This award initiated a new field of research on how elastic structures interact with granular materials. 

Intellectual Merit: Soft matter physics deals with materials and structures that are easily deformed. Soft materials - polymers, granular matter, and many biological materials - display order on length scales that are much larger than an atom, but much smaller than the overall size of the material. Soft structures - like rods, plates, and shells - are slender, where one dimension, such as the thickness, is much smaller than the others. Slender structures deform easily because bending is easier than stretching. This award examined problems at the intersection of soft materials and soft structures, which involved coupling slender elastic structures with granular materials to form "elastogranular" matter. This award found that there tends to be a constant give-and-take between the deformation of the elastic structure and the rearrangement of the surrounding grains. In loosely packed grains, the packing and burrowing of an elastic rod is governed by whatever shape will reduce its energy to the lowest possible amount. Once the grains jam and transition from a "fluid-like" medium to a "solid-like" medium, then the local arrangement of these jammed grains dictates the shape of the elastic rod. This trade-off continues as more elastic material is packed within the granular material. The local arrangement of the grains leads to different packing strategies for the elastic rod: forcing it to change from periodically folding onto itself to spiraling around itself - similar to the growth and burrowing of some plant roots (Aribidopsis). These fundamental insights paved the way for the development of elastogranular structures: large-scale columns, arches, and beams made of only rocks and string. Such structures are able to bear significant loads, and paved the way for a new class of elastogranular composite structures with unique material properties, and unprecedented reconfigurability. This award helped determined the minimum ingredients to form an elastic structure, and built on our understanding of contact mechanics to predict mechanical behavior of the resulting structures.

Broader Impacts: Elastogranular mechanics dictate plant root growth, the burrowing of bivalves and crustaceans, the locomotive strategies of desert dwelling reptiles, and the penetration of a mosquito?s proboscis. These biological systems all exhibit advanced functionality by utilizing the nonlinear deformations of a continuous structure within a discretized material that can either rearrange like a fluid or jam like a solid. A fundamental understanding of these systems may provide natural barriers to sand and soil erosion, produce scaffolds for coral growth, and enable "living bricks" for sustainable architecture through mycellium growth. In particular, we found that the combination of elastic fibers with granular materials can produce elastogranular structures capable of bearing significant loads. These results may enable first responders to build emergency shelters using found and foraged materials following a natural disaster, or engineers to temporarily stabilize damaged infrastructure. In addition, this award supported outreach efforts using online media to improve student communication and education through an assortment of websites focused on teaching the Mechanics of Materials, Structural Mechanics, and Applied Mathematics in Mechanics. The efforts placed a focus on digital media, which enabled us to create a suite of videos freely available on YouTube. This award supported the education and mentoring of two doctoral students, eleven undergraduate students, and six high school students, and culminated in a review article written for a broad audience of scholars within and new to the mechanics of soft matter.

Last Modified: 11/03/2020
Modified by: Douglas P Holmes