CAREER: Microscale Deformations Underlying Multiscale Mechanics of Fiber Networks

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This Faculty Early Career Development Program (CAREER) award supports fundamental research to study properties of materials made of random networks of microscopic fibers. Applications are most direct in human health, as fibrous materials form the structure for numerous tissues in the human body. Mechanical properties of those tissues relate to injury, for example in tearing of ligaments, and to disease, for example in progression of cancer. Fibrous materials also have potential engineering applications, as they are light in weight yet have high tolerance for damage. In both applications--human health and engineering--it is crucial to understand the relationship between structural properties, like fiber size and number, and mechanical properties, like stiffness and strength. This research will establish these crucial relationships, which will advance treatments to disease and enable engineering applications for fibrous materials. As many future applications of this research are in human health, there will be a need for future engineers to be trained in both engineering and biology. Therefore, an additional objective of this project is to enable students to apply principles from multiple different scientific fields to solve engineering problems. For this, undergraduate students in engineering will practice applying concepts of engineering to problems in biology and human health. Additionally, high school students in biology will learn how principles of physics can be used to understand biology. It is expected that this interdisciplinary training will strengthen the engineering and scientific workforce.The specific objective of this research is to determine how properties of the individual fibers within a network affect the mechanics under different loading conditions. To accomplish this, experiments will subject fibrous networks to both global and local loads and measure the displacements at the scale of the fibers. Results will be compared for networks having different fiber concentration, length, and crosslinking. In parallel, a theoretical model simulating the mechanics of how each fiber bends and stretches will be used to test the state-of-the-art theory against experimental data. The results will establish the fiber properties, strain magnitudes, and length scales for which nonlinearity, heterogeneity, nonaffinity, and plasticity each affect the mechanics. Together, these findings will establish which deformation mechanisms must be accounted for in a model that predicts the response of fibrous materials to general loading conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.