Nonlinear Poisson Effect Governed by a Mechanical Critical Transition.

Area of Science:

• Materials Science
• Mechanical Engineering
• Physics

Background:

• Fiber networks exhibit complex mechanical behaviors under deformation.
• The Poisson effect describes a material's transverse strain in response to axial strain.
• Anomalous mechanical responses in networks are not fully understood.

Purpose of the Study:

• To investigate the mechanism behind the anomalously large and nonlinear Poisson effect in fiber networks.
• To identify the critical factors controlling this phenomenon.
• To characterize the associated mechanical phase transition.

Main Methods:

• Applying extensional strain to fiber networks.
• Measuring transverse contraction and volume reduction.
• Analyzing the relationship between strain, network connectivity, and mechanical response.
• Observing critical signatures like Poisson's ratio peaks and nonaffine strain fluctuations.

Main Results:

• Fiber networks demonstrate a dramatic transverse contraction and volume reduction at low applied strains.
• A collective mechanical phase transition governs this Poisson effect.
• The critical strain for this transition is dependent on network connectivity.
• Anomalous peaks in Poisson's ratio and diverging nonaffine strain fluctuations were observed.

Conclusions:

• The anomalous Poisson effect in fiber networks is a result of a critical mechanical phase transition.
• Network connectivity plays a crucial role in determining the critical strain for this transition.
• The findings provide insights into the mechanics of disordered materials and critical phenomena.