Aortic aneurysm

Stress against strength

We propose a dimensionless stress-to-strength ratio that combines pulsatile loading with the local strength of the wall into a single number, evaluated over the whole surface rather than at one point. It was computed on 23 idealised aneurysm models spanning geometry, material properties and physiology, using one-way three-dimensional fluid–structure interaction.

The ratio identified every rupture-prone region, where conventional stress and strain measures found only some of them. Risk rises with thick intraluminal thrombus, with thin thrombus-free segments, with sagging thrombus, with higher blood pressure, with reduced wall thickness and with tissue softening.

Flow in the sac

Flow inside an aneurysm is not laminar and not fully turbulent. Reaching a converged phase-averaged solution takes many cycles, and reporting results before convergence is a common source of disagreement between studies. We quantified how many cycles are required and how the statistics converge, which sets a floor for any transitional aneurysm simulation.