rotating ring fatigue fracture test

Recent improvements in steel-making techniques have much decreased the content of non-metallic inclusions in steels. Inclusions are known to be detrimental to the rolling contact fatigue life of bearings. While bearing life has improved because of advances in steel-making techniques, the conventional method for evaluating non-metallic inclusions is losing its effectiveness. A new method for evaluating the non-metallic inclusion content of steels used for rolling bearings has been developed. In ring-type rotating fatigue fracture tests on quench-hardened specimens a crack usually initiates on the inside surface of the ring specimen. However, a crack initiates near the outside surface when the specimen has been treated, to produce a large residual tensile stress on the outside surface before the test. In this case, the fractured surface remains protected from damage caused by rubbing of the mating fracture surfaces until the test rig stops. A fish eye is observed on the fracture surface and there is a non-metallic inclusion at the centre of the fish eye. There is a correlation between the size of the non-metallic inclusion in the fish eye and the rolling contact fatigue life of the steel.     

辗轧工序对车轮摩擦磨损和接触疲劳性能的影响

为研究辗轧工序对车轮使用性能的影响,选择经辗轧工序成形和直接钢水浇筑成形的2种车轮材料,利用GPM-30试验机开展摩擦磨损和接触疲劳性能研究,采用光学显微镜、扫描电子显微镜、ASPEX分析仪、EBSD分析2种车轮材料在不同接触应力状态下摩擦磨损和接触疲劳裂纹萌生扩展行为。结果表明:辗轧工序能够有效地细化车轮材料晶粒,减小珠光体片层间距,从而改善车轮微观组织,减少不均匀塑性变形,抑制裂纹的萌生和扩展,减少磨损量,延长接触疲劳寿命;同时发现夹杂物的形态影响接触疲劳试验亚表面裂纹的萌生。     

Life estimation of Ti-6Al-4V specimens subjected to fretting fatigue and effect of surface treatments

Suitability of different multi-axial parameters in predicting fretting fatigue life of Ti-6Al-4V specimens has been investigated. Ameliorating effect of surface treatments on fretting fatigue has been studied. In simple uni-axial/multi-axial fatigue tests, nucleation as well as propagation of cracks occur under the influence of identical stresses. Hence nucleation accounts for most of the total life. Fretting fatigue crack nucleation occurs due to very large contact stresses, effect of which is felt only close to the surface (due to steep gradients). Propagation mostly occurs due to lower stresses in the bulk of the material (negligible influence of contact tractions) and forms a significant portion of total life. Total life has to be taken as sum of initiation life calculated from different multi-axial fatigue parameters and propagation life from conventional fracture mechanics approach. Steep stress gradients necessitate the adoption of a statistics based approach to predict the crack initiation life, based on an assumed distribution of flaws. The quality of comparison between predicted and experimentally observed failure lives provides confidence in the notion that conventional fatigue life prediction tools can be used to assess fretting fatigue failure. Effect of surface treatments like shot-peening with or without additional surface coatings on total life of the specimen and on friction coefficient has been studied.     

Sub-surface damage investigation by high frequency ultrasonic echography on 100Cr6 bearing steel

This paper presents an original ultrasonic technique devoted to the early detection of sub-surface fatigue cracks in 100Cr6 bearing steels. Echographic experiments were carried out during interrupted rolling contact fatigue tests. Crack initiation and crack propagation stages were both investigated. Quantitative measurements of sub-surface crack position, depth and angle with respect to the bearing surface are presented. Experimental results are analysed and discussed in relation to rolling contact fatigue theories. Contrary to what is generally accepted the presented results show that the crack propagation stage could represent an important part of bearing life.     

冲击值与金属材料其他力学性能关系的研究

通过试验研究与理论分析,确定缺口应力集中系数,找出缺口应力集中系数和应力强化系数之间的关系;通过40CrMnSiMoA数字化冲击试验数据分析结果,找出冲击值与材料缺口敏感性的关系、冲击裂纹形成功与疲劳裂纹形成寿命之间的关系;从而得出结论:对于高强度和超高强度材料,冲击功值对缺口试样疲劳裂纹形成寿命影响更大,且冲击功值较高的材料比冲击功值较低的材料在等应力条件下疲劳寿命长。     

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。     

有利于提高硬态切削滚动轴承疲劳寿命的残余应力临界条件

超精硬态切削在滚动轴承表面形成的残余压应力 ,经工作应力衰减后才成为影响滚动接触疲劳寿命的应力状态。基于此 ,本文在考虑特定滚动轴承使用条件的基础上 ,推导出滚动轴承采用超精硬态切削加工工艺时 ,已加工表面的残余应力需要满足的两个临界条件 ,即在接触区的每一离散点的残余应力必须与工作应力符号相同 ,且随时间变化残余应力的幅值应小于或等于工作应力幅值的两倍时 ,才有利于提高滚动轴承的使用寿命。该结论澄清了长久以来文献中所提出的残余压应力总是有利于提高工件疲劳寿命的这个似是而非的概念。     

Decarburisation and rolling contact fatigue of a rail steel

Decarburisation is present on all new rails and unless ground off, will be on the running surface once installed. This paper presents a detailed investigation into the effect of decarburisation of rolling contact fatigue and wear. Twin disc testing has been used to study the phenomenon under water-lubricated rolling/sliding contact. Rail discs have been cut from grade 220 rail and heat-treated to give samples with varying depths of decarburisation. It was found that as the depth of decarburisation increased the wear rate of the rail disc increased while that of the wheel disc decreased. The effect of decarburisation on rolling contact fatigue was to increase the crack growth rate of samples with increasing depth. Cracks under rolling contact fatigue were propagated by contact stresses via the fluid pressure mechanism and influenced by microstructure. The effect of decarburisation was predicted to have little effect on rail/wheel contact when scaled from the laboratory tests using the depth of maximum shear stress.