Interview with Dr.-Ing. Thomas Lohner
What are your hobbies?
I generally enjoy cycling, particularly in the mountains. Currently I am focusing on road cycling. I also go bouldering and play several kinds of ball sports. Sport is an important part of my life. I also like travelling to experience other regions and cultures. Since the start of the pandemic, I have had the chance to enjoy my Bulli on several road trips.
Where do you work and what’s your position?
I started at the Gear Research Centre (FZG) at the Technical University of Munich as a research associate of Prof. Karsten Stahl in 2011. I graduated with my PhD thesis as Dr.-Ing in 2016. In my current Post Doc position I am Head of the Department for EHL-Tribological-Contact and Efficiency at FZG. I specialized in the fields of tribology, efficiency and heat balance of powertrains.
How did you end up in the field of tribology?
The first time I learned about tribology was while I was studying mechanical engineering. Soon thereafter I joined FZG to work as a student assistant focusing on the numerical modeling of elastohydrodynamically lubricated contacts. I was fascinated by the complexity and dimensions involved in this topic and eventually started as a research associate at FZG. During that time, I concentrated on elastohydrodynamic contacts, running-in and tribofilms, which lead to my PhD in 2016. Today, I am happy to have the chance to pursue my passion for tribology in drive technology and to have the opportunity to work in the inspiring environment of FZG.
If you were to explain “Elastohydrodynamically Lubricated Contact” in the “Sendung mit der Maus”, how would you do that?
Which kid would ask such an interesting questionJ Let’s try an explanation by using the analogy of a car facing aquaplaning. First, imagine a tire of a car in contact with the road. At the contact zone, you will notice a flattened area, which increases for lower tire pressures and decreases for higher tire pressures. The tire pressure controls the tire stiffness. The flattened area is also present when the car moves and the wheels rotate. On a dry road, there is direct contact of the tires with the road, resulting in good grip. On an very wet road aquaplaning can occur if the car moves sufficiently fast. That means the tire profile is not able to displace the water beneath it. Thereby, the tires “float” on a water layer, which dramatically reduces the grip. What causes a dangerous situation in aquaplaning is actually useful in the car’s powertrain. In this context, when the car moves, machine elements like gears or bearings convert and transmit torque and speed. Lubrication with oil results in elastohydrodynamically lubricated contacts in such machine elements. Although many machine elements are typically made of steel, elastic deformation can occur in the contact zone, similar to the car tire. The motion of machine elements causes a hydrodynamic lift of the contact zones, similar to a car facing aquaplaning. Hence, the contact zones are separated by an oil layer, similar to the water layer in case of aquaplaning. This allows for smooth operation of machine elements with low friction and wear. What is unique about elastohydrodynamically lubricated contacts is the back-coupling of elastically deformed surfaces through the hydrodynamic effect.
The scales in machine elements like gearings or bearings can assume extreme levels. The oil layer separating the surfaces is typically in the range of micrometers and below, approximately 1/50 the diameter of a human hair. Compared to the length and width of the elastically deformed contact zone this oil layer is extraordinarily small – Dr. Michaelis used to compare it to a piece of paper with the thickness of the paper corresponding to the oil layer separating the surfaces. The pressure in bearings for example can reach up to four GPa, which corresponds to approximately seven African elephants on the area of a thumbnail!
Do you have any favorite anecdote about the broad field of tribology?
When a project runs smoothly, Germans like to say “Es läuft reibungslos”. Literally translated, it means “It runs without friction”. This phrase is often reason for amusement, particularly in situations where eliminating friction would be counterproductive, like in synchronizers or clutches. Moreover, I have a few quite funny anecdotes when we made a mess by experimenting on the non-Newtonian rheology of Oobleck.
If you had one wish with the “Young Tribologists”, what would you wish for?
Considering all the complexity involved in today’s technical applications, I think it is very important to have a strong tribology community. It is nice to see that your commitment raises attention and that the working group Young Tribologists has become a permanent part of the Gesellschaft für Tribologie. I wish the Young Tribologists success in continuing their great work and in attracting further young professionals to join the tribology community. The exchange of experiences and knowledge is very important to anchor and advance well-founded tribology knowledge in industry and academia.
Which trends would you see in the field of tribology, especially which applications do you think would gain increasing importance in the future?
The currently greatest challenge of mankind is to make our way of life sustainable. In terms of technical perspective, this means reducing emissions and pollution as well as improving energy and resource efficiency along the value chain. For the field of tribology, this introduces indirect and direct trends. Indirect trends relate to changes in tribosystems due to new machine architectures or designs. An example is the electrification of automobile powertrains, which introduces different materials, lubricants and operating conditions compared to conventional powertrains. Direct trends relate to ways how tribologists can improve and design tribosystems to make them more efficient and sustainable. For technical applications, this may include superlubricity on a macro scale, needs-based lubrication methods, digitalization by tribosensoring, lightweight materials and biodegradable lubricants. Many hereby involved tribological processes need to be thoroughly understood before introducing them into technical applications. These developments unlock the opportunity to apply and showcase the ability of tribologists. Turning to the challenges tribologists face, I am delighted that our available resources have improved a lot over the years, e.g. with respect to the computational resources for computational tribology. However, we should use these resources in a responsible manner and not forget to simplify tribological problems and relate them to analogies where possible and reasonable. In that way tribology research itself becomes sustainable.
What do you think are the three most relevant competences for somebody working in the field of tribology?
Curiosity, diligence, interlinking disciplines.