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A study on contact fatigue mechanisms
KTH, Superseded Departments, Solid Mechanics.ORCID iD: 0000-0001-6896-1834
2000 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Surfaces subjected to rolling and sliding contacts maysuffer from contact fatigue. This thesisdeals with solidmechanic aspects of contact fatigue including the descriptionand verificationof explaining mechanisms. The new mechanism forsurface initiated contact fatigue is basedon tensile surfacestresses from local asperity contacts. It is also realised thatsub-surfaceinitiated contact fatigue is the result of tensileresidual stresses that emanate from plasticdeformation belowthe surface. These mechanisms clearly show that contact fatiguecracksfollow the same rules as ordinary fatigue cracks inhardened steel.

The thesis contains four papers that treat a new testprocedure named Standing ContactFatigue (SCF). The results ofthe test procedure have played an important role inthedevelopment and verification of the mechanisms for surfaceand sub-surface contact fatigue.

The first part of the research work was experimental. Inthis part the SCF test properties wasdecided, crack resultsconfirmed and crack detection methods developed. Herecomparativestudies were performed using some differentmaterials and mechanical properties. It wasverified that SCFcould detect differences in contact fatigue resistance.

Next a finite element model of the SCF test was evaluatedthrough the general-purposeprogram MARC. The model includedgraded material properties that originate from heattreatment.The residual surface deformation and surface compliance wereverified againstexperimental results. Crack initiation wasinvestigated in two ways. Firstly, the principalstresses atcritical locations were computed and plotted in a Haighdiagram. The diagramshowed that the cracks initiate in adirection perpendicular to the principal stress with thelargeststress range provided that the principal stress is tensilesometime during the load cycle.

Secondly, some high cycle multiaxial fatigue criteria,including the Haigh principal stresscriterion, was evaluatedagainst the SCF crack initiation results. The surface cracklocation waspredicted by including statistical effects using aweakest-link criterion and a three-parameterWeibulldistribution.

The SCF crack propagation was investigated by numericalevaluation ofJ1 andJ2integrals. The crack initiation and propagationphases were separated with a threshold criterionand a directioncriterion. It was found that during crack propagation bothsurface andsub-surface contact fatigue cracks follow thedirection with minimum mode II loading.

Key words: contact fatigue mechanism; spall; spalling;surface crack; sub-surface crack;elasto-plastic indentation;contact compliance measurement; mixed-mode fatigue;fatiguecrack growth;J-integral; multiaxial fatigue; weakest-link.

Place, publisher, year, edition, pages
Stockholm: KTH , 2000. , 27 p.
Series
Trita-HFL, ISSN 1104-6813 ; 0271
Keyword [en]
contact fatigue mechanism, spall, spalling, surface crakc, sub-surface crack, elesto-plastic indentation, contact compliance measurement
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-3028ISBN: 993-389332-7 OAI: oai:DiVA.org:kth-3028DiVA: diva2:8776
Public defence
2000-11-10, 00:00 (English)
Note
QC 20100407 NR 20140805Available from: 2000-10-26 Created: 2000-10-26 Last updated: 2010-04-28Bibliographically approved
List of papers
1. Initiation and Growth of Standing Contact Fatigue Cracks
Open this publication in new window or tab >>Initiation and Growth of Standing Contact Fatigue Cracks
2000 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 65, no 1, 89-106 p.Article in journal (Refereed) Published
Abstract [en]

In the standing contact fatigue test an indenter subjects a case hardened test specimen to a stationary but pulsating contact load. Two crack types appearing in the test specimen are investigated. The ring/cone cracks are surface cracks that circumvent the contact area, whereas the lateral cracks are horizontal sub-surface cracks. The initial crack lengths are determined for both crack types. Actual crack paths from experiments are evaluated numerically. For each crack tip position, stress intensity factors are determined from J(1) and J(2) integrals. The stress intensity ranges are compared to criteria for fatigue crack propagation rate and direction. As the cracks propagate, they orient in the direction with mode II loading close to zero.

Keyword
Contact fatigue, Surface crack, Sub-surface crack, Mixed mode fatigue, Fatigue crack growth, J-integral
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12308 (URN)10.1016/S0013-7944(99)00108-3 (DOI)000085867200006 ()
Note
QC 20100407Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2011-02-07Bibliographically approved
2. Applying multiaxial fatigue criteria to standing contact fatigue
Open this publication in new window or tab >>Applying multiaxial fatigue criteria to standing contact fatigue
2001 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 23, no 6, 533-548 p.Article in journal (Refereed) Published
Abstract [en]

The ability of some multiaxial fatigue criteria to predict initiation of standing contact fatigue cracks is investigated. In the standing contact fatigue test an indenter subjects a case-hardened rest specimen to a stationary but pulsating contact load. The initiation of two axi-symmetric crack types appearing in the test specimen is investigated. The surface initiated ring/cone cracks circumscribe the contact area, whereas the lateral cracks are horizontal sub-surface cracks. The effect of the stress-state history at possible crack Locations is evaluated through the Sines, Haigh principal stress, Findley, Me Diarmid and Dang Van multiaxial fatigue criteria. The material fatigue parameters of each criterion are determined from independent bending and torsion fatigue testing. Finally, the mean and spread in radial position of the ring/cone crack are evaluated by considering the statistical effects of a weakest link assumption using a three parameter Weibull distribution. The investigation shows that it is hard to distinguish a single criterion that well describes all aspects of the experimental results. For the current contact situation with highly compressive mean stresses in combination with tensile maximum values the Findley criterion shows the best overall performance followed by the Haigh principal stress criterion

Keyword
contact fatigue, surface cracks, sub-surface cracks, multiaxial fatigue, weakest link
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12323 (URN)10.1016/S0142-1123(01)00008-1 (DOI)000168646800008 ()
Note
QC 20100408Available from: 2010-04-08 Created: 2010-04-08 Last updated: 2011-02-11Bibliographically approved
3. Standing Contact Fatigue
Open this publication in new window or tab >>Standing Contact Fatigue
1999 (English)In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 22, no 3, 225-237 p.Article in journal (Refereed) Published
Abstract [en]

A novel experimental method for testing the resistance of a material to contact fatigue, called standing contact fatigue (SCF), is presented. It comprises a spherical indenter, repeatedly pressed onto a plane specimen in pure normal contact without lubrication, friction or wear. The SCF method is here applied to three case-hardened steels, and results in ring/cone cracks initiated at the surface. The connection between SCF and spalling is discussed.

The experimental results are presented in the form of P-N curves, where P is the normal contact load and N the number of cycles required for fatigue crack initiation. The experimental results are supported by numerical simulations of the tests. The elasto-plastic properties of case-hardened materials are graded, i.e. functions of the depth from the carburized surface. The gradation is estimated from independent experiments and is included in the analysis.

Keyword
contact fatigue, ring cone cracks, elasto-plastic indentation, spalling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12306 (URN)000080462900006 ()
Note
QC 20100407Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2011-02-04Bibliographically approved
4. Standing Contact Fatigue Testing of a Ductile Material: Surface and Sub-Surface Cracks
Open this publication in new window or tab >>Standing Contact Fatigue Testing of a Ductile Material: Surface and Sub-Surface Cracks
2000 (English)In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 23, no 3, 229-240 p.Article in journal (Refereed) Published
Abstract [en]

During standing contact fatigue testing of case hardened steel plates, four different fatigue crack types are found: ring/cone; lateral; radial; and median cracks. Fatigue results are presented as load versus cycle number, with endurance limits and initiation laws for the ring/cone and lateral cracks. The behaviour of the radial surface strain outside the contact is altered by the presence of cracks. In particular this makes in situ crack detection possible for the lateral crack.

The ductility of the tested material is found to be important for fatigue crack initiation. Numerical elastoplastic computations are used to derive the stress cycles responsible for each crack type. Stress cycles at different locations and in different directions are compared in order to explain why a particular crack type initiates. It is noted that cracks are produced normal to principal stresses of sufficient range, which are tensile sometime during the load cycle. Implications for spalling are discussed.

Keyword
contact fatigue, surface crack, subsurface crack, elastoplastic indentation, endurance
National Category
Mechanical Engineering Materials Engineering
Identifiers
urn:nbn:se:kth:diva-12307 (URN)10.1046/j.1460-2695.2000.00269.x (DOI)000087106800005 ()
Note
QC 20100407Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2011-11-11Bibliographically approved

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