Poisson function and volume ratio of soft anisotropic materials under large deformations

Area of Science:

• Materials Science and Engineering
• Biomechanics
• Solid Mechanics

Background:

• Accurate transverse deformation measurement is essential for determining material properties like Poisson's ratio and volume changes, particularly in soft materials undergoing large deformations.
• Traditional methods can be prone to measurement errors, impacting the reliability of derived parameters.
• Understanding the mechanical behavior of soft materials, including biological tissues and engineered elastomers, is critical for various applications.

Purpose of the Study:

• To develop a novel formulation for transverse stretch measurement that minimizes errors in parameter estimation.
• To investigate the large deformation behavior, including Poisson's ratio and volume changes, of pure silicone and a soft composite.
• To analyze the compressibility and anisotropy of biological soft tissues using the developed methodology.

Main Methods:

• Uniaxial tension tests were performed on pure silicone and silicone-composite specimens.
• Digital Image Correlation (DIC) was employed to measure longitudinal and transverse (in-plane and out-of-plane) stretches.
• A new formulation relating transverse stretches to longitudinal stretch, incorporating Poisson's ratios and stretch-dependent parameters, was developed and applied.

Main Results:

• Pure silicone exhibited isotropic and nearly incompressible behavior under large deformations.
• Silicone composites reinforced with extensible fabric demonstrated Poisson's ratios exceeding classical bounds, including auxetic behavior (negative Poisson's ratio).
• Analysis of human skin, aortic wall, and annulus fibrosus revealed that most soft tissues are compressible and anisotropic, with the aortic wall being nearly incompressible.

Conclusions:

• The developed formulation effectively estimates Poisson's functions and volume ratios for soft materials under large strains.
• Pure silicone can be modeled as incompressible, while soft composites require volume ratio considerations.
• Soft biological tissues are generally compressible and anisotropic, highlighting the need for accurate deformation measurement techniques.