Fracture and relaxation in dense cornstarch suspensions

Area of Science:

• Rheology
• Materials Science
• Soft Matter Physics

Background:

• Dense suspensions exhibit tunable properties, transitioning between fluid-like and solid-like states.
• This transition, known as shear jamming (SJ), is crucial for understanding material behavior under stress.
• Fracture formation in such materials is influenced by their dynamic rheological properties.

Purpose of the Study:

• To investigate the implications of the shear jamming transition on fracture formation in dense suspensions.
• To characterize the growth and relaxation dynamics of air-induced fractures in cornstarch suspensions.
• To identify the critical shear rate associated with shear jamming and its role in fracture relaxation.

Main Methods:

• Injecting air into bulk dense cornstarch suspensions.
• Utilizing time-resolved X-ray radiography to visualize air invasion in opaque materials.
• Analyzing fracture morphology and growth dynamics at varying cornstarch concentrations.

Main Results:

• Air injection into suspensions exhibiting discontinuous shear thickening and shear jamming leads to fracture formation.
• At high cornstarch mass fractions, fractures grow as rough cavities.
• At lower mass fractions, fractures relax into smooth bubbles that rise due to buoyancy.
• Fracture relaxation onset correlates with the induced shear rate dropping below the critical shear rate for discontinuous shear thickening.

Conclusions:

• The shear jamming state significantly influences fracture propensity and morphology in dense suspensions.
• The observed fracture relaxation provides a structural signature of the shear jamming transition.
• Understanding these dynamics is key for controlling material failure and behavior in dense particle systems.