Fellow Profile: Sara Salopek


Project title

Real time wear measurement at tribofilm covered surfaces (P3)

Project objective

Systematic investigation of influential factors' effects on the tribosystem's wear performance by means of continuous wear measurement with Radio-Isotope Concentration (RIC) method, with respect to the tribologically modified interface between two bodies in reciprocating sliding motion.

Educational Background

1. Master of Mechanical Engineering, University of Zagreb, Croatia, 2012.

  • Graduated summa cum laude from Faculty of Mechanical Engineering and Naval Architecture,
  • Master thesis: Electrochemical study of sol-gel TiO2 films deposited on stainless steel

2. Bachelor of Mechanical Engineering, University of Zagreb, Croatia, 2011

  • Bachelor thesis:  Effect of polyvinyl alcohol on rheology characteristics of colloidal alumina  suspensions

Research area within ENTICE

Relation of nanoscopic wear behavior to tribofilm's properties


Austrian Center of Competence for Tribology GmbH

For more information contact Sara;   

E-mail: salopek@ac2t.at

Supervisor: Dr. Martin Jech


Extended Summary

1.       Background and motivation

Boundary lubrication is of special importance for industry, as most of the damaging wear occurs in this regime, thus controlling the service life of the components and showing the effectiveness of specially designed anti-wear additives in lubricants. It can occur in many engineering systems, high number of which are found in automotive applications such as: cam and tappet, piston ring and cylinder liner, transmissions, gears, bearings, clutches, etc. It is no surprise that the drive for research is strongly related to automotive industry – as the oil industry and car manufacturers struggle with strict environmental regulations concerning improved fuel economy, use of “green“ lubricants, longer oil drain intervals and lower emissions.

Although positive for the environment, introduction of these regulations often have a negative impact on the engine performance, increasing friction and wear between the engine components. Therefore, it is necessary to make a compromise between the government regulations and a satisfying engine performance, by optimizing engine oil formulations for efficient protection of new, lighter materials, by developing new coatings and surface modification processes which provide improved friction and wear properties.

One way to address this issue is to gain understanding of the tribofilm formation mechanisms, mechanisms by which they provide their anti wear action and the dependence of these on the operating conditions of the system in order to be able to produce similar, but more environmentally-friendly coatings or to develop additives capable of forming such protective tribofilms on the contacting surfaces. Moreover, studying these mechanisms should help in choosing lighter materials, instead of the traditional (and heavy) cast iron and steels, resistant to wear and capable of supporting the formation and durability of both friction- and wear-effective, thin, boundary lubrication films. 

2.       Aim and Objectives

The aim of individual research project was to correlate the nanoscopic wear and the properties of tribofilms forming under the conditions relevant for the internal combustion engines (ICEs) of passenger cars. 

The objectives of the project were:

  1. To evaluate the tribological behavior (via coefficients of friction and wear) of the piston ring – cyinder liner tribocouple, in real time.
  2. To characterize formed tribofilms by appropriate surface analytical techniques.
  3. To analyse the impact of tribofilms on the real-time tribological behavior of piston ring – cylinder liner tribo-couple:
    1. dependent on the contact parameters relevant for the operational regime of ICEs found in the passenger cars,
    2. dependent on the lubricant condition (i.e. fresh and artificially aged lubricant).
  4. To investigate the durability of generated tribofilms, when the lubricant is switched to non-additivated oil.


3.       Methodology

The main feature of the research was the application of an online wear measurement technique (RadioIsotope Concentration technique, AC2T) which allows for a continuous measurement of wear during the tribological experiment without stopping the experiment. Measurement of wear in real time, based on the application of the thin layer activation (TLA) technique, is a relatively new wear measurement method, which enables measurement of extremely low wear in real time, such as in automotive application, where the wear rates are of several nm/h. Usually, wear is measured by determining the depth or volume of wear track using a profilometer or by weighing the worn sample and measuring the mass loss. Such measurement techniques demand a high amount of wear generated during the tribological experiments, which are for economical reasons, carried out in only couple of hours. This way, wear rates of several µm/h are reproduced, leading to discrepancies in wear mechanisms reproduced in the tribometer tests and the real system.

 In contrast to previously developed activation technique using neutron activation, where the sample becomes greatly radioactive, thin layer activation enables easy handling of specimens and no need for intricate radiation safety equipment and strict safety regulations due to the very low radioactivity of the activated samples.

The advantages of the RIC wear measurement technique are clear:

  • a possibility to measure wear continuously, without having to disassemble the tribological contacts or stop the test,
  • the steady-state and running-in wear phases can be distinguished (otherwise not possible with the so-called offline wear measurement systems),
  • ability to measure very small wear rates in short term tests,
  • studying the tribosystem without applying unrealistically high loading conditions (so that wear of the tribological components could be measured),
  • measuring simultaneously wear of more components (by producing different radioactive isotopes in the tested components),
  • no particular radiation safety equipment, other than usual steps taken for safe handling of materials is necessary.

In combination with the RIC wear measurement technique, surface analytical techniques appropriate for the investigation of the tribologically affected surfaces were applied. Tribofilms generated during the tribological experiments were analyzed chemically by utilizing the X-ray Photoelectron Spectroscopy (XPS). Surface topography and tribofilm morphology were investigated by the Atomic Force Microscopy (AFM).

4.       Main contributions of the individual research project to the ENTICE project

The main contributions of the individual research project can be summarized as follows:

  1. Nanoscopic wear behavior of tribofilms forming on cast iron cylinder liners in real time.
  2. Investigation of the influence of testing parameters (relevant to the internal combustion engines) and oil condition on the tribofilm chemistry and the wear response of the tested systems.
  3. Investigation of the durability of tribofilms formed on the cast iron cylinder liners.





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University of Leeds Ecole Centrale LyonUniversity of Ljubljana Mercedes-Benz Act Research Total SKF 

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