Contact Fatigue Life Of Gears Research Articles

Gear contact fatigue prediction under mixed elastohydrodynamic lubrication with ellipsoidal asperity rough surface: Experimental and numerical investigation

A three-dimensional(3D) line-contact mixed lubrication model and contact fatigue life prediction model for gears are established, considering the elastoplastic contact of ellipsoidal asperities and their interactions. The localized lubrication states across the actual 3D rough surfaces are visually depicted. The direct asperity contact pressures calculation exhibits greater accuracy and universality. The proposed mixed lubrication model can be applied accurately and efficiently to heavy-load conditions. The synergistic mechanisms of multi-scale surface integrity parameters, such as surface morphology-lubrication coupling, hardness gradient, and residual stress, on gear contact fatigue has been revealed. The results reveal that surface roughness significantly affects the competitive failure mechanism between surface-initiated micropitting and subsurface-initiated macropitting. The increase in surface compressive residual stress is more sensitive to the enhancement of near-surface and subsurface fatigue lives, compared to the increase of peak residual stress and the depth of peak residual stress. The proposed physics-based gear contact fatigue life prediction model has been validated through gear contact fatigue experiments under various operating conditions. The maximum deviation between the predicted and experimental fatigue lives is within 10%. This paper presents theoretical methodologies and data-driven support for optimizing the design and manufacturing processes of gears, specifically focusing on enhancing anti-fatigue properties.

Numerical modeling and experimental investigation on fatigue failure and contact fatigue life forecasting for 8620H gear

Surface integrity parameters exert an enormous function on contact fatigue performance of gears. In this paper, a gear contact fatigue life prediction model that incorporates surface integrity parameters is proposed. The micropitting and pitting damage of failed gears are quantitatively analyzed through micro-characterization techniques. A three-dimensional contact analysis of rough surface is performed to simulate the morphology evolution during gear running-in. And the coupling effect of residual stress and rough morphology on the contact stress field and fatigue life is analyzed. Finally, residual stress optimization design is carried out based on the failed gear. Gears subjected to shot peening are designed and gear contact fatigue tests under various working conditions are performed. The research results indicate that the plastic deformation at the asperities level in the running-in process mainly occurs during the initial loading. The fatigue life significantly increases by improving the residual stress distribution on the tooth surface through shot peening process. The maximum relative error between predicted fatigue life and measured fatigue life is less than 20%, which effectively verifies the accuracy of the proposed model. The technique presented in this study could provide theoretical basis and data support for the anti-fatigue design and manufacturing of gears.

A hybrid physics-based and data-driven method for gear contact fatigue life prediction

A hybrid physics-based and data-driven method is proposed for gear contact fatigue life prediction. The parameters influencing the fatigue life are determined by the physics-based model. A deep belief network (DBN) model is developed to reveal the relationships between these parameters and fatigue life. A variational autoencoder (VAE) model is presented to expand the size of the training dataset. The proposed method is verified by a gear contact fatigue test, and the predictions are all within a factor of 1.5 scatter band of the experimental results. This work provides an effective method for life prediction with small sample sets.

Gear contact fatigue life prediction based on transfer learning

The gear contact fatigue test is characterised by extraordinarily high costs and a long period of testing. A transfer learning algorithm was applied to develop a gear contact fatigue life prediction strategy to fully use other low-cost fatigue test data, such as twin-disc test data. The twin-disc contact fatigue test data were incorporated into the neural network model to explore the combined effects of surface integrity and stress level on fatigue life, which was further transferred for gear contact fatigue life prediction. The results indicate that this method enables an effective gear fatigue life prediction under minor gear sample conditions. With a small sample amount of 7, the prediction error in the fatigue life of the model with transfer learning is 46.33%, while the typical back-propagation neural network (BPNN) model without transfer learning is 101.66%. To control life prediction error to within 50%, the model without transfer learning requires at least 17 gear samples, while the transfer model calls for only 7 gear samples. The proposed data transfer learning framework can be used to predict the gear contact fatigue S-N curve under minor sample conditions and is straightforwardly applied to extended applications.

A modified model of Lundberg-Palmgren rolling contact fatigue formula considering the effects of surface treatments

The Lundberg-Palmgren (L-P) fatigue life formula, as a statistical fatigue theory, has been widely used in the industry. However, its direct applicability is limited to the components treated by surface strengthening technologies. Rolling contact fatigue tests and surface integrity measurements of American Iron and Steel Institute (AISI) 9310 rollers with several surface treatments were performed to address this issue. Based on these results, a modified L-P fatigue model was proposed, enabling the consideration of surface modification including surface roughness, residual stress, and hardening introduced by different surface treatments. Compared with the original L-P fatigue formula, its results are more accurate for surface strengthened specimens. Furthermore, this method can assess the contact fatigue life of gears treated by surface strengthening techniques.

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.

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.

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.

The simulation and experiment research on contact fatigue performance of acetal gears

Acetal gears are the most widely applied type among these polymer gears. Acetal gears may suffer from many failure forms such as severe wear, tooth breakage or tooth surface cracks depending on the loading conditions and the lubrication and temperature environment. The contact fatigue performance of acetal gear relates to many factors including temperature and load, however, their influences on the mechanical properties and fatigue parameters of the acetal material are still not fully understood. In this work, the thermo-elastic-plastic constitutive equations are derived to describe the acetal material behavior during gear meshing process, and the modified Brown-Miller multi-axial fatigue criterion is proposed to estimate the polymer gear contact fatigue life. Durability tests of acetal gear against steel gear are conducted based upon a developed test rig. Results reveal that the temperature rise could significantly reduce the contact pressure of acetal gear due to the decay of the modulus, but still jeopardize the fatigue life on tooth flank because the fatigue properties are also affected by the temperature rise. The predicted location of fatigue failure zone on the tooth and the lifespan agree well with experimental observation.

Crystal elasticity analysis of contact fatigue behavior of a wind turbine gear

Rolling contact fatigue is the main factor limiting the service performance of wind turbine gears. The inherent microstructure of the gear material has a significant impact on its contact fatigue behavior and service life. In this research, a two-dimensional contact fatigue model considering the gear material microstructure and the elasticity anisotropy characteristics of the crystals is established. The predicted results reveal a pronounced scatter phenomena of the stress distribution in the subsurface and the localized stress concentration at the grain boundaries caused by crystal elasticity anisotropy. Changes of initial grain orientations can cause a certain fluctuation in the critical stress and its depth in the subsurface. Under the same load level, the gear contact fatigue life calculated by the crystal elasticity anisotropy model is lower compared to isotropic material. Considering the anisotropic properties of the crystal elasticity, an S-N curve based on the maximum contact pressure for the wind turbine gear is drawn.

Influence of distribution parameters of rough surface asperities on the contact fatigue life of gears

The influence of the distribution parameters of asperities, i.e. mean radius of curvature of asperities β, density of asperities η, and standard deviation of asperity heights σ, on the contact fatigue life of gears is first studied in this paper. Based on the elastic–plastic contact model of asperities, the surface contact pressure and subsurface stress field during the gear meshing process are calculated by the iterative calculation method. According to the multi-axis fatigue life model, the calculation method of fatigue life under different distribution parameters of asperities in the gear meshing process is obtained. The quantitative calculation results of fatigue life and measured distribution parameters of asperities are analyzed. The relationship between the fatigue life and the distribution parameters of asperities on the measured gear surface is calculated and analyzed quantitatively. The following conclusions are drawn: (1) when the roughness value Ra is less than 0.3 µm, the contact fatigue life of gears with rough surfaces is close to that of smooth surfaces; (2) when the roughness value Ra ranges from 0.5 µm to 0.9 µm, the contact fatigue failure occurs near the surface (micro-pitting); (3) under the same roughness value Ra, the contact fatigue life of the gear decreases with the decrease of the density of the asperity and the mean curvature radius of the asperity. The mean radius of curvature of the asperity has a greater influence on the contact fatigue life than the density of the asperity.

Study on the gear fatigue behavior considering the effect of residual stress based on the continuum damage approach

The fatigue failures of gears have great influence on lifetime and reliabilities of mechanical transmissions. Initial residual stress (IRS) induced in the manufacturing process, together with the applied loading stress, contributes to gear fatigue behavior. Gear fatigue behavior represents a continuous damaging process during a high-cycle period. In the present work, a damage-coupled numerical model considering the effect of IRS is developed to investigate the gear fatigue performance. The deterioration of gear material, the detailed evolution of damage and the stress response during the cyclic loading process are calculated and recorded based on the continuum damage mechanics (CDM) using a user material subroutine (UMAT) in ABAQUS. Both the tooth surface contact fatigue and tooth root bending fatigue of the gear are evaluated, and the influence of IRS on stress response and damage evolution is analyzed. Results show that the risk of surface contact fatigue failure of this gear is much greater than that of the tooth bending fatigue. The initial compressive residual stress has positive effect on contact fatigue performance while the initial tensile residual stress with amplitude of 380 MPa would reduce the gear contact fatigue life by 20%.

Numerical simulation of competing mechanism between pitting and micro-pitting of a wind turbine gear considering surface roughness

Gear rolling contact fatigue displays itself with many failure modes such as micro-pitting, pitting or tooth flank fracture. Competing mechanism exists between these failure modes. Tooth surface micro-topography plays an important role in contact behavior and contact fatigue performance of gears. In particular, the root of mean square (RMS) of surface roughness is extensively characterized as one of the main parameters influencing the service performance. In this work an elastic-plastic finite element contact fatigue model is proposed in which the surface roughness is explicitly measured through an optical profiler. The relationship between the dimensionless normal loads and the contact area ratio is plotted. The critical planes and the characteristic shear strain amplitudes are captured at each material point within the contact area. Then the Brown-Miller multi-axial fatigue criterion is applied to evaluate the fatigue life of rough surface contacts. Results reveal that the surface roughness significantly influences the contact fatigue life of gears, and the competing mechanism between the micro-pitting from near-surface area and pitting from sub-surface area. When the RMS value of surface roughness is considerably small, the pitting failure risk and the micro-pitting risk coexist since the minimum fatigue life appears both at the near-surface area and the sub-surface area.

A method for gear fatigue life prediction considering the internal flow field of the gear pump

Abstract Gear pump is the most widely used volume type hydraulic pump, and it is the main power source of the hydraulic system. Its performance is influenced by many factors, such as working environment, maintenance, fluid pressure and so on. It is different from the gear transmission system, the internal flow field of gear pump has a greater impact on the gear life, therefore it needs to consider the internal hydraulic system when predicting the gear fatigue life. In this paper, a certain aircraft gear pump as the research object, aim at the typical failure forms, gear contact fatigue, of gear pump, proposing the prediction method based on the virtual simulation. The method use CFD (Computational fluid dynamics) software to analyze pressure distribution of internal flow field of the gear pump, and constructed the unidirectional flow-solid coupling model of gear to acquire the contact stress of tooth surface on Ansys workbench software. Finally, employing nominal stress method and Miner cumulative damage theory to calculated the gear contact fatigue life based on modified material P-S-N curve. Engineering practice show that the method is feasible and efficient.

Finite Element Contact Analysis and Life Analysis of Gears in the Double-Sided Grinding Machine

The contact fatigue life of gears has direct influences on the working life of the double-sided grinding machine, in the actual using process, the contact fatigue life of gears cannot meet the requirements of working because of many factors. This paper uses the finite element software ANSYS, establishs the two-dimensional model of gears, and analyzes and calculates it, the research shows that: life expectancy of gears is 2.13 years, so gears should have carburizing or carbonitriding heat treatment to fit process requirements, gears can live up to 5.82 years, it can fit the technological requirements of gear life of 5 years. It is some practical value for increasing the working life of the double-sided grinding machine and improving the stability and accuracy of the whole machine.

Analysis of Non-Standard Gear Contact Fatigue Life

A model of gear contact has been established based on Hertz theory in this thesis, Analysis of non-standard gear contact fatigue life test process . For ha* take 1,1.15,1.25 and c* take 0.25,0.5 respectively ,the gear generates contact fatigue failure, then calculate the meshing ratio under different tooth high coefficients, and gear pairs state with fatigue testing time by the finite element method and orthogonal test. These data are compared with the results of specific experiments verified. They description that tooth height coefficients and headspace coefficients change have a great impact on gear contact fatigue life.

A Study on Contact Fatigue Performance of Nitrided and TiN Coated Gears

This paper discusses the effects of TiN coating on gear contact fatigue performance through contact fatigue experiment and gear rig test. The results reveal that the deposition on gears with hard coating TiN could provide the subsurface protection and improve the contact fatigue life, and the contact fatigue strength of nitrided+TiN coated 32Cr2MoV is 1557 MPa at survival probability of 99%, 284 MPa higher than that of nitrided 32Cr2MoV. Although TiN coating on the the edge of the meshing zone wore out, there is no obvious pitting at the site and the rest of meshed zone of TiN coated gear keeps well without pittings and wear grooves, which is opposite to nitrided gears with pittings and peeling off. TiN coating is dense and smooth with lower surface roughness, and it wraps up the gear tooth so that the gear surface no longer contacts with lubricant and prevents the cracks initiation, prolonging the contact fatigue life of gears.

Development of a Sliding-Rolling Contact Fatigue Tester

Abstract Contact fatigue failure is a common problem experienced in many applications such as bearings, gears, and railway tracks. In recent years, research companies have developed finishing processes that aim to improve components’ contact fatigue life. Preliminary rolling contact fatigue tests have shown that superfinishing processes could potentially improve a component’s contact fatigue life by 300 %. However, before these technologies can move from the laboratories to industrial platforms, more tests are needed to verify the claim. The objective of the work herein is to discuss the completion and verification of a sliding-rolling contact fatigue (S-RCF) test rig. This project is funded by the U.S. Army to assess the real benefit of superfinishing on the contact fatigue life of gears used in helicopter transmission boxes. The proposed tester design uses three rollers around a specimen, a hydraulic loading mechanism, and two servo motors. This configuration of the S-RCF tester allows for shorter testing time, more flexible testing parameters such as any combination of slide-roll ratio between the surfaces, any operating speed, and dry or lubricated testing conditions. Failure is detected with a state-of-the-art eddy current crack detection system, which can also be used to monitor and investigate crack growth for different materials, levels of superfinish, and operating conditions. Preliminary tests on a common gear material (AISI 8620 steel) were performed to assess the mechanical limits as well as the control software performance. This paper presents the detailed development and validation of the tester. It discusses issues involved with servo controllers, electronic gear ratio, and their ability to provide precise speed and slip ratios.