Evaluation of the out-of-plane response of fiber networks with a representative volume element model, TAPPI JOURNAL June 2018

ABSTRACT: Many natural and synthetic materials have fibrous microstructures, including nonwoven fabrics, paper, and fiberboard. Experimentally evaluating their out-of-plane mechanical behavior can be difficult because of the small thickness compared with the in-plane dimension. To properly predict such properties, network-scale mod-els are required to obtain homogenized material mechanics by considering fiber-scale mechanisms. We demon-strate a three-dimensional representative volume element (RVE) for fiber networks using the finite element method. We first adopted the classical deposition procedure to generate fiber networks with random or preferential fiber ori-entations and then an artificial compression to achieve the practical fiber volume fraction. The hollow fibers, described with elastic-plastic brick elements, were joined by interface-based cohesive zone elements introduced in all fiber-fiber contact areas. Thereafter, the fiber networks were subjected to displacement boundary conditions, and their apparent mechanical response was evaluated by a homogenized stress. To determine the RVE dimension, we further conducted an RVE size convergence study for the out-of-plane compression and tension (varying specimen length while keeping the specimen thickness constant). Finally, we evaluated the apparent out-of-plane response of the obtained RVE for four loading cases: out-of-plane compression, tension, simple shear, and pure shear. The results show a quite different mechanical behavior of fiber networks between all these out-of-plane loading cases, particularly between tension and compression.

Application: Virtual fiber networks can be generated to evaluate the out-of-plane mechanical properties.

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