氮化硅陶瓷球滚动接触疲劳寿命模型

针对球与圆柱接触模型中的陶瓷球,利用WEIBULL断裂统计方法导出球疲劳失效概率与寿命之间的关系方程,在相关额定寿命与最大接触应力的数值解基础上,基于最大主拉应力,构建氮化硅陶瓷球的滚动接触疲劳寿命与接触应力的数学模型.经与不同接触应力水平下的滚动接触疲劳寿命试验结果验证,表明该拉应力一寿命模型的正确性,从而验证了氮化硅陶瓷球的滚动接触疲劳失效源于最大主拉应力,而非基于最大切应力的设想.通过与L.P切应力一寿命模型预测结果的比较,表明拉应力一寿命模型适合于陶瓷球的接触疲劳寿命预测.     

纯滚动状态下氮化硅陶瓷球临界应力分析

氮化硅陶瓷球临界应力在很大程度上决定其滚动接触疲劳和磨损寿命.由于陶瓷材料的抗拉能力较弱,所以设想其滚动接触疲劳失效的临界应力为最大主拉应力.应用弹性接触力学和赫兹理论分析纯滚动条件下陶瓷球表面层接触应力,得到表面层最大主拉应力.针对理论计算值,设计相应的纯滚动接触疲劳实验.分析表明,理论值与实验结果趋于一致,从而证实最大主拉应力为氮化硅陶瓷球滚动接触疲劳失效的临界应力.计算结果为陶瓷球的滚动接触疲劳寿命分析提供理论基础.     

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.     

Ring crack propagation in silicon nitride under rolling contact

Silicon nitride has been found to have the optimum combination of properties which are suitable for rolling element bearing applications to withstand high loads, severe environments, and high speeds. Surface ring cracks are difficult to detect but are found on the surface of silicon nitride balls. These ring crack defects decrease the rolling contact fatigue life considerably. This paper presents an experimental study and numerical analysis of ring crack propagation in rolling contact. The contribution of this study is to provide understanding of ring crack propagation behaviour and life prediction in rolling contact. Rolling contact tests are performed on the silicon nitride/steel elements. Silicon nitride ball surfaces are examined before testing using a dye-penetrant technique and optical microscopy. The surfaces are examined using optical microscopy and scanning electron microscopy during testing and after failure. The numerical calculations are based on a 3D model of ring crack growth. The rolling contact loading is simulated by a repeated Hertzian surface load with normal pressure and tangential traction. Fracture mechanics analysis is utilised to determine the stress intensity along the crack front and the stress intensity factors are analysed using a 3D boundary element model. Life predictions from the present calculations are in line with the experimental observations.     

Surface failure of soft and surface-hardened steel rollers in rolling contact

To study the mechanism of rolling contact fatigue failure, annealed thermally refined 0.43% carbon steel and case-hardened nickel chromium steel rollers were tested under conditions of pure rolling and sliding/rolling. The failure mechanism was examined by fractographic observation and by calculation of the amplitudes of the ratio of stress to strength.It was found that pitting cracks initiated on the roller surface and were induced by the normal stress in the circumferential direction of the roller or by the maximum principal stress. Spalling cracks initiated beneath the surface and were induced by the orthogonal shear stress.     

A Model for Rolling Bearing Life with Surface and Subsurface Survival—Tribological Effects

Until now the estimation of rolling bearing life has been based on engineering models that consider an equivalent stress, originated beneath the contact surface, that is applied to the stressed volume of the rolling contact. Through the years, fatigue surface–originated failures, resulting from reduced lubrication or contamination, have been incorporated into the estimation of the bearing life by applying a penalty to the overall equivalent stress of the rolling contact. Due to this simplification, the accounting of some specific failure modes originated directly at the surface of the rolling contact can be challenging. In the present article, this issue is addressed by developing a general approach for rolling contact life in which the surface-originated damage is explicitly formulated into the basic fatigue equations of the rolling contact. This is achieved by introducing a function to describe surface-originated failures and coupling it with the traditional subsurface-originated fatigue risk of the rolling contact. The article presents the fundamental theory of the new model and its general behavior. The ability of the present general method to provide an account for the surface–subsurface competing fatigue mechanisms taking place in rolling bearings is discussed with reference to endurance testing data.     

Influence of a tension stress field introduced in the elastohydrodynamic contact zone on rolling contact fatigue

The rolling contact fatigue life of modified NU 209 roller bearing inner races subjected to tensile stress mechanically induced in the contact zone, has been investigated using the four-contact fatigue machine.A high tensile stress of 80 MN/m² by a clamp pressure, acting on the inner surface of the specimen, has a catastrophic effect on fatigue life; all specimens burst earlier than pitting failure would have occurred at a near zero tensile stress level.A theoretical study of the influence of the axi-symmetrical stress field, induced by the steady pressure applied inside the hollow rotating cylinder on the stress distribution in the e.h.d. contact zone of cylinders showed a significant increase of the resultant shear stresses caused by tension. The pure shear stress state may exist in the contact zone when the tensile stress level is high.     

Rolling contact fatigue of alumina ceramics sprayed on steel roller under pure rolling contact condition

The rolling contact fatigue of sprayed alumina ceramics with a nominal composition of Al₂O₃–2.3 mass% TiO₂ was studied with a two-roller test machine under a pure rolling contact condition with oil lubricant. The influence of undercoating of sprayed Ni-based alloy on the rolling contact fatigue was investigated. The failure mode of all sprayed rollers was spalling caused by subsurface cracking. The undercoating did not contribute to the improvement of the rolling contact fatigue life. The elastic modulus of the alumina sprayed layer evaluated with the nano-indentation method was around 85 GPa. The depths of the observed subsurface cracks corresponded approximately to the depths where the orthogonal shear stress or the maximum shear stress calculated with two-dimensional FEM became maximum.     

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.     

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。     

超硬涂层轴承的滚动接触疲劳试验

介绍了超硬涂层轴承滚动接触疲劳试验机的原理及功能,并对表面涂层的51306型轴承滚动接触疲劳失效进行了试验分析。通过对影响涂层接触疲劳破坏的几个重要参数的动态检测与控制,试验成功捕捉到了超硬涂层轴承表面疲劳裂纹的初始形态,分析了涂层轴承接触疲劳失效机理,为涂层轴承疲劳寿命评估提供了依据。     

滚动轴承疲劳破坏机理和疲劳寿命模型综述

延长轴承疲劳寿命,尤其是滚动轴承的接触疲劳寿命.一直是轴承工作者十分重视的研究课题.本文概括了滚动轴承接触疲劳破坏机理的主要形式和形成原因,总结了不同阶段的滚动轴承接触疲劳寿命计算公式,分析了不同滚动轴承接触疲劳寿命模型的区别.介绍了表面涂层的摩擦学性能在滚动轴承中的应用.     

Experimental Study of Cyclic Rolling-Contact Fatigue of Silicon Nitride Balls

A newly developed pure-rolling fatigue test rig with three contact points for bearing balls was used to perform rolling-contact fatigue (RCF) tests. The fatigue properties of GCr ₁₅ steel balls and two kinds of Si ₃ N ₄ ceramic balls (GSN-200 and NBD-200) produced with different technologies were compared. Life test data, summarized in accordance with the Weibull theory, showed that the life of the GSN-200 balls was close to that of the GCr ₁₅ balls, whereas the life of the NBD-200 balls was much longer than those of GSN-200 and GCr ₁₅ . Under the same working condition, the temperature rise of all the ceramic balls was lower than that of the steel balls. Ball surfaces were examined after failure with optical microscopy and scanning electron microscopy. It was identified by test that the failure mode of ceramic balls was surface spall. The research shows that subsurface cracks play a dominant role in spalling failure. These cracks originated from volume defects of the material and propagate to form elliptical fatigue spalls.     

The effect of changing the rolling direction on the rolling contact fatigue lives of annealed and case-hardened steel rollers

The effects of changing the rolling direction and of repeated loading on the rolling contact fatigue lives of annealed 0.45% carbon steel rollers and case-hardened nickel-chromium steel rollers under conditions of sliding rolling contact were studied. The influence of plastic flow in the subsurface layer on the rolling fatigue life was examined. The increase in the rolling fatigue life of an annealed steel roller due to a change in the rolling direction was significant, especially when the rolling direction was changed just before the formation of macroscopic surface cracks and pits. The effect with case-hardened steel rollers was negligible. The varying effects of changing the rolling direction on the rolling fatigue life were due to differences in work-hardening and the extent of plastic flow in the rollers.     

The inclination of cracking in the peeling failure of a ball bearing steel and its relation to the inclination of the principal residual stress

Peeling is a mode of surface fatigue failure which is produced by rolling contact under specific conditions. X-ray measurements of the residual stress on a peeled surface using the 0–45° method revealed that the stress values in the rolling direction and in the direction opposite to rolling were different, i.e. 2θ?sin²ψ figures for the two measuring directions do not coincide and no linear relation exists between 2θ and sin²ψ. The relation between the inclination of cracking in peeling failure and the residual stress state was investigated by the integral method. The inclination of cracking is explained by the residual tensile stress acting perpendicularly to the principal residual compressive stress.     

Durability of plasma-sprayed Cr3C2-NiCr coatings under rolling contact conditions

The aim of this paper was to address the rolling contact fatigue (RCF) failure mechanisms of plasma-sprayed Cr3C2-NiCr coatings under different tribological conditions of contact stress. Weibull distribution plots of fatigue lives of the coated specimens at different contact stresses were obtained. The failure modes of coatings were identified on the basis of wore surface observations of the failed coatings. Results showed that the RCF failure modes can be classified into four main categories, i.e., surface abrasion, spalling, cohesive delamination, and interfacial delamination. The probabilities of the surface abrasion and spalling type failures were relatively high at low contact stress. When the coatings were subjected to abrasion and spalling type failures, the failure of the coating was depended on the microstrcture of the coating. The stress concentration near the micro-defects in the coating may be the may reason for the formation of spall. The coatings were prone to fail in delamination under higher contact stresses. However, the delamination of coating may be related to distribution of shear stress amplitude within coating. The location of maximum shear stress amplitude can be used as a key parameter to predict the initiation of subsurface cracks within coating in rolling contact.     

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。     

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.     

A Mathematical Model of Spalling Fatigue Failure in Rolling Contact

Variables affecting the fatigue life of a rolling contact are identified. A mathematical model of sub-surface and surface crack propagation is presented. The life to failure of volume elements in the vicinity of a defect (defect life) is formulated. A term “severity” of a microdefect has been defined. The model is characterized by the inclusion of bulk material parameters, defect characteristics and parameters of geometry, stress, lubrication and surface topography. A statistical expression for the life of an entire rolling body is based on the defect life formula. The new model comprises current standard bearing life prediction formulas as a special case.     

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.