PhD candidate On the Thermodynamics of a Complex Fluid and its Application to Rolling Bearings

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The Tribology Group, Faculty of Engineering Technology of the University of Twente has an opening for a PhD candidate in the research area of Grease Lubrication. This project operates at the interface of fluid dynamics, rheology, complex fluids and tribology. The expected outcome of this 4-year project will be a model that can predict the remaining functional life of lubricating grease in rolling bearings.  This requires a thorough understanding of the flow and rheology, phase separation and degradation of the micro-structure of lubricating greases in rolling bearings. The project is sponsored and executed in close collaboration with SKF, a leading global bearing manufacturer.

Lubricating grease is a visco-elastic material, consisting of a thickener matrix (usually a soap, 5-15%), base oil (mineral or synthetic) and additives (anti-corrosion, anti-wear, 1-5%).  At small strains, lubricating grease is apparently solid. This quantity makes grease easy to use: it does not easily leak out of a bearing and acts as a seal, preventing contamination to enter the bearing. The apparent stiffness is ascribed to the thickener matrix that forms a network filled with oil. At larger shear rates the viscous properties dominate. At very high shear rates the viscosity approaches that of the base oil.  The oil is slowly released from the grease (“grease bleed”) into the tribological contacts (ball-ring contacts) providing a feed mechanisms for the lubricant film (with thickness up to typically 0.2 microns).

When the bearing is rotating the grease will be “worked” in the bearing by shear and over-rolling. This results in a degradation of the thickener network. Grease may leak from the bearing, the bleed rate will change and the positioning of the grease inside the bearing will change. In the case of higher temperatures, such as in electric motors, oxidation may take place. At some point in time, the grease is deteriorated such that it no longer lubricates the bearing and the bearing will fail.
In this project a model should be developed for the remaining life of grease in a bearing as a function of the operating conditions and time.  The project starts with a fundamental study on the degradation mechanisms and the development of a model that can be used to predict the degradation as a function of shear, temperature and time (energy/entropy).  Subsequently, this needs to be applied to a bearing where the shear rates vary throughout the internal bearing design.
  • You will study the rheological and phase separation (grease bleed) properties of model greases;
  • You will study the change of these properties under shear and temperature (and possibly pressure) as a function of time/energy and translate this into a model;
  • You will study the rheology and oil separation in ball bearings;
  • You will analyze grease and oil leakage from bearings. Some will be done by you but most will be done at SKF (mainly in Sweden, France  Germany and Italy) where you will need to take samples;
  • You will study the change in micro-structure of grease taken from the bearing tests using Atomic Force Microscopy (AFM) or other techniques;
  • You will develop a model to predict the changes of flow properties and oil separation in rolling bearings (apply the fundamental work to rolling bearings);
  • You will closely collaborate with your research-team colleagues at the University of Twente. If you prefer (for example because of personal reasons), a large part of the research may be executed at SKF Research and Development, Houten/Utrecht, The Netherlands. SKF has excellent facilities;
  • You will mentor BSc and MSc students, in support of your research;
  • You will finish your research with a PhD thesis and publish your work in academic journals and at conferences.

Your profile

  • You hold an MSc degree in Physics,  Mechanical Engineering or Chemical Technology;
  • You have knowledge/demonstrated awareness of modelling using Python, C++ and/or MatLab;
  • You have good experimental skills;
  • You have a strong analytical mind and an eye for detail, as well as a critical attitude towards assessment of experimental results;
  • You like to present your results to colleagues, the industrial partner and at international conferences;
  • You are fluent in English and express yourself easily both in speech and in writing.
INFORMATION AND APPLICATION

Please upload your application before 22 March 2020 with the following documents via the ‘Apply now’ button below:

  • Curriculum vitae;
  • Motivation letter explaining why this position is the best match for your personal development, career and why you are the best fit for our research group;
  • MSc grade lists.

Since only three documents can be up loaded, please combine the documents if needed.
For information, please contact Prof.dr.ir. Piet M. Lugt (p.m.lugt@utwente.nl
or piet.lugt@skf.com)
The start of the project is a.s.a.p. We also invite applications from candidates, who expect to graduate soon.

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