Isotropic Failure Criteria Are Not Appropriate for Anisotropic Fibrous Biological Tissues

Area of Science:

• Biomechanics
• Materials Science
• Tissue Engineering

Background:

• The von Mises (VM) stress is widely used in finite element analysis for tissue mechanics.
• Its isotropic nature raises concerns for anisotropic biological tissues, potentially leading to inaccurate failure predictions.

Purpose of the Study:

• To evaluate the efficacy of the anisotropic Tsai-Hill (TH) failure criterion against the isotropic VM criterion for porcine aorta.
• To determine the suitability of VM stress for assessing the mechanical state of anisotropic tissues.

Main Methods:

• Uniaxial tensile testing of porcine aorta dogbones cut at various angles to failure.
• Testing of shear lap samples to assess failure prediction.
• Two-dimensional failure propagation simulations.

Main Results:

• Porcine aorta exhibited significant anisotropy, with circumferential failure stress nearly double the axial.
• The VM criterion failed to accurately represent the anisotropic tissue response.
• The TH criterion demonstrated a strong fit to experimental data (R² = 0.986).
• TH criterion outperformed VM in predicting failure type, location, and propagation in simulations.

Conclusions:

• Isotropic failure criteria, like VM stress, are inappropriate for anisotropic tissues.
• The Tsai-Hill criterion offers a superior, though not perfect, alternative for predicting failure in anisotropic biological materials.
• Reconsideration of VM stress as a mechanical state metric for anisotropic tissues is warranted.