EPFL researchers simulate the process of adhesive wear

Using high-performance computer simulations, EPFL researchers were able to observe how surface roughness changes when two materials rub together. Their findings, which provide insight into friction and wear mechanisms, have implications for areas ranging from engineering to the study of tectonic faults.


Surface wear depicts the process of material loss when two surfaces come into contact with one another. It has significant economic, social and health consequences – simply think about the fine particles produced by moving vehicles.

In addition, it can be observed at all dimensions, from the nanoscale up to the size of tectonic faults, with the formation of the gouge. There are a few wear systems, yet the adhesive type is generally normal. It happens when two surfaces –, for example, two bits of a similar metal – rub against each other and follow.

One of the parameters that impact the wear instrument is surface roughness. A superior comprehension of how surface unpleasantness changes amid the wear procedure would improve our command over this component. This could prompt noteworthy decreases in energy consumption, greenhouse gas emissions and costs.

Image of the computer simulation showing adhesive wear on a self-affine surface. © LSMS / EPFL
Image of the computer simulation showing adhesive wear on a self-affine surface. © LSMS / EPFL

Scientists at EPFL’s Computational Solid Mechanics Laboratory (LSMS) have taken a vital step toward this path. They have numerically reproduced how surface roughness changes after some time and their outcomes are in accordance with exploratory outcomes.

What separates their reenactments are their term: utilizing a technique created at EPFL, the LSMS analysts had the capacity to reproduce these instruments over an all-inclusive timeframe. At the end of the day, they figured out how to catch the whole procedure – from the underlying geometry to the final fractal geometry.

This is the 3rd study by the LSMS scientists on adhesive wear. Their first study (in 2016) used numerical simulations to describe how the process of adhesive wear produced fine particles. In 2017, taking their simulations further, they came out with a second study. Now, in this 3rd study, scientists demonstrated that it was actually possible to predict the volume, shape and size of these particles.

Scientists are yet to fully understand the physics underlying wear. For that purpose, engineers must still carry out ad hoc experiments for each situation. They only came to know that worn surfaces often display a characteristic fractal morphology, called self-affine, that has some fundamental properties regardless of the material and the scale. The origins of this self-affine morphology are still unknown.

Little work has been done on how surface roughness changes after some time – and it has been for the most part trial. One limitation of trials is that, due to the debris that forms, it is difficult to screen how surface morphology changes amid the rubbing procedure. The scientists defeated this issue through their numerical reenactments, which give a steady stream of information.

Enrico Milanese, a PhD student at the LSMS said, “We used high-performance computer simulations to track the change in surface morphology in 2D materials. In our simulations, we observed that contact between two surfaces always generates a wear debris particle. That particle is then forced to roll between the two surfaces, wearing them down. This led us to conclude that wear debris must be present for the surfaces to develop their characteristic self-affine roughness.”

The study is published in the journal Nature Communications.