Yielding and hardening of flexible fiber packings during triaxial compression

TL;DR

This study investigates the mechanical behavior of flexible fiber packings under triaxial compression, revealing conditions that lead to yielding or hardening, and providing phase diagrams to classify responses based on fiber properties and pressure.

Contribution

It introduces a comprehensive analysis of how fiber aspect ratio, friction, and pressure influence yielding and hardening in fiber packings, including phase diagrams for classification.

Findings

Short fibers yield with constant deviatoric stress after peak.

Long fibers exhibit hardening with increasing stress and packing density.

Hardening packings support larger loads and enhance stability.

Abstract

This paper examines the mechanical response of flexible fiber packings subject to triaxial compression. Short fibers yield in a manner similar to typical granular materials in which the deviatoric stress remains nearly constant with increasing strain after reaching a peak value. Interestingly, long fibers exhibit a hardening behavior, where the stress increases rapidly with increasing strain at large strains and the packing density continuously increases. 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. Large fiber aspect ratio, large fiber-fiber friction coefficient, and large confining pressure promote hardening behavior. The hardening packings can support much larger loads than the yielding packings contributing to the stability and consolidation of the granular structure, but larger internal axial forces occur within fibers.