A common cause for premature bearing failures in wind turbine gearboxes are the so-called White Etching Cracks (WEC). These undirected, three-dimensional cracks are bordered by regions of altered ...microstructure and ultimately lead to a cracking or spalling of the raceway. An accelerated WEC test was carried out on a FE8 test rig using cylindrical roller thrust bearings made of martensitic 100Cr6 steel. The resulting WECs were investigated with several characterisation techniques. Ultrasonic measurements showed the WEC were mainly located in the region of the overrolled surface in which negative slip occurs, which agrees with hypotheses based on an energetic approach for a prognosis. SEM orientation contrast imaging of the area around WEC revealed an inhomogeneous structure with varied grain sizes and a large amount of defects. Microstructure characterization around the WEA using EBSD showed significant grain refinement. Atom probe tomography showed the microstructure in the undamaged zone has a plate-like martensitic structure with carbides, while no carbides were detected in the WEA where the microstructure consisted of equiaxed 10nm grains. A three dimensional characterisation of WEC network was successfully demonstrated with X-ray computerized tomography, showing crack interaction with unidentified inclusion-like particles.
•Accelerated laboratory WEC test successfully carried out.•Electron backscatter diffraction of WEC region.•3D characterization of nanocrystalline WEA using atom probe tomography.•3D characterisation of WEC network using X-ray tomography.
A common challenge in multiple fields of the mechanical driveline technology is the premature failure of rolling bearings due to white etching cracks (WEC). This failure mode is characterized by ...three-dimensional cracks, bordered by regions of altered material microstructure, which eventually lead to cracking or spalling of the raceway. Ultrasonic analysis of cylindrical roller thrust bearings have already shown that WEC are mainly located in the region under negative slip, which agrees with a cumulative frictional energy criteria. In this study, WEC were reproduced on a two-disc test rig using inner rings from radial cylinder roller bearings without pre-charging the samples with hydrogen. The investigations revealed an influence of the sliding direction and the lubrication regime on the WEC formation. The tests showed that a WEC failure induced by sliding occurs under boundary lubrication regime. Furthermore, it was determined that while single axial cracks and small WEC networks formed in the sample under positive slip; large WEC networks formed in the sample under negative slip.
•Laboratory WEC tests successfully carried out on thrust bearing and two-disc test rigs.•Assessment of the influence of sliding direction and lubricating conditions on the formation of white etching crack.•Assessment of the influence of negative and positive slip on the type and extent of damage.•Metallographic characterization of the failed components.
White Etch Cracking (WEC) is a severe and unpredictable failure mode affecting bearings in various industrial sectors. In this work, accelerated WEC laboratory tests have been performed using FE8 ...type test rigs with ceramic rollers to test the WEC resistance of different bearing materials, materials quality and roughness. It is demonstrated that the test method can reliably and consistently provoke WEC in commercially available washers. Tests using washers with different roughness values did not show significant changes in the time to failure. Tests of through hardened bearing steel with a low content of inclusions resulted in a significantly longer time to failure compared to the baseline. Through hardened washers with a black oxide coating did not improve the WEC life as the coating was worn away during testing. Tests with two types of carbo-nitrided washers gave significantly longer time to failure, of which one type in particular showed high resistance towards WEC formation.
•Tests of White Etching Crack resistance for several bearing materials was conducted.•Bearing steel with low inclusion content showed improved performance.•Carbo-nitrided steels showed significant improved performance.•Black oxide coating was worn off during testing and did not improve performance.•Lower roughness did not show improved performance.
WEC is an aggressive and unpredictable failure mode affecting bearings in particular in the wind energy sector. This paper focuses on the most common used method for WEC laboratory accelerated ...testing, the FE8 type test rigs using martensitic through hardened 100Cr6 cylindrical roller thrust bearings, analyzing the load conditions, test results and damage quantification. The surface and sub-surface stress conditions as well as the surface frictional loading were analyzed using a half-space model. Simulations and experiments were conducted under different load conditions, including tests with different number of rollers and tests using dynamic load and speed. Tests under constant loads show a low load influence and prove that a WEC failure can occur both prematurely and after exceeding the rated lifetime. Dynamic conditions did not accelerate WEC failure, and only rollers (not washers) were affected by WEC under dynamic loading conditions. Damage characterization was performed using optical microscopy and ultrasound scanning. Advanced image analysis based on characterization of defect regions in the ultrasound scans was used for quantifying the subsurface damage. Tests showed WEC failure could be achieved consistently, however there were seemingly large random variations in the observed damage.
Thermally induced white etching layers (WEL) are known to increase the risk of rolling contact fatigue (RCF) cracks. This study focuses on the potential of an energetic approach for the prognosis of ...thermally induced WEL in oil-lubricated rolling/sliding contacts. For the determination of power and energy density thresholds a laser surface treatment was selected. The thresholds were determined using non-lubricated flat specimens made of 100CrMn6 bearing steel. The applicability of the energetic approach for the prognosis of WEL appearance in oil-lubricated rolling/sliding contacts was shown using a two-disc test rig. The formation of WEL was achieved by an acceleration process under varying contact parameters such as speed and load. The appearance of WEL was confirmed through metallographic investigations.
•Formation of white etching layers (WEL) in flat specimens through laser treatment.•Formation of WEL in oil-lubricated rolling/sliding contacts in a two-disc test rig.•Definition of an energetic approach to predict the appearance of WEL.•Assessment of the influence of varying contact conditions on WEL formation.•Metallographic characterization of affected components.
High-sucrose high-fat diets are one of the causes of malnutrition, and may induce metabolic alterations such as dyslipidemia, insulin resistance, and adipogenesis. The objective of this work was to ...investigate the possible protective effect of traditionally edible avocado creole peel (
Persea americana
Mill var.
drymifolia
) when consuming a high-sucrose and fat diet (HSFD). The experimental animal model included 21 male Wistar rats divided in three groups: the control group received a standard diet of purina®, the HSFD group received a high fat diet plus 30% sucrose in drinking water, and finally the HSFD + AP group received the HSFD diet supplemented with 200 mg/kg of avocado peel for 14 weeks. It was observed that alterations included higher cholesterol, glucose, insulin, fatty acids and TNF-
α
levels as well as lower HDL, and adiponectin. The addition of avocado peel reverted some of these effects, resulting in normal values of triglicerides, insulin and adiponectin, while attenuated the levels of total cholesterol. Liver weight of the group added with avocado peel was similar to the control group. The neuronal density in the hippocampal areas CA1 and dentate gyrus DC were lower in the high glucose fat group, while the ingestion of the avocado peel showed a neuroprotective effect. The avocado creole ingestion reverted or attenuated most of the metabolic effects caused by a high-sucrose fat diet which was attributed to the compounds detected by HPLC-MS and GC-MS that included bioactive polyphenols such as flavanol quercetin, flavanone naringenin, flavan 3-ol catechin, cyanidin 3-glucoside, pelargonidin 3-glucoside, pelargonidin 3-rhamnoside, hydroxydelphinidin, eugenol and estragole.
•New occurrence of massif-type anorthosite and related Fe-Ti ores at the southeastern state of Chiapas, Mexico.•Set of geochemical and isotopic (Sr-Nd) data for anorthosites and associated ...rocks.•Origin of metamorphic zircon and srilankite from the breakdown of previously exsolved baddeleyite.•Ilmenite, rutile and högbomite as Zr source for baddeleyite formation.•Minimum crystallization age of 909±27 for the anorthosite suite.
Two meta-anorthosite inliers (∼20km2 each) were discovered on each side of the Polochic-Tonalá fault system within the Chiapas Massif Complex (CMC) in southeastern Mexico. The anorthosites occur commonly associated to subordinate hornblendite, rutile-bearing ilmenitite, oxide-apatite-rich amphibolite and nelsonite. An absolute crystallization age for the anorthosite could not be precisely constrained due to the paucity and apparent resetting of the magmatic zircon. However, they are interpreted as remnants of a Proterozoic massif-type anorthosite complex older than 909±27Ma as suggested by U-Pb data and the striking geochemical similitudes (major, trace and REE, Sr-Nd isotopes; TDM=1.39–1.45Ga) to Stenian-Tonian massif-type anorthosites found elsewhere. A complex tectono-thermal history for the anorthosite suite is inferred from the discovery of abundant metamorphic zircon in all samples. Ubiquitous petrographic evidence suggests formation of secondary zircon from reactions involving baddeleyite and srilankite (ZrTi2O6) breakdown at different stages of the anorthosite suite evolution. Two generations of baddeleyite are recognized: (1) exsolution from igneous ilmenite and högbomite (Mg,Fe2+2Al,Ti5O10) during cooling, and (2) exsolution product from metamorphic rutile and högbomite during retrogression. U-Pb zircon data (LA-MC-ICPMS) of three comagmatic rocks, including one anorthosite sample, reflect the complex polymetamorphic nature observed in the petrographical evidence; concordant to sub-concordant ages spread in a range from ∼909Ma to ∼242Ma. Most U-Pb ages cluster around known regional metamorphic events at ≃450Ma and ≃250Ma. In addition, an age cluster at ∼600Ma suggests a Neoproterozoic event, interpreted in terms of reheating of anorthosite during mafic intrusions associated to intra-plate rifting.
Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The ...hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.
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