Materials cannot think or be creative, so in this sense they also can’t be intelligent.Prof. Marc-André Keip
Initially, it strikes one as something of a contradiction that Keip is in fact researching intelligent materials at the Chair of Materials Theory. However, the 40-year-old immediately resolves the confusion: certain materials, he explains, react to physical or chemical stimuli in a controllable manner, which makes them appear to be quite smart after all.
“Essentially, it’s about coupling various phenomena”, says Keip. Materials are considered to be “intelligent” when, for example, magnetic and mechanical forces interact within them. One classic example is found in many lighters, in which the ignition spark is created by a so-called piezoelectric quartz rather than a flint, which is energized by pressure from the user and thus generates a spark.
Of course, such rather mundane applications are of no interest to Keip and the other seven scientists in his research group. “We are not exclusively focused on applications anyway”, he says. “Often we are more interested in the fundamental phenomena. It’s the challenge of expressing these in mathematical models that attracts us.” “We”, he adds with a laugh: “often consider something to be practical if it can be represented on the computer”.
Difficult to research in laboratory experiments
Yet, in this way the Stuttgart-based scientists are providing the basis for practical development work, for example on magnetorheological elastomers, i.e., soft plastics that contain magnetic particles and deform when they interact with magnetic fields, enabling them, for example, to close valves or perform adaptive damping tasks.
According to Keip, intelligent materials could enable many other technical applications, but some of them are difficult to research in laboratory experiments, due, ironically enough, to their otherwise welcome qualities. If a metal component is subjected to a tensile test in the laboratory, for example, external forces which are precisely adjustable from the outside act on it at all points inside. Soft magnetoelastic materials react in a much more complex way in experiments: when they are exposed to a magnetic field, an inhomogeneous state of forces is established inside of them. This, as Keip explains, makes it much more difficult for researchers to empirically determine reliable parameters for such materials. However, without an indepth knowledge of the properties of intelligent materials and their reactions to external stimuli, their further development will also come to a halt.
The Stuttgart-based material theorists are showing the way out of this dilemma. “We are creating the theoretical foundations with which the behavior of materials can be modeled mathematically”, explains Keip. These theoretical models form the basis for numerical simulations, which can be used to investigate and optimize the behavior of materials as well as the structures created from them, which, in turn, enables engineers to better assess whether a given application should be developed at all.
“A good simulation obviates the need to carry out certain experiments in reality”, says Keip. One example is the expensive crash tests used in the development of motor vehicles. Simulations are cheaper, but they also have another advantage, Keip explains: practically any number of parameters can be tested in the simulation cycles. This, among other things, enables the composition of composite materials to be optimized in recurring simulation cycles, which is not easily possible in the laboratory.
His team, explains Keip, is mainly working on the so-called continuum level, i.e., in the size range of connected material structures. “Many intelligent materials have a microstructure, which we investigate and try to draw conclusions about based on what is visible to the naked eye.”
A good simulation obviates the need to carry out certain experiments in reality.Prof. Marc-André Keip
A better understanding of porous media
The research group is also working on a better understanding of porous media in collaboration with the University of Stuttgart’s Sonderforschungsbereich 1313. Among other things, the researchers are looking into how cracks form and continue to form in rocks when liquids are used under high pressure. This knowledge is important, for example, in connection with fracking processes. For example, even if components develop cracks, simulations can provide information about how they could be avoided.
Keip was already looking at intelligent materials and the associated coupling phenomena during his doctoral studies at the University of Duisburg-Essen. When a junior professorship at the University of Stuttgart’s Institute of Applied Mechanics (Civil Engineering) (MIB) was announced in 2013, the Essen-born professor jumped at the chance. The University of Stuttgart was even more attractive to him because of the SimTech Cluster of Excellence. He has held the Chair of Materials Theory since January 2019. “One particularly attractive aspect of researching intelligent materials”, he says, “is that it links mechanics with many other related fields of research”.
Text: Jens Eber