Granular materials are large aggregates of macroscopic, individually solid particles that interact through contact forces. A central problem in understanding and controlling their behavior of is to find a connection between local structural details on the level of individual particles and the global properties of the aggregate as a whole.  The current state of the art proceeds from knowledge about given (or assumed) particle properties to find the overall behavior.  However, in many practical situations it is desirable to proceed in the opposite direction: starting from a desired aggregate behavior to find optimized particle-scale properties. This would make it possible to answer questions such as: What particle shape will produce a random packing that is strongest under compression (or stiffest/softest, toughest,...)? What shape will produce a particular desired stress-strain relationship? Is it possible to make an aggregate that does not yield but instead exhibits strain-stiffening behavior?

So far, there are no established design rules for this inverse problem.  We are pursuing a comprehensive approach to tackle this issue.  On the one hand, to find design rules we are investigating the aggregate packing properties of a wide range of particle shapes (especially non-convex shapes), focusing in particular on aspects such as the packing densities, the stress-strain relationships under shear, bending or compression, and the failure modes at yielding. On the other hand, we recently developed a new computer-aided method that makes it possible, for the first time, to address the inverse problem and find optimized particle shapes for a given performance goal despite the absence of design rules. 

Recently, we have applied these methods to the design of optimized granular media for applications ranging from soft robotics to jamming-based architectural structures. For overviews on these ideas, see

        • Heinrich M. Jaeger, “Toward Jamming by Design”, Soft Matter 11, 12-27 (2015). link

        • Sean Keller and Heinrich M. Jaeger, “Aleatory Architectures”. preprint

This effort makes extensive use of a number of special facilities we have available in our lab, including 3D printing, x-ray tomography, and software suites for large scale simulation of granular materials.

For more info on specific projects click on PROJECTS