Change search
Link to record
Permanent link

Direct link
BETA
Mofidi, Mohammad
Publications (9 of 9) Show all publications
Mofidi, M. & Prakash, B. (2010). Two body abrasive wear and frictional characteristics of sealing elastomers under unidirectional lubricated sliding conditions (ed.). Paper presented at . Tribology - Materials, Surfaces & Interfaces, 4(1), 26-37
Open this publication in new window or tab >>Two body abrasive wear and frictional characteristics of sealing elastomers under unidirectional lubricated sliding conditions
2010 (English)In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 4, no 1, p. 26-37Article in journal (Refereed) Published
Abstract [en]

Since abrasion is a common cause of seal failures, understanding the mechanisms of abrasion of an elastomer in the presence of lubricants is of importance in sealing applications. In this research a block on ring configuration was used to study the influence of lubrication on the two body abrasion of several commonly used sealing elastomers (two acrylonitrile butadiene rubbers, an acrylic rubber and a fluoro rubber). The friction force and the abrasive wear of the samples were measured and the worn surfaces and wear particles were investigated using an optical microscope. The tear strength of the elastomers before and after immersion in monoester oil as well as the oil absorption has been measured. Both scratches (parallel to the direction of sliding) and ridges (perpendicular to the direction of sliding) were observed on the worn surfaces of nitrile rubbers but the surfaces of acrylic and fluoro rubber were characterised by scratches only. The worn surfaces of nitrile rubbers were defined with more continuous ridges at lower sliding velocity and the presence of a lubricant in the contact reduced the continuous ridges. Examination of the wear particles shows that the wear particles (particularly for acrylic rubber) under dry sliding condition were aggregated, but the lubricant dispersed the wear particles and prevented aggregation. In most cases, abrasive wear of the elastomers under lubricated condition is higher than that under dry condition. The results show that the friction coefficient increased with increasing sliding velocity and decreased with contact pressure. Apart from the fluoro rubber, the friction coefficient as well as the tear strength of the elastomers decreased significantly in the presence of lubricant, particularly for acrylic rubber.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-10945 (URN)10.1179/175158310X481745 (DOI)2-s2.0-77950113832 (Scopus ID)9d6b3e40-3765-11df-be5c-000ea68e967b (Local ID)9d6b3e40-3765-11df-be5c-000ea68e967b (Archive number)9d6b3e40-3765-11df-be5c-000ea68e967b (OAI)
Note
Godkänd; 2010; 20100324 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Mofidi, M. (2009). Tribology of elastomeric seal materials (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Tribology of elastomeric seal materials
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Elastomers are the most commonly used materials for various sealing applications owing to their low modulus of elasticity, large elongation-at-break, and high Poisson's ratio. Most seals operate in the presence of lubricants; therefore the sealing elastomeroil interaction plays an important role in determining the tribological performance of elastomers. Furthermore, at times, such as starting up periods, the seals may also operate under dry condition and the seal material can be affected by high friction coefficient and wear.In this work, the tribological behaviour of different sealing elastomers has been studied. The influence of ageing of a sealing elastomer in different lubricants on its tribological behaviour has been investigated. Further studies pertaining to the influence of lubrication on the abrasive wear of a sealing elastomer have also been carried out.The results show that the friction coefficient of an elastomer in lubricated sliding against a hard counterface, at low contact pressure, depends on the surface topography of the elastomer but at high contact pressure, it is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. (Even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction). Ageing of the nitrile rubber in ester base fluids leads to reduction of friction coefficient.In unidirectional dry sliding of an elastomer against a counterface, the friction coefficient decreases during the running-in period. The longest running-in periods have been observed when the elastomers slide against relatively smooth surfaces. Depending on the elastomer-lubricant compatibility, abrasive coarseness, geometry of sliding contact area and contact pressure, the two body abrasive wear of elastomers may increase or decrease in presence of lubricants.Aging of nitrile rubber in lubricating fluids increases the abrasive wear both in dry and lubricated conditions. The abrasive wear of nitrile rubber in ester base fluids and rapeseed oil are higher than that in the mineral oils.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2009. p. 121
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-18512 (URN)8fa29f20-17c1-11de-b1a6-000ea68e967b (Local ID)978-91-86233-26-6 (ISBN)8fa29f20-17c1-11de-b1a6-000ea68e967b (Archive number)8fa29f20-17c1-11de-b1a6-000ea68e967b (OAI)
Note

Godkänd; 2009; 20090323 (mohmof); DISPUTATION Ämnesområde: Maskinelement Opponent: Professor Jozé Vizintin, University of Ljubljana, Slovenien Ordförande: Professor Braham Prakash, Luleå tekniska universitet Tid: Fredag den 17 april 2009, kl 10.00 Plats: D 770, Luleå tekniska universitet

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-02-26Bibliographically approved
Mofidi, M., Simmons, G. & Prakash, B. (2008). Friction and wear characteristics of elastomers in lubricated contact with EALs (ed.). Paper presented at Nordic Symposium on Tribology : 10/06/2008 - 13/06/2008. Paper presented at Nordic Symposium on Tribology : 10/06/2008 - 13/06/2008.
Open this publication in new window or tab >>Friction and wear characteristics of elastomers in lubricated contact with EALs
2008 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

The friction and wear characteristics of several elastomers have been studied during reciprocating sliding conditions when lubricated with uncontaminated environmentally adapted lubricants and the same lubricants contaminated with moisture. The elastomers studied are Nitrile Butadiene Rubber (NBR), Hydrogenated Nitrile Butadiene Rubber (HNBR), and Fluorocarbon Rubber (FKM). The lubricants used are complex ester and polyol ester as well as both aged and non-aged polyol esters with 5% water content. Experiments were conducted using a Cameron-Plint test rig with a steel cylinder sliding in the longitudinal direction with a reciprocating motion against a curved elastomer specimen to avoid any edge contact. Sliding velocities were maintained low to reduce the thermal effects often associated with elastomer friction. In these tests, HNBR resulted in the lowest friction, with NBR the highest. The NBR specimens most often experienced wear, while FKM and HNBR experienced very little wear. The various oils, with some exceptions, had similar friction performance both at the higher and the lower loads. Experiments were also conducted using an SRV Optimol test rig at higher frequencies with a steel cylinder in contact with an elastomer mounted on a steel disc. The results from the SRV test rig differed significantly with those of the Cameron-Plint rig with FKM resulting the greatest wear and NBR producing minimal wear. This difference was primarily caused by the differences in contact geometry and the operating parameters between the tests.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-30021 (URN)3b0127d0-3ac6-11dd-8e42-000ea68e967b (Local ID)3b0127d0-3ac6-11dd-8e42-000ea68e967b (Archive number)3b0127d0-3ac6-11dd-8e42-000ea68e967b (OAI)
Conference
Nordic Symposium on Tribology : 10/06/2008 - 13/06/2008
Note
Godkänd; 2008; Bibliografisk uppgift: Værtspublikationsredaktører: Jaakko Kleemola Værtspublikationsredaktører: Arto Lehtovaara Titel på proceedings: Proceedings of NORDTRIB 2008 Undertitel på proceedings: 13th Nordic Symposium on Tribology; 20080615 (brap)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-01-14Bibliographically approved
Mofidi, M. & Prakash, B. (2008). Influence of counterface topography on sliding friction and wear of some elastomers under dry sliding conditions (ed.). Paper presented at . Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 222(5), 667-673
Open this publication in new window or tab >>Influence of counterface topography on sliding friction and wear of some elastomers under dry sliding conditions
2008 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 222, no 5, p. 667-673Article in journal (Refereed) Published
Abstract [en]

In this work, the friction and wear behaviour of acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), acrylate rubber (ACM), and fluoroelastomer (FKM) against steel surfaces under unidirectional dry sliding conditions have been studied. The influence of surface roughness of the steel counterface on friction and wear was studied using a block-on-ring test configuration. At low load, the friction coefficient decreased after a running-in period and the wear was insignificant, especially for the ACM and FKM. The running-in time in terms of achieving a stable dry friction for the different elastomers, from longest to shortest, is in the order HNBR, NBR, FKM, and ACM, with an exception in case of FKM sliding against a smooth steel counterface. At higher contact pressure, powdery worn particles on the ACM and a decrease in friction coefficient were observed, but for FKM and HNBR, worn particles with roll shapes were produced. The worn particles of FKM were significantly larger than those of the other tested materials, and a considerably higher wear in FKM was observed.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-14236 (URN)10.1243/13506501JET392 (DOI)000259516900004 ()2-s2.0-54349124829 (Scopus ID)d9764870-6f99-11dd-8151-000ea68e967b (Local ID)d9764870-6f99-11dd-8151-000ea68e967b (Archive number)d9764870-6f99-11dd-8151-000ea68e967b (OAI)
Note
Validerad; 2008; 20080821 (brap)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Mofidi, M., Prakash, B., Persson, B. & Albohr, O. (2008). Rubber friction on (apparently) smooth lubricated surfaces (ed.). Paper presented at . Journal of Physics: Condensed Matter, 20(8)
Open this publication in new window or tab >>Rubber friction on (apparently) smooth lubricated surfaces
2008 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 8Article in journal (Refereed) Published
Abstract [en]

We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving ( apparently) smooth surfaces.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-13153 (URN)10.1088/0953-8984/20/8/085223 (DOI)000254100700027 ()2-s2.0-62249165823 (Scopus ID)c55b2300-0226-11dd-9241-000ea68e967b (Local ID)c55b2300-0226-11dd-9241-000ea68e967b (Archive number)c55b2300-0226-11dd-9241-000ea68e967b (OAI)
Note
Validerad; 2008; Bibliografisk uppgift: Paper id:: 85223; 20080404 (pafi)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Mofidi, M. & Prakash, B. (2008). The influence of lubrication on two body abrasive wear of sealing elastomers (ed.). In: (Ed.), Jaakko Kleemola; Arto Lehtovaara (Ed.), Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008. Paper presented at Nordic Symposium on Tribology : 10/06/2008 - 13/06/2008. Tampere: Tampere University of Technology
Open this publication in new window or tab >>The influence of lubrication on two body abrasive wear of sealing elastomers
2008 (English)In: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Conference paper, Published paper (Refereed)
Abstract [en]

Elastomeric seals are prone to failure caused by abrasion during sliding against rough surfaces. In this research, the two body abrasive wear of sealing elastomers in dry and lubricated conditions has been studied. A two body abrasive wear tester has been used to investigate the abrasive wear of the elastomers under varying test parameters. This test aparatus reciprocates a rectangular elastomeric sample against an abrasive paper wrapped around the circumferential surface of a wheel. The samples were weighed using an accurate scale before and after the tests to quantify the abrasive wear. The experiments have been carried out at varying normal load and abrasive size in dry and lubricated conditions. The influence of two different lubricants, including a synthetic ester and a mineral oil, together with the test parameters on the abrasive wear has been studied. The results show that, depending on the material, lubricant, abrasive size, normal load and test duration, the abrasive wear of elastomers may increase or decrease in the presence of lubricants, however, in most cases, the abrasive wear in the lubricated condition is higher than that in the dry condition. The influence of lubricant on the increase in abrasive wear is more significant when a fine abrasive is used. Increase in the abrasive wear in presence of the synthetic ester is more pronounced than in presence of the mineral oil.

Place, publisher, year, edition, pages
Tampere: Tampere University of Technology, 2008
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-32751 (URN)7568d390-3ac7-11dd-8e42-000ea68e967b (Local ID)978-952-15-1959-8 (ISBN)7568d390-3ac7-11dd-8e42-000ea68e967b (Archive number)7568d390-3ac7-11dd-8e42-000ea68e967b (OAI)
Conference
Nordic Symposium on Tribology : 10/06/2008 - 13/06/2008
Note
Godkänd; 2008; 20080615 (brap)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-01-14Bibliographically approved
Mofidi, M., Kassfeldt, E. & Prakash, B. (2008). Tribological behaviour of an elastomer aged in different oils (ed.). Paper presented at . Tribology International, 41(9-10), 860-866
Open this publication in new window or tab >>Tribological behaviour of an elastomer aged in different oils
2008 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 9-10, p. 860-866Article in journal (Refereed) Published
Abstract [en]

This paper presents the influence of aging the nitrile rubber, the most popular seal material, in various base fluids on sliding friction and abrasive wear. The lubricants used are synthetic esters, natural esters, different types of mineral base oils, poly-*-olefins and very high viscosity index oils. Friction has been studied for two directions of motion with respect to lay on the elastomer sample by using the SRV Optimol test machine. These findings show that as compared to all other lubricant formulations, ageing the elastomer in polyol ester leads to the maximum reduction of friction coefficient especially in perpendicular sliding to the initial lay on the surface. The abrasive wear studies were carried out by using a two-body abrasive wear tester against dry and lubricated elastomer. It was interesting to note that two-body abrasive wear of elastomeric material was higher during rubbing in presence of the fluids as compared to that in dry condition. Further, aging the elastomer in these base fluids especially in ester base fluids, results in more abrasive wear.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-3942 (URN)10.1016/j.triboint.2007.11.013 (DOI)000257736800007 ()2-s2.0-44749085458 (Scopus ID)1c9f5160-3ace-11dd-8e42-000ea68e967b (Local ID)1c9f5160-3ace-11dd-8e42-000ea68e967b (Archive number)1c9f5160-3ace-11dd-8e42-000ea68e967b (OAI)
Note
Validerad; 2008; Bibliografisk uppgift: Nordtrib 2006; 20080615 (brap)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Mofidi, M. (2007). Tribology of elastomers (ed.). (Licentiate dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Tribology of elastomers
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this work, the tribological behaviour of different sealing elastomers has been studied. The influence of aging of a sealing elastomer in different lubricants on its tribological behaviour has been investigated. Tribological behaviour of sealing elastomers in dry condition and the mechanisms occurring in run-in period have been studied. Further studies pertaining to the influence of lubrication on the abrasive wear of a sealing elastomer have also been carried out.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2007. p. 34
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757 ; 2007:62
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-18278 (URN)7bfd3400-9dc2-11dc-9810-000ea68e967b (Local ID)7bfd3400-9dc2-11dc-9810-000ea68e967b (Archive number)7bfd3400-9dc2-11dc-9810-000ea68e967b (OAI)
Note

Godkänd; 2007; 20071128 (ysko)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-02-26Bibliographically approved
Mofidi, M., Kassfeldt, E. & Prakash, B. (2006). Influence of ageing an elastomer lubricating fluids on its tribological behavior (ed.). In: (Ed.), (Ed.), 12th Nordic Symposium on Tribology, NORDTRIB 2006: LO-skolen, Helsingør, Denmark, June 7-9 2006. Paper presented at Nordic Symposium on Tribology : 07/06/2006 - 09/06/2006. Kongens Lyngby: Technical University of Denmark
Open this publication in new window or tab >>Influence of ageing an elastomer lubricating fluids on its tribological behavior
2006 (English)In: 12th Nordic Symposium on Tribology, NORDTRIB 2006: LO-skolen, Helsingør, Denmark, June 7-9 2006, Kongens Lyngby: Technical University of Denmark , 2006Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Kongens Lyngby: Technical University of Denmark, 2006
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-26844 (URN)01a3fac0-c269-11db-9ea3-000ea68e967b (Local ID)87-90416-17-1 (ISBN)01a3fac0-c269-11db-9ea3-000ea68e967b (Archive number)01a3fac0-c269-11db-9ea3-000ea68e967b (OAI)
Conference
Nordic Symposium on Tribology : 07/06/2006 - 09/06/2006
Note
Godkänd; 2006; Bibliografisk uppgift: 1 CD-ROM; 20070122 (elka)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-01-14Bibliographically approved

Search in DiVA

Show all publications