Comparison between step strains and slow steady shear in a bubble raft

Area of Science:

• Materials Science
• Soft Matter Physics
• Rheology

Background:

• Bubble rafts model two-dimensional foams, exhibiting stress increases and decreases during deformation.
• Discrepancies exist between quasistatic foam simulations and continuous strain simulations regarding stress drop distributions.

Purpose of the Study:

• To compare stress relaxation behavior in a bubble raft under step strain versus continuous strain.
• To investigate the distribution of stress drops in these two deformation modes.
• To reconcile apparent disagreements between quasistatic and continuous strain simulation results.

Main Methods:

• Applied step strains to a bubble raft as an approximation of quasistatic simulations.
• Applied slow, continuous strain to the bubble raft.
• Analyzed and compared the distribution of stress drops in both experimental conditions.

Main Results:

• Both step and continuous strain exhibited periods of stress increase and decrease.
• General agreement was found in the dependence of average stress drop on the strain rate.
• No evidence of the divergence in average stress drop size, as reported in some quasistatic simulations, was observed.

Conclusions:

• Applied step strains in bubble rafts generally agree with continuous strain results regarding stress drop dependence on strain rate.
• The specific divergence of average stress drops seen in some quasistatic simulations was not replicated in this bubble raft study.
• Further research may be needed to fully understand the discrepancies between simulation types and experimental observations.