AEM Colloquium Series: Professor Manuel K. Rausch

The Mechanics of Embedded Fiber Networks: Experiments and Models

Fiber networks embedded in a soft matrix carry load in many materials. They form the backbone of soft tissues such as heart valves and blood clots, and they appear in engineered materials such as fiber-reinforced hydrogels and elastomers, electrospun nonwovens, and soft composites for flexible devices. These materials resemble classical fiber composites, but their fibers are semi-flexible and randomly networked, and their matrix can be orders of magnitude softer. As a result, simple rules of mixtures break down. Yet most of what we know about fiber networks comes from studying them in isolation.

In this talk, I will present our work on how an embedding matrix changes fiber network mechanics. I will begin with elementary studies of individual straight and undulated fibers, modeled as geometrically exact isogeometric beams. Next, I will scale up to free-standing networks. Then I will embed these networks in a hyperelastic matrix using a mortar-type finite element approach. Along the way, I will ask how the matrix changes the way fibers bend, reorient, and stretch, and what that means for stiffness and fracture. I will then turn to experiments, from the mechanics of individual electrospun fibers to composites of these fibers in a soft matrix. We test the composites at the macroscale and use two-photon microscopy to track fiber kinematics with and without the matrix. Finally, I will share preliminary work on a phase-field fracture model that couples the matrix and fiber phases.