# Computer Simulations of Soft Responsive Gels with Embedded Regular Arrangements of Stiff Fibers

## TL;DR

This paper uses computer simulations to study how embedding stiff fibers in gels can improve material resilience and mechanical properties.

## Contribution

The study introduces design rules for composites based on fiber geometry and Poisson’s ratio mismatch to achieve auxetic behavior.

## Key findings

- Embedded fiber geometries like hourglass and honeycomb induce auxetic behavior in composites.
- Poisson’s ratio mismatch between fibers and gel affects shape changes under deformation.
- Rectangular fiber arrangements do not cause significant shape changes when Poisson’s ratios are similar.

## Abstract

Designing polymeric composites that enhance the material’s
resilience and mechanical properties is vital in the production of
such technologically important systems as aeronautic components, biomimetic
architectures and thin film displays. Taking advantage of the rich
deformation behavior exhibited by regular, geometric arrangements
of stiff fibers, we used computer simulations to analyze the properties
of composites formed by embedding a layer of fibers, arrayed into
rectangular, hourglass and honeycomb structures, into the middle of
a thicker hydrogel. We determined how the geometry of fiber layer
affected the composite’s resistance to finite deformations
and changes in shape. Our computer simulations revealed cooperative
interactions between the embedded stiff fibers and the gel matrix
that led to mechanical reinforcement under both small and finite shear
and tensile deformations, and to shape changes under finite tensile
deformations. The latter effects depended on a mismatch between the
Poisson’s ratio of the gel matrix and fiber geometry of the
fiber layer. When the Poisson’s ratio for the fiber layer and
the gel were both positive and comparable in value, the composite
did not undergo significant shape change, as evidenced in the case
involving the rectangular fiber arrangement. The computer simulations
showed that for particular fiber arrangements (hourglass and honeycomb),
the composite could exhibit the auxetic behavior (negative Poisson’s
ratio) in one or two directions. Our results yield design rules for
enhancing the resilience and mechanical properties of the polymer
matrices and thus yield superior composites for technological applications.