A study of the aorta rupture under pressure loading

Rupture of the thoracic aorta accounts for nearly 20% of the fatalities from automobile crashes. The mechanisms of aorta rupture, however, remain a mystery due to the complexity of the connections, movements and the contacts among internal organs during the impact event. Although several hypotheses of aortic rupture mechanisms are presented in the literature, none has been validated owing to the difficulty of observing the aortic response and failure experimentally. One of the hypotheses is that sharp pressure increase cause aorta rupture. This dissertation is carried out to study aorta ruptures under pressure loading.; This dissertation constructed a finite element model of the aorta, investigated and applied the advanced technique of coupling Lagrangian and Eulerian finite element methods, developed a Pseudo-Elastic material model and integrated the material model into LS-DYNA3D, a widely used commercial finite element code. In addition, this dissertation analyzed the effect of aortic cross-section shape on the stress distribution.; Prior to implementation of the aorta structure model and material model, an excised aorta test was simulated. An inverse method was applied: the material parameter optimizations were conducted until general agreement was obtained between the simulation and the experiments.; Upon successful development of an isolated finite element model of aorta and a material model with failure criterion, the aorta model was further validated with the tests performed on in situ cadaveric aortas. The pressure increasing mechanism is thereafter investigated and it is found that the pressure itself was not enough to introduce aorta ruptures at 1000 mmHg level.; Finally, an elliptic aorta arch model was developed. An analytical study was conducted based on this model. The different shapes of aortic cross-section were investigated. It was found that the shape of the aortic cross-section dramatically affected the stress distribution. For a certain arch structure, the longitudinal stress might be greater than the circumferential stress, so the rupture occurs in the transverse direction. This analytical study explains the observed rupture direction.; The significant advance represented by this dissertation is the construction of a detailed human aorta finite element model with failure criterion that can effectively predict human aortic injury. It is a large step in the construction of an integral finite element model of a human body to aid in the design of more effective equipment to protect humans from potentially fatal injuries.; An additional contribution of this research is that the pressure alone is not enough to rupture the aorta at 1000 mmHg. The dynamic interaction between fluid and aortic wall, however, can cause aorta rupture at a relatively low-pressure level.