The aim of this work is to determine the rolling contact fatigue (RCF) strength of steel AISI 52100 (DIN 100Cr6) as a common bearing steel in different heat treated conditions. In order to study and ...evaluate the steel cleanliness and its influence on the fatigue behavior the results are compared to AISI L3 (DIN 102Cr6) as a cold-working tool steel containing higher amounts of non-metallic inclusions as a consequence of a different metallurgical processing. In this work experimental results obtained from both materials with martensitic and bainitic microstructures are presented. In addition, the inclusion content in each material was analyzed using extreme value statistics, and the endurance limits are predicted based on the maximum expected inclusion in the maximum loaded volume as a critical crack initiating defect. The predicted RCF values are in good agreement with the experimental results. Irrespective of the microstructure, the hardness after heat treating dominates the endurable Hertzian pressure. The second important parameter, which determines the endurance limit, is the cleanliness of the steel. Furthermore, the crack pattern in the surface and microstructure of the RCF specimens were analyzed by optical microscopy. The results show no microstructural modifications such as dark etching regions or white etching bands. However, the formation of butterflies was detected around non-metallic inclusions in both steels.
•Systematical study of the classical rolling contact fatigue behavior of steel AISI 52100 and AISI L3.•Determination of the endurance limit at ultimate load cycles of NG = 108.•Investigation of the influence of steel cleanliness and heat treatment conditions on the fatigue behavior.•Prediction of the endurance limit based on the extreme value statistics of non-metallic inclusions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
White etching cracks (WECs) have been studied over the last decades as a common cause for premature failure of roller bearings in various applications. As a consequence of the non-directional and ...branched crack networks associated with an altered microstructure named as white etching area (WEA) the damage pattern appears as cracking or flaking of the bearing components. In most published literature dealing with WEA/WEC, it is assumed that WEA/WEC formation should only occur under the condition of an additional load superposed to the bearing operation. The formation mechanisms of this damage are still under debate, though. In this work, the influence of diffusible hydrogen on the formation of WEA/WEC has been investigated systematically using hydrogen pre-charged rollers made from the bearing steel SAE 52100 (DIN 100Cr6) prior to testing. These rollers were tested on a four-wheel test rig using different hydrogen concentration, Hertzian pressure and number of load cycles. As a result of testing, thresholds for WEA/WEC formation were found for different hydrogen concentrations, Hertzian pressures and running time of the rollers. Further investigation with manually interrupted tests revealed the formation of the damage being beneath the raceway surface of the rollers. Detailed microstructure studies using comprehensive analysis in the scanning electron microscope including EDX and EBSD as well as plasma focused ion beam (PFIB) have been conducted to give detailed information of the altered microstructure.
•Experimental study of the premature failure in SAE 52100 bearing using a rolling contact fatigue test rig.•Systematical investigation of the influence of diffusible hydrogen on White Etching Area and White Etching Crack formation.•Thresholds for WEA/WEC formation were found for different hydrogen concentrations, Hertzian pressures and number of cycles.•Detailed information about the microstructural change under rolling contact fatigue on manually stopped tests.•Combined SEM/3D PFIB analysis on manually stopped test showed microstructural altered regions without any link to a crack.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Underwater acoustic signal waveforms recorded during the 2015 Chile earthquake (Mw 8.3) by the hydrophones of hydroacoustic station HA03, located at the Juan Fernandez Islands, are analyzed. HA03 is ...part of the Comprehensive Nuclear‐Test‐Ban Treaty International Monitoring System. The interest in the particular data set stems from the fact that HA03 is located only approximately 700 km SW from the epicenter of the earthquake. This makes it possible to study aspects of the signal associated with the tsunamigenic earthquake, which would be more difficult to detect had the hydrophones been located far from the source. The analysis shows that the direction of arrival of the T phase can be estimated by means of a three‐step preprocessing technique which circumvents spatial aliasing caused by the hydrophone spacing, the latter being large compared to the wavelength. Following this preprocessing step, standard frequency‐wave number analysis (F‐K analysis) can accurately estimate back azimuth and slowness of T‐phase signals. The data analysis also shows that the dispersive tsunami signals can be identified by the water‐column hydrophones at the time when the tsunami surface gravity wave reaches the station.
Key Points
Hydroacoustic (ocean acoustic) observation of a tsunamigenic earthquake from a relatively short distance to the epicenter
Hydroacoustic features of T phases originating from a tsunamigenic earthquake are observed in the low‐frequency end of the hydrophone signal
Observation and detectability of a passing tsunami wave using water‐column hydrophones are demonstrated
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
White Etching Cracks (WEC) are currently discussed as a common cause for premature failure of roller bearings in various applications. The formation mechanism of WEC is still under debate in the ...literature. However, it is emphasized that varying additional loads like electrical current or hydrogen, have an amplifying effect on the formation of WEC. In this work, the formation of WEC under the influence of electrical current was investigated. The testing was conducted on a three-ring on roller test rig using rollers made from the steel AISI/SAE 52100. These rollers were tested utilising different electrical polarities, current intensities, Hertzian pressures and slide-roll-ratios. As a result of the testing, possible WEC formation values for the tested electrical intensities and Hertzian pressures were found. Furthermore, no additional slip has to be present for the WEC formation under the influence of electrical current. Detailed microstructure analysis using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) have been conducted to investigate the effect of electrical current, polarisation and slide-roll- ratio on the microstructural alterations. The analyses showed that in the investigated regions different reaction layers are formed depending on the electrical polarity. Furthermore, the formation of the nanocrystalline structure can be attributed to high local plastic deformation.
•Experimental rolling contact fatigue study of White Etching Cracks under the influence of electrical current flow.•Investigation regarding the influence of factors such as electrical current, Hertzian pressure, slip and polarity.•Determination of formation values of WEA/WEC under the influence of electrical current.•Detailed information about the microstructural change under rolling contact fatigue under different load conditions.•TEM investigations of the formed reaction layer showing a two-layer or one-layer film.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We present several cases of optical observations during unk-ray bursts (GRBs) which resulted in prompt limits but no detection of optical emission. These limits constrain the prompt optical flux ...densities and the optical brightness relative to the unk-ray emission. The derived constraints fall within the range of properties observed in GRBs with prompt optical detections, although at the faint end of optical/ unk-ray flux ratios. The currently accessible prompt optical limits do not require a different set of intrinsic or environmental GRB properties, relative to the events with prompt optical detections.
Following axon pathfinding, growth cones transition from stochastic filopodial exploration to the formation of a limited number of synapses. How the interplay of filopodia and synapse assembly ...ensures robust connectivity in the brain has remained a challenging problem. Here, we developed a new 4D analysis method for filopodial dynamics and a data-driven computational model of synapse formation for R7 photoreceptor axons in developing Drosophila brains. Our live data support a “serial synapse formation” model, where at any time point only 1–2 “synaptogenic” filopodia suppress the synaptic competence of other filopodia through competition for synaptic seeding factors. Loss of the synaptic seeding factors Syd-1 and Liprin-α leads to a loss of this suppression, filopodial destabilization, and reduced synapse formation. The failure to form synapses can cause the destabilization and secondary retraction of axon terminals. Our model provides a filopodial “winner-takes-all” mechanism that ensures the formation of an appropriate number of synapses.
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•Stochastic filopodia dynamics are required for robust synapse formation in fly brains•Only 1–2 filopodia at a time contain synaptic seeding factors and are synaptogenic•4D tracking and computational modeling support a serial synapse formation model•Synapse formation prevents axonal retraction
How random axon filopodia dynamics lead to precise numbers of synaptic contacts during development is unknown. Özel et al. show, through live imaging and computational modeling, that a “winner-takes-all” distribution of synaptic seeding factors renders one filopodium at a time synaptogenic, thereby pacing development and ensuring robust connectivity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This chapter contains sections titled:
Introduction
Manufacturing and Joining of Membrane Tubes
Experimental Investigations
Pilot Module
Results
Conclusion
Acknowledgements
Linear flow splitting is a multi-station sheet-bulk metal forming process which allows continuous production of bifurcated profiles without joining, lamination or external heating of sheet metal. ...This process induces high hydrostatic stresses in the forming zone which leads to an elevated formability of the workpiece material. The aim of this research is to bend linear flow split profiles in transverse direction in a continuous manner. This is achieved by combining the linear flow splitting process with a continuous bending process. An analytical and a numerical model are described in this paper which predict bending moments for different radii. Results from both models are validated with experimental results. It is found that combining the linear flow splitting with a bending process leads to a severe reduction in the bending moments due to superposition of stresses in the forming zone. The superposition maintains the cross sectional shape of the bent profiles.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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