Experimentally Measuring Rolling and Sliding in Three-Dimensional Dense Granular Packings

Area of Science:

• Physics
• Materials Science
• Mechanical Engineering

Background:

• Granular materials exhibit complex behaviors under stress.
• Understanding energy dissipation in granular systems is crucial for various applications.

Purpose of the Study:

• To experimentally investigate the reversibility of three-dimensional (3D) granular systems under cyclic compression.
• To elucidate the role of 3D rotational motions in granular flow dynamics and energy dissipation.

Main Methods:

• Experimental measurement of a 3D granular system's response to cyclic compression.
• High-resolution imaging using refractive-index-matched fluid.
• Analysis of grain images with artificial intelligence (AI) via variational autoencoders (VAEs) to track 3D translations and rotations.

Main Results:

• Accurate tracking of all grains' 3D translations and rotations.
• Identification of unique roles for 3D rotational motions in granular flows, dominating bulk dynamics.
• Determination that 3D rotations are irreversible under cyclic compression, leading to accumulated sliding and dissipation.
• Numerical simulations confirm bulk dissipation, particularly where grains exhibit greater rotation than translation.

Conclusions:

• 3D rotational motions are critical and irreversible components of granular system dynamics under cyclic compression.
• Granular material's energy absorption and dissipation capabilities are intrinsically linked to the analysis of 3D rotations.
• Further research into 3D rotations is essential for a comprehensive understanding of granular material mechanics.