| The mechanical interactions between fibers in a dense random-fiber network transmit stress, cause fiber curvature, and influence fiber orientation in the processing of many types of composites. A few theories describe the mechanics of fiber networks, but almost no simulation results are available. Here, we report a direct numerical simulation of the mechanical behavior of random-fiber networks.;The finite element method is used, and each fiber is represented by a small number of 3-D beam elements. The calculations assume a periodic structure to avoid boundary effects, but within the unit cell the fibers are placed randomly. A special algorithm that uses the random sequential adsorption process creates an initial structure of straight, random, non-intersecting fibers, from which a unit cell with periodic boundary conditions is built automatically. The simulation uses an explicit time integration of dynamic equations, with a general contact algorithm (ABAQUS/Explicit).;A typical run involves 5000 fibers with l/d = 100, compressing the network from an initial volume fraction of 5% to a final volume fraction of 25% using 105 time steps. At the final volume fraction, there are 200, 000 fiber-fiber contacts. Results from the simulation are in good agreement with van Wyk's (1946) theory for compaction pressure at low-to-moderate fiber density. They show fair agreement with Toll's (1998) theory for the number of fiber-fiber contacts, and they also show good agreement with a simple slender-body model for fiber orientation, at least during the initial uniaxial compression.;The simulation then extends the uniaxial compression to large shear deformation. A maximum shear strain of about 2.0 is applied. Results from the simulation are shown for the bulk shear stress, the number of fiber-fiber contacts and the fiber orientation. This simulation provides an interesting tool for understanding the mechanics of random-fiber networks, and building models of composite materials processing. |
