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A flow-chart showing the multi-length-scale computational analysis, of HAWT-gearbox roller-bearing premature-failure, utilized in the present work. Nomenclature: A-hydrogen diffusion parameters; B-hydrogen embrittlement parameters; C-effective grainboundary hydrogen diffusivity
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To help overcome the problem of horizontal-axis wind-turbine (HAWT) gear-box roller-bearing premature-failure, the root causes of this failure are currently being investigated using mainly laboratory and field-test experimental approaches. In the present work, an attempt is made to develop complementary computational methods and tools which can pro...
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... spreading and branching assisted by hydrogen-embrittlement and corrosion effects under normalwind loading conditions which may result in the formation of spalls/fragments within the inner race and, in turn, lead to the bearing-element failure. A flowchart of the multi-physics computational approach used in the present work is shown in Fig. ...
Citations
... It was found that wearing particles of bearing steel was a major cause of gearbox failure while proper lubrication could precisely reduce the bearing wear and micropitting. Grujicic et al. [30] analyzed the causes of premature failure of gearbox bearings using finite elements. It was argued that white etched cracks and the spalling of material were the major causes of bearing failure. ...
Bearings are crucial components that decide whether or not a wind turbine can work smoothly and that have a significant impact on the transmission efficiency and stability of the entire wind turbine’s life. However, wind power equipment operates in complex environments and under complex working conditions over long time periods. Thus, it is extremely prone to bearing wear failures, and this can cause the whole generator set to fail to work smoothly. This paper takes wind turbine bearings as the research object and provides an overview and analysis for realizing fault warnings, avoiding bearing failure, and prolonging bearing life. Firstly, a study of the typical failure modes of wind turbine bearings was conducted to provide a comprehensive overview of the tribological problems and the effects of the bearings. Secondly, the failure characteristics and diagnosis procedure for wind power bearings were examined, as well as the mechanism and procedure for failure diagnosis being explored. Finally, we summarize the application of fault diagnosis methods based on spectrum analysis, wavelet analysis, and artificial intelligence in wind turbine bearing fault diagnosis. In addition, the directions and challenges of wind turbine bearing failure analysis and fault diagnosis research are discussed.
... A study on simulating the formation of WECs by using grain-boundary modelling and a semi-empirical quantum mechanical method (Austin Model 1) analyses the effect of local microstructure characteristics on the mobility of hydrogen at the area around the crack tip. This simulation work shows that the mobility of hydrogen at grain boundaries is much lower than that in the grain (neighbouring bulk) [98], [99], indicating the mobility of hydrogen diffusion at the crack tip is dominated by the neighbouring bulk area. However, this mechanism has not been entirely accepted, as it cannot fully explain the mechanisms of how hydrogen causes detrimental damage to steels [100]. ...
White Etching Cracks (WECs) in bearings are found to cause unexpected failures and can result in economic losses in many applications, such as wind turbine gearbox and automotive components. Although the problem of WECs is established as important and many researchers have studied the phenomenon, the effect of different drivers, whether the initiation point is subsurface or surface and the order of formation of cracks and white etching areas (WEA) are still the subject of debate. A better understanding of these particular issues will help to inform the reliability of roller bearings by improving their design through further mechanistic insight. A systematic literature review was carried out first to assess previous relevant research related to WECS, such as the detailed microstructural features observed, proposed drivers of the phenomenon and initiation mechanisms in proposed bearing steel. In this project, the initiation mechanisms of WECs have therefore been further studied via experimental observation of a series of AISI 52100 steel bearing samples tested on an FAG-FE8 rig at Schaeffler under a contact pressure of 1.35 GPa over a range of test durations, where WECs at different stages were created. All bearing tests used the “WEC critical lubricant”, a common lubricant to create WECs. Microstructure characterisation techniques, including optical microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), were then used to characterize the different stages of WEC formation, with an especial focus on the initiation stages. The bearings with the longest test duration that have surface damage were examined first to help to determine the area where WECs were likely to initiate. These areas in tested samples with shorter testing duration time were then observed in detail to find the earliest stages of WECs. By comparing the different microstructure characteristics of WECs at these different stages and comparing with prior knowledge in the literature, a growth mechanism of WEA related to a transitional area containing crack-like structures and an initiation mechanism of WECs related to the aligned/clustered carbide aggregation have been hypothesised.
... The problem is becoming increasingly important due to the higher susceptibility of modern, highstrength alloys; hydrogen can reduce the toughness of highstrength steels by 90% [20][21][22][23], compromising decades of metallurgical progress. Hydrogen embrittlement is pervasive in numerous applications across engineering sectors, such as bridges [24], buildings [25], cars [26], trains [27], wind turbines [28] and aeroplanes [29]. Moreover, hydrogen embrittlement could jeopardise the future that hydrogen holds as the energy carrier of the future. ...
Environmentally assisted cracking phenomena are widespread across the transport, defence, energy and construction sectors. However, predicting environmentally assisted fractures is a highly cross-disciplinary endeavour that requires resolving the multiple material-environment interactions taking place. In this manuscript, an overview is given of recent breakthroughs in the modelling of environmentally assisted cracking. The focus is on the opportunities created by two recent developments: phase field and multi-physics modelling. The possibilities enabled by the confluence of phase field methods and electro-chemo-mechanics modelling are discussed in the context of three environmental assisted cracking phenomena of particular engineering interest: hydrogen embrittlement, localised corrosion and corrosion fatigue. Mechanical processes such as deformation and fracture can be coupled with chemical phenomena like local reactions, ionic transport and hydrogen uptake and diffusion. Moreover, these can be combined with the prediction of an evolving interface, such as a growing pit or a crack, as dictated by a phase field variable that evolves based on thermodynamics and local kinetics. Suitable for both microstructural and continuum length scales, this new generation of simulation-based, multi-physics phase field models can open new modelling horizons and enable Virtual Testing in harmful environments.
... The problem is becoming increasingly important due to the higher susceptibility of modern, highstrength alloys; hydrogen can reduce the toughness of highstrength steels by 90% [20][21][22][23], compromising decades of metallurgical progress. Hydrogen embrittlement is pervasive in numerous applications across engineering sectors, such as bridges [24], buildings [25], cars [26], trains [27], wind turbines [28] and aeroplanes [29]. Moreover, hydrogen embrittlement could jeopardise the future that hydrogen holds as the energy carrier of the future. ...
Environmentally assisted cracking phenomena are widespread across the transport, defence, energy and construction sectors. However, predicting environmentally assisted fractures is a highly cross-disciplinary endeavour that requires resolving the multiple material-environment interactions taking place. In this manuscript, an overview is given of recent breakthroughs in the modelling of environmentally assisted cracking. The focus is on the opportunities created by two recent developments: phase field and multi-physics modelling. The possibilities enabled by the confluence of phase field methods and electro-chemo-mechanics modelling are discussed in the context of three environmental assisted cracking phenomena of particular engineering interest: hydrogen embrittlement, localised corrosion and corrosion fatigue. Mechanical processes such as deformation and fracture can be coupled with chemical phenomena like local reactions, ionic transport and hydrogen uptake and diffusion. Moreover, these can be combined with the prediction of an evolving interface, such as a growing pit or a crack, as dictated by a phase field variable that evolves based on thermodynamics and local kinetics. Suitable for both microstructural and continuum length scales, this new generation of simulation-based, multi-physics phase field models can open new modelling horizons and enable Virtual Testing in harmful environments.
... Nacelle Examples of WECs found in WTGB[8][9] Schematics of WECs[10] ...
It has been clearly observed that wind turbine energy gearbox bearings are being subjected to premature and unpredicted failure during the first one-fourth duration of their lifespan. This failure is related to many effective factors that have multiple criteria for many available alternative bearings. This article deals with Analytic Hierarchy Process (AHP) and uses a software tool, so called (Expert Choice EC) to select the best compromise solution of the most efficient bearings in wind turbine gearbox. Three types of bearings have been entered in EC comparison: (single-row tapered, single-row cylindrical and double-row cylindrical) roller bearings under five main elements of criteria: (cost, durability, reliability, feature design and availability). Based on the synthesis results and sensitivity analysis of EC software, it can be concluded that single-row tapered bearing is the best choice to be used in wind turbine gearbox of about 52.1% than the other two alternatives taking in considering that the main two criteria, which cause premature failure, are durability and reliability.
... Nacelle Examples of WECs found in WTGB[8][9] Schematics of WECs[10] ...
It has been clearly observed that wind turbine energy gearbox bearings are being subjected to premature and unpredicted failure during the first one-fourth duration of their lifespan. This failure is related to many effective factors that have multiple criteria for many available alternative bearings. This article deals with Analytic Hierarchy Process (AHP) and uses a software tool, so called (Expert Choice EC) to select the best compromise solution of the most efficient bearings in wind turbine gearbox. Three types of bearings have been entered in EC comparison: (single-row tapered, single-row cylindrical and double-row cylindrical) roller bearings under five main elements of criteria: (cost, durability, reliability, feature design and availability). Based on the synthesis results and sensitivity analysis of EC software, it can be concluded that single-row tapered bearing is the best choice to be used in wind turbine gearbox of about 52.1% than the other two alternatives taking in considering that the main two criteria, which cause premature failure, are durability and reliability.
... H ydrogen embrittlement (HE) of engineering alloys is characterized by a loss of ductility and sudden, often unexpected fracture 1 causing an ever widening spectrum of component failures 2 . In the energy industry alone, HE has been reported in petrochemical 3,4 , nuclear 5,6 , renewables 7 , and hydrogen storage technologies 8 . Hydrogen (H)-related failures also affect the transportation and construction industries 9, 10 . ...
Hydrogen embrittlement (HE) causes sudden, costly failures of metal components across a wide range of industries. Yet, despite over a century of research, the physical mechanisms of HE are too poorly understood to predict HE-induced failures with confidence. We use non-destructive, synchrotron-based techniques to investigate the relationship between the crystallographic character of grain boundaries and their susceptibility to hydrogen-assisted fracture in a nickel superalloy. Our data lead us to identify a class of grain boundaries with striking resistance to hydrogen-assisted crack propagation: boundaries with low-index planes (BLIPs). BLIPs are boundaries where at least one of the neighboring grains has a low Miller index facet-{001}, {011}, or {111}-along the grain boundary plane. These boundaries deflect propagating cracks, toughening the material and improving its HE resistance. Our finding paves the way to improved predictions of HE based on the density and distribution of BLIPs in metal microstructures.
... The assistance of hydrogen is suggested to be a driving force for this type of crack propagation, lubricant penetration inside the crack allowing for a release of hydrogen at the crack tip driving growth. [27,64,72,73] 3. High surface shear forces due to the tribofilm formed (heterogeneous tribofilms propagating in the negative sliding zones due to crack face rubbing (see previous section 1. 3.1). [62] Detailed schematic representations and examples of these mechanisms can be seen in an updated review by Evans in [74], with the exception of (3). ...
... The assistance of hydrogen is suggested to be a driving force for this type of crack propagation, lubricant penetration inside the crack allowing for a release of hydrogen at the crack tip driving growth. [27,64,72,73] ...
Wind turbine gearbox bearing (WTGB) failure is dominated by the premature failure mode known as White Structure Flaking (WSF), where WSF is caused by White Etching Cracks (WECs) formed beneath the contact surface under rolling contact fatigue (RCF), WECs being associated with a microstructural alteration known as White Etching Area (WEA). WSF failure is unconventional and has been of great interest to the Wind industry for a number of years. This failure mode is not well understood, it involving a number of complex factors due to its unpredictability. Formation drivers and initiation mechanisms continue to be highly debated and are suggested to be driven by combinations of mechanical, tribochemical, and electrical/electrothermal effects. Two key cited drivers are transient operating conditions and hydrogen diffusion into the steel during operation. By replicating and using combinations of these drivers, studies have been able to recreate WECs so that their formation mechanisms can be investigated.
An array of RCF tests have been conducted using FAG-FE8 and PCS Micro-pitting (MPR) test rigs to create WECs under non-hydrogen charged conditions using 100Cr6 steel lubricated with oils containing sulfonate additives. Over-based calcium sulfonates (OBCaSul) are specifically focused upon; these additives being considered critical in driving WEC formations and their ‘driving’ effect remaining unclear. Serial sectioning techniques have enabled this study to capture and investigate the WEC evolution mechanisms from initiation to final flaking failure. Clear evidence for subsurface initiation of WECs at non-metallic inclusions has been observed at the early infant stages of WEC formation, WECs propagating from the subsurface to the contact surface eventually causing flaking with increase in RCF test duration. The effect of differing concentrations of OBCaSul in the oil on WECs have also been examined, serial sectioning being used to quantify WEC damage formations. An increase in WEC formations with increase in OBCaSul concentration from 1.4% (no WECs found), to 2.8% and 5.6% (WECs found) is shown. However, no WECs were found to have formed in the MPR tested rollers under the lubrication of oils containing 2.8% and 5.6% OBCaSul while a number of WECs had formed in those lubricated by the 1.4% OBCaSul oil. This is thought to be due to the different contact dynamics and potentially different tribofilm formations on the two test rigs.
Thermal desorption analysis (TDA) was used to measure the concentration of diffusible hydrogen in FE8 RCF tested bearings so that hydrogen diffusion effects on WEC formations could be assessed. By coupling TDA with serial sectioning, relationships between hydrogen diffusion and WEC formations were examined. A positive correlation between the increase in diffusible hydrogen concentration and the formation of WECs over the increased RCF test duration was found in the FE8 rollers, while negligible hydrogen concentrations corresponding to no WECs were measured in the raceways.
Detailed analysis of the tribofilms formed during RCF operation using SEM/EDX was conducted so that the influence of OBCaSul additives on tribofilm formation, and thus WEC formations via hydrogen diffusion could be explored. Overall, OBCaSul containing oils have been found to form thick Ca dominated tribofilms, which may have promoted hydrogen diffusion and WEC formations in the FE8 rollers. The thinner Zn-S tribofilms formed on the FE8 raceways on the other hand may have demoted hydrogen diffusion and WEC formations.
... In contrast to extensive experimental research, very few theoretical or modelling works regarding WECs have been published to date, most of which deal with contact mechanics, material transformations, hydrogen diffusion, crack propagation (not initiation) or attempt to explain how WEAs are formed (for instance, see [16,20,[29][30][31][32][33][34][35][36][37][38][39]; while [36] is not directly related to bearing steels, in author's opinion, it demonstrates microstructure modelling capabilities very well). This is especially true in case of electricity, in which, to the author's knowledge, no modelling results were published that would showcase the influence of electrical current on fatigue acceleration, except for the article by Scepanskis et al. [17], wherein it has been proposed that electrothermally generated stress is concentrated at defect sites, such as carbides, due to discharge current generated Joule heat where current flows around defects. ...
This work is the study of one particular candidate for white etching crack (WEC) initiation mechanism in wind turbine gearbox bearings: discharge current impulses flowing through bearing steel with associated thermal stresses and material fatigue. Using data/results from previously published works, the authors develop a series of models that are utilized to simulate these processes under various conditions/local microstructure configurations, as well as to verify the results of the previous numerical studies. Presented models show that the resulting stresses are several orders of magnitude below the fatigue limit/yield strength for the parameters used herein. Results and analysis of models provided by Scepanskis, M. et al. also indicate that certain effects predicted in their previous work resulted from a physically unfounded assumption about material thermodynamic properties and numerical model implementation issues.
... in order to bring the cost of wind energy down to competitive levels, substantial improvements in the durability and reliability of gearboxes need to be achieved [5]. One of the most common causes of the premature fault of WTGs is attributed to the fracture of gear teeth due to fatigue [10]. ...
... For this reason, the adoption of advanced prognostics and health management strategies is crucial to ensure the turbine reliability and the profitable operation of wind farms [4]. Among all components, wind turbine gearboxes (WTGs) represent a critical problem in terms of durability and reliability [5]. Since the scale of wind turbines dimensions has increased considerably in the past years, gearboxes have been reported as one of the components that is most prone to premature failure [6,7]. ...
... Therefore, 1. It has been reported that WTGs represent a critical problem in terms of reliability due to the high incidence of premature failure [5][6][7], which contributes considerably to the increase of wind energy cost [8,9]. For this reason, enhanced reliability analysis on WTGs can contribute to reducing the costs of wind energy; 2. ...
Failure prediction of wind turbine gearboxes (WTGs) is especially important since the maintenance of these components is not only costly but also causes the longest downtime. One of the most common causes of the premature fault of WTGs is attributed to the fatigue fracture of gear teeth due to fluctuating and cyclic torque, resulting from stochastic wind loading, transmitted to the gearbox. Moreover, the fluctuation of the torque, as well as the inherent uncertainties of the material properties, results in uncertain life prediction for WTGs. It is therefore essential to quantify these uncertainties in the life estimation of gears. In this paper, a framework, constituted by a dynamic model of a one-stage gearbox, a finite element method, and a degradation model for the estimation of fatigue crack propagation in gear, is presented. Torque time history data of a wind turbine rotor was scaled and used to simulate the stochastic characteristic of the loading and uncertainties in the material constants of the degradation model were also quantified. It was demonstrated that uncertainty quantification of load and material constants provides a reasonable estimation of the distribution of the crack length in the gear tooth at any time step.
