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Surface initiated rolling contact fatigue based on the asperity point load mechanism-A parameter study
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
2012 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 294, 457-468 p.Article in journal (Refereed) Published
Abstract [en]

The influence of asperity size, friction and residual surface stress on surface initiated rolling contact fatigue damage was investigated using the asperity point load mechanism. A parametric study was performed in two steps, first with a classic one-parameter-at-a-time approach, then as a 2-level full factorial design. The effect on fatigue initiation, damage size and spalling life for both early and developed spalling damage was examined for a gear application. Simplified response surfaces were derived as an engineering design tool for improved spalling resistance. The parametric investigation suggested that among the investigated parameters, reduced asperity height and local asperity friction will have the largest effect on the crack initiation risk. The simulations agreed with the engineering experiences that reduced surface roughness improves rolling contact fatigue resistance and that improved lubrication lengthens spalling lives and decreases fatigue risk. With compressive residual surface stresses the predictions suggested reduced fatigue risk and substantially decreased depth of individual spalls. Finally, predictions of experimentally observed effects of changing asperity size, friction and residual surface stress on spalling further motivates the asperity point load mechanism as the source behind surface initiated rolling contact fatigue.

Place, publisher, year, edition, pages
2012. Vol. 294, 457-468 p.
Keyword [en]
Crack path, Fatigue life, Friction, Initiation, Rolling contact fatigue, Spalling
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-105261DOI: 10.1016/j.wear.2012.07.005ISI: 000311003200027Scopus ID: 2-s2.0-84866884023OAI: oai:DiVA.org:kth-105261DiVA: diva2:570608
Funder
Swedish Research Council
Note

QC 20121120

Available from: 2012-11-20 Created: 2012-11-19 Last updated: 2017-12-07Bibliographically approved
In thesis
1. On fatigue crack growth modelling of surface initiated rolling contact fatigue using the asperity point load mechanism
Open this publication in new window or tab >>On fatigue crack growth modelling of surface initiated rolling contact fatigue using the asperity point load mechanism
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Load transfer in applications or between machine components is generally achieved through contact. In case of recurrent high contact loads in combination with a rolling motion, i.e. with a relatively small amount of slip, the contact surface may eventually suffer from rolling contact fatigue (RCF). The damage consists then of cracks and craters or spalls, which can cause dysfunctionality of the application leading to inefficiency or increased maintenance costs. Ultimately the damage may cause total failure of the machine component. The damage process is still not fully understood due to the complexity of the problem. Different mechanisms have been suggested to explain initiation and propagation of RCF damage. The current work focused on crack growth modelling of surface initiated RCF in case hardened gear steel. The study was based on the asperity point load mechanism, which emphasizes the importance of the surface roughness in the damage process. Asperities on the contact surface act as stress raisers inducing locally high tensile surface stress when entering the contact. Improved understanding of the damage process and further validation of the asperity point load mechanism was achieved.

In Paper A, the crack path of surface initiated RCF was simulated in the symmetry plane of the damage with the trajectory of the largest principal stress in the uncracked material. The mode I fracture mechanism was found applicable as well as linear elastic fracture mechanics (LEFM). The evolvement of the asperity contact parameters during the load cycle was determined through a finite element (FE) contact model based on an equivalent contact geometry. The predicted RCF crack path agreed with experimental spall profiles both in entry details as in overall shape. An experimental series was performed in Paper B to investigate the crack closure behaviour in presence of large negative minimum loads. The experimental results suggested a crack closure limit close to zero. The choice of the equivalent mixed-mode stress intensity factor range and especially the crack closure limit had a significant effect on the predicted RCF or spalling life. The two-dimensional crack growth model was further developed in Paper C and used to investigate the influence of asperity size, friction and residual surface stress on the simulated RCF damage. The simulations agreed qualitatively with experimental observations where reduced surface roughness, improved lubrication and compressive residual surface stress increased RCF resistance. In Paper D, a three-dimensional stationary crack was studied using an FE model and a simplified RCF load. A new crack geometry was proposed allowing the investigation of the spall opening angle of the typical vshaped damage. Crack arrest through crack closure was suggested as explaining mechanism. A qualitative study indicated increased spread of the surface damage with increased friction. The results also depended on the crack inclination angle. The different studies supported the asperity point load mechanism to explain not only fatigue initiation but also fatigue crack propagation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 46 p.
Series
TRITA-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0551
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-141151 (URN)978-91-7501-999-4 (ISBN)
Public defence
2014-02-20, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140210

Available from: 2014-02-10 Created: 2014-02-10 Last updated: 2014-02-10Bibliographically approved

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Alfredsson, Bo

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