# Nonlinear Poisson effect governed by mechanical critical transition

## TL;DR

This paper reveals that fiber networks exhibit a nonlinear Poisson effect driven by a mechanical phase transition at a critical strain, characterized by a peak in Poisson's ratio and diverging strain fluctuations.

## Contribution

It uncovers a collective mechanical phase transition controlling the nonlinear Poisson effect in fiber networks, dependent on network connectivity.

## Key findings

- Large nonlinear Poisson effect observed at small strains
- Critical uniaxial strain depends on network connectivity
- Diverging nonaffine strain fluctuations at transition

## Abstract

Under extensional strain, fiber networks can exhibit an anomalously large and nonlinear Poisson effect accompanied by a dramatic transverse contraction and volume reduction for applied strains as small as a few percent. We demonstrate that this phenomenon is controlled by a collective mechanical phase transition that occurs at a critical uniaxial strain that depends on network connectivity. This transition is punctuated by an anomalous peak in the apparent Poisson's ratio and other critical signatures such as diverging nonaffine strain fluctuations.