Contact Fatigue Life Research Articles

A novel prediction approach of polymer gear contact fatigue based on a WGAN‐XGBoost model

AbstractPolymer gears have long been used on power transmissions with the fundamental durability data, including fatigue S‐N curves, yielding important data informing reliable and compact designs. This paper proposed a prediction method for polyformaldehyde (POM) gear fatigue life based on the innovative WGAN‐XGBoost algorithm. The findings generated herein revealed that the proposed method performs well in terms of prediction accuracy. The predicted fatigue lives, analyzed under different loading conditions, were within 1.5 times dispersion band compared with experimental results. Furthermore, based upon the enhanced fatigue dataset, a thermo‐mechanical coupled prediction formula for POM gear contact fatigue life was proposed. These findings offered a new approach for high‐power density design of polymer gears.

Modeling and dynamic characteristic analysis of high speed angular contact ball bearing with variable clearance

In this paper, an analytical calculation model based on Jones raceway control hypothesis model was proposed for high-speed ball bearing, clearance, centrifugal displacement and thermal deformation are considered. The validity of the proposed model was verified by comparing with the Jones model, and the fatigue life model of bearing was established. The bearing dynamic characteristics under axial load and combined load are analyzed, and the change rule of each parameter is revealed. In addition, the influence of different clearances on high-speed bearing is studied, and the dynamic characteristics of bearing are further analyzed. The research show that the proposed model can break the limitation of Jones raceway control hypothesis model, and the bearing ball-raceway contact state and fatigue life are greatly affected by the change of working clearance. Therefore, the analytical calculation model in this paper not only meets the dynamic characteristics analysis of ball bearing under different operation conditions, but also has great significance for the design and use of bearing.

Nonproportionally multiaxial cyclic plastic deformation of U75 rail steel: Experiment and modeling

U75V rail steel exhibits cyclic softening and hardening under uniaxial and multiaxial strain-controlled cyclic loadings, respectively. The ratcheting behavior of U75V rail steel depends on the loading paths due to nonproportionally additional hardening. New evolution equations incorporating Tanaka’s nonproportional parameter are introduced into the isotropic and kinematic hardening rules of the cyclic plastic constitutive model to describe the cyclic softening/hardening features and multiaxial ratcheting behavior. The simulated results agree with the corresponding experimental results. A finite element model of wheel-rail cyclic rolling contact is established to investigate the nonproportionally multiaxial effect on the rolling contact fatigue life.

Numerical and experimental research of helical gear contact stress considering the influence of friction

Helical gears are widely used in various mechanical transmissions. Thus, analysing gear contact stresses is crucial to improve the fatigue limit and life of gears. In this paper, the contact stress of helical gear is analyzed by finite element simulation and experimental verification. The effect of coefficient of friction on the contact stress of helical gears is analysed, with given coefficients of friction. The following conclusions can be drawn through simulation and test. 1) The contact stress increases with the coefficient of friction in the early stage of meshing. 2) The contact stress decreases with the increase in the coefficient of friction in the late stage of meshing. 3) The gear contact fatigue test shows that the location of fatigue pitting on the tooth surface is consistent with that of the simulated maximum stress point. The friction-reducing coating on the gear surface can decrease the coefficient of friction between the tooth surfaces and thus effectively improve the gear contact fatigue life.

Tolerance Analysis of Cylindrical Roller Bearing under Combined Radial and Axial Loads

In order to analyze the influence of tolerance values of key parameters for cylindrical roller bearings under combined axial and radial loads, a coupled model, incorporating a dynamic model of cylindrical roller bearings, contact model, and fatigue life model, is developed to investigate the effect of flange angle, roller-end radius, interval of roller length gauge, and roller profile on contact performance and fatigue life. The results show that the grouping design of flange angle and roller-end radius in the tolerance range was helpful for reducing contact ellipse truncation. The difference of the roller length would change the axial load distribution of the bearings. For the longest roller located in the bottom position, the bigger the difference, the bigger the roller tilt angle and carried-axial load. The (0, +2.5 μm) tolerance range of the crown drop can limit the difference of the fatigue life within 20% in the current analysis.

Investigation and optimization of hypoid gear micro-geometry parameters and axle deflections to improve the contact stress distribution and fatigue life of hypoid gears

The automotive industry always demands more torque per kilogramme of weight. On the other hand, there is always a growing demand for increased warranty kilometres for customers. This puts increased pressure on the life of the drive axle, which is the major load and torque-carrying member in commercial vehicles. Drive head unit is a crucial contributor to this aim. This paper focuses on the work done towards the above targets wherein advanced tools helped to achieve them in the minimum time. Due attention is given to the hypoid gear system to sustain higher stress because of the heavy torque demanded by the application. It is accomplished by the optimum design of the gear tooth profile and system design. Gear durability is a major concern in heavily loaded axles. To have an optimum design with higher performance torque is a key challenge. The paper talks about the challenges overcome during the design, development, and validation of a single-reduction large-size gear axle to replace the hub reduction rear axle. It demands a better understanding of gear tooth and system behavior, which was analyzed by advanced software tools and measurement machines. The same is validated on the test bench, and the results are discussed.

An Investigation of the Contact Fatigue Characteristics of an RV Reducer Crankshaft, Considering the Hardness Gradients and Initial Residual Stress.

The crankshaft is one of the core components of a Rotate Vector (RV) reducer. The fatigue life of the RV reducer is severely hindered by fatigue failure on the eccentric cylindrical surface of the crankshaft. The hardness gradients and residual stress in the crankshaft, associated with machining operations, exert an enormous impact on the rolling contact fatigue (RCF). In this work, a finite element method (FEM)-based three-dimensional elasto-plastic contact model is established to calculate the stress-strain field by taking hardness gradients and initial residual stress into account. The RCF characteristics of an RV reducer crankshaft is investigated by applying modified Fatemi-Socie (FS) multiaxial fatigue criterion. The results indicate that initial residual stress plays an influential role in the fatigue damage by altering the distribution of the maximum normal stress near the contact surface. The modified FS fatigue criterion could better consider the effect of initial residual stress and the shear stress, which significantly improves the prediction accuracy of the contact fatigue life model. The contact fatigue performance could be considerably improved by designing appropriate shot peening parameters to obtain optimized residual stress distribution. Therefore, the technique presented may serve as an important guideline for the anti-fatigue design of an RV reducer crankshaft.

Effects of Cerium on Non-metallic Inclusions and Rolling Contact Fatigue Life of a High-Carbon Chromium Bearing Steel

Effects of Cerium on Non-metallic Inclusions and Rolling Contact Fatigue Life of a High-Carbon Chromium Bearing Steel

Gear tribodynamic modeling and analysis considering tooth profile modification

A novel two-part gear tribodynamic model considering tooth profile modification (TPM) is established. One part is a coupling model of gear dynamics and elastohydrodynamic lubrication theory, so that the lubricant-induced backlash reduction and geometry of modified tooth profiles can be described. The other is the Chebyshev subinterval decomposition method that calculates the tribodynamic response intervals efficiently when the correlated uncertainty is considered. Using this model, tribodynamic characteristics of gears with TPM are analyzed. Results show that high viscosity suppresses the torsional and translational vibrations concurrently. Excessive modification amount, length and too small power exponent amplify the vibration and contact pressure. Moreover, the correlated uncertain TPM leads to a nonnegligible influence on the intervals of vibration and contact fatigue life.

A rolling contact fatigue health prediction model based on load interaction and damage energy accumulation

Rolling contact is one of the main contact modes of all kinds of mechanical equipment at present. This investigation studied the rolling contact fatigue behaviors under various slip ratios and surface roughness with the consideration of loading history, loading sequence, and mutual influence between different load levels. In this paper, a fatigue crack initiation life prediction model based on strain energy accumulation caused by slip dislocations is proposed. The effect of increasing slip dislocation density and friction resistance on strain energy accumulation under alternating load is studied. The experimental results show that compared with the existing models, the proposed model can effectively improve the prediction accuracy of contact fatigue life under variable stress loading.

Influences of the characteristics of carbide particles on the rolling contact fatigue life of rare earth modified, highly clean bearing steel

Machine tool bearings made of rare earth modified, highly clean bearing steel subjected to rolling contact fatigue (RCF) under the same bench test conditions were studied. The morphology and initiation position of contact fatigue cracks of bearings were characterized macroscopically and microscopically. According to the characteristics of carbide particles in the metallographic structure of the crack source areas, the corresponding relationships between the difference of particle size and roundness of carbide and the change in RCF lives of bearings were proposed, as well as the corresponding different failure mechanisms. The results show that RCF life increases with the decrease in the percentages of large-sized and irregular carbides in the microstructure. When early RCF failure occurs, cracks originate mainly at the surface, and the size of carbides affects RCF; with the increase of service life, the cracks begin to originate at the subsurface, and at this time, the roundness of carbides exerts a significant influence.

Effect of Ultrasonic Rolling on Surface Microstructure and Contact Fatigue Life of Carburized Bearing Steel

Effect of Ultrasonic Rolling on Surface Microstructure and Contact Fatigue Life of Carburized Bearing Steel

Low-oxygen rare earth steels.

Rare earth (RE) addition to steels to produce RE steels has been widely applied when aiming to improve steel properties. However, RE steels have exhibited extremely variable mechanical performances, which has become a bottleneck in the past few decades for their production, utilization and related study. Here in this work, we discovered that the property variation of RE steels stems from the presence of oxygen-based inclusions. We proposed a dual low-oxygen technology, and keeping low levels of oxygen content in steel melts and particularly in the raw RE materials, which have long been ignored, to achieve impressively stable and favourable RE effects. The fatigue life is greatly improved by only parts-per-million-level RE addition, with a 40-fold improvement for the tension-compression fatigue life and a 40% enhancement of the rolling contact fatigue life. We find that RE appears to act by lowering the carbon diffusion rate and by retarding ferrite nucleation at the austenite grain boundaries. Our study reveals that only under very low-oxygen conditions can RE perform a vital role in purifying, modifying and micro-alloying steels, to improve the performance of RE steels.

A new method for contact characteristic analysis of the tapered roller bearing in wind turbine main shaft

Premature failures of TRB in wind turbine remain a significant contributor to high operation and maintenance costs. The analysis of contact characteristics is the premise of the TRB failure investigation. In this paper, a novel five degrees of freedom (5DOF) TRB model which considers bearing clearance and preload, is established. Instead of the Newton-Raphson method, the meta-heuristic optimization is adopted to solve the nonlinear system by the L2-norm minimization control. This improvement can intelligently judge the load region of TRB, avoid the selection of initial values and improve the convergence speed. The load distribution results are compared to the simulation results of the finite element model, Romax model and Harris model to verify the effectiveness of the proposed model. Besides, the proposed method has a higher efficiency than the existing methods. Finally, the influences of bearing clearance and preload on the contact characteristic and fatigue life are discussed.

Study on the relation between surface integrity and contact fatigue of carburized gears

Surface integrity is critical for gear contact fatigue performance. The relation between gear surface integrity and contact fatigue remains unclear, which is a challenge for gear anti-fatigue design. This study investigates the relation between surface integrity and contact fatigue of 18CrNiMo7-6 carburized gears through fatigue experiments and data-driven modeling. A series of gear contact fatigue tests, with approximately 110 × 106 running cycles in total, has been conducted. P-N curves and fatigue limits of the tested gears are investigated for four typical manufacturing processes: carburizing and grinding, shot peening, barrel finishing, and barrel finishing after shot peening. The influence of different surface integrity components on contact fatigue is explored with a Pearson correlation coefficient analysis and a random forest algorithm. Formulae of gear contact fatigue life and fatigue limit considering surface integrity are proposed. Results show that a high surface integrity state with surface hardness of 686.5 HV, maximum compressive residual stress of −1162 MPa, and surface roughness Sa of 0.36 μm, exhibits the highest gear contact fatigue limit, which is 15.1% higher than the carburizing and grinding state, indicating the benefits of improving surface integrity. For both the gear contact fatigue life and fatigue limit, the most significant surface integrity components are surface hardness, maximum compressive residual stress, and surface roughness. The proposed formulae considering surface integrity illustrate reasonable prediction accuracy, with 1.5 times dispersion band for the predicted fatigue life and a maximum relative error of 2.1% for the predicted fatigue limit.

Design of Downhole Robot Actuator System and Mechanical Behavior Analyses of the PRSM by Considering Elastic Errors and Radial Loads

This paper designs a new class of actuators for the downhole traction robot system to achieve high-accuracy transmission, which is realized by the planetary roller screw mechanism (PRSM). As the downhole environment is a non-structure one, which increases the difficulty of the load analyses and distributions of the downhole robot system to complete a predesigned mission. Traditional achievements about the mechanical behavior analyses of PRSM ignore the effects of radial loads and torque elastic deformation errors, which are inevitable for the downhole robot actuator, and the results of which would affect the load distribution and fatigue life of the PRSM-aided actuator. To assist the complex task, in this study the mechanical behavior analyses of PRSM for the downhole robot system are investigated by considering axial loads, torque elastic deformation errors, and radial loads. Moreover, the calculation models for contact load distribution and fatigue life are established by utilizing the equivalent contact load and Hertz contact theory. Two cases for the robot actuator in the downhole environment are addressed, the results of which indicate that the contact load change and decrease with the thread growth direction of the PRSM, the first several threads bore most of the loads, and the last several threads only took a few loads. Additionally, the fatigue life reduces sharply under the condition that the axial loads, radial loads, and rotation speeds increase. Compared with the other two effectors, the fatigue life is more sensitive to the radial loads. The results show the sustainability of the presented screw–roller–nut and provide a potential reference for the downhole robot actuator motion analyses.

Grinding sustainability analysis using a fatigue failure-related product life indicator

Grinding is considered as a rather environmental-unfriendly process, where the aspects involving the high demanding process energy input and required fluid application can lead to severe environmental impacts while achieving high product quality. However, the reduction of the cutting fluids raises the cutting temperature, leading to negative alterations of the ground subsurface. Such detrimental aspects are usually not factored into a life cycle inventory analysis. Therefore, this study introduces a new sustainability indicator based on the rolling contact fatigue life of the component, as determined by the grinding process. A method for calculating this indicator is presented, and a case study is illustrated. The subsurface damage thickness can be loosely correlated with fatigue life and introduced as a new indicator. The selected indicators were used as decision-making parameters to showcase the potential of the product life factor as an aggregate sustainability indicator.

Fatigue Life Analysis of Main Reducer Gears for Battery Electric Bus Considering Regenerative Braking

The braking mode of the battery electric urban bus (BEUB) is different from the friction braking of the traditional fuel bus due to the introduction of a regenerative braking system. The intervention of electromagnetic braking changes the working condition of the main reducer gears, thus affecting their service lives. Based on the Urban Dynamometer Driving Schedule (UDDS) driving cycle condition, the stress–time history of the main reducer gears is calculated. Combined with the static analysis results and the S-N curve of the material, the fatigue lives of the main reducer gears considering electromagnetic braking and traditional friction braking are analyzed. The reverse torque on the driving axle during electromagnetic braking is taken into account to be closer to the real situation. Results show that, under the electromagnetic braking mode, the bending fatigue lives of the tooth root on the convex and concave surfaces of the pinion are 78.5% and 78.9% of that under the traditional friction braking mode, respectively, while the contact fatigue life of the pinion working surface is 78.2% of that under the friction braking mode, indicating that the introduction of the regenerative braking system into the BEUB will cause a significant reduction in the service life of the main reducer gears. This study provides a high-precision fatigue life calculation method for the BEUB main reducer gears and the accurate prediction of their remaining life.

Contact fatigue life estimation for asymmetric helical gear drives

The numerical model for an asymmetric helical gear is developed through analytical equations, and the contact fatigue life (CFL) is estimated based on the Basquin and Coffin-Manson method. Further, the numerically simulated CFL and bending fatigue life are validated with the experimental results based on the literature. By employing the proposed model, the significant asymmetric helical gear parameters of helix angle, gear ratio, teeth number, module, face width, pressure angle and coefficient of friction are estimated for customized power transmission by improving the CFL. Finally, it is revealed that an asymmetric helical gear exhibits enhanced CFL over symmetric helical gear.

Research on calculation of contact fatigue life of rough tooth surface considering residual stress

Grinding and shot peening produce large residual stresses on the gear teeth. Research on the calculation of contact stress and fatigue life of rough gear teeth considering the residual stress has not been published in the literature. The influence of residual stress and rough surface on contact fatigue is difficult to be ignored, so the research of the paper is of significance. Based on the finite element modeling method of rough surface contact and multiaxial fatigue criterion, the gear contact stress and fatigue life under the action of rough surface and residual stress is obtained. The study found that residual compressive stress can reduce the high stress area of the near-surface and lead to a low-stress area between the near-surface and the sub-surface. In addition, residual compressive stress can reduce the near-surface fatigue failure depth (NFFD) and make the sub-surface fatigue failure area tend to be deeper while increasing the contact stiffness of the tooth surface. The logarithmic value log10(2Nf) of the sub-surface fatigue life is quantitatively related to the roughness Sq and the residual stress amplitude σrs, and the fitting polynomial of the three variables is obtained, which provides a theoretical reference for the prediction and calculation of the contact fatigue life of the tooth sub-surface.