Ultrasound induces aging in granular materials

Area of Science:

• Physics of granular materials
• Non-linear acoustics
• Materials science

Background:

• Granular materials exhibit aging and rejuvenation under confinement.
• Ultrasound can influence material properties, but its precise effect on granular matter aging is not fully understood.

Purpose of the Study:

• To investigate the impact of high-intensity ultrasound on the mechanical behavior and aging of granular materials.
• To explore the phenomenon of acoustic fluidization in granular systems.

Main Methods:

• Creep experiments were conducted using a triaxial configuration.
• High-intensity ultrasound waves were propagated through the granular material.
• Step perturbations in ultrasound intensity were applied to observe material response.

Main Results:

• Ultrasound induces significant weakening and plasticity in granular materials.
• The effect of ultrasound can be described by a fluidity variable, dependent on an effective aging parameter.
• The aging parameter decreases with increasing ultrasound amplitude, vanishing at the yield stress.
• Acoustic fluidization was evidenced by measurable jumps in effective viscosity.

Conclusions:

• High-intensity ultrasound can effectively fluidize granular materials, overcoming aging effects.
• Acoustic fluidization is a tunable process influenced by ultrasound amplitude and related to material fluidity.
• The study provides a method to quantify acoustic fluidization through viscosity measurements.