Mechanics, Department System Dynamics and Friction Physics



A tribologist would give a very simple answer to Goethe's Faust's question about "what holds the world together at its core" - adhesion. The term "adhesion" is used in science to describe the forces at the interfaces between bodies. We rely on adhesion forces when we use a bonded joint - be it a shoe sole, a car roof or a carbon-fibre airplane wing, a note on the wall or a medical plaster. Locusts and geckos rely on their feet to adhere to the various surfaces they walk on. Adhesion of living cells connects trillions of these microscopic units to a living organism. The strength of the adhesion between cells also determines their mobility and growth, a disorder can be cause for the development of tumors. Adhesion is not always useful - valves with rubber seals must be able to open at any time, so excessive adhesion can lead to malfunction. Many microtechnology systems, such as the position sensors in smartphones, are prone to unwanted adhesion simply because of their tiny size. Many areas of technology and medicine are urgently interested in influencing adhesion. Depending on the application or needs, by increasing or decreasing them.

Influence of contact geometry on the adhesive strength

In a series of numerical simulations and experiments, the most important influencing factors on the adhesiveness of adhesive contacts have been researched at the department. Results are published in the paper:

Popov, V. L., Pohrt, R., & Li, Q. (2017). Strength of adhesive contacts: Influence of contact geometry and material gradients. Friction, 5(3), 308–325.

The video of the experiments can be seen at: 

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Sticky or Not Sticky?

The adhesive contact between a parabolic indenter with superimposed roughness and an elastic half space is studied in the JKR-limit (infinitely small range of action of adhesive forces) using the boundary element method with mesh-dependent detachment criterion suggested in 2015. Three types of superimposed roughness are considered: one- and two-dimensional waviness and randomly rough roughness. It is shown that in the case of regular waviness, the character of adhesion is governed by the Johnson adhesion parameter. For our randomly rough surfaces a new adhesion parameter has been identified numerically, which uniquely determines the adhesive strength of the contact.

Li Q, Pohrt R and Popov VL (2019) Adhesive Strength of Contacts of Rough Spheres. Front. Mech. Eng.5:7. doi: 10.3389/fmech.2019.00007