| 1. |
- Holmén, Jessica, 1971, et al.
(författare)
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Mucins and their O-Glycans from human bronchial epithelial cell cultures.
- 2004
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Ingår i: American journal of physiology. Lung cellular and molecular physiology. - : American Physiological Society. - 1040-0605 .- 1522-1504. ; 287:4
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Tidskriftsartikel (refereegranskat)abstract
- A longstanding question in obstructive airway disease is whether observed changes in mucin composition and/or posttranslational glycosylation are due to genetic or to environmental factors. We tested whether the mucins secreted by second-passage primary human bronchial epithelial cell cultures derived from noncystic fibrosis (CF) or CF patients have intrinsically different specific mucin compositions, and whether these mucins are glycosylated differently. Both CF and non-CF cultures produced MUC5B, predominantly, as judged by quantitative agarose gel Western blots with mucin-specific antibodies: MUC5B was present at approximately 10-fold higher levels than MUC5AC, consistent with our previous mRNA studies (Bernacki SH, Nelson AL, Abdullah L, Sheehan JK, Harris A, William DC, and Randell SH. Am J Respir Cell Mol Biol 20: 595-604, 1999). O-linked oligosaccharides released from purified non-CF and CF mucins and studied by HPLC mass spectrometry had highly variable glycan structures, and there were no observable differences between the two groups. Hence, there were no differences in either the specific mucins or their O-glycans that correlated with the CF phenotype under the noninfected/noninflammatory conditions of cell culture. We conclude that the differences observed in the mucins sampled directly from patients are most likely due to environmental factors relating to infection and/or inflammation.
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| 2. |
- Ahlfors, Reetta, et al.
(författare)
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Arabidopsis RADICAL-INDUCED CELL DEATH1 belongs to the WWE protein-protein interaction domain protein family and modulates abscisic acid, ethylene, and methyl jasmonate responses.
- 2004
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Ingår i: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 16:7, s. 1925-37
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Tidskriftsartikel (refereegranskat)abstract
- Experiments with several Arabidopsis thaliana mutants have revealed a web of interactions between hormonal signaling. Here, we show that the Arabidopsis mutant radical-induced cell death1 (rcd1), although hypersensitive to apoplastic superoxide and ozone, is more resistant to chloroplastic superoxide formation, exhibits reduced sensitivity to abscisic acid, ethylene, and methyl jasmonate, and has altered expression of several hormonally regulated genes. Furthermore, rcd1 has higher stomatal conductance than the wild type. The rcd1-1 mutation was mapped to the gene At1g32230 where it disrupts an intron splice site resulting in a truncated protein. RCD1 belongs to the (ADP-ribosyl)transferase domain–containing subfamily of the WWE protein–protein interaction domain protein family. The results suggest that RCD1 could act as an integrative node in hormonal signaling and in the regulation of several stress-responsive genes.
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| 3. |
- Baecklund, Eva, et al.
(författare)
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Rheumatoid arthritis and malignant lymphomas
- 2004
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Ingår i: Current Opinion in Rheumatology. - : Ovid Technologies (Wolters Kluwer Health). - 1040-8711 .- 1531-6963. ; 16:3, s. 254-261
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE OF REVIEW:The reason for the increased lymphoma risk in patients with rheumatoid arthritis (RA) has remained unclear. Reports of lymphomas in patients treated with TNF-blockers have brought renewed interest in this issue. This review summarizes data on possible associations between RA and lymphomas, including different treatments and RA disease related risk factors.RECENT FINDINGS:Some recent studies reported increased lymphoma risks linked to RA disease activity. The hypothesis that disease-modifying drugs, and in particular methotrexate, would increase the lymphoma risk receives little support. Observation times for the TNF-blocking therapies are still short, but so far no clear increased risk for lymphoma has been observed. Presence of Epstein-Barr virus, as analyzed with EBER in situ hybridization, appears to be uncommon in RA related lymphomas. Hypothetically, an increased proliferative drive caused by self or non-self antigens may play a role in lymphoma development in RA patients, but this has to be further studied.SUMMARY:Rheumatologists need to be aware of the increased lymphoma risk in their RA patients. The reason for the increased lymphoma risk in RA patients is still unclear, but available studies rather support the hypothesis of a link between RA disease severity and the risk of lymphoma than increased risks associated with specific treatment regimens. To facilitate the future evaluation of lymphoma risks in connection with treatment, we suggest that patients treated with new drugs should be subject to structured surveillance. Collected information should include data about RA disease activity and severity.
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| 4. |
- Bharti, K, et al.
(författare)
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Tomato heat stress transcription factor HsfB1 represents a novel type of general transcription coactivator with a histone-like motif interacting with the plant CREB binding protein ortholog HAC1
- 2004
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Ingår i: The Plant cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 16:6, s. 1521-1535
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Tidskriftsartikel (refereegranskat)abstract
- In contrast with the class A heat stress transcription factors (HSFs) of plants, a considerable number of HSFs assigned to classes B and C have no evident function as transcription activators on their own. However, in the following article, we provide evidence that tomato (Lycopersicon peruvianum) HsfB1 represents a novel type of coactivator cooperating with class A HSFs (e.g., with tomato HsfA1). Provided the appropriate promoter architecture, the two HSFs assemble into an enhanceosome-like complex, resulting in strong synergistic activation of reporter gene expression. Moreover, HsfB1 also cooperates in a similar manner with other activators, for example, with the ASF1/2 enhancer binding proteins of the 35S promoter of Cauliflower mosaic virus or with yet unidentified activators controlling housekeeping gene expression. By these effects, HsfB1 may help to maintain and/or restore expression of certain viral or housekeeping genes during ongoing heat stress. The coactivator function of HsfB1 depends on a histone-like motif in its C-terminal domain with an indispensable Lys residue in the center (GRGKMMK). This motif is required for recruitment of the plant CREB binding protein (CBP) ortholog HAC1. HsfA1, HsfB1, and HAC1/CBP form ternary complexes in vitro and in vivo with markedly enhanced efficiency in promoter recognition and transcription activation in plant and mammalian (COS7) cells. Using small interfering RNA–mediated knock down of HAC1 expression in Arabidopsis thaliana mesophyll protoplasts, the crucial role for the coactivator function of HsfB1 was confirmed.
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| 5. |
- Christenson, Andreas, et al.
(författare)
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Direct electron transfer between ligninolytic redox enzymes and electrodes
- 2004
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 16:13-14, s. 1074-1092
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Forskningsöversikt (refereegranskat)abstract
- The electrochemistry of the ligninolytic redox enzymes, which include lignin peroxidase, manganese peroxidase and laccase and possibly also cellobiose dehydrogenase, is reviewed and discussed in conjunction with their basic biochemical characteristics. It is shown that long-range electron transfer between these enzymes and electrodes can be established and their ability to degrade lignin through a direct electron transfer mechanism is discussed.
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| 6. |
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| 7. |
- Ferapontova, Elena
(författare)
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Direct peroxidase bioelectrocatalysis on a variety of electrode materials
- 2004
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 16:13-14, s. 1101-1112
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Forskningsöversikt (refereegranskat)abstract
- The role of the electrode material in the efficiency of direct (non-mediated) bioelectrocatalytic reduction of H2O2, catalyzed by horseradish peroxidase (HRP) is studied and discussed. The variations in direct peroxidase bioelectrocatalysis when coming from carbon/graphite to metal electrodes and oxides, as well as modified electrodes, are analyzed regarding the variations in adsorption/orientation of peroxidase at the electrodes, interfacial electron transfer rates and mechanism of catalysis.
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| 8. |
- Gomez, Federico, et al.
(författare)
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Factors affecting quality and postharvest properties of vegetables: Integration of water relations and metabolism
- 2004
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Ingår i: Critical Reviews in Food Science and Nutrition. - : Informa UK Limited. - 1040-8398 .- 1549-7852. ; 44:3, s. 139-154
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Tidskriftsartikel (refereegranskat)abstract
- Growing of vegetables in the field, harvesting, handling in the packing house and storage are events in the lifetime of vegetables that arc analysed from the point of view of the complex series of physiological transitions taking place in each of these events. Water is the major factor limiting plant metabolism and plants have developed fascinating mechanisms to cope with this limiting factor. Therefore, water relations (water, pressure and osmotic potential) are used as criteria for discussing plant stress physiology aspects such as osmotic, elastic adjustment and cold acclimation, as well as mechanical stress when the vegetable is harvested and during handling in the packing house. Consequences for the storage potential and quality of the vegetable arc discussed. After harvesting, the postharvest cell has the ability to complete a complex series of physiological transitions that will influence vegetable quality and further processing operations. Metabolic changes in the cytosol, cell membrane and cell wall are described.
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| 9. |
- Henter, JI, et al.
(författare)
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Histiocyte disorders
- 2004
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Ingår i: Critical reviews in oncology/hematology. - 1040-8428. ; 50:2, s. 157-174
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Tidskriftsartikel (refereegranskat)
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Lundström, Linda, et al.
(författare)
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Unwrapping Hartmann-Shack images from highly aberrated eyes using an iterative B-spline based extrapolation method
- 2004
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Ingår i: Optometry and Vision Science. - : Ovid Technologies (Wolters Kluwer Health). - 1040-5488 .- 1538-9235. ; 81:5, s. 383-388
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Tidskriftsartikel (refereegranskat)abstract
- Purpose. When the wavefront aberrations of the eye are measured with a Hartmann-Shack (HS) sensor, the resulting spot pattern must be unwrapped, that is, for each lenslet the corresponding spot must be identified. This puts a limitation on the measurable amount of aberrations. To extend the range of an HS sensor, a powerful unwrapping algorithm has been developed. Methods. The unwrapping algorithm starts by connecting the central HS spots to the central lenslets. It then fits a B-spline function through a least squares estimate to the deviations of the central HS spots. This function is then extrapolated to find the expected locations of HS spots for the unconnected lenslets. The extrapolation is performed gradually in an iterative manner; the closest unconnected lenslets are extrapolated and connected, and then the B-spline function is least squares fitted to all connected HS spots and extrapolated again. Results. Wavefront aberrations from eyes with high aberrations can be successfully unwrapped with the developed algorithm. The dynamic range of a typical HS sensor increases 3.5 to 13 times compared with a simple unwrapping algorithm. Conclusions. The implemented algorithm is an efficient unwrapping tool and allows the use of lenslets with a low numerical aperture and thus gives a relatively higher accuracy of measurements of the ocular aberrations.
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| 14. |
- Mak, Wing Cheung, et al.
(författare)
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Nanoengineered encapsulation of mediator microcrystals and their use as a non-metallic label system for the silver enhancement technique
- 2004
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Ingår i: Electroanalysis. - : John Wiley & Sons. - 1040-0397 .- 1521-4109. ; 16:1-2, s. 156-160
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Tidskriftsartikel (refereegranskat)abstract
- We report on the nanoengineered encapsulation and functionalization of mediator microcrystals and their use as a non-metallic bioassay label system for the silver enhancement technology. Mediator microcrystals were encapsulated and functionalized by using a Layer-by-Layer (LbL) based approach. This is a generic way to transform most low-soluble mediators (e.g., ferroceneacetic acid) into a label for electrochemical bioassays. Instead of using conventional gold particles, encapsulated mediator microcrystals are used as the primary label for the silver enhancement technique. After the biorecognition reaction the unbound labels were separated and a silver(I) ion solution was added. The mediator reduces silver ions into metallic silver and the mediator microcrystal was transformed into a silver particle. Consecutively a reducing agent was added leading to a further silver growth, representing the silver enhancement step. A large amount of silver was developed from the mediator, resulting in signal amplification. The amount of developed silver was studied in a bioassay and was found proportional to the analyte concentration.
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| 15. |
- Nordborg, Elisabeth, 1948, et al.
(författare)
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Giant cell arteritis: strategies in diagnosis and treatment.
- 2004
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Ingår i: Current opinion in rheumatology. - 1040-8711. ; 16:1, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE OF REVIEW: This review summarizes current diagnostic assessments and therapeutic strategies in giant cell arteritis. Giant cell arteritis or temporal arteritis is a chronic vasculitis of large and medium-size vessels. Concurrent symptoms of proximal muscular ache and morning stiffness, polymyalgia rheumatica, are commonly seen. Recent investigations support the contention that polymyalgia rheumatica and temporal arteritis are two different expressions of the same underlying vasculitic disorder. RECENT FINDINGS: The symptomatology of giant cell arteritis is quite varying. Recently a frequent occurrence of audiovestibular manifestations was demonstrated, which should be actively searched for in the clinical investigation. Although color Doppler ultrasound, MRI, and positron emission tomography have illustrated the widespread nature of giant cell arteritis, none of these techniques may currently replace temporal artery biopsy. Biopsy of the superficial temporal artery is a safe and simple procedure, and remains the gold standard for the diagnosis of giant cell arteritis. The importance of long biopsies and meticulous histologic examination using sub-serial sectioning is emphasized. Numerous recent publications confirm the low diagnostic yield of a second, contralateral biopsy. Corticosteroids remain the cornerstone in the treatment of giant cell arteritis. Although steroid treatment promptly eliminates symptoms of systemic inflammation, its effect on inflammatory morphology is delayed. Consequently, there is a need for new therapeutic strategies. The potential role of aspirin has recently been implicated.
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| 16. |
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| 17. |
- Rasmusson, Allan, et al.
(författare)
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Alternative NAD(P)H dehydrogenases of plant mitochondria
- 2004
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Ingår i: Annual Review of Plant Physiology and Plant Molecular Biology. - : Annual Reviews. - 1040-2519. ; 55, s. 23-39
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Forskningsöversikt (refereegranskat)abstract
- Plant mitochondria have a highly branched electron transport chain that provides great flexibility for oxidation of cytosolic and matrix NAD(P)H. In addition to the universal electron transport chain found in many organisms, plants have alternative NAD(P)H dehydrogenases in the first part of the chain and a second oxidase, the alternative oxidase, in the latter part. The alternative activities are nonproton pumping and allow for NAD(P)H oxidation with varying levels of energy conservation. This provides a mechanism for plants to, for example, remove excess reducing power and balance the redox poise of the cell. This review presents our current understanding of the alternative NAD(P)H dehydrogenases present in plant mitochondria.
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| 18. |
- Runeson, Sverker, et al.
(författare)
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On two modes of apprehension
- 2004
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Ingår i: Ecological Psychology. - 1040-7413. ; 16:1, s. 37-44
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Tidskriftsartikel (refereegranskat)abstract
- We argue that two qualitatively distinct modes of apprehension, two cognitive modes, are brought into play in our knowing the world. This sort of claim is not new to Psychology (e.g., Baron, 1981; Brunswik, 1966; Heft, 1993; Michotte, 1955/1991; Polanyi, 1966; Ryan, 1938) but with reliance on basic ecological tenets, a more substantial treatment should be possible. Drawing on recent theoretical development and empirical results (Runeson, Juslin & Olsson, 2000), and in radical contrast to timeworn constructivist notions, it is maintained that use of meaningful specificational information is the hallmark of perception, whereas “cognition” provides various supplementary functions. Tentatively, we characterize the two modes as follows:
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| 19. |
- Schrader, J., et al.
(författare)
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A high-resolution transcript profile across the wood-forming meristem of poplar identifies potential regulators of cambial stem cell identity
- 2004
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Ingår i: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 16:9, s. 2278-2292
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Tidskriftsartikel (refereegranskat)abstract
- Plant growth is the result of cell proliferation in meristems, which requires a careful balance between the formation of new tissue and the maintenance of a set of undifferentiated stem cells. Recent studies have provided important information on several genetic networks responsible for stem cell maintenance and regulation of cell differentiation in the apical meristems of shoots and roots. Nothing, however, is known about the regulatory networks in secondary meristems like the vascular cambium of trees. We have made use of the large size and highly regular layered organization of the cambial meristem to create a high-resolution transcriptional map covering 220 mum of the cambial region of aspen (Populus tremula). Clusters of differentially expressed genes revealed substantial differences in the transcriptomes of the six anatomically homogenous cell layers in the meristem zone. Based on transcriptional and anatomical data, we present a model for the position of the stem cells and the proliferating mother cells in the cambial zone. We also provide sets of marker genes for different stages of xylem and phloem differentiation and identify potential regulators of cambial meristem activity. Interestingly, analysis of known regulators of apical meristem development indicates substantial similarity in regulatory networks between primary and secondary meristems.
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| 20. |
- Taeymans, D., et al.
(författare)
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A review of acrylamide : An industry perspective on research, analysis, formation, and control
- 2004
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Ingår i: Critical reviews in food science and nutrition. - : Informa UK Limited. - 1040-8398 .- 1549-7852. ; 44:5, s. 323-347
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Tidskriftsartikel (refereegranskat)abstract
- Acrylamide is a synthetic monomer with a wide scope of industrial applications, mainly as a precursor in the production of several polymers, such as polyacrylamide. The main uses of polyacrylamides are in water and wastewater treatment processes, pulp and paper processing, and mining and mineral processing. The announcement by the Swedish National Food Administration in April 2002 of the presence of acrylamide predominantly in heat-treated carbohydrate-rich foods sparked intensive investigations into acrylamide, encompassing the occurrence, chemistry, agricultural practices, and toxicology, in order to establish if there is a potential risk to human health from the presence of this contaminant in the human diet. The link of acrylamide in foods to the Maillard reaction and, in particular, to the amino acid asparagine has been a major step forward in elucidating the first feasible chemical route of formation during the preparation and processing of food. Other probably minor pathways have also been proposed, including acrolein and acrylic acid. This review addresses the analytical and mechanistic aspects of the acrylamide issue and summarizes the progress made to date by the European food industries in these key areas. Essentially, it presents experimental results generated under laboratory model conditions, as well as under actual food processing conditions covering different food categories, such as potatoes, biscuits, cereals, and coffee. Since acrylamide formation is closely linked to food composition, factors such as the presence of sugars and availability of free amino acids are also considered. Many new findings that contribute towards a better understanding of the formation and presence of acrylamide in foods are presented. Many national authorities across the world are assessing the dietary exposure of consumers to acrylamide, and scientific projects have commenced to gather new information about the toxicology of acrylamide. These are expected to provide new scientific knowledge that will help to clarify whether or not there is a risk to human health from the consumption of foods containing law amounts of acrylamide.
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| 21. |
- Trysberg, Estelle, 1960, et al.
(författare)
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Cerebral inflammation and degeneration in systemic lupus erythematosus
- 2004
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Ingår i: Curr Opin Rheumatol. - 1040-8711. ; 16:5, s. 527-33
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Forskningsöversikt (refereegranskat)abstract
- PURPOSE OF REVIEW: This review deals with new information related to central nervous system lupus, with special emphasis on mechanisms engaged in inflammation and neurodegeneration. RECENT FINDINGS: We report the very recent findings related to neuropsychiatric lupus in areas of (1) neuroimaging, (2) immunology and genetics, (3) biochemistry, and (4) neuropsychological tests. The relation between treatment of central nervous system lupus and immunologic/biochemical parameters as an outcome variable is also reported. SUMMARY: The recent advances in the field of neuropsychiatric lupus allow better understanding of the pathogenesis of the disease and follow-up of disease activity during immunosuppressive treatment.
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| 22. |
- Weissmann, Mikael, 1977, et al.
(författare)
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Chinese influence on the DPRK negotiations
- 2004
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Ingår i: Peace Review. - 1040-2659 .- 1469-9982. ; 16:2, s. 219-224
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Tidskriftsartikel (refereegranskat)abstract
- Despite its isolation, and its social and economic problems, the DPRK continues to disregard negotiations with the U.S. and has, according to the U.S., violated established agreements. It's true that the U.S. policy towards the DPRK has been less than cooperative, which has worried North Korea's Northeast Asian neighbors. Pyongyang's only reliable ally has traditionally been the People Republic of China (PRC), but even the Chinese have recently begun to revaluate the advantages of supporting Pyongyang. The Chinese support is partly born out of the fear of having U.S. troops at the Chinese-Korean border, but also because a DPRK collapse would, apart from a probable war, create huge waves of refugees. The Chinese impact on negotiations has been affected by its ambivalence both toward the DPRK and toward the U.S. military position in the Korean peninsula. The Chinese fear that a U.S. intervention would dissolve the DPRK and create a united Korea controlled by the Americans. There is also a strong concern in Beijing over Pyongyang's interest in developing nuclear weapons. Apart from the inherent dangers of Kim Jong-Il being armed with such weapons, his acquisition of them would undoubtedly lead to a popular demand in Japan and the Republic of Korea (ROK) to acquire nuclear capabilities, something that would further threaten regional security. This ambivalence, in combination with the potentially severe economic and political consequences of war and refugee flows, makes the Chinese an uncomfortable ally of Pyongyang. Beijing has been accused by the West of pressuring Pyongyang to take a hard position against the United States, rather than encouraging cooperation. On the other hand Beijing has also been a positive force in urging the North Koreans to communicate with the United States. Thus, it's worth examining what role and impact the PRC has had to date in the negotiations with DPRK, and what role it may play in the future.
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| 23. |
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| 24. |
- Yan, Zhenghua
(författare)
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A fast spectral approximation of narrow-band model for thermal radiation calculation
- 2004
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Ingår i: Numerical Heat Transfer Part B: Fundamentals. - : Informa UK Limited. - 1040-7790 .- 1521-0626. ; 46:2, s. 165-178
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Tidskriftsartikel (refereegranskat)abstract
- A fast spectral approximation of a narrow-band computer model is proposed for prediction of thermal radiation in a generally nonisothermal and nonhomogeneous combustion environment. The approximation is made by assuming each discretized spatial element along a line of sight to be locally "gray" within each small narrow-band spectrum interval. For each spatial element, the local equivalent spectral absorption coefficient of the combustion products, including carbon dioxide, water vapor, and soot, is calculated based on formulas from the narrow-band model. Compared with the previously developed fast narrow-band model, FASTNB, which is an order of magnitude faster and gives almost exactly the same result as Grosshandler's original narrow-band model RADCAL, this approximation method provides calculation result with small deviation at substantially faster speed. Furthermore, the speed-up ratio increases linearly with the number of discretized spatial elements along a line of sight. This makes this approximation method particularly useful in computational combustion, where the grid number used in computation is steadily becoming larger and larger as the computation goes toward large eddy simulation (LES) and direct numerical simulation (DNS).
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| 25. |
- Yuan, Jinliang, et al.
(författare)
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Three-dimensional analysis of two-phase flow and its effects on the cell performance of PEMFC
- 2004
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 46:7, s. 669-694
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Tidskriftsartikel (refereegranskat)abstract
- For a cathode duct of a proton-exchange membrane fuel cell, a three-dimensional analysis method is further developed to include two-phase, multicomponent gas and heat transport processes. A set of momentum, heat transport, and gas species equations is solved for the whole duct by coupled source terms and variable thermophysical properties. The effects of the electrochemical reactions on the heat generation and mass consumption/generation are taken into account. The effects of liquid water on the local current density and cell performance are discussed by incorporating the Tafel formula and a liquid-phase saturation function. The numerical predictions are compared with experimental results, and good agreement is demonstrated between the present results and the measured ones in terms of polarization curve.
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| 26. |
- Baart, Pieter, et al.
(författare)
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Non-newtonian effects on film formation in grease-lubricated radial lip seals
- 2010
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 53:3, s. 308-318
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Tidskriftsartikel (refereegranskat)abstract
- In existing models, the only lubricant property used for predicting film thickness in radial lip seals is the (base) oil viscosity. Lubricating greases show non-Newtonian behavior, and additional normal stress components develop that may contribute to the load-carrying capacity. This study investigates the shear rheology of greases and determines whether this "normal stress effect" in grease can significantly contribute to film formation in radial lip seals. First, the rheological behavior of grease is studied in a rotary plate-plate rheometer at small gaps of 25-500 μ m up to shear rates of 5 · 104 s-1. The rheology measurements are used for a rheology model that predicts the first normal stress difference in the grease. Second, a seal lip model was developed to predict the lift force generated by the normal stress effect that separates the seal from the shaft. The model results show that the load-carrying capacity depends very much on the operating conditions: lip geometry, speed, and temperature. The model predicts a lift force that is over 50% of the seal specific lip force for low-contact pressure-bearing seals. The model can easily be used in existing oil seal models and makes it possible to optimize seal design by utilizing the normal stress effect.
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| 27. |
- Baart, Pieter, et al.
(författare)
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Oil-bleeding model for lubricating grease based on viscous flow through a porous microstructure
- 2010
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 53:3, s. 340-348
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Tidskriftsartikel (refereegranskat)abstract
- One of the criteria in selecting lubricating grease for rolling-element bearing applications is its ability to bleed oil, sometimes called ogrease bleeding.o Oil bleeding is assumed to be the dominating mechanism supplying new oil to the rolling track for lubrication. In this study, a physical model has been developed to understand the relation between parameters that control oil bleeding. In the model, lubricating grease is described as a porous network, formed by the thickener fibers, that contains the base oil. This type of structure is confirmed by SEM and AFM images of a lithium complex grease showing a matrix of rigid fibers with random orientation. A relatively simple flow model based on Darcy's law for viscous flow in porous media and an anisotropic microstructure deformation model was developed. The model relates the pressure gradient, oil viscosity, thickener structure deformations, and permeability to the volumetric oil flow out of the thickener network. The permeability depends strongly on the thickener microstructure. The model was verified with experiments at a wide variety of temperatures and rotational speeds.
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| 28. |
- Baart, Pieter, et al.
(författare)
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On the Normal Stress Effect in Grease-Lubricated Bearing Seals
- 2014
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 57:5, s. 939-943
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Tidskriftsartikel (refereegranskat)abstract
- The film formation in lip seals, due to non-Newtonian rheology of the lubricant, has been a topic of speculation. Earlier work suggests that normal stresses in grease would be favorable for the film build-up between the seal lip and shaft or bearing ring. In the current paper we evaluate this earlier work and our earlier theoretical seal lip model with a series of experiments. We use a modified concentric cylinder geometry and a model fluid to study the fluid pressure distribution in the seal type geometry. The results are then related to grease lubricated seals and our earlier theoretical predictions. The present analysis shows that this earlier work and our earlier predictions are not correct and indicate that normal stresses in the grease pull the seal lip towards the shaft, increasing the contact pressure. However, normal stresses also ensure the presence of grease on the shaft or bearing inner ring which enhances replenishment of the sealing contact.
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| 29. |
- Baart, Pieter, et al.
(författare)
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The influence of speed, grease type, and temperature on radial contaminant particle migration in a double restriction seal
- 2011
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 54:6, s. 867-877
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Tidskriftsartikel (refereegranskat)abstract
- Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile. In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication.
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| 30. |
- Bair, Scott S., et al.
(författare)
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New EHL Modeling Data for the Reference Liquids Squalane and Squalane Plus Polyisoprene
- 2018
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Ingår i: Tribology Transactions. - : Society of Tribologists and Lubrication Engineers. - 1040-2004 .- 1547-397X. ; 61:2, s. 247-255
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Tidskriftsartikel (refereegranskat)abstract
- An important part of the new quantitative approach to elastohydrodynamic lubrication (EHL) is the use of reference liquids with well-characterized thermophysical properties. New measurements are reported for the thermal and rheological properties of squalane to high pressure and of high shear rate and high-frequency viscosity of squalane thickened with polyisoprene (SQL + PIP) at ambient pressure. The glass transition viscosity of squalane at ambient pressure was found from published viscosity measurements and new glass transition measurements by transient hot wire. The glass transition viscosity so determined was incorporated into the improved Yasutomi model and the calculated glass transition temperatures as a function of pressure are comparable to those directly measured, although the hybrid model yields better agreement. The glass transition viscosity of squalane by any definition must be substantially lower than the “universal value” of 1012 Pa·s. The second Newtonian inflection cannot be characterized in steady shear at ambient pressure for SQL + PIP due to cavitation; however, acoustic viscometry with matching layer does characterize the second Newtonian inflection. To form the analogy between steady and oscillatory shear requires that the steady shear rate be compared with the ordinary frequency rather than the angular frequency for SQL + PIP.
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| 31. |
- Baran, Özlem, et al.
(författare)
-
Mechanical and Tribological Properties of TiTaBN Graded-Composite Coatings Deposited Using the CFUBMS Technique
- 2016
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 59:6, s. 1089-1097
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Tidskriftsartikel (refereegranskat)abstract
- In this study, TiTaBN graded-composite coatings were deposited utulizing different process parameters on D2 steel and glass substrates using pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS). The morphology and structure of the coatings were analyzed using SEM, EDS, XPS and Raman spectroscopy. The hardness and critical load values of the coatings were determined using a microhardness tester and scratch tester, respectively. The tribological properties of the coatings were analyzed in different testing environments using a pin-on-disc tribometer. The properties of the coatings were found to be strongly affected by the coating parameters. The maximum thickness and hardness were obtained at the lowest nitrogen flow rate and highest frequency. Critical load values of coatings were increased with increased nitrogen flow rate. The low nitrogen flow rate and high frequency across the coatings caused enhanced tribological properties.
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| 32. |
- Bergseth, Ellen, 1979-, et al.
(författare)
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A Wear Detection Parameter for the Wheel–Rail Contact Based on Emitted Noise
- 2019
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 62:3, s. 496-503
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Tidskriftsartikel (refereegranskat)abstract
- This article describes how a wheel–rail wear detection parameter based on noise was developed by running a rapid transit train instrumented with microphones in a depot with a small curve radius. This full-scale test made use of previous knowledge gained from lab-scale tests. The lab- and full-scale tests showed that noise could be used as an indicator of wear transition, when normal wear turns into severe or catastrophic wear. This transition was accompanied by a significant increase in sound pressure and a broader sound pressure amplitude spectrum; that is, a narrow initial amplitude distribution in the normal wear regime and a broader distribution in the severe wear regime. The measured noise from the inner/low and outer/high rails was analyzed in conjunction with the wear from the outer wheel and comparisons were made between cleaned (exposed to severe wear) and lubricated (no wear) rail. Based on those analyses, a wear detection parameter criterion was developed for this specific train. This wear parameter has been implemented in a real-time condition monitoring system so that warnings of the risk for severe wear could be sent to the maintenance department. Validation of the wear parameter and challenges linked to open system conditions are discussed in this article.
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| 33. |
- Bergstedt, Edwin, et al.
(författare)
-
Influence of the DIN 3962 Quality Class on the Efficiency in Honed Powder Metal and Wrought Steel Gears
- 2020
-
Ingår i: Tribology Transactions. - : Taylor and Francis Inc.. - 1040-2004 .- 1547-397X. ; 63:6, s. 1076-1084
-
Tidskriftsartikel (refereegranskat)abstract
- To increase the efficiency of a gearbox, research on gear mesh loss is of importance. Britton et al. concluded that the surface finishing method affects the gear mesh efficiency. The efficiency benefits of superfinishing a surface and reducing the surface roughness have been reported by Kahraman. A novel method for calculating the bearing loss torque was proposed by Tu et al. Andersson et al. found that the efficiency can vary between 2 and 5% during repeated efficiency tests due to variations in the assembly process. This work investigates how the honing surface finishing process and DIN 3962 quality class affect the gear mesh efficiency by performing tests in an FZG back-to-back test rig. Two materials, a powder metal and a wrought steel, were tested. All gears were finished using a honing process and sorted according the measured quality class. Powder metal gears of class 6, 7, 8, and ≥9 and wrought steel gears of class 6, 7, and ≥9 were tested. The efficiency were calculated from measuring the torque required to maintain a constant velocity of the FZG test rig. The results from the efficiency tests showed no significant difference in efficiency between the wrought steel and powder metal steel gears. In addition, no obvious correlation between the DIN 3962 quality class and the gear mesh efficiency could be found. When examining the wrought steel material it was found that the reproducibility of the efficiency was comparable to the assembly error of the test rig, despite the variation in quality class.
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| 34. |
- Dittes, Nicholas, 1987-, et al.
(författare)
-
Automated Dielectric Thermoscopy Characterization of Water Contaminated Grease
- 2019
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 62:5, s. 859-867
-
Tidskriftsartikel (refereegranskat)abstract
- Machine maintenance is important for improving machine uptime, reliability, and reducing costs. Grease is used in most rolling element bearings, and one common failure criterion is water contamination, so developing a sensor which can detect water content automatically without human input could be a useful endeavor. The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this paper with computer logged instrumentation. This method has been termed Dielectric Thermoscopy (DT). Several off the shelf (two lithium, one lithium complex, and two calcium sulphonate complex) and one unadditivized lithium grease are tested with varying amounts of water contamination from 0% to approximately 5%. Another grease is tested with small increments of added water from 0% to 0.97% to test the resolution of the measurement. The purpose is to use the capacitance temperature slope (termed dielectric thermoscopy) to show correlations to the water content of the grease sample and investigate if any grease types will pose problems in the measurement. A small, custom made fringe field capacitance sensor with an integrated temperature sensor has been used for this characterization and data is logged automatically with laboratory equipment and a PC. A useable and positive correlation to water content and the DT measurement of roughly 0.5 pF per 10 °C and percentage of water is found, although it was found that some greases have different behavior than others.
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| 35. |
- Dittes, Nicholas, et al.
(författare)
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Dielectric Thermoscopy Characterization of Water Contaminated Grease
- 2018
-
Ingår i: Tribology and Lubrication Technology. - : Society of Tribologists and Lubrication Engineers (STLE). - 1545-858X. ; 61:3, s. 393-402
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this article. The purpose of this investigation was to identify the dielectric properties that could be measured to differentiate varying levels of water contamination in calcium sulfonate complex (CaS-X) grease with three different test cells with the purpose of eventually developing a grease condition sensor. Measuring the change in dielectric constant over a small temperature change yielded useful estimations of water content and amount of grease where the added water content ranged from 0.22% to about 5.5%. Additionally, other parameters such as incomplete fill/coverage of the sensors were investigated as a prestudy. The results from this set of experiments show that the measurement has potential to be developed into a condition monitoring sensor in the future.
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| 36. |
- Dittes, Nicholas J., 1987-, et al.
(författare)
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Corrosion Sensor for Water-Contaminated Grease
- 2020
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 63:5, s. 891-896
-
Tidskriftsartikel (refereegranskat)abstract
- A simple and inexpensive corrosion sensor has been manufactured to study the corrosion rate of new and water contaminated lubricating grease using a galvanic cell. The galvanic charge is developed between ENIG (electroless nickel immersion gold) and zinc, manufactured by selectively plating on a custom manufactured interdigitated PCB (printed circuit board). This paper shows the methodology in using this concept for any application which may require quantifying the corrosivity of a liquid or semisolid which could be applied to the surface of the sensor. Water contamination is a problem in many grease lubricated machine components, so a sensor concept was developed and a correlation between water content and the corrosion rate is shown. This method could be used to precisely study the corrosion rate of aged or contaminated lubricants and could potentially be used as a cheap and simple way to estimate water contamination of grease. To the knowledge of the authors, this sensor concept has not been used in industry or literature.
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| 37. |
- Dittes, Nicholas, 1987-, et al.
(författare)
-
Optical Attenuation Characterization of Water Contaminated Lubricating Grease
- 2018
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 61:4, s. 726-732
-
Tidskriftsartikel (refereegranskat)abstract
- Water-contaminated grease samples are investigated with attenuation spectra in the visible and near-infrared (NIR) regions in this article. The purpose of this investigation was to identify a model with optical attenuation spectra such that the water content of grease samples could be characterized with a simple measurement setup using common methodology from the field of instrumental chemistry. The ratio between two chosen wavelengths of light appears to approximate the water content of grease samples with an acceptable coefficient of determination using a methodology to show what can potentially be done to develop condition monitoring tools. To illustrate the outlined method, a prestudy of grease aging and oxidation levels is also investigated to show that other variables do not significantly change the measurement.
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| 38. |
- Duenas Dobrowolski, Jan, et al.
(författare)
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Experimental Study of Lubricating Grease Flow inside the Gap of a Labyrinth Seal Using Microparticle Image Velocimetry
- 2018
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 61:1, s. 31-40
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the flow of lubricating greases in a labyrinth seal geometry is studied using microparticle image velocimetry (µPIV). The aim is to evaluate the grease velocity distribution inside the gap of a labyrinth seal and to find a relationship between the grease consistency and the transferred speed from the rotating ring in order to choose the correct grease as a sealing medium. In addition, the grease flow characteristics are important for the understanding of fracture due to grease layer displacement. For these purposes, four greases with different rheological properties were used in µPIV experiments. It was found that the grease consistency plays a crucial role in speed development as well as the grease composition and presence of a slip effect at the grease–rotating wall interface.
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| 39. |
- Fatima, Nowshir, et al.
(författare)
-
Influence of clutch output shaft inertia and stiffness on the performance of the wet clutch
- 2013
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 56:2, s. 310-319
-
Tidskriftsartikel (refereegranskat)abstract
- Being a part of the complex mass, spring and damper system in a driveline, the choice of design factors like, output shaft stiffness and inertia of a wet clutch system can influence its performance. The effects of these parameters are experimentally evaluated in this paper. Widely used commercial paper based friction plates with standard steel reaction plates are tested with four different stiffness and inertia combinations in a recently developed wet clutch test rig. A low inertia system in general showed a faster degradation and shorter clutch life for high torsional oscillation. Besides the system becomes more shudder sensitive for lower natural frequency in case of less stiff system. The less stiff output shaft with low inertia showed the highest shudder tendency among the four conditions. The differences in performance for different output shaft conditions become noticeable for numerous clutch engagements or a degraded system. The effect of different shaft design conditions is also illuminated in the topographical analysis of the separators’ surfaces and morphological study of frictional surfaces. This study reveals the influence of both inertia and stiffness not only on shudder sensitivity of the system but also on the clutch frictional performance as well as the overall clutch life.
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| 40. |
- Fatima, Nowshir, et al.
(författare)
-
Wet Clutch Friction Interfaces under Water Contaminated Lubricant Conditions
- 2016
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 59:3, s. 441-450
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of wet clutches used for automatic transmissions or other applications usually includes the desired positive friction characteristics and a shudder-free torque generation. Changes in the operating variables such as the lubricant conditions influence the formation of tribofilm, friction characteristics and can alter the degradation of the friction interfaces. In this work, the friction characteristics and degradation of the paper-steel friction interfaces were monitored when a commercial fully-formulated automatic transmission fluid (ATF) was contaminated with water. It was found that water in ATF influenced the clutch stability by increasing the mean coefficient of friction (µ) and the negative friction-velocity slope. Surface studies of the post-test friction interfaces clearly indicated reduced surface porosity and permeability, increased wettability and changed elemental composition on the contacting surfaces after tested with water- contaminated ATF. Moreover, water-contaminated paper-liners’ thermal decomposition shifted to a lower temperature compared to an uncontaminated liner during thermal analyses. These results displayed faster degradation and reduced service life of the clutch friction interfaces for water contamination. The resultant surface condition can be associated with the observed unstable friction and negative friction-velocity slopes.
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| 41. |
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| 42. |
- Glavatskih, Sergei, et al.
(författare)
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Hydrodynamic performance of a thrust bearing with micropatterned pads
- 2005
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 48:4, s. 492-498
-
Tidskriftsartikel (refereegranskat)abstract
- The primary objective of this study was to investigate the influence of surface texturing on hydrodynamic lubrication of tilting-pad thrust bearings in terms of bearing power loss, operating temperature, and oil-film thickness. For this purpose, the working faces of six thrust pads from a 228.6-mm-outer-diameter bearing were textured. The textured surface consisted of a system of crossing channels of less than 10 Όm in depth. Tests were conducted with a VG68 mineral turbine oil supplied to the bearings at a constant temperature of 50°C and flow rate of 15 L/min. The following parameters were measured: frictional torque, pad and collar temperatures, oil-film thickness, and pressure profiles along two circumferential lines. No significant change in collar and pad temperature could be observed when the patterned bearing was used. However, the textured bearing showed a tendency to exhibit lower power loss especially when an optimum oil flow supply rate was used. At the same time, inlet and outlet film thicknessesfor the patterned bearing showed larger values than those obtained during tests on the plain babbitt pads.
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| 43. |
- Green, Torbjörn M., et al.
(författare)
-
A new method to visualize grease flow in a double restriction seal using microparticle image velocimetry
- 2011
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 54, s. 784-792
-
Tidskriftsartikel (refereegranskat)abstract
- A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.
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| 44. |
- Gustavsson, Fredrik, et al.
(författare)
-
A High-Resolution TEM/EELS Study of the Effect of Doping Elements on the Sliding Mechanisms of Sputtered WS2 Coatings
- 2015
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 58:1, s. 113-118
-
Tidskriftsartikel (refereegranskat)abstract
- It has been shown many times that cosputtering low-friction coatings of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) with other elements can improve the structural, mechanical, and tribological properties. To achieve the lowest friction, MoS2 or WS2 should be doped with element(s) improving the hardness and density of the coatings. On the other hand, such elements, or their compounds, should not be present in the outermost molecular layers at the sliding interface. This article suggests that there are important differences between how MoS2 and WS2 coatings respond to or react with doping elements, despite the almost identical structure and behavior of the undoped materials. Two systems have been investigated by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) electron energy loss spectroscopy (EELS), W-S-C-Cr and W-S-C-Ti, and showed significant amounts of oxides, which typically formed a layer just underneath the crystalline WS2 top layer. Further, carbon was almost completely absent in the tribofilms, despite the fact that the as-deposited coatings contained as much as 40-50 at% C. An interesting observation here is that WS2 basal planes surround or embed Fe wear particles, suggesting a relatively strong adhesion or a Fe-S chemical bonding between iron/steel and WS2. The result of this is that the wear particles become pacified and remain in the contact as low-friction material.
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| 45. |
- Hernandez, Sinuhe, et al.
(författare)
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High-Temperature Friction and Wear of Boron Steel and Tool Steel in Open and Closed Tribosystems
- 2018
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 61:3, s. 448-458
-
Tidskriftsartikel (refereegranskat)abstract
- More and more components in automotive, material processing and mining industries are operating under harsh conditions involving high temperatures and high contact pressures. Tribotesting for such applications is done using both open (one surface meeting a fresh counter-surface) and closed (one surface follows the same track on the counter-surface) test configurations. In order to enable development of new materials and processes intended for such conditions, there is a need for better understanding pertaining to tribological phenomena occurring under these different test configurations.In this work, friction and wear characteristics of quenched and tempered tool steel sliding against boron steel (22MnB5) have been studied. The experiments were conducted using a specially designed hot strip tribometer (HST) under dry conditions at R.T. and 400°C in open as well as closed configurations. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were carried out to analyse the worn surfaces. Additionally, the results from the closed test configuration were compared to previous tests carried out with the same materials and parameters using a pin-on-disk (POD) test rig. The results have shown that wear was reduced at higher temperatures as well as with repeated sliding on the same contacting surfaces (i.e. closed configuration) compared to those with open configuration. A good correlation of wear mechanisms and coefficient of friction between closed configuration tests and those carried out with the POD test rig was observed especially at 400°C.
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| 46. |
- Johansson, Jens E., et al.
(författare)
-
Improving Hypoid Gear Oil Pitting Performance through Friction Reduction
- 2020
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 63:2, s. 280-295
-
Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have shown that the load-dependent friction behavior of various gear oils can affect their pitting performance; that is, low friction resulted in a long pitting life. These studies were limited, however, to test methods and running conditions quite different from those occurring in actual gear transmissions. In the present study, a more gear-like twin-disc machine with test specimens and running conditions relevant for gear contacts was used to investigate whether the same trends could be found. To analyze this possible correlation, the first step was to prepare a set of hypoid gear oils and to test their friction performance to compare various ways of improving friction behavior but also to form an understanding of why their friction performance varied. The second step was to test the pitting performance of the oils. The pitting results could then be compared to the friction properties of the oils to analyze the correlation. Other possible mechanisms behind the formation of pits are also discussed. The results show that for the oils included, the antiwear and extreme-pressure additive package and the base oil type affect friction. The results further show that additive combinations and/or base oils that result in low friction lead to enhanced pitting performance.
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| 47. |
- Johansson, Jens, et al.
(författare)
-
Effects of gear oil properties on pitting life in rolling four-ball test configuration
- 2013
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 57:1, s. 104-113
-
Tidskriftsartikel (refereegranskat)abstract
- There is a connection between the efficiency of oils and their wear and/or surface damage protective properties, an area not so well described in the literature. One such damage mode is macroscale contact fatigue on gear tooth flank surfaces, also called pitting. The present study is aimed at investigating the correlation between gear oils' physical properties, important in terms of gear transmission losses, and pitting life. Eight gear oils were formulated giving different combinations of base oil, viscosity, and concentration of friction modifiers. All eight oils also contained an additive package designed to meet GL-5 specifications. This study consists of three parts. In the first, the oils' physical properties were measured using a set of bench tests. In the second, the pitting lives of the oils were evaluated using rolling four-ball tests. The third part deals with the correlation between the measured physical properties of the oils and their pitting lives. This is achieved through multiple linear regression, with a view to finding the salient properties that have a significant influence on pitting life. The results show that gear oils' physical properties do have a large influence on the pitting lives. Oil properties that lower interfacial tangential stresses are beneficial in enhancing pitting life.
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| 48. |
- Khan, Sharjeel Ahmed, et al.
(författare)
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Surface Roughness Influence on Tribological Behavior of HiPIMS DLC Coatings
- 2023
-
Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 66:3, s. 565-575
-
Tidskriftsartikel (refereegranskat)abstract
- The application of diamond-like carbon (DLC) coatings in dry machining of difficult-to-machine materials has been gaining popularity due to high inertness, low coefficient of friction (COF), and high hardness of these coatings. Although the effect of surface roughness on the tribological properties of DLC coatings is of paramount importance, usually it is overlooked and coatings performance analysis was accomplished generally on highly polished substrates. The generation of polished surfaces is a time-consuming, labor-intensive process and, in most cases, not feasible for the industry due to its high cost. This article focuses on determining the effect of substrate (cemented carbide, WC-Co) surface roughness on the load-bearing capacity and tribological properties of DLC coatings deposited by High Power Impulse Magnetron Sputtering (HiPIMS) in Ne–Ar gas plasma. The DLC films were deposited onto WC-Co substrates with three different surface roughness profiles and their tribological performance were evaluated using a reciprocating tribotest. The high surface roughness resulted in increased wear rate due to high levels of asperities and increased potential for premature delamination of the coatings, while also causing severe damage to the counterbody due to inhibition of transfer film formation.
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| 49. |
- Kohli, A. K., et al.
(författare)
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Contact pressure dependency in frictional behaviour of burnished molybdenum disulphide coatings
- 2001
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 44:1, s. 147-151
-
Tidskriftsartikel (refereegranskat)abstract
- The drop of coefficient of friction of MoS2 coatings with increase in contact pressure has been reported by various earlier researchers. Different hypothesis have been put forward to explain this phenomenon. This paper covers details of experiments carried out to investigate this further. Experiments have been carried out on reciprocating sliding wear and friction machine to bring out the influence of different parameters on the tribological behavior of MoS2 films. Role of frictional heating in this behavior has also been brought out. It is concluded that frictional properties of MoS2 are dependent on prevalent humidity as well as contact pressure and the drop of μ with contact pressure is independent of frictional heating.
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| 50. |
- Larsson, Roland, et al.
(författare)
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Observations in transiently loaded EHL contacts under pure sliding conditions
- 1998
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Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 41:4, s. 489-496
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Tidskriftsartikel (refereegranskat)abstract
- An elastohydrodynamically lubricated contact is experimentally investigated during loading and pure sliding motion. This is a combination of motions where lubricant film failures sometimes occur. The experimental setup consists of a 70-mm diam. ball segment mounted on a pendulum. The ball segment can be rotated while it impacts a lubricated glass disc. The deformation of the surfaces in the contact region is studied by means of optical interferometry and high-speed video recording equipment. Two poly-α-olefin-type lubricants with viscosities of 94 and 2600 mm2/s are used in the experiments. The squeeze velocity, i.e., the normal approach velocity, is approximately 0.06 m/s, giving an impact time of about 20 ms. The sliding velocity is varied from 0 to 34 m/s. Some of the observed phenomena are that lubricant film breakdown occurs at high sliding velocities while full film is maintained at no or low sliding velocity and that the traditional horseshoe-shaped fringes are found even for this load situation. At very high sliding velocities, the interferograms are distorted from their normal circular shape to a pear-like shape. (
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