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
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
Previous tests with various sintered and case hardened steels have shown that chemistry plays no major role for rolling contact fatigue (RCF) with slip. The most decisive parameter is the density in ...the topmost stressed volume. Without slip, the influence of chemistry is less well investigated until now. This work compares the RCF strengths without slip of two low alloyed PM steels. The materials are Ancorsteel30HP - prealloyed with 0.35 % molybdenum - to which 1.5 % copper and 0.3 % graphite were added (FeMoCuC) and Ancorsteel1000C to which the same amounts of copper and graphite were added (FeCuC). Specimens were compacted and sintered to densities of 7.11 g/cm^sup 3^ and 7.33 g/cm^sup 3^. Samples of as-sintered density of 7.05 g/cm^sup 3^ were surface densified to 7.85 g/cm^sup 3^ by rolling. All samples were carbonitrided, ground and tested in RCF without slip so as to generate full S-N curves to one hundred million cycles without extrapolations. The functional relationship between density and RCF strength without slip for the previously investigated FeCuC and the FeMoCuC PM steels are presented and compared. PUBLICATION ABSTRACT
The locus coeruleus (LC) is a small brainstem nucleus with widely distributed noradrenergic projections to the whole brain, and loss of LC neurons is a prominent feature of age-related ...neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). This article discusses the hypothesis that in early stages of neurodegenerative diseases, the discharge mode of LC neurons could be changed to a persistent high tonic discharge, which in turn might impair phasic discharge. Since phasic discharge of LC neurons is required for the release of high amounts of norepinephrine (NE) in the brain to promote anti-inflammatory and neuroprotective effects, persistent high tonic discharge of LC neurons could be a key factor in the progression of neurodegenerative diseases. Transcutaneous vagal stimulation (t-VNS), a non-invasive technique that potentially increases phasic discharge of LC neurons, could therefore provide a non-pharmacological treatment approach in specific disease stages. This article focuses on LC vulnerability in neurodegenerative diseases, discusses the hypothesis that a persistent high tonic discharge of LC neurons might affect neurodegenerative processes, and finally reflects on t-VNS as a potentially useful clinical tool in specific stages of AD and PD.
Purpose
The field of immunotherapy combinations for advanced renal cell carcinoma (aRCC) has been expanded in recent years. However, the treatment response varies widely among individual patients. It ...is still a challenge to predict oncological outcome in clinical practice. We assessed the impact of an activated immune system reflected by changes in C-reactive protein (CRP) levels and the early onset of treatment-related adverse events (TRAEs) on the treatment response.
Methods
In this retrospective analysis of 57 aRCC patients, CRP kinetics based on previous descriptions of CRP flare-response, CRP response or CRP non-response, and the TRAEs, which occurred within a month after therapy initiation, were obtained for this study. According to logistic regression analysis of both factors, we stratified the patients into risk groups: the presence of CRP flare-response/response and early onset of TRAE (low-risk group); the presence of a single factor (intermediate-risk group); and without both factors (high-risk group).
Results
Ten patients (17%) experienced primary disease progression. No progressive disease was observed in the low-risk group, while 60% (
n
= 6/10) of the high-risk group showed a primary disease progression. Significantly, an increased risk of disease progression was observed by patients without CRP response and TRAEs (
p
< 0.001).
Conclusion
The present analysis displays the predictive value of the on-treatment risk model based on CRP kinetics and the early onset of TRAEs, which can be easy to implement in clinical practice to optimize the treatment monitoring.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is a common observation that rolling bearings fail due to the formation of white etching areas and white etching cracks (WEA/WEC). Branching crack networks beneath the surface and an altered ...microstructure known as WEA are characteristics of the failure mode. Therefore, the WEA-related cracks are known as WEC. In order to shed more light on this so far not fully understood phenomenon, the present study focussed on the role of specific oil additives and their influence on the formation of reaction layers and how these possibly affect the WEA/WEC formation. For this purpose, comprehensive tests were conducted on a three-ring-on-roller test rig using two different fully formulated oil lubricants with samples of SAE 52100 bearing steel. A subsequent carried out analysis by wavelength dispersive X-ray spectroscopy (WDX) and transmission electron microscopy (TEM) revealed the differences in the formed additive-derived reaction layers. While a known WEA/WEC-critical oil formulation, containing the two additives zinc dithiophosphate (ZDDP) and overbased calcium sulfonate (OBCaSul), did not result in any significant formation of reaction layers during mixed / boundary lubrication at an oil influx temperature of 95 °C, an oil formulation containing barium and phosphorus performed excellent in this respect. This finding is related to the observation that provocation of WEA/WEC failures in our experiment was always unsuccessful when the barium- and phosphorus-containing oil was used. The use of barium phosphate containing lubricants could therefore be an effective measure to prevent or significantly delay WEA/WEC damage to bearings.
•RCF tests examining the role of oil additives and their influence on the formation of reaction layers and WEA/WEC formation.•WDX and TEM investigations revealing the differences in the formed additive-derived reaction layers.•Usage of barium phosphate containing lubricants could be an effective measure to prevent or delay WEA/WEC damage to bearings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract Intense stressful events can result in chronic disorders such as posttraumatic stress disorder (PTSD). In vulnerable individuals, a single aversive experience can be sufficient to cause ...long-lasting behavioral changes. Candidate brain regions implicated in stress-related psychopathology are the amygdala, the bed nucleus of the stria terminalis (BNST), and the hypothalamic pituitary adrenal (HPA) axis. In rodents exposure to 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), an ethologically relevant stressor, has been shown to induce intense stress and innate anxiety responses. To study dispositions for the development of maladaptive stress responses, mice models are required. Therefore C57BL/6J mice were exposed to TMT and Fos expression was studied in key brain regions implicated in stress responses and anxiety-like behavior. Our results show TMT-induced activation of a distinct neural circuit involving the BNST, the lateral septum (LS), the paraventricular nucleus of the hypothalamus (PVN), the periaqueductal gray (PAG) and the locus coeruleus (LC). Anatomical interconnection of the BNST with all these regions could point to an important modulatory role of this nucleus. Since, the BNST gets direct input from the olfactory bulbs and projects to the PVN and PAG and is therefore well positioned to modulate behavioral and endocrine stress responses to TMT. Hence, we suggest that TMT exposure is suitable to investigate uncontrollable stress responses in mice which exhibit similarities to maladaptive stress responses underlying PTSD in humans.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
One of the main failure indications in rolling bearings subjected to rolling contact fatigue (RCF) is premature subsurface cracking accompanied by white etching areas (WEAs). The cracks that are ...linked with WEAs are called white etching cracks (WECs). The formation mechanisms of WEAs/WECs are still highly debatable according to international state of art. Often SAE 52100 steel is used for bearing rings. Its microstructure consists of a martensitic or bainitic matrix and homogeneously distributed chromium rich cementite precipitations. There are two main hypotheses based on what forms first, the cracks or WEAs (hypothesis 1 & 2 respectively). There are many numerical studies that examine non-metallic inclusions as a source of cracks that leads to WEAs (hypothesis 1), but none that considers carbides as the source of severe plastic deformation subjected to RCF that leads to WEAs and, eventually WECs (hypothesis 2). In this study, the testing was conducted on a ZF-type modified RCF test rig with hydrogen charged samples to reproduce WEAs/WECs formation. Later the influence of the microstructural features of the carbides on the steel matrix, during the formation of WEAs was investigated by microstructural investigations and multiscale finite element modelling. It was found that carbides can contribute to severe local plastic deformation which leads to formation of WEAs. Thus, it also supported the likelihood of hypothesis 2. Additionally, the surface traction and microstructural characteristics of carbides are correlated with the wide range of WEAs formation depths and timescales.
•Influence of slip and Hertzian pressure on WEA/WEC failures under diffusible hydrogen.•Microstructural investigations SEM BSE, SE imaging and SEM EBSD measurements: shearing of carbides, WEA/WECs.•Simulation models enable a detailed understanding of the impact of carbides under RCF during formation of WEAs.•Multi-scale simulation model: RCF, Influence of the microstructural features of the carbides, ratcheting effect.•Carbide shearing simulation during formation of WEAs under adiabatic and non-adiabatic conditions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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