Horst Czichos

Multilaboratory tribotesting: Results from the Versailles Advanced Materials and Standards programme on wear test methods

Abstract The Versailles Project on Advanced Materials and Standards (VAMAS) on wear test methods is one of the rapidly growing suite of projects initiated as a result of decisions following the 1982 Versailles Summit Meeting of the Heads of State or Governments of Canada, France, Germany, Italy, Japan, United Kingdom, United States of America and representatives of the Commission of the European Communities. In the frame of VAMAS an international round robin comparison on the reproducibility and comparability of friction and wear data has been performed under conditions of dry sliding. The tribological behaviour of α-Al 2 O 3 ceramic and AISI 52100 steel combinations in a defined ball-on-disc configuration was determined under specified operating conditions of load, speed, temperature and sliding distance. For the different material combinations typical wear patterns were observed, including substantial material transfer for the steel-steel and steel-ceramic systems, but very minor wear was observed for the ceramic couple. Comparison of the numeric friction and wear data shows good agreement in tribological terms. The test methodology and the numeric tribological data may serve as a reference for other comparable tribotests.

Advances in tribology: the materials point of view

The application of advanced materials in various areas of contemporary technology can lead to improvements in the function, quality and performance of engineering components and systems. In this paper, an overview of the developments in high performance materials, both organic and inorganic based, is given. This includes thin hard coatings because of their increasing importance in tribological improvements. For these types of materials the requirements for tribo-engineering applications are analysed. Research results from BAM concerning ceramics and ceramic composites, polymers and polymer composites as well as hard coatings illustrate the friction and wear behaviour of these materials and their potential for tribo-engineering applications.

International multilaboratory sliding wear tests with ceramics and steel

Abstract Within the framework of the Versailles Project on Advanced Materials and Standards (VAMAS) a second international round robin comparison on the reproducibility and comparability of friction and wear tests has been performed with combinations of α-Al2O3 ceramic, Si3N4 ceramic and AISI 52100 steel under conditions of dry sliding. The stationary and the moving components of the ball-on-disc test system respond differently to the interfacial tribological action. Various interfacial tribological processes, e.g. microfracture, ploughing, materials transfer, tribo-oxidation and corresponding appearances of the wear surfaces were identified by means of scanning electron microscopy and energydispersive analysis of X-rays. If for a given unlike material pairing the materials of the stationary and the moving partners are exchanged, a significant variation in the system wear as well as in the wear of the two components may result. The great importance of the proper definition and control of component and system parameters of the materials bulk and surface conditions, the contact geometry, and the operating and environmental conditions for the reproducibility of the tribological tests was clearly demonstrated. For an unambiguous report of wear data, values related to the wear system and to the two individual materials components of the system must be distinguished. From the results of these multilaboratory studies, conclusions for the performance of reproducible tribotests can be drawn.

Influence of adhesive and abrasive mechanisms on the tribological behaviour of thermoplastic polymers

Abstract Results of investigations on thermoplastic polymers are presented which can be interpreted by prevailing adhesive or abrasive mechanisms as well as by an overlap of different tribological processes. For polymer-polymer sliding pairs it was found that friction is decisively connected with adhesion. When data on the surface energy of the examined polymers were used, the experimentally determined friction values could be related to the adhesion energies of the different polymer-polymer sliding pairs. For polymer-steel sliding pairs the wear behaviour under prevailing abrasive mechanisms was studied. A relationship was established between the combined stresses in the interfacial area and the tensile or rupture strength of the polymers studied. The tribological behaviour of glass-fibre-reinforced polymers such as polyamides and poly(phenylensulphide) is determined by an overlap of different processes which are influenced by the orientation of the glass fibres with respect to the sliding area rather than by the percentage of the glass fibres added. Different investigation methods, e.g. scanning electron microscopy and energy-dispersive analysis of X-rays, revealed that numerous individual processes such as adhesion, material transfers, retransfers, abrasion, deformation and rupture processes as well as surface fatigue overlap in the complex wear behaviour of glass-fibre-reinforced polymers.

Tribology and Its Many Facets: From Macroscopic to Microscopic and Nano-scale Phenomena

The key features of tribology – interfacial phenomena of interacting bodies in relative motion – are as origin of friction and wear scientifically interesting and have important applications in technology and engineering. The interfacial interactions have been studied in various theoretical and experimental approaches. Depending on the scope of the investigation and the nature of the tribological solid/fluid/solid or solid/solid system under study, these approaches apply contact mechanics, hydrodynamics, and rheology as well as solid state physics and chemistry. Accordingly, also various experimental techniques have been used, ranging from Coulombs classical tribometer to the contemporary atomic force microscope.This paper reviews by way of examples some of the basic interfacial facets of tribology – from bulk continuum to atomistic/discrete phenomena – in a macroscopic, microscopic, and nano-scale point of view. For tribo-testing it is important to characterize the tribo-system under study by an appropriate choice of a systems envelope and to consider the hierarchy of interaction levels.

Influence of asperity contact conditions on the failure of sliding elastohydrodynamic contacts

Abstract In continuation of the cooperative IRG-OECD program, the lubrication regimes as well as critical failure conditions of sliding concentrated steel contacts have been studied with surfaces of different roughnesses. Measurements of the friction force and the electrical contact resistance were combined with surface topography studies and with calculations of the EHD film thickness-to-roughness ratio λ. Results for line and point contacts between rough surfaces, lubricated with plain mineral oils, show a gradual changeover from the fluid-film regime of 100% “no-contact time” to full asperity contact as a function of increasing contact pressure or bulk oil temperature. The breakdown of the EHD film is initiated by thermal and topographical interfacial changes. Additional tests with lubricant additives indicate that the onset of “incipient scuffing” depends on the physical and chemical nature of surface films in addition to critical interfacial conditions for the EHD film breakdown.

A systems analysis data sheet for friction and wear tests and an outline for simulative testing

Abstract Recent research results show that the application of systems thinking and systems analysis can provide a convenient framework for a coherent description of the multidisciplinary subject of tribology. Using this systems approach, a data sheet for a systematic compilation of parameters relevant to tribo-testing and tribo-engineering has now been developed. According to this “checklist”, the main tribologically relevant parameters can be divided into four groups under the headings: technical function of the tribosystem, operating variables, structure of the tribosystem, and tribological characteristics. The details of the systems analysis checklist are described and examples of its application are given. Based on the systems approach to tribology a guideline for simulative tribo-testing is outlined.

Tribological studies on rubber-modified epoxies: influence of material properties and operating conditions☆

Abstract An epoxy material has been modified by chemically incorporating siloxane to improve fracture toughness. In this work the friction and wear properties are compared in two test configurations, a steel ball sliding on a cast epoxy surface and an epoxy pin sliding on a glass or a steel disk. The morphologies of the wear surfaces are compared. The friction and wear results indicate that the test configuration has a significant influence on the effect of the siloxane modifier. These effects are a result of different “tribological stresses” acting on the polymers and different wear mechanisms which respond to the different mechanical properties of the polymers. The effect of the siloxane modifier is more pronounced in the steel-ball-on-epoxy-disk configuration in which the wear rate is very sensitive to the size and spacing of the elastomeric domains which segregate during curing.

Tribological transition phenomena of ceramic materials

On discute brievement de plusieurs types de transitions observees dans le glissement de paires ceramique-ceramique ou ceramique-metal

Wear of medium carbon steel: A systematic study of the influences of materials and operating parameters☆

Abstract The tribological behaviour of medium carbon steel has been systematically studied as a function of (i) material properties, such as hardness and microstructure, (ii) kinematics, i.e. sliding and rolling, and (iii) lubrication modes and environmental conditions, including vacuum, air and boundary lubrication. As characteristic results it is found that not only the material properties per se but also system-dependent characteristics, such as the ratios of the hardness and roughness values of the stationary and moving specimens, are important parameters in the friction and wear behaviour. Scanning electron microscopy studies revealed that the tribological behaviour is governed by different prevailing basic wear mechanisms.