Granular jamming and rheology in microgravity

TL;DR

This study investigates how granular materials behave in microgravity, revealing that gravity influences densification and flow, and providing experimental data to improve models for space applications.

Contribution

The paper presents novel microgravity experiments on granular jamming and rheology, highlighting gravity's dual role and informing tailored models for low-gravity environments.

Findings

Jamming occurs at lower density in microgravity

Cohesive forces increase flow stress in microgravity

Gravity promotes densification and flow in granular media

Abstract

Understanding how granular materials behave in low gravity is crucial for planetary science and space exploration. It can also help us understand granular phenomena usually hidden by gravity. On Earth, gravity dominates granular behavior, but disentangling its role from intrinsic particle interactions is challenging. We present a series of compression and shear experiments conducted in microgravity using the Center of Applied Space Technology and Microgravity (ZARM) drop tower and GraviTower Bremen (GTB). Our in-house developed experimental setup enables precise measurement of packing density and in-situ shear stress via a Taylor-Couette rheometer. We find that the jamming transition occurs at lower packing density in microgravity than on Earth, confirming that gravity promotes densification. Rheological measurements further reveal that in microgravity, the lack of a secondary force field and predominance of cohesive interparticle forces increase the stress needed for granular media to flow. These findings highlight gravity's dual role in enhancing both compaction and flow, and demonstrate the need for tailored granular models, valid in low- and microgravity environments.