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Granular materials, ranging from sand and soil to coffee beans and sugar, form a fundamental part of our everyday lives and are ubiquitous across various industries. Yet, understanding how these materials move and react to external forces has remained a complex challenge, with most research confined to limited two-dimensional experiments. Now, researchers at the Massachusetts Institute of Technology (MIT) have broken new ground with a method that enables detailed three-dimensional experiments, shedding light on the intricate behavior of granular materials and their response to forces.
Published in the journal PNAS, the study by MIT professor of civil and environmental engineering Ruben Juanes and former MIT student Wei Li, now faculty at Stony Brook University, presents a revolutionary approach to analyzing granular materials’ behavior. By employing advanced techniques, the researchers have unlocked a deeper understanding of how forces are transmitted through these materials and how grain shapes influence outcomes.
“Granular materials are a part of our everyday infrastructure, from soil and sand to the ballast of railroad beds,” says Li. “Understanding their behavior is crucial for predicting and preventing disasters like landslides.”
The study reveals a significant finding: the strength of a granular material is profoundly influenced by the shapes of its constituent grains. Through meticulous experiments, the researchers demonstrated why packs of angular particles are stronger and more stable than those composed of spherical grains.
Traditionally, modeling the behavior of granular materials has relied on two-dimensional representations, limiting the understanding of their complex dynamics. However, Li’s prior work in creating three-dimensional particles through squeeze-molding provided the foundation for this breakthrough research. By utilizing specially designed photoelastic particles, which change color and brightness under stress, the researchers were able to visualize the internal stresses within granular materials in three dimensions.
“What’s remarkable is that we’re not just imaging the porous medium itself; we’re imaging the forces transmitted through it,” explains Juanes. This innovative approach offers unprecedented insights into the distribution of forces within granular materials, paving the way for more accurate predictions of phenomena such as landslides and earthquakes.
The method combines photoelasticity with computed tomography to reconstruct detailed three-dimensional images of the stress distribution within granular materials. By immersing the grains in a fluid with the same refractive index, the researchers were able to observe stress changes while fluid flowed through the material, offering a comprehensive understanding of how forces are transmitted.
While the full potential of the method is yet to be realized, it holds promise for diverse applications beyond geotechnical engineering. From designing robust infrastructure to enhancing industrial processes and even studying biological systems, the method offers a versatile tool for understanding and controlling granular materials.
Supported by the U.S. National Science Foundation, this groundbreaking research represents a significant step forward in unraveling the mysteries of granular materials and their role in shaping our world. As the researchers continue to refine their techniques, the insights gained could lead to transformative advancements in various fields, ensuring safer, more resilient infrastructure and a deeper understanding of natural phenomena.
