The Experts below are selected from a list of 29469 Experts worldwide ranked by ideXlab platform
R. Yavari - One of the best experts on this subject based on the ideXlab platform.
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multi length scale computational analysis of roller bearing Premature Failure in horizontal axis wind turbine gear boxes
International Journal of Structural Integrity, 2015Co-Authors: M Grujicic, V. Chenna, J. S. Snipes, Rohan Galgalikar, R. Yavari, S RamaswamiAbstract:Purpose – To make wind energy (one of the alternative-energy production technologies) economical, wind-turbines (convertors of wind energy into electrical energy) are required to operate, with only regular maintenance, for at least 20 years. However, some key wind-turbine components (especially the gear-box) often require significant repair or replacement after only three to five years in service. This causes an increase in both the wind-energy cost and the cost of ownership of the wind turbine. The paper aims to discuss these issues. Design/methodology/approach – To overcome this problem, root causes of the gear-box Premature Failure are currently being investigated using mainly laboratory and field-test experimental approaches. As demonstrated in many industrial sectors (e.g. automotive, aerospace, etc.) advanced computational engineering methods and tools cannot only complement these experimental approaches but also provide additional insight into the problem at hand (and do so with a substantially sho...
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Wind-Turbine Gear-Box Roller-Bearing Premature-Failure Caused by Grain-Boundary Hydrogen Embrittlement: A Multi-physics Computational Investigation
Journal of Materials Engineering and Performance, 2014Co-Authors: Mica Grujicic, V. Chenna, J. S. Snipes, Sesh Ramaswami, Rohan Galgalikar, R. YavariAbstract: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 provide additional insight into the problem at hand (and do so with a substantially shorter turn-around time). Toward that end, a multi-physics computational framework has been developed which combines: (a) quantum-mechanical calculations of the grain-boundary hydrogen-embrittlement phenomenon and hydrogen bulk/grain-boundary diffusion (the two phenomena currently believed to be the main contributors to the roller-bearing Premature-Failure); (b) atomic-scale kinetic Monte Carlo-based calculations of the hydrogen-induced embrittling effect ahead of the advancing crack-tip; and (c) a finite-element analysis of the damage progression in, and the final Failure of a prototypical HAWT gear-box roller-bearing inner raceway. Within this approach, the key quantities which must be calculated using each computational methodology are identified, as well as the quantities which must be exchanged between different computational analyses. The work demonstrates that the application of the present multi-physics computational framework enables prediction of the expected life of the most Failure-prone HAWT gear-box bearing elements.
Kenred Stadler - One of the best experts on this subject based on the ideXlab platform.
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Investigation on the mechanisms of white etching crack (WEC) formation in rolling contact fatigue and identification of a root cause for bearing Premature Failure
Wear, 2016Co-Authors: Junbiao Lai, Kenred StadlerAbstract:This paper reports on a study that has resulted in the identification of one of the root causes for bearing Premature Failure characterized by sub-surface ‘white etching’ cracks (WEC) and surface axial cracks leading to spalling on ring raceways. Failure analysis performed on some failed rolling bearings used in wind turbines revealed fretting corrosion bands on the inner ring bore having positions that coincide circumferentially with zones of sub-surface WECs and surface axial cracks on the raceways. Appearance of fretting corrosion bands on the bearing bore is an indication of bearing seat form deviation. It was demonstrated by FE simulation that bearing seat form deviation such as waviness can result in tensile stress near raceway, which, if exceeding a certain limit, can weaken the material and, in combination with Hertzian stress, result in early initiation and accelerated growth of cracks from the pre-existing material defects, leading to Premature Failure of the bearing. Rubbing between the crack faces during subsurface crack propagation causes microstructure alteration of the crack surfaces and the formation of WECs. The tensile stress drives the propagation of the subsurface cracks towards raceway, leading to occurrence of the surface-breaking cracks or the so-called “hair-line” axial cracks, and eventually spalling of the ring raceway. A specially designed bearing test has successfully reproduced the Failure mode occurring in Prematurely failed bearings in wind turbine gearbox. Such a test involves a wavy sleeve shaft that results in sufficiently high tensile stresses in the raceway region of a cylindrical roller bearing inner ring. All tested bearings failed Prematurely under a relatively low-load due to axial cracks on the raceway surface with associated clusters of sub-surface white etching cracks, i.e. the mode of Failure that is commonly representative for wind turbine bearings.
Lokesh Choudhary - One of the best experts on this subject based on the ideXlab platform.
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in vitro characterization of stress corrosion cracking of aluminium free magnesium alloys for temporary bio implant applications
Materials Science and Engineering: C, 2014Co-Authors: Lokesh Choudhary, R Singh K Raman, Joelle Hofstetter, Peter J UggowitzerAbstract:The complex interaction between physiological stresses and corrosive human body fluid may cause Premature Failure of metallic biomaterials due to the phenomenon of stress corrosion cracking. In this study, the susceptibility to stress corrosion cracking of biodegradable and aluminium-free magnesium alloys ZX50, WZ21 and WE43 was investigated by slow strain rate tensile testing in a simulated human body fluid. Slow strain rate tensile testing results indicated that each alloy was susceptible to stress corrosion cracking, and this was confirmed by fractographic features of transgranular and/or intergranular cracking. However, the variation in alloy susceptibility to stress corrosion cracking is explained on the basis of their electrochemical and microstructural characteristics.
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mechanical integrity of magnesium alloys in a physiological environment slow strain rate testing based study
Engineering Fracture Mechanics, 2013Co-Authors: Lokesh Choudhary, R Singh K RamanAbstract:Abstract When used as implants, magnesium alloys will simultaneously encounter mechanical loading and corrosive physiological environment, which can cause a Premature Failure due to stress corrosion cracking (SCC). Therefore, it is essential to characterize the SCC behavior of magnesium alloys, before they can be actually used as implants. In the present study, the SCC behavior of a common magnesium alloy, AZ91D, and a biocompatible alloy, Mg–3 wt.% Zn–1 wt.% Ca, was evaluated in the physiological environment using slow strain rate tensile (SSRT) testing. The susceptibility of the alloys to SCC was confirmed by analyzing the fracture surfaces using scanning electron microscope. The slow strain rate tensile testing results, together with fractography, confirmed that both the magnesium alloys were susceptible to SCC in the physiological environment.
Mica Grujicic - One of the best experts on this subject based on the ideXlab platform.
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Wind-Turbine Gear-Box Roller-Bearing Premature-Failure Caused by Grain-Boundary Hydrogen Embrittlement: A Multi-physics Computational Investigation
Journal of Materials Engineering and Performance, 2014Co-Authors: Mica Grujicic, V. Chenna, J. S. Snipes, Sesh Ramaswami, Rohan Galgalikar, R. YavariAbstract: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 provide additional insight into the problem at hand (and do so with a substantially shorter turn-around time). Toward that end, a multi-physics computational framework has been developed which combines: (a) quantum-mechanical calculations of the grain-boundary hydrogen-embrittlement phenomenon and hydrogen bulk/grain-boundary diffusion (the two phenomena currently believed to be the main contributors to the roller-bearing Premature-Failure); (b) atomic-scale kinetic Monte Carlo-based calculations of the hydrogen-induced embrittling effect ahead of the advancing crack-tip; and (c) a finite-element analysis of the damage progression in, and the final Failure of a prototypical HAWT gear-box roller-bearing inner raceway. Within this approach, the key quantities which must be calculated using each computational methodology are identified, as well as the quantities which must be exchanged between different computational analyses. The work demonstrates that the application of the present multi-physics computational framework enables prediction of the expected life of the most Failure-prone HAWT gear-box bearing elements.
Michael R Wisnom - One of the best experts on this subject based on the ideXlab platform.
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a novel technique to accurately measure the fibre Failure strain in composite laminates under a combined in plane tension and shear stress state
21st International Conference on Composite Materials ICCM 2017, 2017Co-Authors: Meisam Jalalvand, Mohamad Fotouhi, Mun Choong Leong, Michael R WisnomAbstract:A simple and accurate test method is presented to investigate the influence of shear stresses on tensile Failure of unidirectional carbon fibre/epoxy. Glass/carbon hybrid laminates are used to eliminate stress concentrations and avoid Premature Failure at the end-tabs. Free-edge delamination is suppressed using thin-plies. Angle-ply carbon/epoxy laminates have been designed to achieve combinations of tensile and shear stresses. It is shown that in-plane shear does not significantly affect the fibre Failure strains.
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size effects in unnotched tensile strength of unidirectional and quasi isotropic carbon epoxy composites
Composite Structures, 2008Co-Authors: Michael R Wisnom, B Khan, Stephen R. HallettAbstract:A series of fully scaled tests on unidirectional and quasi-isotropic carbon fibre-epoxy has been carried out. Unidirectional specimens showed a decreasing tensile strength with increasing specimen size, with a reduction of 14% over a factor of 8 change in linear dimension. Quasi-isotropic specimens increased in strength with size when the thickness was changed by repeating the sublaminate stacking sequence, with a 10% increase from a single to four stacked sublaminates. However, strength decreased when the thickness was increased by changing the ply block thickness, with a 62% reduction from 1 to 8 blocked plies. None of the laminates reached the equivalent strength of the unidirectional material, indicating that transverse cracking and edge delamination caused Premature Failure in all cases.
