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PhD: Grease Life Prognostics: Remaining Grease Life via Measurements and Predictive Models

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Job description

The end of grease life is the point at which the grease can no longer build up a sufficiently thick film to fully separate the contacting surfaces in a rolling bearing. Empirically, it has been shown that grease life can be determined via measurement of grease consistency (given by its yield stress) and/or base oil content. Via modeling, the end of grease life can be estimated by calculating the point in time where the film thickness is equal to the interfacial roughness. Such a model does not currently exist. The film thickness in a grease-lubricated bearing is essentially the compressed combined thickness of the lubricant layers entering the tribological (ball-ring) contacts. These layers are reduced in thickness by side flow induced by the high pressures in the contacts and are fed by grease bleed and replenishment. Grease bleed is the slow release of base oil from the grease into the contacts, providing a feed mechanism for the lubricant film. Replenishment is related to the base oil viscosity and the remaining grease volume, which is related to the yield stress of the grease. Recent works have shown that mechanical degradation of lithium and polyurea greases (the most widely used grease types) leads to a decrease in the yield stress and an increase in grease bleed.
The goal of this project is to develop a model for the prediction of the remaining useful life of grease via the grease yield stress and oil content, including the effects of temperature changes.
•             You will study the rheological behavior of some model greases.
•             You will study the thermodynamics of grease degradation.
•             You will study how grease behavior changes in a rolling bearing by “mechanical load” on the grease matrix (the matrix deteriorates due to large shear and pressure).
•             You will study the oil separation behavior in a ball bearing.
•             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 criteria for using oil content to measure end of grease life.
•             You will develop criteria for using yield stress to measure end of grease life.
•             You will generate enough data for the validation of the remaining grease life concept and for the applicabili

Your profile

•             You hold an MSc degree in Physics or Mechanical Engineering or a closely related discipline.

•             You have good 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 passionate about learning new concepts and doing original research.

•            You are fluent in English and express yourself easily both in speech and in writing.

Our offer

·         We provide excellent mentorship and a stimulating research environment with excellent facilities.

·         You are offered a professional and personal development program within Graduate School Twente.

·         A starting salary of  € 2.395 gross per month in the first year and a salary of € 3.061 in the fourth year gross per month.

·         A holiday allowance of 8% of the gross annual salary and a year-end bonus of 8.3%.

·         A solid pension scheme.

·         Minimum of 29 holidays per year in case of fulltime employment.

Information and application

For information, please contact Prof.dr.ir. Piet M. Lugt (p.m.lugt@utwente.nl) or Dr. Jude A. Osara, PE (j.a.osara@utwente.nl).

The start of the project is May 1st. We also invite applications from candidates, who expect to graduate soon. Your application should be submitted before February 28, 2021.

Please send the following documents through the link below:

·         Letter of motivation and/or research interest.

·         Curriculum vitae.

·         List with grades of courses attended from both Bachelor and Master degrees.

·         References and, if applicable, a list of publications.

About the department

The SKF University Technical Centre for Grease Lubrication of the University of Twente has an opening for a PhD candidate. This project operates at the interface of fluid dynamics, rheology, complex fluids, thermodynamics and tribology. The expected outcome of this 4-year project will be a model that can predict the remaining grease life based on the condition of the grease for bearings operating at medium and low temperatures (typically temperatures lower than 90oC). This requires a thorough understanding of the grease rheological and thermodynamic properties, as well as degradation mechanisms in rolling bearing applications, among others. The project is executed in close collaboration with SKF, a leading global bearing manufacturer.

Lubricating grease is a visco-elastic semi-solid, 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 nearly solid. This quality makes grease easy to use: it does not easily leak out of a bearing and acts as a seal, preventing contamination from entering the bearing. Only creep flow may occur. This is ascribed to the thickener matrix that forms a network filled with oil. At higher shear rates, the viscous properties dominate. At very high shear rates, grease viscosity approaches that of its base oil.

About the organization

The Faculty of Engineering Technology (ET) engages in education and research Mechanical Engineering, Civil Engineering and Industrial Design Engineering with a view to enabling society and industry to innovate and create value using sound, efficient and sustainable technology. We are part of a ‘people-first' university of technology, taking our place as an internationally leading centre for smart production, processes and devices in five domains: Health Technology, Maintenance, Smart Regions, Smart Industry and Sustainable Resources. Our faculty is home to some 1,800 Bachelor's and Master's students, 400 employees and 150 PhD candidates and offers three degree programmes: Mechanical Engineering, Civil Engineering and Industrial Design Engineering. Our educational and research programme are closely connected with UT research institutes Mesa+ Institute, TechMed Centra and Digital Society Institute.

As an employer, the ET Faculty offers jobs that matter. We equip you as a staff member to shape new opportunities both for yourself and for our society. With our Faculty, you will be part of a leading tech university that is changing our world for the better. We offer an open, inclusive and entrepreneurial climate, in which we encourage you to make healthy choices, for example, with our flexible, customizable conditions.

University of Twente (UT)

University of Twente (UT) has entered the new decade with an ambitious, new vision, mission and strategy. As ‘the ultimate people-first university of technology' we are rapidly expanding on our High Tech Human Touch philosophy and the unique role it affords us in society. Everything we do is aimed at maximum impact on people, society and connections through the sustainable utilisation of science and technology. We want to contribute to the development of a fair, digital and sustainable society through our open, inclusive and entrepreneurial attitude. This attitude permeates everything we do and is present in every one of UT's departments and faculties. Building on our rich legacy in merging technical and social sciences, we focus on five distinguishing research domains: Improving healthcare by personalised technologies; Creating intelligent manufacturing systems; Shaping our world with smart materials; Engineering our digital society; and Engineering for a resilient world.

As an employer, University of Twente offers jobs that matter. We equip you as a staff member to shape new opportunities both for yourself and for our society. With us, you will be part of a leading tech university that is changing our world for the better. We offer an open, inclusive and entrepreneurial climate, in which we encourage you to make healthy choices, for example, with our flexible, customisable conditions.

PhD: Grease Life Prognostics: Remaining Grease Life via Measurements and Predictive Models
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