(456c) Computational and Experimental Studies of Mechanical Compression of Flexible Fiber Packings

A numerical flexible fiber model is developed based on the Discrete Element Method (DEM). The model is thereafter applied to simulate the compressions of flexible fiber packings. The normal and tangential fiber-fiber contact force models for the simulations are determined and verified by comparing with experimental results of uniaxial compression in a fixed container. To achieve a good prediction, the normal contact force needs to account for the various contact types between the sphero-cylinder elements, and the tangential contact force model has to take into account the process of static friction before sliding friction occurs. Simulations and experiments are also performed to investigate triaxial compressions of flexible fiber packings. It is observed that instead of yielding, long fibers exhibit a hardening behavior, where the stress increases rapidly with increasing strain at large strains and the packing density continuously increases. Thus, phase diagrams for classifying the bulk mechanical response as yielding, hardening, or a transition regime are generated as a function of the fiber aspect ratio, fiber-fiber friction coefficient, and confining pressure. The hardening packings can support much larger loads than the yielding packings, but larger internal axial forces within fibers and larger fiber-fiber contact forces occur.