Computational Investigation of Potential Failure Modes in Arterial Hemodynamic Flowpath

The formation of an arterial disease for large and medium size vessels is believed to be a multifactorial interplay of bio - mechanical - chemical processes in the arterial wall and the hemodynamic flow path. The present research presents the viewpoint of a mechanical engineer assuming that mechanical factors are of the key importance in the formation of aneurism, atherosclerotic plague and rupture. The repetitive pressure and shear stresses exerted by the blood flow on the weakened arterial wall may cause its progressive degrade, resulting in aneurism with the following potential rupture. Elevated blood pressure results in an elevated repetitive stress distributions, which according to biomechanical fatigue theory can reduce notably the life cycles, both for the artery in a pristine condition, or attached to the stent. 2-D and 3-D Navier-Stokes based fluid-structure interactive analysis is applied to three different graftartery bypass configurations. Wall shear stress gradients (WSSG) have been considered as the trigger for the abnormal biological processes leading to rapid restenosis. It appeared that this problem can be significantly optimized by finding graft - artery bypass configurations for which the WSSG is minimal. Mechanical outcome, caused by the abrupt change of flow path wall stiffness due to the vascular prosthesis, is estimated by analysis of the corresponding edge effects for the stress components in arterial wall. In case of the composite stent material (reinforced elastollan) an optimal orthotropy is calculated and interpreted. Arterial vessel fatigue analysis is based on a significantly nonlinear model, comprising hyperelastic constitutive relations and finite deformation, coupled with the membrane thin walled shell theory. Contributions of different nonlinearities are analyzed. Conclusions made comparing cyclic lives relating to the mechanical stress level for the normal and elevated blood pressures, with and without stent