Gear Fatigue Research Articles

Experimental and numerical study of contact fatigue for 18CrNiMo7-6 and 20MnCr5 carburized gear tooth

Gear manufacturers must make decisions about the manufacturing materials and superficial treatments. The best performance as to a type of failure should be evaluated. However, it is a time-demanding and costly process. The present work proposes a methodology for a comprehensive assessment (experimental and computational) of contact fatigue of gears in FZG test rig. The materials investigated were 18CrNiMo7-6 and 20MnCr5 alloy steels, widely used in industrial and automotive transmission systems, but with very different raw material costs, which can exceed twice the first compared to the second. The study evaluated the contact analysis between gears from the macroscopic point of view and the microscopic (inclusion of roughness). At the same time, the evolution of roughness and pit-damaged area after each test stage was monitored. The approach determined the stress field after each loading cycle and thus correlating the regions of higher stresses with surface and subsurface fatigue (micropitting and pitting). In addition, Weibull’s statistical analysis and SEM-EDS observations were executed. In many cases, the methodology correlated the increased roughness and pitting affected area with the regions submitted to the higher contact stress. Observations by SEM-EDS revealed that the occurrence of plastic deformation as a mechanism of wear should be considered in the equations of microscopic stress analysis. The similar fatigue life of such different materials may be correlated to the competitive mechanisms of higher mechanical strength of 18CrNiMo7-6 and better crack propagation characteristics of 20MnCr5. The methodology proved to be consistent for fatigue failure analysis of gears in FZG test rig.

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.

Experimental research of wear-fatigue interaction of gears

Gear failures are commonly caused by wear and fatigue and past research on gear failures has primarily focused on individual failures. A gear testing machine was developed to explore the mechanism of gear wear-fatigue interaction, and four sets of wear-fatigue interaction tests were performed by changing the operating conditions of the gear drive by regulating the quantity of lubricant in the test gearbox. The K-S test method was used to investigate the gear life distribution under wear-fatigue interaction. The frequency domain properties of the wear-fatigue interaction were compiled and analyzed using Fast Fourier Transform (FFT) analysis. A coordinate measuring machine was implemented to obtain the exact amount of wear at each stage of the gear test. The mechanism of gear wear-fatigue interaction was analyzed by scanning electron microscope observation of tooth surfaces. The results are as follows. The life distribution under wear-fatigue interaction obeys a log-normal distribution. With the increase of the lubrication the pitting fault occurs, the fault gear rotation frequency and its harmonic frequency appear in the low frequency region, and its amplitude increases with the increase of the pitting fault. In the high-frequency region, a sideband with the faulty gear rotation frequency as the interval appears around the meshing frequency and its two times frequency, and its amplitude increases with the increase of the pitting fault. With the decrease of lubrication, the gear wear failure increases, the amplitude of the meshing frequency and its two times frequency increases in the high frequency region. In the gear transmission process, wear and fatigue exist in a competitive relationship of mutual constraints.

Unsupervised Health Indicator Construction by a Novel Degradation-Trend-Constrained Variational Autoencoder and Its Applications

Health indicator (HI) affects the accuracy and reliability of the remaining useful life (RUL) prediction model. The hidden variables of variational autoencoder (VAE) can represent the HI values for a life-cycle dataset with obvious degradation trend. However, for an irregular dataset of a rotary machine, it is still a great challenge to construct the HI that can effectively represent the machinery degradation tendency. Therefore, this article proposes a novel degradation-trend-constrained VAE (DTC-VAE) to construct the HI vector with the distinct degradation trend. First, the multidimensional time-domain and frequency-domain characteristics are calculated via the collected vibration samples. Second, a new degradation-constraint loss term is proposed and introduced into VAE for constructing DTC-VAE. Third, with the multidimensional features and DTC-VAE, various HIs can be generated without supervision. The proposed method is applied to construct the HI vectors of bearing life-cycle datasets and gear fatigue datasets, and then macroscopic-microscopic-attention-based long short term memory (MMALSTM) is used to predict the corresponding RULs with the constructed HIs. Via several contrast experiments, the results prove that the proposed unsupervised HI construction approach is superior to other typical methods, and the obtained HI vectors are more suitable for the RUL prediction.

Load Spectrum Compilation Method of Hybrid Electric Vehicle Reducers Based on Multi-Criteria Decision Making

This article proposes a method for compiling the load spectra of reducers for hybrid electric vehicles. Selecting typical working conditions for real vehicle data collection, the load data under each typical working condition were divided into five categories according to the state of the power source and the data were preprocessed. The optimal sample loads for compiling load spectra were obtained based on a multi-criteria decision-making method, rainflow counting for optimal sample loads was performed according to different power source output patterns, non-parametric extrapolation was performed to obtain the full-life two-dimensional load spectrum after dimensionality reduction, and a full-life eight-level programmed load spectrum that could be used for bench tests was obtained. Using the programmed load spectrum and the extracted sample load as the load input, a fatigue life prediction simulation of the reducer gear of a hybrid electric vehicle was carried out. The reducer gear fatigue life from the programmed load spectrum was compared to the gear fatigue life under actual load. The fatigue life of the reducer gear when the programmed load spectrum was used as the input was 1.412 × 103. When the actual load was used as the input load, the fatigue life of the reducer gear was 1.933 × 103. The relative error between the two is only 26%, which is in the normal range. The results show that the programmed load spectrum is effective and reliable and that the load spectrum compilation method provides a basis for accurately evaluating the reliability of the hybrid electric vehicle reducer.

Ultrasonic assisted machining of gears with enhanced fatigue resistance: A comprehensive review

In recent years, ultrasonic-assisted machining (UAM) has been widely implemented to improve the performance and element quality of machined products. This paper comprehensively reviews the ultrasonic vibration effects on such ultrasonic vibration-assisted (UVA) processes as hobbing (UVAH), lapping (UVAL), electrochemical gear machining (UVAEGM), honing (UVAH), and grinding (UVAG), respectively. Compared with the conventional machining, the UAM significantly reduced the surface roughness, improved the surface microstructure, and quality. Considering the UAM applications surface modification and surface strengthening, the available technologies of ultrasonic impact, ultrasonic shot peening, and ultrasonic deep rolling were analyzed for gears and similar components. It was concluded that the surface was strengthened under UAM through introducing the high-amplitude and large-depth residual compressive stresses, restraining crack propagation to a certain extent, and improving the gear fatigue resistance. Finally, the ultrasonic machining effect on gear fatigue resistance was theoretically substantiated from the ultrasonic vibration system and surface integrity standpoints. This review aims to optimize the application of ultrasonic-assisted machining, in order to produce gears with enhanced fatigue resistance and surface integrity.

An improved estimation method of gear fatigue strength based on sample expansion and standard deviation correction

The conventional data processing of gear fatigue staircase test is based on the Dixon-Mood method. Extreme estimates might appear under small-sample condition. To solve the aforementioned limitation, this paper proposes an improved estimated method based on standard deviation correction and sample expansion. Meanwhile, the bending fatigue test is carried out for validation. Results show that the relative error of fatigue strength between the Dixon-Mood method and the proposed method is only 0.51% with 22 samples. As the sample number reduces to 12, the maximum errors of the fatigue strength of the Dixon-Mood method and the proposed method are 12.70% and 5.32%, respectively. To control the maximum error within 10%, the sample number required by the Dixon-Mood method is 14, while the proposed method is 8. The proposed method provides a more effective gear fatigue estimation.

Application of Similarity Theory and Dimensional Analysis for Helical Gear Fatigue Model Test

Gear fatigue test is an important way to verify the reliability of gears, but the test period is too long and costly, especially for the high-speed and heavy-load helical gears, the working process of them are difficult to simulate in the laboratory. For reducing the cost of gear fatigue test, we can use the scaled similar model to replace full-size gear in the fatigue test, process and the results can be applied to the full-size gear according to the similarity principle. In this paper, the similarity principles of helical gears are established with dimensional analysis method. A scale-up and a scale-down similarity gear models are designed for a helical gear pair, and the fatigue damages of them are analysed under eight-stage load spectrum. The results show that the scaled similarity gear models and the full-size gears have nearly the same fatigue damages. This study can bring us an economic and effective fatigue test method for the helical gears.

Effect of Material Change from 20MnCr5 to EN 353 on Fatigue Performance of Crown Wheel Pinion ( Hypoid Gear Sets) of Full Float Axles - Case study

Crown wheel pinion is a prime member in transferring the power from transmission to wheel ends in automotive truck axles. Gear material is one of the deciding factors to estimate the fatigue life of the part. Higher the fatigue characteristics of the material better the fatigue performance of the part. In this case study, heavy truck axle with particular size having deep gear ratio is considered for material change from DIN 20MnCr5 to BS-EN 353, because its challenging to meet the life requirement in deeper gear ratios typically above 6. The basic material comparison conducted for metallurgical properties, jominy values, heat treatment properties, fatigue endurance limits, impact strength & fracture toughness. The analysis shows the EN 353 has 50% better impact strength, 35% better fracture toughness & 6.5% better endurance limit than that of 20MnCr5. The impact strength of EN 353 is 50J where as 20 MnCr5 is 25J, the fracture toughness of EN353 is 99.5 MPa√m & that of 20MnCr5 is 64.3MPa√m. The fracture toughness is calculated using Roberts-Newton formula. The endurance limit for EN 353 is 1000MPa & that of 20MnCr5 is 935MPa. The case carburized results show EN 353 has better case structure than 20MNCr5. The total 12 Numbers of gear sets, 6 each for 20 MnCr5 & EN 353, are validated for gear set fatigue on bench for particular torque. The performance of EN 353 is 24% better than 20MnCr5. The fatigue life of EN 353 is 39983 Cycles & that of 20MnCr5 is 30212 Cycles. The fracture mode is same in both the grades & typical fracture is on the Pinion. This study shows us the material change over is contributed significantly by improving the fatigue life of crown wheel pinion particularly for deeper gear ratios in heavy truck axles.

Effect of boron addition on the gear fatigue strength of Fe-Ni-Mo-B-C sintered alloys

Effect of boron addition on the gear fatigue strength of Fe-Ni-Mo-B-C sintered alloys

Prediction of Mechanical and Toughness Properties of Ni-Modified Cr-Mo Alloy Steels for Transmission Gear

The purpose of the study was to predict the mechanical and toughness properties of Ni-modified alloy steels by adding 1.55%, 1.75%, and 1.95% of Ni-content to the existing Cr-Mo alloy steel of transmission gear material. Typically transmission gears have been working under severe working situations of loads and rotations. Due to these situations, the properties and qualities of gear materials are highly affected consequently, fatigue failure is instigated. So, improving the mechanical and toughness properties of the existing gear material is very vital and compulsory since these properties have a direct impact on gear fatigue failure. Investigations have been done on determining the mechanical and toughness properties of the Ni-modified Cr-Mo alloy steels, through ANN modeling prediction by associating the complex relation of input (chemical composition, tempering temperature) and output parameters (mechanical and toughness properties), and verified by experimental test approaches. Explored these materials property with ANN modeling and experimental test show that the more Ni-content added to the Cr-Mo alloy steel, the higher the ultimate and yield strength can achieve at every instant of tempering temperature. Likewise, fracture toughness, impact toughness, and percent of retained austenite of these materials were also investigated thoroughly as tempering temperature varies. Thus, a 1.55 % Ni-modified Cr-Mo alloy steel has a higher value of both impact toughness and fracture toughness compared with other Ni-modified alloy steels. Similarly, surface hardness was slightly decreased as the amount of Ni-content added increased at each instant of tempering temperature. Lastly, based on both predicted and experimental results, 1.55 % of Ni-modified Cr-Mo alloy steel showed a better combination of mechanical and toughness properties. Keywords: ANN modeling; Yield strength; Ni-modified; Tempering temperature; Fracture toughness; Surface hardness

Experiment study on traveling wave resonance of fatigue fracture of high-speed bevel gear in aero-engne based on acoustic measurement method

High-speed, light-weight and high-load gearing is widely used in the transmission systems of modern aero-engines. Some dynamic phenomena, such as the traveling wave resonance, can be more easily encountered. It generally occurs quite suddenly and causes catastrophic accidents. This study presents an experimental investigation of the signal characteristics of the gear fatigue fracture process caused by the traveling wave resonance. The acoustic waveguide system and the dynamic calibration system are developed. The traveling wave resonance monitoring test and the fatigue performance test of the central drive bevel gear in an aero-engine are carried out. The results show the traveling wave resonant frequency and rotational speed of the driven bevel gear are identified and monitored effectively by the acoustic waveguide system. The dangerous rotational speeds range and the sound pressure energy radiated of the vibration are discussed. The results reveal the gear resonant phenomena are narrow rotational speed band sensitivity and more dangerous at high speed. The fracture mode of the driven bevel gear of aero-engine is reproduced. When the gear has initial defects and works within the dangerous rotational speed of the traveling wave resonance, the gear fatigue fracture will occur quickly. The harmonic frequency, the frequency of forward traveling wave (FTW) and backward traveling wave (BTW), and their combination frequency will appear alternately in the noise spectrum of the gear before fatigue fracture.

Damage behavior due to rolling contact fatigue and bending fatigue of a gear using crystal plasticity modeling

AbstractGear fatigue issues, including bending and contact fatigue, are attractive problems with significant engineering safety implications. Currently, no fatigue analysis model can combine the effects of bending and contact fatigue to predict gear fatigue life because of their different failure mechanisms. In addition, most gear fatigue studies are still limited to the understanding at the macro level, thus cannot provide theoretical interpretations for practical engineering observations such as scattered experimental data and material deterioration. Here, we proposed a unified microstructure model by considering different failure mechanisms of rolling contact and bending fatigue. The crystal plasticity model combing the multiaxial fatigue criteria was established to capture the stress–strain history at the microlevel. The deterioration of mechanical properties of the material was simulated based on the continuum damage theory. This work provides more insight into the physical understanding of gear fatigue failure mechanism and theoretical support for gear antifatigue design.

Investigation on the high-cycle tooth bending fatigue and thermo-mechanical behavior of polymer gears with a progressive curved path of contact

A systematic combination of experimental and numerical methods was employed in a comprehensive study on the high-cycle tooth bending fatigue of polymer gears with a progressive curved path of contact (S-gears). A polymer/polymer combination was tested where the drive gear was made of POM and the driven one from PA 66. Gears were tested at three different torque levels, i.e. 0.6 Nm, 0.8 Nm, and 1.0 Nm, with no additional lubrication and until gear failure. S-gear pairs showed increased durability over the involute gear pairs. A 100% pronounced lifespan increase was observed at the tested load 0.6 Nm.

Digital Twin-Driven Remaining Useful Life Prediction for Gear Performance Degradation: A Review

AbstractAs a transmission component, the gear has been obtained widespread attention. The remaining useful life (RUL) prediction of gear is critical to the prognostics health management (PHM) of gear transmission systems. The digital twin (DT) provides support for gear RUL prediction with the advantages of rich health information data and accurate health indicators (HI). This paper reviews digital twin-driven RUL prediction methods for gear performance degradation, from the view of digital twin-driven physical model-based and virtual model-based prediction method. From the view of the physical model-based one, it includes a prediction model based on gear crack, gear fatigue, gear surface scratch, gear tooth breakage, and gear permanent deformation. From the view of the digital twin-driven virtual model-based one, it includes non-deep learning methods and deep learning methods. Non-deep learning methods include the wiener process, gamma process, hidden Markov model (HMM), regression-based model, and proportional hazard model. Deep learning methods include deep neural networks (DNN), deep belief networks (DBN), convolutional neural networks (CNN), and recurrent neural networks (RNN). It mainly summarizes the performance degradation and life test of various models in gear and evaluates the advantages and disadvantages of various methods. In addition, it encourages future works.

Investigation on the relationship between macropits and wear particles in a gear fatigue process

Macropitting is one of the most common gear wear mechanisms, and monitoring its initiation and propagation is critical to ensure the safe operation of gearboxes. Wear debris analysis (WDA) is widely used to monitor and diagnose gear macropitting and its diagnostic capability relies on good understanding of the relationship between wear particle features and those of actual gear macropits. However, the study on this relationship has been impeded by on-going challenges in characterising gear macropits during the wear process. As a result, detailed experimental data of macropits and the quantitative relationships between wear particles and macropits evolving in the fatigue process are scarce.In order to address the above issues, this study examines macropits and wear particles generated on gear surfaces and their evolution in a gear fatigue process through employing a moulding method to obtain 38 batches of gear teeth moulds in the wear process. 2D characterisations of macropits on the moulds and sampled wear particles were conducted using optical microscopy. Qualitative and quantitative relationships between different features of macropits and wear particles were investigated. Results showed the concentration of wear particles had a similar trend to pitted area growth, yet with a delay. This behaviour was also found in 4 non-dimensional numerical features characterising the geometry of particles and pits. The results of this study provide further insight in the evolution of the fatigue process of gears and can assist in its monitoring.

The Influence of Pulling Up on Micropitting Location for Gears with Interference Fit Connections of Their Conical Surface

Micropitting is a surface fatigue phenomenon that occurs in Hertzian type of rolling and sliding contact that operates in elastohydrodynamic or boundary lubrication regimes and can progress both in terms of depth and extent. If micropitting continues to propagate, it may result in reducing gear tooth accuracy, increasing dynamic loads and noise. Eventually, it can develop into macropitting and other modes of gear failure such as flank initiated bending fatigue. Micropitting has become a particular problem in the gear surface fatigue. Usually micropitting initiates in the dedendum of the driver and driven at the asperities on the surface. However, the authors found for some gears with interference fit connections of their conical surface, micropitting on the pinion occurs in the addendum. This study attempted to find the reason using a 3D–TCA method based on ISO/TR 15144-1 to predict the micropitting and try to understand the key influence likely to affect micropitting location.

Simulation of the fatigue-wear coupling mechanism of an aviation gear

The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears. Meanwhile, the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures. To address this issue, a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method. The tooth profile surface roughness was considered, and its evolution during repeated meshing was simulated using the Archard wear formula. The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion. The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable. Variations in the wear depth and fatigue damage around the pitch point are described, and the effect of surface roughness on the fatigue life is addressed. The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness. Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.

РАЗРАБОТКА МИНИМАЛЬНО ЛЕГИРОВАННОЙ КОНСТРУКЦИОННОЙ СТАЛИ ДЛЯ КРУПНОМОДУЛЬНЫХ ЗУБЧАТЫХ КОЛЕС ТРАНСМИССИЙ

In the world practice of manufacturing gears for automotive equipment, a search is being made for new, more effective steel grades and ways to realize their advantages, achieved both during smelting and during further thermal, deformation and chemical-thermal treatment. There is a tendency to reduce the nickel content in structural steel grades and replace them with sparingly alloyed, microalloyed with strong carbide-forming elements. The condition for using sparingly alloyed structural steels is the ability to find a compromise between increasing the reliability and durability of machine parts and saving deficient alloying materials. Based on this, the article formulates the main provisions that should be taken into account when developing minimally alloyed structural steel compositions for manufacturing highly stressed gears of mobile machine transmissions. It is shown that the introduction of new sparingly alloyed steel grades leads to the need to develop new technologies with the solution in each case of the problem of assessing the impact of alloying elements and microadditives on the hardenability of steel. The method of minimum doping of steel for gears with a module of 10 mm is given. Based on the application of a new approach, a new minimally alloyed structural steel has been developed that provides high strength, fatigue and technological characteristics of large module gears. The hardenability of the core and cemented layers of the developed steel is determined, which provides the life of the gears for at least 1,000 hours in operating conditions at contact stresses in the engagement pole σН = 1,800 MPa.

Dynamic Fatigue Tests Of Landing Gears

Abstract Landing gears are one of the main components of an aircraft. The landing gear is used not only during take-off and landing but also, in most cases, during ground manoeuvres. Due to its function, the landing gear is also one of the key safety components of the aircraft due to dissipating landing loads acting on the aircraft. The mentioned loads come from both the vertical and horizontal speeds during touchdown and by the aircraft’s losing the speed by braking. The landing gear is then loaded with constantly changing forces acting in various directions during every landing, with the only difference coming from their magnitude. The repeatable loading conditions cause significant wear of the landing gear. This wear can be divided into two categories, one is the wear of consumable parts such as the brake linings and the other is the fatigue wear of the structural components. The latter type of wear is much more dangerous due to its slow, and in many cases, unnoticeable progression. Fatigue wear can be estimated by numerical analyses – this method works with a great degree of probability on single components but due to the complexity of the landing gear as a whole it is not precise enough to be applied to the full structure. In order to evaluate the fatigue of the whole landing gear the best method accepted by regulations is the laboratory testing method. It involves a series of various drop tests resembling the real landing condition distribution. The aim of the tests is to check the fatigue wear of the landing gear and to prove its reliability for certification and/or operational purposes. In this paper the author describes the basics of the landing gear fatigue wear, possibilities of its evaluation and presents laboratory dynamic method used for extensive tests in life-like operation conditions.