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Influence of a single axisymmetric asperity on surface stresses during dry rolling contact
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).ORCID iD: 0000-0001-6896-1834
2007 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 29, no 5, 909-921 p.Article in journal (Refereed) Published
Abstract [en]

The effect from contact loading of some single axisymmetric asperities as a potential mechanism for surface initiated rolling contact fatigue was investigated numerically using FEM. Computational results were compared to properties of some rolling contact fatigue craters, or spalls, in the teeth surfaces of four driving gear wheels. The gears were geometrically identical but had experienced slightly varying load conditions. The residual surface stresses of a used teeth with spalls were measured using the hole drilling technique. The combined cylinder asperity contact was first modelled with a stationary model in which an asperity was introduced at the contact rim. By varying asperity height, width, position and contact load dangerous asperity configurations were sought for. The gear contact close to the rolling circle was modelled as two rolling cylinders. A single asperity was introduced into the contact surface of one of them. Due to the presence of the asperity a three-dimensional contact model was required. The simulation included residual stresses from heat treatment and plastic deformation due to the first roll cycle. Thus, the stress results were computed from the second roll cycle. The important overall conclusion was that a single asperity may serve as a stress raiser in the contact surfaces. Furthermore, the computed values of the increased surface stresses were comparable to those that are reported in the literature to give cracks. Example of dangerous asperity dimensions were noted and changes in residual stresses from moderate plastic deformation during rolling were estimated. The asperity deformed plastically during over-roll but remained sufficiently high. The trajectory of the largest principal stress was computed, starting from the position in front of a loaded asperity with maximum tensile stress. The trajectory was compared to the spalling entry angle of a representative spall. For some asperity-cylinder configurations a convex region with large stress was found in the surface. The presence of such a convex stress region was compared to the convex shaped of the spalling tip that sometimes could be found.

Place, publisher, year, edition, pages
2007. Vol. 29, no 5, 909-921 p.
Keyword [en]
rolling contact fatigue, spalling, asperity, residual stress
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-7770DOI: 10.1016/j.ijfatigue.2006.08.002ISI: 000245773000013Scopus ID: 2-s2.0-33846186866OAI: oai:DiVA.org:kth-7770DiVA: diva2:12895
Note
QC 20100702Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2011-11-11Bibliographically approved
In thesis
1. On the asperity point load mechanism for rolling contact fatigue
Open this publication in new window or tab >>On the asperity point load mechanism for rolling contact fatigue
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Rolling contact fatigue is a damage process that may arise in mechanical applications with repeated rolling contacts. Some examples are: gears; cams; bearings; rail/wheel contacts. The resulting damage is often visible with the naked eye as millimeter sized surface craters. The surface craters are here denoted spalls and the gear contact served as a case study.

The work focused on the asperity point load mechanism for initiation of spalls. It was found that the stresses at asperity level may be large enough to initiate surface cracking, especially if the complete stress cycle was accounted for.

The gear contact is often treated as a cylindrical contact. The thesis contains experimental and numerical results connected to rolling contact fatigue of cylindrical contacts. At the outset a stationary cylindrical contact was studied experimentally. The stationary test procedure was used instead of a rolling contact. In this way the number of contact parameters was minimized. The cylindrical contact resulted in four different contact fatigue cracks. The two cracks that appeared first initiated below the contact. The other two cracks developed at the contact surface when the number of load cycles and the contact load increased.

The influence of a surface irregularity (asperity) was studied numerically with the Finite Element Method (FEM). Firstly, the stationary contact was modelled and investigated numerically. At the cylindrical contact boundary a single axisymmetric was included. The partially loaded asperity introduced a tensile surface stress, which seen from the asperity centre was radially directed. Secondly, FE simulations were performed where a single axisymmetric asperity was over-rolled by a cylindrical contact. The simulations were performed for pure rolling and rolling with slip. For both situations, tensile forward directed stresses in front of the asperity were found. The presence of slip and a surface traction greatly increased the stresses in front of the asperity. Finally, when rolling started from rest with applied slip, the distance to steady-state rolling was determined for elastic similar cylindrical rollers.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 14 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0440
Keyword
Rolling contact fatigue, Spalling, Asperity contact, Point load; Micro-cracks, Traction, Applied slip
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-4569 (URN)
Public defence
2007-12-17, F3, Lindstedsvägen 26, Stockholm, KTH, 10:15
Opponent
Supervisors
Note

QC 20100702

Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2013-01-14Bibliographically approved
2. A numerical and experimental investifgation on surface and sub-surface initiation of contact fatigue cracks at cylindrical contacts
Open this publication in new window or tab >>A numerical and experimental investifgation on surface and sub-surface initiation of contact fatigue cracks at cylindrical contacts
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 13 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 95
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-3887 (URN)
Presentation
2006-03-07, Sal D3, Lindstedsvägen 5, Stockholm, 10:15
Opponent
Supervisors
Note

QC 20101111

Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2013-01-15Bibliographically approved

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