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Surface stresses at an axisymmetric asperity in a rolling contact with traction
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
2008 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 30, no 9, 1606-1622 p.Article in journal (Refereed) Published
Abstract [en]

Rolling contact between a smooth cylinder and a cylinder with an axisymmetric surface asperity was modelled numerically. The influence of tangential slip and friction was investigated through relative contact movement between the cylinders. As the asperity entered the rolling contact it acted as a point type contact force, which gave a tensile surface stress in the forward rolling direction. The tensile stress maximum was greatly influenced by slip and coefficient of friction.

Data for the simulations were captured from a gear example with surface initiated rolling contact fatigue or spalling. The cylindrical contact load and geometry corresponded to that at the roll-circle of the gear. The geometrical properties of the asperity were based on surface profiles of the gear flank. The combined isotropic and non-linear kinematic Chaboche material model was used with parameters determined from cyclic compression-tension tests on the gear material. The residual stress profile due to heat-treatment of the gear was included into the model.

Two different frictional set-ups were investigated. One contained a non-zero coefficient of friction throughout the rolling contact. This was believed to compare to dry contacts. The other set-up was supposed to model lubricated rolling with asperity break-through to metal contact. Here friction was non-zero on the asperity and zero elsewhere in the contact. With traction throughout the cylindrical contact a sufficiently long start distance had to be travelled before the asperity interaction. Thus, the transient rolling distance was determined together with the slip limit for sliding in the cylindrical contact. Numerical predictions of residual stresses and surface distress angles suggested that the asperity friction model agreed with gear conditions.

Evaluation of elastic-plastic asperity indentation suggested that the asperity deformation was approximately as severe as repeated macro-scale experiments with fatigue cracks. Since the stresses at the asperities were of the same size as those at the repeated indentations and since the Findley multi-axial fatigue criteria predicted fatigue damage, it was concluded that the stresses in front of the asperity could be sufficient to initiate rolling contact fatigue cracks in applications. The influences of some parameters on the stress maximum were also evaluated.

Place, publisher, year, edition, pages
2008. Vol. 30, no 9, 1606-1622 p.
Keyword [en]
asperity contact, rolling contact fatigue, spalling, transient rolling, gear contact
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-7771DOI: 10.1016/j.ijfatigue.2007.11.008ISI: 000257001700008ScopusID: 2-s2.0-43949102372OAI: diva2:12896
QC 20100702. Uppdaterad från Accepted till Published i DiVA 20100702.Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2012-03-19Bibliographically 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.
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0440
Rolling contact fatigue, Spalling, Asperity contact, Point load; Micro-cracks, Traction, Applied slip
National Category
Engineering and Technology
urn:nbn:se:kth:diva-4569 (URN)
Public defence
2007-12-17, F3, Lindstedsvägen 26, Stockholm, KTH, 10:15

QC 20100702

Available from: 2007-12-10 Created: 2007-12-10 Last updated: 2013-01-14Bibliographically approved

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