DEVELOPMENT AND 3D FINITE ELMENT IMPLEMENTATION OF A MULTIAXIAL CONSTITUTIVE RELATION FOR ABDOMINAL AORTIC ANEURYSMS

摘要

Abdominal aortic aneurysm (AAA), a localized dilation of the infrarenal aorta, represents a significant disease in the western population. There are approximately 200,000 patients in the US and 500,000 patients worldwide diagnosed with AAAs every year (Bosch, et al. 2001), and rupture of AAAs currently ranks as the 13th leading cause of death in the US. (Silverberg and Lubera 1987) In the past 30 years, the diagnosis of AAA has tripled in the Western world, and this will likely increase in the coming years as the average age of the population is increasing. (Bosch, et al. 2001) Our laboratory and others have previously reported the biomechanical response of AAA tissue to uniaxial loading conditions. (He and Roach 1994, Raghavan, et al. 1996, Raghavan and Vorp 2000, Thubrikar, et al. 2001) The abdominal aorta, however, undergoes three-dimensional deformation in-vivo, and the information derived from uniaxial tensile testing is insufficient for the characterization of the multi-axial mechanical response of this tissue. More rigorous biomechanical testing, such as biaxial testing, allows for more appropriate modeling of aneurysmal tissue. Finite element analyses of AAA utilizing our previous uniaxially-derived constitutive relation have been used in the assessment of patient-specific AAAs. (Raghavan, Vorp et al. 2000, Fillinger, et al. 2002, Wang, et al. 2002, Fillinger, et al. 2003) The use of a multi-axial constitutive relation in the finite element simulations of patient specific AAAs may lead to a more accurate prediction of local wall stress and thus a better estimate of rupture potential for a specific AAA. The current study investigates the development and implementation of a biaxially derived constitutive relation into finite element analyses of patient specific AAAs. The differences in wall stresses predicted using this material model versus the previously used uniaxially derived constitutive relation are examined.