Analysis of micropitting of prototype surface fatigue test gears

The early stages of micropitting were examined on experimental gears designed for surface fatigue studies by the Helical Gear Rating Committee of the American Gear Manufacturers Association. Optical profilometry, scanning electron microscopy, and metallographic examinations were conducted on the first prototype gearset tested. The gearset was tested in an FZG test rig. To evaluate tooth bending fatigue strength, the gears were loaded to load stage 12. A tooth broke from bending fatigue in 0.88 h (the expected time). This short runtime allowed for the examination of micropitting at an early stage of development. The distribution and morphology of micropitting over the tooth face and associated relationships with surface micro‐ and macrogeometry features and traction have been examined. Micropitting was primarily associated with finish geometry. A few pits were associated with sulphide inclusions and one pit was possibly initiated by a small non‐metallic inclusion. Metallographic examinations revealed asperity‐related lines of dark etching alterations caused by high asperity contact and traction stresses.     

Surface initiated tooth flank damage. Part II: Prediction of micropitting initiation and mass loss

Following the first part of this work, where a numerical model of surface initiated fatigue damage was presented, that model is applied here to the prediction of micropitting and mass loss of gear teeth. This is achieved by simulating a real micropitting test and by comparing it to the actual test results. On the way, a possible approximation to the mechanism by which mass is removed from the flank surface is discussed.     

Subsurface damage development during fretting fatigue of high strength steel

The results of fretting fatigue experiments performed on two high-strength structural steels, PH 13-8 Mo stainless steel and quenched and tempered 4340 steel, are evaluated. Observations regarding the subsurface deformation and cracking behavior of the steels are compared and contrasted. It was found that the fretting stresses influenced early crack growth to a greater depth in PH 13-8 Mo stainless steel than in 4340 steel. In addition, experiments on PH 13-8 Mo led to the development of a region below the fretting scar that underwent a microstructural transformation, while experiments on 4340 steel did not. Likely reasons for this discrepancy are suggested. Differences in the formation of oxide layers and the occurrence of adhesion between the two materials are also discussed.     

Wear and micropitting of steel ball sliding against TiN coated steel plate in dry and lubricated conditions

Wear of the steel part sliding against titanium nitride both in lubricated and unlubricated conditions have been investigated. An unexpected micropitting like wear on the steel surface was found in lubricated conditions, after very short run time. Possible wear mechanisms—fatigue, chemical reaction or electrical discharge—are discussed. A special attention is given to electrical discharge mechanism. A remarkable result was obtained when the lubricant, white oil—a good insulator fluid—was replaced with glycerin, an electrical conductive fluid. With glycerin as lubricant no micropitting was observed on the steel surface even after long run time.In unlubricated condition intense, predominant oxidative wear of steel part was found.     

Investigation of rolling contact fatigue damage of a case-carburized low alloy steel

Experimental investigations were carried out on case-carburized En 36 A steel to study contact fatigue behaviour and pit formation. The effects of case depth, specimen hardness, different combinations of hardness of the specimen and mating roller and the influence of grinding operations before or after heat treatment were assessed. Optical and electron microscope studies revealed the formation of subsurface cracks which propagate because of the alternating shear stresses in the subsurface and which then turn towards the surface where the final failure occurs by ductile and then brittle fracture. Surface cracks initiated by micropits were also observed in some specimens.     

Effect of lubricants on micropitting and wear

Micropitting was studied using a three-contact disc machine having a central roller in contact with three harder, annular counter-discs (“rings”) of precisely controlled roughness. Roughness, running conditions, base stock and additive concentration were varied. The response of the same lubricants in a reciprocating sliding wear test operating in the boundary regime was also studied.Results of experimental studies of the rolling contact behaviour of carburised steel rollers are reported. All the tests with the additive present led to micropitting. However, severe micropitting wear was only observed when the calculated film thickness exceeded 12% of the centre-line average roughness of the rings.It was found that there was an approximately inverse correlation between the micropitting damage in the disc machine test and the mild wear in the reciprocating sliding test. This was attributed to the tendency of anti-wear additives to prevent running-in of the rough surface.     

Effect of lapping on the fatigue strength of a hardened 13Cr-0.34C stainless steel

Reversed plane-bending fatigue tests were carried out on 13Cr-0.34C stainless steels, heated treated to two hardness levels. Their surfaces were prepared by grinding and lapping according to the procedure actually used in the production of compressor valves. It was found that the larger compressive residual stresses in the subsurfaces produced by lapping raised the fatigue strength in spite of the increased surface roughness and the embedding of lapping particles, the latter being effective in reducing wear.     

Improved extrapolation method for the fatigue damage of bus structural steel under service loading

Journal of Mechanical Science and Technology - This paper shows a technical study and analysis of the fatigue damage assessment of bus structural steel under service loading. Two bus prototypes...     

螺栓疲劳寿命预测

通过材料疲劳寿命方程回归、有限元计算,应用局部应力应变法,预测了螺栓试样疲劳寿命,螺栓试样疲劳试验验证了该方法的适用性及螺栓接触有限元计算结果的精确性.     

加载频率对钢铁材料超长寿命疲劳性能的影响

使用82 Hz轴向加载疲劳试验机和20 kHz非间歇式加载的超声疲劳试验机,对比研究了超声加载频率对轴承钢GCr 15和35CrMo超长寿命疲劳性能的影响.断口观察表明:82 Hz轴向加载和20 kHz超声加载的GCr15试样,在全应力幅范围既发生表面破坏又发生由夹杂物引起的内部破坏;而35CrMo试样在两种频率下均为...     

Prediction of the fretting fatigue resistance of various surface-modification layers on 1045 steel: the role of fretting maps

In this work, fretting maps of various surface modifications were established based on the friction logs of fretting experiments. The fretting fatigue resistance of the coatings was analyzed according to the features of the fretting maps of the coatings. The results showed clearly that fretting maps of materials are effective tools to predict the fretting fatigue properties of substrates and surface-modification coatings. It was also demonstrated that the fretting fatigue resistance of a 1045 steel substrate could be improved to different extents through surface modification. The fretting fatigue resistance of solid lubricating coatings was the best and the tendency for initiation and propagation of cracks in the substrate material could also be restrained by depositing hard coatings.     

车轴轮座微动损伤对车轴疲劳寿命的影响

使用有限元软件ANSYS计算轮座损伤对车轴疲劳寿命的影响.首先计算车轴的稳态受力,这时主要考虑两种栽荷:过盈应力和额定载重应力,关键是考虑两种载荷的复合作用效应.采用外推方法获得车轴材料的S-N曲线,然后将其导入有限元程序进行计算.计算结果表明:有微动损伤的车轴疲劳寿命比无微动损伤的疲劳寿命明显减少.     

螺栓用钢ML35CrMoV最佳热处理制度的选择

通过实验,确定了钢ML35CrMoV最佳热处理工艺,使之达到12.9级高强度螺栓用钢的要求.     

A new fatigue life prediction method based on nonlinear fatigue cumulative damage generalized expression

Ye’s nonlinear cumulative damage model has been widely used in engineering because of its simple mathematical form and clear physical meaning. However, it does not consider the interaction between two different loads, so its prediction accuracy has large room for improvement. In this paper, the k-th power of load ratio is introduced into Ye’s model to reflect the influence of the interaction between two different loads on fatigue damage during the damage evolution process, and a generalized expression of the model is obtained. Based on this generalized expression, a new fatigue life prediction method is proposed. The proposed method is validated by comparison with existing versions based on the experimental data of typical engineering materials under two-level and multilevel loads. The results show that the prediction method proposed here can well reflect the load interaction effect, and compared with other models, this method has a more accurate prediction effect on the fatigue life of four materials.

     

Study of microstructural influences on machinability of case hardening steel

The overall aim of this study is to establish knowledge about how the material specification of case hardening steel should be modified in order to create a robust and predictable production process with focus on machinability. In this study, emphasis is laid on studying microstructure variations produced by changing holding time and temperature in the annealing process. A standardized milling test was used to assess machinability (with respect to tool wear) as this method has the advantage of only needing small diametrical samples and low material volumes. From the results of the test, it can be concluded that machinability is more influenced by pearlite nodular size than by pearlite morphology. Furthermore, it can be stated that hardness is not a suitable criterion for determining machinability of case hardening steel. In the manufacturing process of transmission parts (such as gear milling/hobbing), high speed steel tools are commonly used. The same type of tool is applied in the standardized milling test. However, the obtained ranking (of machinability) for the different materials is also applicable if other types of cutting tools are used.     

疲劳损伤状态的模糊等效性试验研究

针对复杂载荷下以等效损伤假设为基础的材料疲劳寿命的估算误差较大的问题,基于模糊理论并结合耦合损伤概念提出模糊等效损伤假设,考虑加载顺序对疲劳损伤累积的影响来回避等效损伤假设。利用45钢材料进行了L-H和H-L加载顺序两级应力下的疲劳损伤累积规律验证,并选取16Mn材料的疲劳试验数据验证基于Miner线性损伤法则和本假设对材料疲劳寿命预测的准确性。结果表明,根据本假设计算的损伤量在两种加载顺序下均与试验值吻合良好,疲劳寿命估算结果比较接近于试验值,该假设以模糊理论为依据,为疲劳分析和寿命预测提供了一定的理论参考。     

A study on fatigue damage modeling using neural networks

Fatigue crack growth and life have been estimated based on established empirical equations. In this paper, an alternative method using artificial neural network (ANN) -based model developed to predict fatigue damages simultaneously. To learn and generalize the ANN, fatigue crack growth rate and life data were built up using in-plane bending fatigue test results. Single fracture mechanical parameter or nondestructive parameter can’t predict fatigue damage accurately but multiple fracture mechanical parameters or nondestructive parameters can. Existing fatigue damage modeling used this merit but limited real-time damage monitoring. Therefore, this study shows fatigue damage model using backpropagation neural networks on the basis of X-ray half breadth ratioB/B ₀ , fractal dimensionD _f and fracture mechanical parameters can estimate fatigue crack growth rateda/dN and cycle ratioN/N _f at the same time withinengineering limit error (5%).     

弯曲疲劳损伤的检测与控制

用控制工程的理论，检测弯曲疲劳损伤过程，建立传递函数，提取疲劳损伤参数。试验结果表明，该方法能够直观、敏感地反映材料的弯曲疲劳损伤过程，为疲劳损伤的深入研究提供一种新手段。     

Radial fretting fatigue damage of surface coatings

Radial fretting tests with a 52100 steel ball-on-flat contact have been carried out under different normal loads. TiN, MoS₂ and TiN+MoS₂ coatings on a 1045 steel flat were examined. The normal loads amplitude used were 200, 400 and 800 N at speeds of 12 and 1.2 mm/min. Dynamic analysis in combination with microscopic examinations by SEM and EDX have been performed. It was observed that the vertical stiffness increased with the increase of loading speed and number of cycles. The metallographic examinations showed that little damage was observed for the MoS₂ coating, which exhibited excellent radial fretting fatigue resistance. For the TiN coating, micro-cracks appeared at the lower load while delamination occurred at the higher load. For the TiN+MoS₂ composite coating, the vertical stiffness increased but accompanied by some micro-cracks. As a result of the study, the radial fretting test is proposed as one possible new method to evaluate coating life.     

多轴低周疲劳寿命预测软件

通过Visual Basic6.0各种控件和算法的运用，编制的“多轴低周疲劳寿命预测软件（MLCFP1.0）”，涉及多种疲劳寿命预测方法，特别适用于结构中出现非比较、多轴应力状态的情况，为多轴疲劳下的寿命预测提供了解决的有力工具。本软件还留有新模型的嵌入接口，数据处理过程实现多文件操作。后处理绘图软件LCF FIGURE1.0，能给出标准的疲劳寿命预测图形，其保存文件形式多样。