Rotating structures in A) metal deformation experiments with aluminium (white) and copper (reddish), B) computer simulations and C) rocks in Western Australia. All these structures were created by a similar physical process.
A) Mohsen Pouryazdan | KIT, B) Boris Kaus | JGU, C) Cees Passchier | JGU
The research group led by Prof. Dr. Boris Kaus from the Institute of Geosciences at the Johannes Gutenberg University of Mainz (JGU) has demonstrated in its work that the same instability that causes kilometre-thick rock layers to fold over long periods of time also acts at the micrometre level, in this case with metals. The starting point was a study conducted by colleagues from Prof. Dr. Horst Hahn's team at Karlsruhe Institute of Technology (KIT), who for the first time were able to show mechanical mixing of metals in three-dimensional form. Mechanical mixing occurs when, for example, two metals are pressed together and deformed. The three-dimensional representation of the mixing showed that this process is more complicated than might have been expected from the experiment. In particular, rotating structures appear that are similar to clouds or liquids and were therefore initially interpreted as Kelvin-Helmholtz instability.
Structures resemble rock deformations
In fact, the rotating structures resemble geophysical structures far more. "Kelvin-Helmholtz instabilities could not explain this problem because air and water move much faster than metals and therefore the basic physics is different", Kaus explains. The Mainz researchers have established that the structures found in Karlsruhe resemble mountainous rock formations and the basic physics is practically identical. The research work, which was carried out in cooperation with KIT, was published by "Nature Communications". In this study, the researchers have presented a strategy that shows how the morphological development of deforming multiphase solids proceeds on a micrometre scale. Computer simulation makes it relatively easy to reproduce the seemingly complex experimental observations by inputting only a few material parameters such as viscosity and stress exposure. According to this study, the shear instability shown in this experiment on metals can be compared with geological systems, which change on a large scale and over millions of years.
The model is not limited to multilayer metals under shear stress but can also be applied to other material systems, regardless of morphology. This makes the model a versatile tool for investigating a wide range of materials and material processing techniques. "We could show for the first time that modelling techniques from basic geoscience research can have very practical applications for materials science", Kaus remarks: "Our software had been developed to simulate mountain formation processes – this has been a fine example of how basic research can always have unexpected applications."