Recent improvements in the quality and manufacture of steels have meant that rolling bearings are largely free from material defects. It is therefore damage generated during the operating life of the component that is the main source of failure. This damage is frequently caused by the over-rolling of debris particles in the lubricant. This damage can lead to premature failure of the component by abrasive wear or surface initiated fatigue.
The figure shows a fatigue spall which has initiated at a debris dent on a bearing surface. The indent has acted as a stress raiser in the normal rolling contact. A fatigue crack has initiated and propagated to a spall. Smaller sized indents caused, for instance, by sand particles do not give a large enough stress concentration. In these cases a large number of indentations build up to cause material removal by abrasive wear. This project has been aimed at measuring, understanding, and modelling these processes.
The investigation has covered the following areas;
- A study of the entry of particles into rolling lubricated contacts
- An optical elastohydrodynamic investigation of the behaviour of particles in and around lubricated contacts
- Work to relate the surface damage caused by particles to the properties of the debris material (hardness and fracture toughness)
- Elastic/plastic finite element analysis of the debris denting process to determine the stresses and deformations associated with the indentation process
- Development of a model to predict the fatigue life of indented surfaces
- Fundamental experiments, using a ball on disk, to study the mechanisms of abrasive wear
- Development of models to predict the abrasive wear of deep groove ball bearings (based on the kinematics and contamination conditions)
- Experiments on the wear of deep groove ball bearings using lubricants of known contamination levels
The figure compares a worn and new ball bearing. Wear has been caused by the presence of sand particles in the lubricant. A model has been developed to predict the level of wear and hence the life of a bearing in a contaminated environment.
- Dwyer-Joyce, R. S., (1999), "Predicting the Abrasive Wear of Ball Bearings by Lubricant Debris", Wear, Vol. 233-235, pp 692-701.
- Dwyer-Joyce, R. S. , Sayles, R. S., and Ioannides, E (1994), "An Investigation into the Mechanisms of Closed Three Body Abrasive Wear", Wear, Vol. 175, pp 133-142.
- Dwyer-Joyce, R. S. and Heymer, J., (1996), "The Entrainment of Solid Particles into Rolling Elastohydrodynamic Contacts", Proceedings of 22nd Leeds-Lyon Symposium on Tribology (The Third Body Concept: Interpretation of Tribological Phenomena), Elsevier, Amsterdam, edited by: D. Dowson, C.M. Taylor, T.H.C. Childs, G. Dalmaz, Y. Berthier, L. Flamand, J.-M. Georges, A.A. Lubrecht, Elsevier Tribology Series No. 31, pp. 135-140. (ISBN: 0-444-82502-9). RAE 4D.
- Dwyer-Joyce, R. S., Hamer, J. C., Sayles, R. S. and Ioannides, E., (1992), "Lubricant Screening for Debris Effects to Improve Fatigue and Wear Life", Proceedings of 18th Leeds-Lyon Symposium on Tribology (Wear Particles - from the cradle to the grave), Elsevier, Amsterdam, paper II (iv), pp. 57-63.
- Dwyer-Joyce, R. S., Hamer, J. C., Hutchinson, J. M., Ioannides, E. and Sayles, R. S., (1991), "A Pitting Fatigue Life Model For Gear Tooth Contacts", Proceedings of 17th Leeds-Lyon Symposium on Tribology (Vehicle Tribology), paper XIV (ii), pp 391-400.
- Dwyer-Joyce, R. S., Hamer, J. C., Sayles, R. S. and Ioannides, E., (1990), "Surface Damage Effects Caused by Debris in Rolling Bearing Lubricants with a Particular Emphasis on Friable Debris Materials", Rolling element bearings - towards the 21st Century, pp. 1-8, Mechanical Engineering Publications for the I.Mech.E.