(479a) Cracking and Self-Healing of Shrinkable Granular Packings

We study the drying of shrinkable granular materials—materials composed of hydrated grains that individually shrink when dried. Prominent examples include clays, soils, biological tissues, foods, and coatings. In many cases, these materials crack during drying, critically hindering applications. By combining experiments, discrete-element simulations, and poroelasticity theory, we reveal how grain shrinkability dramatically alters crack evolution during drying—in some cases, even causing cracks to spontaneously self-heal. We also obtain a universal scaling law that quantifies how the ultimate crack pattern depends on the interplay between grain shrinkage, stiffness, and size. Our work helps to elucidates the rich physics underlying cracking, and yields new strategies to controlling crack evolution and patterning in a diverse array of shrinkable, granular materials.