Crack formation and self-closing in shrinkable, granular packings

Area of Science:

• Materials Science
• Physics
• Geology

Background:

• Many natural and synthetic granular materials (clays, soils, tissues, foods) shrink upon drying.
• Cracking during drying is a common phenomenon that limits material applications.
• The cracking behavior of shrinkable granular packings is poorly understood compared to non-shrinkable grains.

Purpose of the Study:

• To investigate how grain shrinkage affects crack evolution in granular packings during drying.
• To elucidate the underlying physics governing cracking in shrinkable granular systems.
• To develop strategies for controlling crack formation and propagation.

Main Methods:

• Experimental studies using model shrinkable hydrogel beads.
• Development of both granular and continuum mechanical models.
• Quantification of factors including grain shrinkage, poromechanics, packing size, drying rate, capillarity, and substrate friction.
• Investigation of crack evolution under varying spatial drying profiles.

Main Results:

• Differential grain shrinkage significantly alters crack evolution, leading to phenomena like spontaneous crack self-closure.
• Packings can shrink without cracking or exhibit irreversible cracking depending on conditions.
• Cracking behavior can be precisely controlled by manipulating the spatial drying profile.
• Models successfully quantified the complex interplay of factors influencing cracking.

Conclusions:

• Grain shrinkage introduces complex behaviors in drying granular packings, including crack self-closure.
• Understanding the interplay of shrinkage, poromechanics, and drying conditions is key to controlling cracking.
• This research provides novel strategies for managing crack evolution in shrinkable granular materials for diverse applications.