Granular materials—such as sand, powders, and pharmaceutical pills—are ubiquitous in daily life and industry. When grains of similar size are packed regularly, they can form crystal-like structures that are strong but can suddenly fail under stress. A new study has identified a precursor to this failure: soft vibrational modes that appear before the material yields.
Researchers at the University of Chicago and the University of Pennsylvania conducted experiments with photoelastic disks, which change color under stress, to observe how granular crystals respond to compression. They found that as the material approaches its yield point, certain low-frequency vibrations become increasingly prominent, signaling an impending rearrangement of grains. These 'soft spots' are regions where the material is more susceptible to deformation.
The findings, published in the journal Physical Review Letters, could have implications for predicting failures in a wide range of granular systems, from pharmaceutical manufacturing to construction and geophysics. By monitoring these vibrational signatures, engineers might be able to detect early warning signs of material failure before it occurs.
Lead author and postdoctoral researcher at the University of Chicago, Dwaipayan Biswas, noted that the study provides a new tool for understanding the mechanics of granular materials. The team used machine learning to analyze the vibrational modes and identify the soft spots, which could lead to more robust designs and safer handling of granular materials.
