A method for planar biaxial mechanical testing that includes in-plane shear.

Area of Science:

• Biomechanics
• Materials Science
• Biomedical Engineering

Background:

• Planar biaxial testing of soft tissues traditionally excludes in-plane shear effects due to device complexity and cost.
• Existing mechanical testing limitations hinder the comprehensive analysis of soft tissue behavior under combined stress states.

Purpose of the Study:

• To present a straightforward method for planar biaxial testing that induces simultaneous in-plane shear and normal strains.
• To demonstrate the applicability of this method using glutaraldehyde-treated bovine pericardium.

Main Methods:

• A novel testing approach involving specimen material axes rotation relative to device axes.
• Utilizing rotating carriages to freely accommodate in-plane shear during testing.
• Orienting bovine pericardium specimens at 45 degrees to induce maximum shear and applying various biaxial strain states.

Main Results:

• The developed method successfully induced combined in-plane shear and normal strains in soft tissue specimens.
• A strain energy function accurately fitted the experimental data, with constants A5 and A6 found to be insignificant for modeling shear strain response.
• The method proved effective in analyzing anisotropic planar tissues with identifiable material axes.

Conclusions:

• The presented method provides a practical means to incorporate in-plane shear into planar biaxial testing of soft tissues.
• While not enabling independent shear control or pure shear states, it effectively captures simultaneous shear and normal strains.
• This generalizable technique is suitable for characterizing various anisotropic planar biological tissues.