Fatigue Pitting Research Articles

Measuring instantaneous angular speed using a gear wheel as material measure to detect pitting damage during an endurance test

Gearbox condition monitoring is mostly carried out using accelerometers at the housing. The long transfer path interferes with the information on damaged gears. Therefore, new technologies such as measuring the instantaneous angular speed (IAS) are gaining interest. But these require constructive changes in the power-transmitting elements. Therefore, this contribution uses magnetoresistive (MR) sensors and a minimally invasive integration approach to measure IAS. Three sensor classes are integrated: accelerometers at the gearbox housing, MR sensors, which use a gear wheel as a material measure and MR sensors, which use an encoder magnet at the end of the shaft. These sensor concepts are introduced by Koch et al. 2022 [1] and applied to a 3-stage bevel helical gearbox in this contribution. The first results are on artificial tooth flank damage. Therefore, this contribution focuses on real fatigue pitting damage.A back-to-back test stand is set up for the endurance test. The tests are carried out with an overload load at a constant speed to generate fatigue pitting damage. The results are evaluated in the frequency domain by exploring the gear mesh frequency (GMF) and sidebands modulated with the shaft frequency of the damaged pinion. Results show that with all sensor concepts, the damages can be detected. Influences when using a gear wheel as a material measure are described for one measurement concept. A feature to compare the damage-specific information over the endurance test is introduced and the influence of the transfer path is evaluated through analysis of the relative rise of damage-specific amplitudes.

Effect of manganese phosphate conversion coating with different crystal sizes on fatigue life of 20MnCrS5 steel helical gears

Fatigue pitting is the main failure form of automatic transmission gear at present. In this paper, the contact stress of the tooth surface under different coefficients of friction is calculated by the finite element method. The contact fatigue test and transmission performance were carried out on the 20MnCrS5 helical gears after carburizing with different thicknesses of manganese phosphate conversion coating by a special gear test bench. And the influence of the solid lubricating coating on gear contact fatigue performance was deeply discussed. The results show that the contact fatigue life of the gear treated by manganese phosphate conversion coating is improved by more than 100 %, and the manganese phosphate coated gear with a thickness of 12 µm has a higher fatigue life.

A novel vibration indicator to monitor gear natural fatigue pitting propagation

Fatigue pitting can reduce the gear surface durability and induce other severe failures, which will eventually lead to the complete loss of transmission function of the transmission system. Thus, monitoring fatigue pitting progression is vital to avoid unexpected economic losses and incidents. Thanks to the unique characteristics of the gear meshing process, there is a close relationship between the tribological features of fatigue pitting and gear vibration cyclostationarity. Based on the vibration cyclostationarity, this paper develops a novel second-order cyclostationary (CS2) fatigue pitting monitoring indicator, which can accurately assess the degradation status of the gear system and benefit subsequent health management. The advantage of the developed cyclostationary indicator in evaluating and monitoring the process of fatigue pitting propagation is demonstrated with the natural fatigue pitting progression test, through comparisons with other conventional indicators.

Wear analysis and simulation of small module gear based on Archard model

With the development of micro machining technology, small module gears are widely used in the field of high precision technology. In view of the failure problems such as tooth fracture and fatigue pitting caused by dynamic wear in the process of small module gear transmission, this paper takes a micro planetary gear reducer as the research object and establishes the analysis framework of small module gear wear calculation model based on Archard wear model and Hertz contact theory. Considering the influence of installation error and position tolerance, tooth contact analysis (TCA) model of small module gear is established based on the theory of small displacement torsor (SDT) and space coordinate transformation, and the impact of these errors on the dynamic contact trajectory, contact stress, and tooth surface wear is analyzed based on the numerical simulation. The numerical simulation results show that with the increase of the installation error, the contact trajectory will deviate significantly, which will finally result in increased contact stress and wear. Moreover, with the decrease of tolerance level, the service life of the device increases under the same reliability level. The above analysis of tooth surface wear can provide references for the design and installation of a small module gear transmission.

Failure analysis of a bearing bush of a feed water pump

BACKGROUND: A rolling bearing bush alloy of a feed water pump that is part of a waste heat boiler of an oil refinery has failed. OBJECTIVE: We try to analyze the reasons that caused the working surface of the bearing bush of the water pump to fall off and then give some suggestions to this failure. METHODS: The composition, microstructure, pit, and crack morphology of the bearing bush alloy were analyzed by the X-ray fluorescent analysis, the energy spectrum analysis, the optical microscope and the scanning electron microscope, respectively. RESULTS: The content of Pb in the bearing bush alloy was high, and the Cu content was low. The primary crystal Cu6Sn5 was low, and the crystal of SnSb with low density moved upward and segregated. The above phenomenon reduced the fatigue resistance of the babbitt alloy. The bearing bush was subjected to alternating loads in service, and several small cracks were generated on the bearing bush alloy working surface. The cracks continued to expand and connected with each other. Fatigue pitting occurred on the bearing bush working surface, a large number of pits were formed, and several large alloy blocks fell off. CONCLUSIONS: The Pb content in the failed bearing bush alloy was too high and did not meet the requirements of the Sn-based babbitt alloys in the national standard. At the same time, the primary crystal Cu6Sn5 formed by Cu and Sn was low due to the low Cu content, and the crystal SnSb with a small density moved upward and segregated. The composition of the babbitt alloy, especially the Cu content, should be strictly controlled to ensure the safe and reliable operation of the bearing.

Vibration-based monitoring and prediction of surface profile change and pitting density in a spur gear wear process

Gear wear often results in both tooth profile changes caused by abrasive wear, and fatigue pitting. Being able to accurately monitor and predict the profile change (i.e., the wear depth in the direction normal to the gear surface) and surface pitting propagation can bring enormous benefits to industrial practice. However, there is a lack of efficient, reliable, and effective tools to do so. To address this, this paper proposes a gear wear monitoring and prediction approach through the integration of: (i) a dynamic model, to simulate the dynamic responses of the gear system; (ii) two tribological models, to estimate wear depth (in the direction normal to the gear surface) and pitting density (on the gear surface); and (iii), model updating, by comparing simulated and measured vibration signals.More specifically, a 21-degree-of-freedom dynamic model is used to simulate a spur gearbox setup and produce simulated vibrations and contact forces between the meshing gear teeth. Using the contact pressure (calculated from the force) as an input, the wear depth and pitting density are then predicted by the tribological models and used to modify the gear geometry profile and contact area in the dynamic model. The developed approach allows the dynamic model and the wear models to communicate so that both the gear tooth profile change and pitting density can be simulated continuously. To guarantee accurate prediction results from the models, novel approaches are developed to update the wear coefficients in the tribological models by comparing simulated and measured vibrations. The paper demonstrates the ability and effectiveness of the proposed vibration-based methodology in monitoring and predicting gear wear, specifically the tooth profile change and surface pitting propagation, using measurements from both a lubricated test, dominated by surface pitting propagation with mild tooth profile change, and a dry test dominated by tooth profile change.

The influence of type of dispersed phase on rolling contact fatigue of lubricating greases on mineral base oil

The paper discusses the influence of type dispersed phase on value of rolling contact fatigue of bearings lubricated with selected lubricating compositions. The compositions, which were produced on the mineral base oil were thickened of lithium stearate, calcium stearate, aluminum stearate, lithium complex soap and modified silica, montmorillonite, and polytetrafluoroethylene were evaluated.
 Were carried out the investigations of rolling contact fatigue (pitting) of bearings, which were lubricated of the compositions prepared on the above-mentioned thickeners. Then was evaluated the influence of various thickeners on changes of rolling contact fatigue. The tribological tests were carried out using T-03 four-ball machine under high load conditions.
 On the basis of obtained results it may be concluded, that used of thickeners such as: modified amorphous silica, montmorillonite and polytetrafluoroethylene to produce of lubricating compositions, positively affected on the change of rolling contact fatigue of tribosystems lubricated with the above-mentioned compositions in comparison to the compositions, when as a dispersed phase were used a soap thickeners.

Use of cyclostationary properties of vibration signals to identify gear wear mechanisms and track wear evolution

Fatigue pitting and abrasive wear are the most common wear mechanisms in lubricated gears, and they have different effects on the gear transmission system. To develop effective methods for online gear wear monitoring, in this paper, a vibration-based wear mechanism identification procedure is proposed, and then the wear evolution is tracked using an indicator of vibration cyclostationarity (CS). More specifically, with consideration of the underlying physics of the gear meshing process, and the unique surface features induced by fatigue pitting and abrasive wear, the correlation between tribological features of the two wear phenomena and gearmesh-modulated second-order cyclostationary (CS2) properties of the vibration signal is investigated. Differently from previous works, the carrier frequencies (spectral content) of the gearmesh-cyclic CS2 components are analysed and used to distinguish and track the two wear phenomena. The effectiveness of the developed methods in wear mechanism identification and degradation tracking is validated using vibration data collected in two tests: a lubricated test dominated by fatigue pitting and a dry test dominated by abrasive wear. This development enables vibration-based techniques to be used for identifying and tracking fatigue pitting and abrasive wear.

A phase linearisation–based modulation signal bispectrum for analysing cyclostationary bearing signals

Bearings are used as the most important load-carrying transmission components in various machines, thus subjecting to a number of faults including wear, fatigue pitting, cracks and so on. Fault detection and diagnosis of bearings can effectively prevent the machine from such typical failures and subsequent consequences. The faults in bearings can lead to the vibration signals that exhibit cyclostationary characteristics due to the inevitably random phase noise (or slippage between bearing components). In this article, a phase linearisation–based modulation signal bispectrum is proposed to tune up the cyclostationary bearing signal into a periodic waveform by linearizing the instantaneous phase of the narrow frequency band signals. In this way, the signal becomes more deterministic and modulation signal bispectrum can be effectively applied to suppression noise and obtain accurate and robust diagnosis results. As a result, this fault detector can achieve high performance in characterising the nonstationary bearing vibration signals and hence diagnose the bearing faults even in the case of extremely low signal-to-noise ratio (<−20 dB), which is benchmarked by the method of conventional modulation signal bispectrum in both simulation and experiment studies.

Application of surface replication combined with image analysis to investigate wear evolution on gear teeth – A case study

Gear wear is a critical degradation process in many applications and its monitoring is important to ensure safe operation of machines. The case study presents a novel approach to obtain comprehensive and high-resolution wear information for monitoring the evolution of gear wear. This is achieved through the combination of a moulding method and non-contact imaging-based measurements in two- and three-dimensions and without gearbox disassembly and tooth removal. Optical and laser scanning confocal microscopy and image processing tools were employed to provide quantification of surface roughness, wear severity and wear depth on gear teeth during a lubricated endurance test. Also, a detailed qualitative analysis on the progression of the two main wear mechanisms (abrasive wear and fatigue pitting) was provided, alongside an evaluation of the diagnostic capabilities offered by the proposed methodology. The insights on gear wear offered in this case study also represent a valuable guideline for researchers and engineers in the field of gear condition monitoring. Moreover, the proposed wear analysis technique can be used to characterise and understand wear phenomena in other conditions and geared transmissions.

Development of Terminology in Gearing and Power Transmissions. Part 3. Identification of Notions on Gear Failure Modes

Изложены результаты анализа нормативных источников по видам повреждений зубчатых колес и разработки Межгосударственного стандарта [6] по их классификации и описанию. В оборот включены разнообразные информационные источники - Международный ISO и национальные (AGMA, DIN) стандарты; нормативный документ немецкого концерна «Zahnradfabric Friedrichshafer AG» с определениями терминов, их характеристик и причин, вызывающих повреждения; атлас «Анализ видов повреждений» американской фирмы «Geartech»; методические указания по расчетам и испытаниям на прочность к классификации видов изломов металлов, а также результаты собственных исследований. Описаны принципы, положенные в основу классификации, - отнесение того или иного повреждения к определенному классу, общему виду, виду и степени повреждения. В общей сложности повреждения классифицируются по 76 наименованиям классов, видов и степеней повреждения. Подробно описаны количественные показатели усталостного выкрашивания рабочих поверхностей зубьев - степень выкрашивания по поверхности и глубине; степень искажения профиля и распространения выкрашивания; стадии его развития; параметры и характеристики, а также расчетные формулы для их определения. В заключение подводятся итоги деятельности по идентификации и классификации понятий в области зубчатых зацеплений и передач.

Fatigue failure of 45# steel in dry sliding against Kevlar/PTFE hybrid composite under elevated load

Frictional failure is inevitable for friction pairs. A common sense about the frictional failure of steel-polymer composite friction pair is that the polymer composites are the primary failure part rather than the steel counterpart. However, an opposite case was newly found in the case of fabric self-lubricating liner (Kevlar/PTFE hybrid composite) spherical plain-bearing under elevated load: the steel counterbody suffered a fatigue failure before the fabric composite fails, which resulted in the final failure of the bearing. This paper investigated such fatigue failure of surface chrome plated 45# steel by systematically studying the wear characteristics of 45# steel and fabric composite, the stress distribution of the 45# steel and fatigue features within cross section of the 45# steel. Results showed that wear characteristics of both fabric composite and 45# steel exhibited regional characters. Failure mechanism of the 45# steel was found to be fatigue failure (mainly fatigue pitting), which was revealed by mathematical analysis of the stress distribution of the 45# steel and the fatigue cracks found within subsurface of the cross section of the 45# steel.

Friction and Wear Behaviors of Gear Steel under Coupling of Rolling and Sliding

In this paper, the gear material 20CrMnTi was selected as the research object. Friction and wear behavior was performed on the M2000 friction and abrasion tester. The friction and wear mechanisms of 20CrMnTi steel were discussed under coupling of rolling and sliding. The results show that damage of steel-steel couples under coupling of rolling and sliding is caused by the interaction of mechanical fatigue with dynamical phenomena of rolling and sliding friction. Lubrication directly determines the friction and wear behaviors. Under dry friction, the wear mechanisms of 20CrMnTi steel are mainly adhesive wear, abrasive wear, oxidation wear and fatigue pitting under dry friction. Under lubricating conditions, the wear mechanism of 20CrMnTi steel is mainly surface fatigue wear.

Friction and Wear Behaviors of Gear Steel under Coupling of Rolling and Sliding

In this paper, the gear material 20CrMnTi was selected as the research object. Friction and wear behavior was performed on the M2000 friction and abrasion tester. The friction and wear mechanisms of 20CrMnTi steel were discussed under coupling of rolling and sliding. The results show that damage of steel-steel couples under coupling of rolling and sliding is caused by the interaction of mechanical fatigue with dynamical phenomena of rolling and sliding friction. Lubrication directly determines the friction and wear behaviors. Under dry friction, the wear mechanisms of 20CrMnTi steel are mainly adhesive wear, abrasive wear, oxidation wear and fatigue pitting under dry friction. Under lubricating conditions, the wear mechanism of 20CrMnTi steel is mainly surface fatigue wear.

Analysis of Dynamic Contact and Carrying Capacity Factors for Super-Modulus Pinion and Rack

Jack-up platform jacking system which undertakes the weight of the platform and working load is very important during the lifting, and its performance exerts a direct influence on the safety and application effect of the whole platform. The super-modulus pinion and rack of jack-up platform jacking system are most likely to damage by fracture and fatigue pitting, which are due to the hostile environments. As a result of dynamic load, the analysis of dynamic contact has important engineering significance in an actual project. For strengthening the carrying capacity of pinion and shortening the design period, the research of carrying capacity factors is very meaningful. In this paper, the changing of stresses on the pinion and rack are gained by FEM, and main parameters that influence the carrying capacity of the pinion in a jacking system are analyzed according to the calculation method in GB standard. The study results shows the contact stresses and bending stress are higher throughout the meshing process, which implies the dangerous position of the pinion. In single meshing period, the trend of bending stress in the compression side of pinion and rack is opposite, while the bending stress in the tension side of both rack and pinion are minimum near the pitch circle. The carrying capacity of pinion can be strengthened by changing the main parameters, such as tooth width, normal modulus, pressure angle, modification coefficient, but the influence degree of each parameter is different.

混合潤滑状態下にある転がり－すべり接触面の接線力とピッチング発生限界の関係

Design for pitting (surface crack initiated rolling fatigue wear) at rolling-sliding contact surface under mixed lubrication condition is based on the combination of maximum contact pressure (Hertzian stress) and lubrication condition (ratio of surface roughness value and oil film thickness value). However there is indirect relationship in the combination of contact pressure and lubrication condition to the pitting phenomena. The origins of rolling fatigue pit are the micro cracks at contact surface due to tangential force. In this paper, the pitting test results are re-examined from a standpoint of influence of the tangential force on pitting. The new parameter f·(pH/HB)2 based on the friction coefficient estimation formula by Matsumoto for pitting design is introduced. And it is cleared that the new parameter has same value in pitting limit to every different contact pressure and lubrication condition. In conclusion, it is necessary to reconsider the pitting design method for power transmission gears excepted tangential force from consideration.

Investigation of rolling contact fatigue cracks in ball bearings

Rolling contact fatigue in a ball bearing is studied using the experimental method. Fatigue pits and spallings on the rolling surface are investigated, and the strain-hardening beneath the contact surface is studied using the microhardness profile. Moreover, surface and subsurface crack layouts and the effect of inclusions on crack nucleation are studied by optical and electron microscopy. Additionally, a simulated model is used to study the influences of the crack inclined angle and the inclusion’s hardness on fatigue damage in bearings.

Wear and Friction of Diamondlike-Carbon Coated and Uncoated Steel Roller Bearings Under High Contact Pressure Oil Lubricated Rolling/Sliding Conditions

Diamondlike-carbon (DLC) coatings have received a lot of research attention by physicists and engineers, especially in the past 25 years. Attempts to use such materials in tribological applications have achieved variable success. The rationale for this work was to investigate the wear durability of three types of DLC coatings applied to hardened and tempered bearing steel and subject them to realistic high pressure cyclic loading under oil lubricated conditions for long duration. A thrust bearing design was deployed for this purpose. The wear and friction behavior of the DLC coated materials relative to uncoated materials was compared when using base (additive free) oils and typical autoengine formulated oils. The type of oil used made no difference to the dynamic friction and oil temperature for all the material and oil combinations used. Durability of the coated and uncoated roller bearings was determined by the type of material. For the uncoated bearings, life was limited after very many test cycles (approaching a billion) via classical rolling contact fatigue pitting. For all the DLC coated rollers life was governed by wear of their coatings. In the case of the tungsten doped DLCs (a-C:H:W), these were worn progressively and uniformly via microabrasion, whereas the nondoped ta-C and a-C DLC coatings were principally worn via delamination and tearing. The latter effect was relatively rapid and was considered to be initiated by blistering of the coating, a process that was probably driven by the high elastic energy/internal stress within the nondoped coating materials. The durability to delamination and tearing of the ta-C coatings was slightly lowered in formulated oil compared to tests made in base oil. Overall, for the test conditions used here, there was no apparent benefit in using DLC coatings.

The tribological performance of TiN, WC/C and DLC coatings measured by the four-ball test

An innovative approach to improving the wear resistance and load-carrying capacity of surfaces is by development of novel systems featuring coating treatment. Evaluation of the tribological performance of three physical vapor deposition (PVD) coatings, namely, TiN, WC/C, and DLC (diamond-like carbon), is necessary to determine their suitability as coatings for high-speed and heavy-duty power-transmitting gears. The uncoated and coated steel balls were subjected to four-ball tests under lubricated conditions. An optical microscope and a scanning electron microscope were used to observe wear scars, and energy-dispersive X-ray analysis was performed to determine the chemical compositions of the materials; these methods were also used to analyze the wear mechanisms. The wear performance of the three coatings was compared, and a four-ball method extreme pressure test was performed to determine the last nonseizure load of each tribo-pair. The WC/C and DLC coatings showed excellent tribological performance under high contact pressures and thermal loads, and the benefits of these coatings increased with decreasing performance of the lubricating medium. Therefore, WC/C and DLC coatings are suitable for application in high-speed and heavy-duty gears. Oxidation wear and peeling, fatigue pitting, and adhesive transfer are the main coating failure modes of the TiN, WC/C, and DLC coatings, respectively.

S112034 転がり・すべり接触面の接線力とピッチング発生限界の関係([S112-03]伝動装置の基礎と応用(3))

The design for pitting (rolling fatigue) of rolling-sliding contact surface under mixed lubrication condition is based on the combination of maximum contact pressure (Hertzian stress) and lubrication condition (ratio of surface roughness value and oil film thickness value). But there is indirect relationship in the combination of contact pressure and lubrication condition to the pitting phenomena. The origins of rolling fatigue pit are the micro cracks in contact surface due to tangential force. In this paper, the pitting test results are re-examined from a standpoint of influence of the tangential force on pitting. The new parameter f(p_H/H_B)^2 based on the friction coefficient estimation formula by Matsumoto for pitting design is introduced. And it is cleared that the new parameter has same value to every different contact pressure and lubrication condition. In conclusion, it is necessary to reconsider the pitting design method for power transmission gears excepted tangential force from consideration.