Traumatic rupture of the aorta (TRA) is believed to be the second most common cause of death associated with automotive crashes. Approximately 8,000 people die because of TRA in the United States every year. Several laboratory experiments and retrospective studies, aimed at investigating TRA, have led researchers to propose a variety of possible injury mechanisms for TRA. However, there is no consensus regarding the mechanisms actually involved in TRA resulting from automotive crashes. The objectives of current study were to obtain material and failure properties for the aortic tissue and investigate underlying injury mechanisms of TRA by simulating real-world accidents in which occupants sustained aortic injuries.

A specially designed high-speed tissue testing device was used to conduct equibiaxial tension tests at an average strain rate of 85 s^-1. A total of 27 tests were conducted on cruciate-shaped samples obtained from the ascending, peri-isthmus, and descending regions of human cadaver aortas. The aortic tissue was found to be nonlinear and anisotropic with an average circumferential modulus (11.37 MPa) greater than the average longitudinal modulus (7.79 MPa). The structural response of seven whole aortas obtained from human cadavers was evaluated in longitudinal stretch using a hydraulic machine that was actuated at a nominal rate of 1 m/s. The whole aorta ruptured in the peri-isthmic region at an average 92 N force and 22.1% strain. For both biaxial and longitudinal stretch tests, the aortic tissue failed with transverse tears and the intima layer failed before either the media or adventitia. An orthotropic linear elastic material model was employed for modeling the aortic tissue. The material constants were obtained using optimization techniques and the response of orthotropic material matched very well with the biaxial tissue testing data.

Four real-world aortic injury crashes were reconstructed in two phases using finite element (FE) techniques. In the first phase, car-to-car simulations were conducted and kinematics of selected vehicle structures was recorded. In the second phase, interaction of the FE occupant model was simulated using boundary conditions obtained from the first phase simulation. The FE occupant model was a whole-body FE human model developed by integrating previously developed thorax, abdomen, and shoulder models. The whole-body FE human model included detailed modeling of internal tissues and organs, and all major bony structures. High stresses and strains were observed in the peri-isthmus region for the side impact simulations. For frontal impact simulations, the junction between the ascending and arch of the aorta and peri-isthmus region showed high stresses and strains. Finally, in side impact crashes the mechanism of anterior sternum displacement was evaluated by simulating sled tests by Cavanaugh et al. (1990) using a whole-body FE human model. There was approximately 20 mm anterior sternum displacement relative to the spine during this simulation. The anterior sternum displacement may be important to TRA, as the aorta is pulled away from the spine by the sternum during side impacts.