Biomechanical Characterization of Stress Concentration in Aneurysmal Aortas Using Hole-Based Biaxial Testing

Ascending thoracic aortic aneurysms (ATAAs) are at high risk of developing aortic dissection, particularly near the ostia of arterial bifurcations or branches. These geometric discontinuities are regions where blood pressure-induced stress rises locally, creating stress concentrations. This study aimed to quantify the stress concentration factor in ATAA tissues by combining experimental biaxial testing with computational stress predictions. Conventional biaxial testing was modified by introducing a through-the-thickness circular hole in the tissue samples, mimicking the branch ostia that creates a "hole"in the artery. The stress-strain response of plain and hole-based specimens was analyzed under biaxial loading, and experimental data were used to develop a finite element model for predicting the stress field. Digital image correlation (DIC) was employed on hole-based samples to compare strain estimates with numerical predictions. Stress-strain curves exhibited hyperelastic behavior with a loss of material directional dependency in both plain and hole-based specimens. Both DIC and simulations confirmed a localized increase in the strain field near the hole. Stress concentration factors were 1.91 ± 0.31 for a hole diameter of 1.5 mm and 1.84 ± 0.25 for a diameter of 3 mm. These findings enhance our understanding of the biomechanics of aortic dissection and may contribute to the development of fracture mechanics criteria for the early diagnosis of ATAA at high risk of failure.