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Friction and wear of soft surfaces by rough hard counterfaces and entrapped abrasive particles

Abrasive wear contributes significantly to many industrially significant wear problems. When an individual hard asperity (which might represent a single trapped abrasive grain in a bearing contaminated by hard particles) is dragged across a flat softer surface the degree of damage depends on both geometric and material parameters. The analytical treatment developed for this 'unit event' for an angular indenter is also applicable to the scratch hardness test [1]. If the asperity is more rounded then conditions are less severe and the elastic response of the softer surface can be important: this elastic-plastic transition is being explored [2,3]. In multiple pass situations, the profile of the abraded surface is no longer simple and becomes an input to the problem: the development of worn surfaces as individual wear events are superimposed on one another has been studied using a novel pin-on-cylinder wear machine with very precise positional control [4-8]. A review paper of laboratory methods in abrasive wear testing has also been prepared [9]. Practical bearing surfaces often deteriorate with time as a result of hard particulate contaminants being swept through the clearance gap. These particles may arise from the external environment or be wear debris from other pairs of surfaces lubricated by the same service fluid. The mechanics of surface damage in such circumstances has been examined both experimentally and analytically [10-13]. Paradoxically, there can be circumstances in which increasing the hardness differential between the loaded surfaces can lead to an increase in the damage done to the harder component.

These ideas, which can also be considered relevant to the understanding, analysis and optimisation of various abrasive machining processes such as lapping and polishing, have been discussed in relation to problems of filtration and contamination in lubricated contacts and hydraulic systems [14-16]. They have also been influential in the design of the ASTM Ball cratering procedure which uses lubricated abrasive wear to bring about a rapid assessment of the wear resistance of hardened and coated materials. Chemo-mechanical polishing or planarization is a vital stage of abrasive machining in the production of many semi-conductor devices and is likely to be important in the more laminar forms of MEMS and MMA's. The mechanics of this production process have a strong similarity to that of lubricated abrasive wear and discussions on collaborative in this are have been opened with groups in the Departments of Mechanical Engineering at Georgia Tech, the University of California at Berkeley and NTU Singapore.

Relevant/recent publications

  1. Williams J. A. 'Analytical models of scratch hardness' Tribology International, 29 pp675-694 (1996).
  2. Bressan, J. D., Genin, G. M. and Williams, J. A. 'The influence of pressure, boundary film shear strength and elasticity on the friction between a hard asperity and a deforming softer surface' presented at 25th Leeds-Lyon Symposium on Tribology (September 1998).
  3. Bressan, J. D. and Williams, J. A. 'The interaction between a hard asperity with a cylindrical profile and a softer deforming surface' in preparation.
  4. Kirkpatrick, R. J., Williams, J. A. and Paetke, S. J. 'Groove formation and interaction during the abrasion of copper' Proc. Int. Tribology Conf., I Mech E, London (1987).
  5. Williams, J. A. and Xie, Y. 'The generation of wear surfaces by the interaction of parallel grooves' Wear, 155, pp363-379 (1992).
  6. Williams, J. A. and Xie, Y. 'The generation of wear surfaces' J. Phys., D25, pp A158-164 (1992).
  7. Williams, J. A. and Xie, Y. 'The generation of wear surfaces by the repeated interaction of parallel grooves' Wear, 162-164, pp864-872 (1993).
  8. Xie, Y. and Williams, J. A. 'The prediction of friction and wear when a soft surface slides against a harder rough surface' Wear, 196, pp21-34 (1996).
  9. Williams, J. A. 'The laboratory simulation of abrasive wear' Tribotest, 3(3), pp267-306 (1997).
  10. Williams, J. A. 'Wear by solid particles in lubricated contacts' in Solid-solid Interactions, Royal Society-Unilever Indo-UK Forum , Imperial College (September, 1994).
  11. Eve, R. W. and Williams, J. A. 'Abrasive wear of lubricated carbon-graphite contacts' Proc. Int. Tribology Conference, Instn. Mech. E., London (1987).
  12. Williams, J. A. and Hyncica, A. M. 'Mechanisms of abrasive wear in lubricated contacts' Wear, 152, pp57-74 (1992).
  13. Williams, J. A. and Hyncica, A. M. 'Abrasive wear in lubricated contacts' J. Phys., D25, ppA81-90 (1992).
  14. Williams, J. A. 'Wear by hard particles in lubricated contacts' IMechE Seminar on Filtration and Contamination Control in Lubrication and Fluid Power Systems, London, March 1993.
  15. Williams, J. A. 'Mechanisms of Abrasive Wear in Lubricated Contacts' in Hydraulic Failure Analysis: Fluids, Components and System Effects, G E Totten, D K Wills and D Feldman (eds) American Society for Testing and Materials, ASTM STP 1339.
  16. Roylance, B. J., Williams, J. A. and Dwyer-Joyce, R. W., 'Wear debris and associated wear phenomena - fundamental research and practice' J. Engineering Tribology, 214, pp79-105(2000).

Contact Details

For further information on the work summarised above contact Dr J A Williams at Cambridge University Engineering Department, Trumpington St, Cambridge, CB2 1PZ, UK. Tel: 01223 332641, Fax: 01223 332662. E-mail: jaw@eng.cam.ac.uk
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