Tezin Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Technische Universitaet Graz, Faculty of Computer Science and Biomedical Engineering , Institute of Biomechanics , Avusturya
Tezin Onay Tarihi: 2018
Tezin Dili: İngilizce
Öğrenci: Hager Sandra Priska
Asıl Danışman (Eş Danışmanlı Tezler İçin): Gerhard A Holzapfel
Eş Danışman: Osman Gültekin
Açık Arşiv Koleksiyonu: AVESİS Açık Erişim Koleksiyonu
Özet:
An aortic dissection is detected in 2 to 3.5 out of 100,000 people every year. This type of disease in the aortic wall can appear in an acute or a chronic form and can proceed with a fatal outcome if not treated. An aortic dissection is generally caused by a minimal defect in the intima, which can occur due to an accident or other traumatic events. During a pumping cycle, the aorta undergoes various deformations, such as extension, torsion and inflation. This deformation allows the initially minimal defect to spread inside the aortic wall and generate a second pathway for the blood inside the wall of the artery. The aim of this study is to numerically simulate the crack formation between two medial sub–layers and to determine important parameters for crack formation in a physical environment. The thermodynamic approach for the crack phase–field of fracture developed by Miehe et al. (2010) for an isotropic material is used as a basis for crack propagation modeling. Since the aorta is a highly anisotropic material it is necessary to expand the model presented by Miehe et al. (2010), which was done by Gultekin et al. (2017). To validate the ¨ model of Gultekin et al. (2017) for anisotropic materials, the result ¨ s were compared with the geometrically anisotropic model of Teichtmeister et al. (2017). In the same study, the sensitivity of the model proposed by Gultekin et al. (2017) in terms of anisotropy parame- ¨ ters was also analyzed. In the next step, the model from Gultekin et al. (2017) was applied ¨ to a cylinder, with the dimensions of an aorta (Mao et al., 2008). This cylinder consists of six sub–layers; four layers show the material parameters of a medial layer including a diseased one and the other two layers correspond to the adventita layer. For the simulation of an aortic dissection, an incision in the mesh of the cylinder with different lengths and widths up to the diseased media layer was implemented and then a pumping cycle was simulated in the physiological and supra–physiological range. It was found that with the same deformation, the dissection spreads further in the case of a larger initial defect in the intima. In addition, it was also found that the crack spread helical in the aorta, indicating that the crack arranges itself along the fiber direction in the material.