Markus J. Buehler

Modeling of complex materials phenomena across multiple length-and time scales

Past research

The past research focused on theoretical and computer modeling of dynamical materials failure phenomena. Starting from the atomistic level of detail, he modeled complex phenomena such as fracture, diffusion and dislocation motion in a variety of different materials. Understanding the failure of matter under critical external conditions is an important, fundamental aspect in describing properties of condensed matter.

Among other aspects, he focused on size effects, that is, how materials properties and mechanisms change as characteristic dimensions of materials are reduced. This was exemplified in studies of ultra thin copper films, or in research in the area of carbon nanotubes (CNTs). Another central question was, when does the continuum description of materials break down, and the atomistic viewpoint needs to be considered? This question was addressed in several projects including studies on CNTs, thin films and dynamical fracture. In studies of dynamic materials failure, an important research objective was to investigate the role of nonlinear material behavior at large deformations, referred to as "hyperelasticity". A key finding in this area is the possibility of cracking faster than all wave speeds, a phenomenon in clear contrast to the classical understanding but recently verified in the lab (see for example, studies on supersonic fracture). Other research was focused on using computer modeling to design new materials and structures. For instance, he developed computational methods to perform topology optimization with the objective of designing hierarchical, multifunctional materials and structures utilizing piezoelectric, active as well as conventional material.

The vision

Everything we know, any substance or material consists of atoms, and the atoms interact based on the principles developed by quantum mechanical theories in the last decades. Many complex materials phenomena playing a critical role in physics, chemistry, engineering and biology can not only be understood at a single time and length scale. Instead, they are consequences of dynamical processes occurring across multiple scales in both length (dimension) and time. Dynamical events occurring on multiple time and length scales, with complex, largely unknown interaction across the scales, together with non-trivial chemistry, physics and mechanics are believed to play a dominating role in many materials phenomena found in nature, in particular in biological processes. In complex dynamical phenomena, nonlinearity, fractality and self-similarity play a key role in structure formation and therefore need to be considered in modeling.

How can we achieve understanding of multiscale materials phenomena? Computer modelling encompassing multiple scales is considered to play a key role in scientific achievements in this area. Such modeling needs to start from the quantum level of detail, proceed to the atomistic level, the mesoscale, the microscale, and up to the macroscopic level. However, seamless modeling across the scales is far from being achieved. The aim of Dr. Buehler’s research is thus to push the frontier in the field of multiscale modeling, and to apply such methods to solve timely problems in physics, engineering as well as biology.

This research will significantly help to shape pathways to tomorrow’s scientific breakthroughs and eventually technological innovations. An example for a vital field are the emerging bio-nano-technologies. Development of these areas is largely motivated by the fact that man-made engineering as we know it today will reach severe limitations with respect to performance, unless humans start to incorporate principles of complex multiscale dynamics into their technologies. Nature, on the other hand, is the master in utilizing such principles since many million of years. Understanding the concepts of nature's material and machine design is therefore believed to play a critical role in the next decades. Since nature does not distinguish human's scientific disciplines, and instead optimizes its materials in terms of mechanical, chemical and physical properties simultaneously at various scales, research in the area is highly interdisciplinary. In some sense, some aspects of his research vision could be understand as "reinventing" classical, macroscopic engineering at very small scales, while making use of novel physical, chemical and biological phenomena helping to define new, superior machine design principles. One of his long-term dreams is to develop rigorous computer models of phenomena related to life. As an example, can we develop a computer model reproducing cell biology, for instance apoptosis, that is based on first principles?

Immediate research interests

A current study is related to modeling biological bulk and surface materials such as bone-like material and adhesion systems of Geckos with the objective of extracting nature's design principles of these superior materials systems. The central question in this project is to understand the coupling of mechanics and chemistry in structural design of the micro- or nanostructure of biological materials.

An immediate research interest is the development and application of computational methods for modeling of complex multiscale and multi-physics phenomena. These methods will play the critical role in future research endeavors in the field of modeling phenomena including biological processes.

Another concern is combination of atomistic modeling of materials and property optimization, that is, design of new materials by rigorous computer simulation (solving the "inverse problem"). For example, given a set of atom species, constraints such as maximum volume concentration, and boundary conditions along with design objectives, can computers be used to design novel materials, possibly along with optimal structure?