# Enlightening force chains: a review of photoelasticimetry in granular matter

## TL;DR

This review explores the history, applications, and protocols of photoelasticimetry in studying granular materials, highlighting its scientific, educational, and public outreach uses over the past 50 years.

## Contribution

It provides a comprehensive overview of photoelastic techniques in granular matter research and offers practical protocols for diverse users, fostering broader understanding and application.

## Key findings

- Photoelasticimetry reveals internal stresses in granular materials.
- The method has been influential in physics research and public education.
- Protocols are provided for artists, educators, and scientists.

## Abstract

A photoelastic material will reveal its internal stresses when observed through polarizing filters. This eye-catching property has enlightened our understanding of granular materials for over half a century, whether in the service of art, education, or scientific research. In this review article in honor of Robert Behringer, we highlight both his pioneering use of the method in physics research, and its reach into the public sphere through museum exhibits and outreach programs. We aim to provide clear protocols for artists, exhibit-designers, educators, and scientists to use in their own endeavors. It is our hope that this will build awareness about the ubiquitous presence of granular matter in our lives, enlighten its puzzling behavior, and promote conversations about its importance in environmental and industrial contexts. To aid in this endeavor, this paper also serves as a front door to a detailed wiki containing open, community-curated guidance on putting these methods into practice.