prof. Ing. Martin Hartl, Ph.D.

E-mail:   Martin.Hartl@vut.cz  WWW:   http://www.uk.fme.vutbr.cz/ Dept.:   Institute of Machine and Industrial Design Position:   Director of Institute Room:   A3/514 Dept.:   Institute of Machine and Industrial Design Dept. of Tribology Position:   Professor Room:   A3/514 Dept.:   Institute of Machine and Industrial Design Dept. of Tribology Position:   Research Worker Room:   A3/514 Dept.:   NeTME Centre NCC MESTEC - Machine and Industrial Design Division Position:   Head of Subdivision Dept.:   NeTME Centre NCC NaCCAS - Machine and Industrial Design Division Position:   Head of Subdivision Dept.:   Institute of Machine and Industrial Design NCC JOBNAC - Machine and Industrial Design Division Position:   Head of Subdivision

Supervised courses:

• Advanced Tribology (9EHD)
• Diploma Project - Bibliography and Goals (ZD2)
• Diploma Project – Concept (ZD1)
• Exponential Technologies (ZNV)
• Machine Design - Machine Elements (5KS-A)
• Machine Design - Machine Elements (5KS)
• Machine Design - Machine Elements (5KS-K)
• Machine Design - Mechanical Drives (6KT)
• Machine Design - Mechanical Drives (6KT-A)
• Machine Design and Machine Elements (CKP)
• Master Thesis Project - Methods and Results (ZDP)
• Master Thesis Project - Results and Discusion (ZD5)
• Methodologies of Scientific Work (9MOP)
• Tribology (ZTR)

Publications:

• NEČAS, D.; VRBKA, M.; URBAN, F.; GALLO, J.; KŘUPKA, I.; HARTL, M.:
  In situ observation of lubricant film formation in THR considering real conformity: The effect of diameter, clearance and material, Elsevier Ltd.
  journal article in Web of Science
• GALAS, R.; OMASTA, M.; KŘUPKA, I.; HARTL, M.:
  Laboratory investigation of ability of oil-based friction modifiers to control adhesion at wheel-rail interface, Elsevier
  journal article in Web of Science
• ŠPERKA, P.; KŘUPKA, I.; HARTL, M.:
  Experimental Study of Roughness Effect in a Rolling–Sliding EHL Contact. Part I: Roughness Deformation, Taylor & Francis Inc
  journal article in Web of Science
• ALI, F.; KŘUPKA, I.; HARTL, M.:
  Mechanism for Controlling Oil Replenishment in Starved Elliptical EHL Contacts, Springer US
  journal article in Web of Science
• KOŠŤÁL, D.; NEČAS, D.; ŠPERKA, P.; SVOBODA, P.; KŘUPKA, I.; HARTL, M.:
  Lubricant Rupture Ratio at Elastohydrodynamically Lubricated Contact Outlet, Springer
  journal article in Web of Science
• 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
• ALI, F.; KŘUPKA, I.; HARTL, M.:
  Effects of out-of-contact lubricant channeling on friction and film thickness in starved elastohydrodynamic lubrication point contacts, SAGE
  journal article in Web of Science
• KUMAR, P.; BAIR, S.; KŘUPKA, I.; HARTL, M.:
  Newtonian quantitative elastohydrodynamic film thickness with linear piezoviscosity,
  Tribology International, Vol.43, (2010), No.11, pp.2159-2165, ISSN 0301-679X, Elsevier
  journal article - other

List of publications at Portal BUT

Abstracts of most important papers:

• KŘUPKA, I.; HARTL, M.; BAIR, S.; KUMAR, P.; KHONSARI, M.M.:
  An Experimental Validation of the Recently Discovered Scale Effect in Generalized Newtonian EHL,
  Tribology Letters, Vol.33, (2008), No.X, pp.1-9, ISSN 1023-8883, Springer
  journal article - other
  New quantitative numerical simulations of the elastohydrodynamic lubrication (EHL) film forming ability of generalized Newtonian liquids have elucidated a previously unrecognized property of EHL films. The dependency of the film thickness on the scale of the contact is greater when the viscosity is shear dependent within the inlet. Measurements of film thickness were performed in a ball on disc experiment using balls ranging from 5.5 to 35 mm in diameter. Three liquids were investigated with varying shear dependence in the range of stress important to film forming. The experimental results confirm the previous analytical findings. Numerical simulations using the measured viscosities show that the increased scale sensitivity is substantially the result of shear-thinning. However, the smallest scales produced films thinner than even the shear-dependent prediction, possibly indicating molecular degradation. It is quite likely that some machine components, which were designed using the effective viscous properties derived from a larger scale film thickness measurement, are operating with substantially lower film thickness than the designer had intended.
• KŘUPKA, I.; HARTL, M.:
  The effect of surface texturing on thin EHD lubrication films,
  Tribology International, Vol.40, (2007), No.7, pp.1100-1110, ISSN 0301-679X, Elsevier
  journal article - other
  Surface texturing has been successfully used for conformal contacts in many tribological applications in an effort to diminish friction and wear. However, the use of such a surface modifications are still in nascent as far as highly loaded contacts between non-conformal surfaces are concerned. It is mainly caused by the fact that the presence of such micro-features within these contacts can significantly influence the pressure distribution within the contact. Nevertheless, it has been shown in recent studies that the surface texturing can also have beneficial tribological effects if the depth of micro-features is properly designed. This paper is devoted to the experimental study of the effect of the micro-dents of various depths on thin lubrication films to find an experimental evidence of the micro-feature depth threshold for surface texturing applications in highly loaded non-conformal surfaces. The behaviour of an array of micro-dents within thin EHD contacts has been studied by thin film colorimetric interferometry. The influence of surface texturing on lubricant film formation has been observed under sliding/rolling conditions. The significant effect of micro-dents depth on lubricant film thickness is observed for positive slide-to-roll ratio when the disc is moving faster than the micro-textured ball. The presence of deep micro-dents within lubricated contact results in film thickness reduction downstream. As the depth of micro-dents is reduced, this effect diminishes and beneficial effect of micro-dents on film thickness formation has been observed. No significant influence of micro-dents depth on lubricant film shape has been observed in case of negative slide-to-roll conditions when micro-dents do not cause film thickness reduction regardless of their depths.
• HARTL, M., FUIS, V., LIŠKA, M.:
  Experimental study of lubricant film thickness behavior in the vicinity of real asperities passing through lubricated contact,
  Tribology Transactions, Vol.47, (2004), No.3, pp.376-385, ISSN 0569-8197
  journal article - other
  This paper presents an experimental study of the influence of real surface micro-geometry on the film thickness in a circular elastohydrodynamic (EHD) contact formed between a real, random, rough surface of steel ball and smooth glass disc. The Phase Shifting Interferometry has been used to measure in situ initial undeformed rough surface profiles whereas Thin Film Colorimetric Interferometry has provided accurate information about micro EHD film thickness behavior over a wide range of rolling speed. Two real roughness features were studied in detail 56 nm high ridge and 90 nm deep groove, both transversely oriented to the direction of surface motion. It has been shown that ridge is heavily deformed in a loaded contact and its height increases with increasing rolling speed. The asperity tip film thickness behavior is quite similar to the contact average film thickness when the film thickness is higher than the undeformed ridge height. However below this limit the film is thicker than what the EHD theory predicts. For the groove, a local reduction in film thickness at the leading edge has been observed. When the groove is passing through the EHD conjunction, it maintains its undeformed shape. The behavior of both roughness features studied shows good agreement with previous experimental observations conducted using artificially-produced ridge and groove.
• LIU, Y., WANG, Q. J., WANG, W., HU, Y., ZHU, D., KŘUPKA, I., HARTL, M.:
  EHL simulation using the free-volume viscosity model,
  Tribology Letters, Vol.23, (2004), No.1, pp.27-37, ISSN 1023-8883, Springer Netherlands
  journal article - other
  The free-volume viscosity model can accurately predict the temperature pressure viscosity relationship of lubricants. However, it is seldom used in elastohydrodynamic lubrication (EHL) simulation. This paper presents the application of the free-volume viscosity model in a Newtonian EHL simulation of a squalane-lubricated circular contact. Good agreement is observed between available experimental data and simulation results. The pressure viscosity coefficients fit from viscometer data are also discussed. A recently developed definition of the coefficient is used to compare the coefficient value extracted from EHL film thickness interference measurements. Results indicate that the coefficient values from the curve fitting and EHL film thickness extraction agree well which has not been previously observed.
• HARTL, M., LIŠKA, M.:
  Thin film colorimetric interferometry,
  Tribology Transactions, Vol.44, (2001), No.2, pp.270-545, ISSN 0569-8197
  journal article - other
  Measurement technique for the study of very thin lubrication films down to one nanometer in a point contact between a steel hall and a transparent disc is used to explore the relationship between central and minimum film thickness and rolling speed at the interface between elastohydrodynamic and boundary lubrication for a series of lubricating fluids. This technique based on the colorimetric interferometry combines powerful film thickness mapping capabilities with high accuracy. It was confirmed that both hexadecane and mineral base oil obey the linear relationship between log central and minimum film thickness and log rolling speed predicted by elastohydrodynamic theory down to approximately one nanometer. Conversely, squalane and additive-treated mineral base oil showed film thickness enhancement at slow speeds caused by boundary layers formation within the lubricant film. Obtained experimental data was used for the determination of pressure-viscosity coefficients of test fluids. The measurement technique also enabled us to produce information about the influence of boundary layers on film thickness shape.