10:30–11:30 am
Please join us:
Nidhi Pashine’s PhD Thesis Defense
MECHANICAL METAMATERIALS FROM DISORDER
Disordered materials are different from crystals not only because of their disordered structure but also because they live in a rugged energy landscape with an enormous number of local minima. By manipulating a disordered material in subtle ways, the system can be easily moved from one local minima to another, thereby dramatically changing its behavior. This concept can be used to make materials with unusual and interesting properties. Starting from a computer simulation of a random spring network, we can transform the network’s mechanical response by simply removing or modifying a small fraction of bonds. We have then been able to fabricate physical realizations of such systems in experiments where they show the predicted response in both two- and three- dimensional materials.
We have also been able to modify disordered systems in experiments in order to create a desired response. By making disordered networks out of a photoelastic material, we can measure the stress distribution in these networks under various external forces and prune those networks in-situ based on the stress information alone. Thus, the network response is transformed in a desired way without the need of prior design using simulations.
This approach of material design is successful; however, it is hard both to scale up the system size as well as scale down the size of individual bonds. Since a disordered system is often out-of-equilibrium and ages over time, it has a memory of its history which affects its properties, including its response to external perturbations. By controlling the external conditions under which a material evolves, we can direct the aging process to modify its behavior in a favorable way. We use directed aging as a method for modifying and tuning a material’s elastic properties in the non-linear as well as the linear regimes without having to control the material at the microscopic level. “Directed aging” thus has the potential to become a general, new and unconventional methodology for creating specific functionality in materials.
Committee:
Sidney Nagel (Chair)
Margaret Gardel
Arvind Murugan
Scott Wakely