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A numerical and experimental investifgation on surface and sub-surface initiation of contact fatigue cracks at cylindrical contacts
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
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: urn:nbn:se:kth:diva-3887OAI: oai:DiVA.org:kth-3887DiVA: diva2:9879
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
List of papers
1. Standing contact fatigue with a cylindrical indenter
Open this publication in new window or tab >>Standing contact fatigue with a cylindrical indenter
2005 (English)In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 28, no 7, 599-613 p.Article in journal (Refereed) Published
Abstract [en]

A hardened steel cylinder was repeatedly pressed against a flat case-hardened steel specimen that was equally wide as the cylinder was long. Some contact end effects were noted as a result of limited plastic deformation. A strain gauge on the contact surface, just outside the contact and oriented perpendicular to the cylinder detected a surface strain when the cylinder was loaded. The non-zero surface strain was the result of boundary effects of the finite specimen. Four different types of contact fatigue cracks developed in and below the specimen contact surface. The cracks were named lateral, median, contact end and edge cracks. Changes in the measured surface strain values could be used to determine when the lateral and edge cracks developed. The order in which all four crack types typically developed was determined from optical crack observation at test termination, strain measurements and stress computations. Numerical computations using finite-element (FE) analyses were used to verify the surface strain behaviour due to loading and cracking, to verify contact end effects; crack locations and crack orientation by aid of the Findley multi-axial fatigue criterion.

Keyword
contact fatigue, lateral crack, spalling, sub-surface cracks
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-7769 (URN)10.1111/j.1460-2695.2005.00904.x (DOI)000229934300003 ()2-s2.0-21344454861 (Scopus ID)
Note
QC 20100702Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved
2. Influence of a single axisymmetric asperity on surface stresses during dry rolling contact
Open this publication in new window or tab >>Influence of a single axisymmetric asperity on surface stresses during dry rolling contact
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.

Keyword
rolling contact fatigue, spalling, asperity, residual stress
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-7770 (URN)10.1016/j.ijfatigue.2006.08.002 (DOI)000245773000013 ()2-s2.0-33846186866 (Scopus ID)
Note
QC 20100702Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2017-12-14Bibliographically approved

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