Tribology in Germany: Latest Research and Development

Sixty-five years ago, in November 1959, the “Gesellschaft für Schmiertechnik” (GST, Society for Lubrication Technology), the predecessor organization of today’s German Society for Tribology, was founded in the form of a non-profit technical scientific association. The society initially saw itself as a platform for the discussion and clarification of issues within lubrication technology in science and industry. The inclusion of the fundamental findings of friction and wear led to the renaming of the society in 1967 to “Gesellschaft für Schmierungstechnik und Tribologie” (Society for Lubrication Technology and Tribology), and then in 1974 to “Gesellschaft für Tribologie” (GfT, German Society for Tribology).

Since the beginning of the GST, regular annual conferences have been held on the topics of friction, lubrication, and wear; thus, The Tribology Conference celebrated its 65th anniversary in 2024.

To mark the occasion of our anniversary, this Special Issue intends to present the latest tribological results in research and development in Germany. However, the beginnings of systematic tribology research in Germany go back several centuries.

Let us start in the year 1557. In 1557, Georgius Agricola (Georg Bauer), who was a major of the city of Chemnitz in Saxonia, a medical doctor, a metallurgist, and a miner, published twelve printed books on “von Bergwergk” (“from the mine”) with colored illustrations, in which the mining and metallurgy of the late Middle Ages were very well documented. The illustrations clearly illuminate and label an unlimited number of different types of tribosystems, but unfortunately no details are given.

After that, there is a gap until 1710. We know that this gap was filled by famous French and British scientists. In 1710, the philosopher and mathematician Gottfried Wilhelm Leibniz (1646 to 1716) published an essay “on the nature and means of overcoming resistance in machines caused by the interaction of bodies, on the occasion of a previous treatise on the same subject”, in which he clearly described that in gears, the involutes are created by unrolling a straight line. “It is well known to those who combine the practical application of mechanics with the knowledge of its principles that–for a given driving force to be applied–the effect of machines can only be increased if unnecessary resistances are removed which require a superfluous application of forces; so that here any gain consists in saving effort”. More than 300 years ago, Leibniz described the great economic benefits of reducing friction losses and energy consumption, which was very topical.

Regardless of the great individual achievements of Leibniz, Agricola, and a few others, scientists and engineers have only been working collectively and systematically on tribological issues in a broad sense for about 150–170 years. How do we define systematic research on tribology? Any research needs meaningful tools. If tribometry and viscometers are regarded as necessary tools, then their beginnings can be traced back to around this time.

In the second third of the 19th century, tribological problems increasingly arose in railroad locomotives and carriages. In 1862, Director Kirchweger of the General Directorate for Railway Carriages and Telegraphs in Hanover published a testing device for “Tests on journal friction on railroad carriage axles”.

Theoretical reflections are as important as metrological devices. In 1881, Prof. Dr. Heinrich Hertz published his theory on contact mechanics, which is globally acknowledged as “Hertzian contact theory”. He had not thought about tribology but was very concerned about how the beam path of optical lenses changes when they are pressed together.

In this decade, around 1885, Prof. Dr. Carl Oswald Viktor Engler of the University of Karlsruhe published an “Ausflußapparat” (outflow device) to measure and quantify the viscosity called, at this time, “Flüssigkeitsgrade” (the degree of fluidity). The so-called “Engler-Grade” (Engler degrees) were used in Europe until the 1960s and were superseded by the ISO-viscosity grades.

Prof. Dr. Adolf Martens, the eponym for “Martensite” or “Martens Universal Hardness”, in 1885, published studies similar to later works of Stribeck. The progress made in Martens “Ölprobirmaschine” (Oil-tasting machine) was the ability to control speed, which was phenomenal at this time. Through publications in the semi-official journal of his royal Prussian institute, Martens had a much smaller reach than Stribeck, who published in the journal of the Association of German Engineers (VDI).

With Prof. Dr. Richard Stribeck’s systematic studies on plain and roller bearings, which were published in 1901 and were acknowledged globally as the well-known Stribeck-type curves, these years were the beginning of systematic tribology research in Germany. It should be noted at this point that while Prof. Stribeck was honored for this work with the technical term “Stribeck-type curve”, the assignment of his “curves” to lubrication regimes was carried out by Prof. L. Gümbel around 1913. On the other hand, Stribeck was the creator of the standard ball bearing steel 100Cr6 = AIS 52100 = SUJ2, which is still the work horse in the ball bearing industry today.

In today’s world of ever-increasing energy demands, combined with an environmentally and cost-driven desire to conserve resources, friction and wear are becoming increasingly important. To avoid friction and wear, save energy, protect the environment, and improve the performance of machines and systems, lubrication is one of the most effective strategies. However, design measures, new materials and coatings, a better understanding of the fundamental tribological relationships, and the predictability of tribological systems also make a decisive contribution toward environmentally compatible and efficient machines and systems, with the goals of having lower energy consumption in the utilization phase, less wear, and the longer service life of mechanical systems.

The visibility of German tribology is internationally characterized by the automotive industry and mechanical engineering. Despite its basic orientation, tribological research is always focused on products and machine elements like rolling and journal bearings, gears, and elastomers. Currently, tribological work is concentrating on topics such as sustainability, raw material availability, the reduction of emissions in the use phase, recyclability, defossilization in mobility and industry, and digitalization.

With the 65th anniversary of the GfT, this Special Issue presents the latest results of tribological research and development in Germany with 21 contributions.

Five papers focus on aspects of rolling bearings. New results are presented on White Etching Cracks (contribution 5), the failure mechanisms in oil-lubricated rolling bearings with small oscillating movements (contribution 9), the tribological behavior of hydrocarbons in mixed friction areas with axial cylindrical roller bearings (contribution 16), the influence of damaging bearing currents on the lifetime of rolling bearings (contribution 14), and a review of the changes in the surface topography in axial bearings because of triboelectric loads (contribution 21).

Regarding plain bearings, there are two papers on the use of planetary gear plain bearings (instead of rolling bearings) in wind turbine gearboxes (contribution 20), and a study on a machine-learning-based approach for wear prediction in plain bearings (contribution 7).

Regarding gears, there is an interesting paper on gears made from high-performance thermoplastics (contribution 1).

With references to lubricants and lubrication, there are three papers on the improved operating behavior of self-lubricating rolling sliding contacts under high load with oil-impregnated porous sintered material (contribution 10), the practical evaluation of ionic liquids–as ‘non-evaporating liquids’–for use as lubricants in clean rooms and under vacuum conditions (contribution 17), and an approach to “intrinsic lubrication” using high-molecular siloxane dispersion in a polybutylene terephthalate (contribution 18).

There are three papers on surface modifications of triboelements, namely a tribological study of ta-C, ta-C:N, and ta-C:B coatings on plastic substrates under dry sliding conditions (contribution 3), the run-in of amorphous carbon coatings and their transfer film formation (contribution 4), and the micro texturing of a cam follower contact (contribution 6).

Two papers deal with the modeling of static and dynamic elastomer friction in dry conditions (contribution 12) and the effect of hydrogen pressure on the fretting behavior of rubber materials (contribution 13).

Finally, four papers focus on fundamental tribological aspects, namely whether mixed friction can exist in fully lubricated elastohydrodynamic contacts (contribution 2), the influence of lubrication cycle parameters on hydrodynamic linear guides through the simultaneous monitoring of oil film pressure and float heights (contribution 8), the numerical simulations and experimental validation of squeeze film dampers for aircraft jet engines (contribution 11), and an experimental approach for friction modes in adhesive contacts of a hard, rigid steel indenter and a soft elastomer (contribution 19).

Following Germany’s long tradition as an ice sports nation, one paper deals with an advanced numerical approach for competitive winter sports applications (contribution 15).