30 results found
De Laurentis N, Cann P, Lugt PM, et al., 2017, The Influence of Base Oil Properties on the Friction Behaviour of Lithium Greases in Rolling/Sliding Concentrated Contacts, TRIBOLOGY LETTERS, Vol: 65, ISSN: 1023-8883
Guegan J, Kadiric A, Gabelli A, et al., 2017, Reply to the 'Comment on "The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness'' by Guegan, Kadiric, Gabelli, & Spikes' by Scott Bair, TRIBOLOGY LETTERS, Vol: 65, ISSN: 1023-8883
Hajishafiee A, Kadiric A, Ioannides S, et al., 2017, A coupled finite-volume CFD solver for two-dimensional elasto-hydrodynamic lubrication problems with particular application to rolling element bearings, TRIBOLOGY INTERNATIONAL, Vol: 109, Pages: 258-273, ISSN: 0301-679X
Kanazawa Y, Sayles RS, Kadiric A, 2017, Film formation and friction in grease lubricated rolling-sliding non-conformal contacts, TRIBOLOGY INTERNATIONAL, Vol: 109, Pages: 505-518, ISSN: 0301-679X
Morales-Espejel GE, Rycerz P, Kadiric A, 2017, Prediction of micropitting damage in gear teeth contacts considering the concurrent effects of surface fatigue and mild wear, Wear, Vol: 398-399, Pages: 99-115, ISSN: 0043-1648
The present paper studies the occurrence of micropitting damage in gear teeth contacts. An existing general micropitting model, which accounts for mixed lubrication conditions, stress history, and fatigue damage accumulation, is adapted here to deal with transient contact conditions that exist during meshing of gear teeth. The model considers the concurrent effects of surface fatigue and mild wear on the evolution of tooth surface roughness and therefore captures the complexities of damage accumulation on tooth flanks in a more realistic manner than hitherto possible. Applicability of the model to gear contact conditions is first confirmed by comparing its predictions to relevant experiments carried out on a triple-disc contact fatigue rig. Application of the model to a pair of meshing spur gears shows that under low specific oil film thickness conditions, the continuous competition between surface fatigue and mild wear determines the overall level as well as the distribution of micropitting damage along the tooth flanks. The outcome of this competition in terms of the final damage level is dependent on contact sliding speed, pressure and specific film thickness. In general, with no surface wear, micropitting damage increases with decreasing film thickness as may be expected, but when some wear is present micropitting damage may reduce as film thickness is lowered to the point where wear takes over and removes the asperity peaks and hence reduces asperity interactions. Similarly, when wear is negligible, increased sliding can increase the level of micropitting by increasing the number of asperity stress cycles, but when wear is present, an increase in sliding may lead to a reduction in micropitting due to faster removal of asperity peaks. The results suggest that an ideal situation in terms of surface damage prevention is that in which some mild wear at the start of gear pair operation adequately wears-in the tooth surfaces, thus reducing subsequent micropitting, fo
Rycerz P, Olver A, Kadiric A, 2017, Propagation of surface initiated rolling contact fatigue cracks in bearing steel, INTERNATIONAL JOURNAL OF FATIGUE, Vol: 97, Pages: 29-38, ISSN: 0142-1123
Rydel JJ, Pagkalis K, Kadiric A, et al., 2017, The correlation between ZDDP tribofilm morphology and the microstructure of steel, TRIBOLOGY INTERNATIONAL, Vol: 113, Pages: 13-25, ISSN: 0301-679X
De Laurentis N, Kadiric A, Lugt P, et al., 2016, The influence of bearing grease composition on friction in rolling/sliding concentrated contacts, TRIBOLOGY INTERNATIONAL, Vol: 94, Pages: 624-632, ISSN: 0301-679X
Guegan J, Kadiric A, Gabelli A, et al., 2016, The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness, TRIBOLOGY LETTERS, Vol: 64, ISSN: 1023-8883
Kadiric A, Rycerz P, 2016, Influence of contact conditions on the onset of micropitting in rolling-sliding contacts pertinent to gear applications, AGMA 2016 - Fall Technical Meeting
Copyright © 2016 American Gear Manufacturers Association. Micropitting is a type of rolling contact fatigue surface damage that occurs in concentrated, rolling-sliding contacts, such as those between gear teeth. In contrast to macropitting, where the damage initiates and progresses on the macro contact level, micropitting damage initiates on the surface asperity level. Despite the fact that it is one of the major modes of gear failure, there are currently no universally accepted design guidelines for prevention of micropitting. This paper attempts to provide further understanding on the tribological conditions that may lead to the onset of micropitting in lubricated, concentrated contacts representative of those occurring between gear teeth. In particular, an attempt is made to establish the effect of slide-roll ratio on the extent of microptting. Experimental results obtained on a triple-disc microptting rig under conditions designed to isolate the effects of slide-roll ratio and specific film thickness are presented. In parallel, the potential effect of sliding on film thickness is studied experimentally using a well-proven optical interferometry technique. The results show that increasing the slide-roll ratio increases the extent of micropitting but that the mechanisms responsible for this are not related to any potential effects of the slide-roll ratio on prevalent film thickness as suggested elsewhere, but rather to the increased number of asperity stress cycles at higher slide-roll ratios.
Guegan J, Kadiric A, Spikes H, 2015, A Study of the Lubrication of EHL Point Contact in the Presence of Longitudinal Roughness, TRIBOLOGY LETTERS, Vol: 59, ISSN: 1023-8883
Nyqvist J, Kadiric A, Ioannides S, et al., 2015, Semi-analytical model for rough multilayered contacts, TRIBOLOGY INTERNATIONAL, Vol: 87, Pages: 98-112, ISSN: 0301-679X
Christodoulias AI, Olver AV, Kadiric A, et al., 2014, The efficiency of a simple spur gearbox - A thermally coupled lubrication model, Pages: 81-98
Copyright © 2014, American Gear Manufacturers Association. A thermally coupled efficiency model for a simple dip-lubricated gearbox is presented. The model includes elastohydrodynamic (EHL) friction losses in gear teeth contacts as well as bearing, seal and churning losses. An iterative numerical scheme is used to fully account for the effects of contact temperature, pressure and shear rates on EHL friction. The model is used to predict gearbox efficiency with selected transmission oils whose properties were first obtained experimentally through rolling-sliding tribometer tests under representative contact conditions. Although the gearbox was designed using standard methods against a fixed rating, the model was used to study efficiency over a much wider range of conditions. Results are presented to illustrate the relative contribution of different sources of energy loss and the effect of lubricant properties on the overall gearbox efficiency under varying operating conditions.
Fowell M, Ioannides S, Kadiric A, 2014, An Experimental Investigation into the Onset of Smearing Damage in Nonconformal Contacts with Application to Roller Bearings, TRIBOLOGY TRANSACTIONS, Vol: 57, Pages: 472-488, ISSN: 1040-2004
Fowell MT, Myant C, Spikes HA, et al., 2014, A study of lubricant film thickness in compliant contacts of elastomeric seal materials using a laser induced fluorescence technique, TRIBOLOGY INTERNATIONAL, Vol: 80, Pages: 76-89, ISSN: 0301-679X
Balcombe R, Fowell MT, Kadiric A, et al., 2013, Modeling the propagation of Rolling Contact Fatigue (RCF) cracks in the presence of lubricant, Pages: 3577-3579
Fowell MT, Kadiric A, Morales-Espejel G, et al., 2013, Smearing damage in rolling element bearings, Pages: 1135-1137
Guégan J, Kadiric A, Reddyhoff T, et al., 2013, Friction and lubrication of textured surfaces in elasto-hydrodynamic contacts, Pages: 1659-1661
Hajishafiee A, Dini D, Kadiric A, et al., 2013, A fully-coupled finite volume solver for elasto-hydrodynamic lubrication problems with particular application to rolling element bearings, Pages: 1105-1108
Imai Y, Sayles RS, Kadiric A, 2013, A study of the tribological benefits offered by various surface features and roughness conditions within grease-lubricated interfaces, Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2013, Pages: 134-140
The use of lubricant in machine elements requires a fundamental understanding of the lubrication mechanisms, particularly in components such as bearings and sliding parts. Various kinds of greases which have different concentration of thickener agent are studied as to whether there is an effect on the plastic deformation of surface roughness. On smooth surfaces, the fluid load support of all greases was the same or lower than the base oil because the entrapped base oil was not allowed to escape from the inside of the pre-indent. On rough surfaces, the fluid load support of all greases was higher than the base oil because the base oil was allowed to escape easily from pre-indent through the valleys of surface roughness, thus the base oil is not compressed enough and cannot support the load. On much rougher surfaces, the fluid load support of all greases decreased and there was no difference. Benefits are optimized by linking together the surface finish and the grease formulation. This is an abstract of paper presented at the 2013 STLE Annual Meeting and Exhibition (Detroit, MI 5/5-9/13).
Nyqvist JT, Kadiric A, Sayles RS, et al., 2013, Three-dimensional analysis of multilayered rough surface contacts, Pages: 181-183
Hajishafiee A, Dini D, Zaki T, et al., 2012, MODELLING ELASTO-HYDRODYNAMIC LUBRICATION USING CFD, 15th International Conference on Experimental Mechanics (ICEM), Publisher: INEGI-INST ENGENHARIA MECANICA E GESTAO INDUSTRIAL
Rycerz P, Kadiric A, Pasaribu R, et al., 2012, EFFECT OF ADDITIVES ON SURFACE PERFORMANCE, 15th International Conference on Experimental Mechanics (ICEM), Publisher: INEGI-INST ENGENHARIA MECANICA E GESTAO INDUSTRIAL
Nyqvist J, Kadiric A, Sayles R, et al., 2009, ROUGHNESS EFFECTS IN THERMO-MECHANICALLY LOADED CONTACTS, STLE/ASME 2008 International Joint Tribology Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 637-639
Underwood RJ, Sayles RS, Kadiric A, et al., 2009, An investigation of the load support of fluid trapped in dents, World Tribology Congress 2009 - Proceedings
The load support by lubricants trapped in a dent was investigated using combined experimental and modeling study. The plastic deformation of the pre-indent shoulders for the dry case was greater than for the lubricated case, indicating that the entrapped lubricant was supporting a significant proportion of the applied load. By varying the pre-indent geometry, the load support depended on the conformity of the contacting surfaces, the relative change in volume, and thus the pressure increase of the trapped lubricant. For a conforming geometry, and assuming no leakage of oil from the pre-indent, the entrapped lubricant can support 60% of the applied load, assuming 50% leakage, the entrapped lubricant supported 34% of the applied load. By ignoring the effect of lubricants trapped in dents, the fatigue life of rolling element bearings could be underestimated. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/209).
Kadiric A, Sayles RS, Ioannides E, 2008, Thermo-mechanical model for moving layered rough surface contacts, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 130, ISSN: 0742-4787
Kadiric A, Sayles RS, Ioannides E, 2006, Thermo-mechanical effects in layered rough surface contacts, Proceedings of STLE/ASME International Joint Tribology Conference, IJTC 2006, Vol: 2006
A recently developed thermo-mechanical model was used to study the temperature distribution in a sliding contact of a cylinder and a coated real rough surface. The model conducts a full thermo-mechanical analysis of the contact including the interactions between the thermal and elastic displacements and full heat division. Following a brief description of the numerical model, results are presented to illustrate the thermo-mechanical effects of various contact parameters, coating properties and surface roughness structure Copyright © 2006 by ASME.
Kadiric A, Sayles RS, Zhou XB, et al., 2003, A numerical study of the contact mechanics and sub-surface stress effects experienced over a range of machined surface coatings in rough surface contacts, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 125, Pages: 720-730, ISSN: 0742-4787
Lee-Prudhoe I, Sayles RS, Kaderic A, 1999, Investigations Into Asperity Persistence in Heavily Loaded Contacts, Journal of Tribology, Vol: 121, Pages: 441-441, ISSN: 0742-4787
Lee-Prudhoe I, Sayles RS, Kaderic A, 1998, Investigations into asperity persistence in heavily loaded contacts, American Society of Mechanical Engineers (Paper), Pages: 1-8, ISSN: 0402-1215
Experimental results are presented along the lines of the early work of Moore (1948) where a hard smooth roller is pressed into a softer rough surface to study the resulting real to apparent areas of contact and their associated local contact pressures. Results are presented for a hard steel roller deforming mild-steel and aluminum-alloy rough surface specimens. An analysis of the local contact mechanics is performed before and after indentation using a recently developed numerical elastic contact simulation method which allows local asperity contact pressures and areas to be studied in detail. The method is shown to reveal the level and distribution of pressures and asperity contact areas prevalent during the indentation process, and therefore allows the contribution of elastic and plastic load support to be quantified. The persistence of asperities during such indentation tests is discussed in terms of the pressures the asperities can support in relation to reported mechanisms of persistence. Results of subsequent sub-surface stresses are also presented and discussed in terms of how the method might be used to create an elastic-plastic deformation model that can account for asperity persistence in future numerical contact simulation models.
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