prof. Ing. Ivan Křupka, Ph.D.
E-mail:   krupka@fme.vutbr.cz  Dept.:   Position:   Vice-Dean Room:   A3/506 Dept.:   Institute of Machine and Industrial Design Dept. of Tribology Position:   Head of Department Room:   A2-old/405 Dept.:   Institute of Machine and Industrial Design Dept. of Tribology Position:   Professor Room:   A2-old/405

Supervised courses:

• Design of Instruments and Optomechanics II (TK2)
• Experimental Methods in Tribology (9EXT)
• Research and Development Project (ZKR)

Publications:

• CHOUDHURY, D.; CHING, H.A.; MAMAT, A.B.; ČÍŽEK, J.; ABU OSMAN, N.A.; VRBKA, M.; HARTL, M.; KŘUPKA, I.:
  Fabrication and characterization of DLC coated microdimples on hip prosthesis heads, Wiley Periodicals, Inc.
  journal article in Web of Science
• SVOBODA, P.; KOŠŤÁL, D.; KŘUPKA, I.; HARTL, M.:
  Experimental study of starved EHL contacts based on thickness of oil layer in the contact inlet,
  Tribology International, Vol.67, (2013), No.1, pp.140-145, ISSN 0301-679X, ELSEVIER
  journal article - other
• ALI, F.; KRUPKA, I.; HARTL, M.:
  Enhancing the parameters of starved EHL point conjunctions by artificially induced replenishment,
  Tribology International, Vol.66, (2013), No.1, pp.134-142, ISSN 0301-679X, Elsevier
  journal article - other
• KANETA, M.; KŘUPKA, I.; HARTL, M.:
  Pressure Increase in Elliptical Impact Elastohydrodynamic Lubrication Contacts With Longitudinal Asperities,
  ASME Transaction, Journal of Tribology, Vol.135, (2012), No.1, pp.1-6, ISSN 0742-4787, ASME
  journal article - other
• ŠPERKA, P.; KŘUPKA, I.; HARTL, M.:
  The Behavior of Surface Roughness in EHL Contacts Under Small Slide to Roll Ratios, Springer
  journal article in Web of Science

List of publications at Portal BUT

Abstracts of most important papers:

• STAHL, K.; MICHAELIS, K.; MAYER, J.; WEIGL, A.; LOHNER, T.; OMASTA, M.; HARTL, M.; KŘUPKA, I.:
  Theoretical and Experimental Investigations on EHL Point Contacts with Different Entrainment Velocity Directions,
  TRIBOLOGY TRANSACTIONS, Vol.56, (2013), No.5, pp.728-738, ISSN 1040-2004, Taylor & Francis
  journal article - other
  This study investigates the effect of different lubricant entrainment velocity angles on film thickness distribution. For this purpose, a steady-state isothermal EHL model is used under a wide range of parameter sets including varying sum velocity, contact pressure, and sum velocity angle. The results are compared with experimental measurements by means of an optical ball-on-disc tribometer and a twin-disc machine using capacitance method.
• VRBKA, M.; NÁVRAT, T.; KŘUPKA, I.; HARTL, M.; ŠPERKA, P.; GALLO, J.:
  Study of film formation in bovine serum lubricated contacts under rolling/sliding conditions, SAGE Publications Ltd
  journal article in Web of Science
  The aim of this study is to perform a detailed experimental analysis of lubricant film thickness of bovine serum within the contact between the artificial metal and ceramic heads (balls) and the glass disc to analyse the effect of proteins on film formation under various rolling/sliding conditions. Lubricant film observation of bovine serum solutions was carried out using an optical test rig. Chromatic interferograms were recorded with a high-speed CMOS digital camera and evaluated with thin film colorimetric interferometry. Film thickness was studied as a function of time. Under pure rolling conditions, film thickness increases with time as well as with rolling distance for all mean speeds and for both materials of the balls; however the metal ball always forms a thicker lubricating film in comparison to the ceramic ball. Under rolling/sliding conditions, when the disc is faster than the ball, the formation of lubricant film thickness is different compared to pure rolling conditions. At first, film thickness increases rapidly with a rolling/sliding distance for all mean speeds. When maximum film thickness is reached, then this effect is lost and film thickness starts to fall and finally, at the end of the measurement, film thickness drops down to a few nanometres. For the metal ball, maximum values of central film thicknesses are proportional to the mean speed; however this is not observed with the ceramic ball. An absolutely different formation of bovine serum film thickness is observed when the ball is faster than the disc. Under this condition, the protein layer is very thin for both materials of balls, and central film thickness reaches only about a few nanometres. Local protein spots are formed in a very small area of the contact zone and reach the thickness between 20 and 25 nm for the metal ball and 5 nm for the ceramic ball. From the performed experiments under rolling/sliding conditions, it is obvious that the formation of lubricant film thickness is markedly dependent on kinematic conditions acting in the contact, especially on the positive and negative slide-to-roll ratio and the mean speed. In addition, the material of the artificial head has a certain influence on the formation of bovine serum lubricating film.
• KANETA, M.; KŘUPKA, I.; HARTL, M.:
  Pressure Increase in Elliptical Impact Elastohydrodynamic Lubrication Contacts With Longitudinal Asperities,
  ASME Transaction, Journal of Tribology, Vol.135, (2012), No.1, pp.1-6, ISSN 0742-4787, ASME
  journal article - other
  The phenomena that occur when an elliptical steel body impacts a stationary steel plate with surface asperities are discussed through isothermal Newtonian numerical analysis using sinusoidal roughness. The ridges of the surface asperities produce large local pressures, especially at a large ellipticity ratio, when the surfaces are approaching each other under the applied load. The values of the local pressures are larger when the ridges are along the major axis than when the ridges are along the minor axis. Furthermore, as the loading speed increases, the pressure increases. As a result, the microgrooves are produced in the ridges and the horseshoe-shaped constrictions are formed at the ridges located around the contact edge.
• ŠPERKA, P.; KŘUPKA, I.; HARTL, M.:
  Experimental study of real roughness attenuation in rolling-sliding concentrated contacts, Elsevier
  journal article in Web of Science
  A surface roughness attenuation approach based on the Fourier decomposition of surface roughness into harmonic components may allow predictions of the behavior of real rough surfaces within concentrated lubricated contacts. Recent experiments performed under pure rolling conditions have shown an amplitude reduction of different components that agreed well with the data predicted by the theory. This study represents the next step in the experimental verification of the surface roughness attenuation approach under rolling/sliding conditions. Obviously, the behavior of roughness in the rolling/sliding elastohydrodynamic (EHD) contacts is more complex than for pure rolling. It has been theoretically suggested by other researchers that the modification of the original roughness alone cannot explain all of the major effects that significantly affect film thickness, and a model was proposed in which, along with the roughness attenuation, a complementary wave was generated in the inlet region and moved at the entrainment speed. This paper is focused on the possibility of extracting complementary waves from experiments with real rough surfaces conducted under rolling/sliding conditions and of determining whether the amplitudes of the complementary wave can be determined. This represents the first attempt to study both effects of rough surface behavior separately. The complementary wave was extracted from the measured data by subtracting the attenuated original roughness from the measured film thickness. Although the experimental results were quite scattered, a trend similar to that of the theoretical curves was observed. Based on the results, it can be suggested that the significance of the complementary wave is comparable to the attenuation principle.
• KŘUPKA, I.; HARTL, M.; BAIR, S.; SVOBODA, P. ;KUMAR, P.:
  Mechanical Degradation of the Liquid in an Operating EHL Contact,
  Tribology Letters, Vol.40, (2010), No.3, pp.1-7, ISSN 1023-8883, Springer
  journal article - other
  Elastohydrodynamic lubrication (EHL) calculations using the real pressure and real shear dependence of viscosity have revealed that the shear and load dependences of film thickness are often greater than the classical prediction. Experimental measurements have confirmed the increased sensitivity to scale and load; however, the sensitivities are even greater than would be expected from shear-thinning. Time-dependent film thickness measurements and stress-history-dependent flow curves are employed to show that molecular degradation may occur at nominal rolling EHL stress levels and that this degradation affects the film thickness.