Le pourcentage élevé de blessures dues à des traumatismes abdominaux survenant lors d’accidents de la route mais également la nécessité de détecter des maladies (l'hépatite virale, la cirrhose, le cancer etc.), ont conduits plusieurs chercheurs à étudier les propriétés mécaniques des organes abdominaux à la fois in vivo et in vitro. Dans tous les MEF de corps humain actuellement disponibles, les organes abdominaux sont caractérisés par des lois élastiques linéaires ou viscoélastiques linéaires, alors que ces matériaux montrent un comportement non linéaire hyper élastique. L’objectif de ce travail de thèse est de développer des modèles par éléments finis (MEF) robustes des différents organes de l’abdomen tels que le foie, le rein et la rate. Pour ce faire des tests expérimentaux sur chacun des constituants de ces organes ont été réalisés dans le but de caractériser le comportement mécanique de ceux-ci et de déterminer les propriétés mécaniques inhérentes à ces constituants. Pour caractériser mécaniquement ces différents constituants, des tests statiques ont donc été réalisés pour chacun des constituants du foie et du rein porcin à savoir, des tests de traction de la capsule de Glisson et de la capsule rénale ainsi que des veines hépatiques, des tests de compression et de cisaillement pour le parenchyme hépatique et le cortex rénale. Finalement la rate a été testée en compression statique. Les résultats expérimentaux obtenus ont été utilisés afin de caractériser les tissus par des lois de comportement de type hyper élastique, viscoélastique et hyper viscoélastique sous la forme de modèles d'Ogden, Mooney Rivlin et Maxwell et implémentés dans les MEF porcin et humain développés dans le cadre de cette thèse. Ces MEF ont ensuite été validés en regards de tests expérimentaux dynamiques in vivo réalisés sur modèle porcin et vis-à-vis de la littérature pour les MEF d’organes humains. Ainsi, les MEF développés dans cette étude sont les premiers modèles détaillés et validés et peuvent désormais être utilisés dans le cadre de reconstructions d’accidents mais également pour des applications biomédicales dans le but de développer des environnements virtuels de chirurgie, de planifier les actes chirurgicaux et d’aider les chirurgiens à l’apprentissage de gestes. / The objective of this study is to develop robust finite element models of abdominal organs (viz. liver, kidney and spleen), by performing experiments on each organ’s constituents to extract the material properties. Understanding the mechanical properties of the organs of the human body is the most critical aspect of numerical modeling for medical applications and impact biomechanics. Many researchers work on identifying mechanical properties of these organs both in vivo and in vitro considering the high injury percentage of abdominal trauma in vehicle accidents and for easy detection of diseases such as viral hepatitis, cirrhosis, cancer etc. In all the current available finite element human body models the abdominal organs are characterized as linear elastic or linear visco-elastic material, where as the materials actually show a non linear hyper elastic behavior. In this study the organs are modeled for first time as hyper visco-elastic materials and with individual constituents of each (viz. the capsule and veins). To characterize the tissue, static experiments are performed on individual parts of the abdominal organs, like incase of liver, Glisson’s capsule and hepatic veins are tested under static tension where as liver parenchyma is tested under static compression and under shear at low frequency. In case of kidneys, renal capsule is tested under static tension and renal cortex is tested under static compression, where as spleen tissue is tested under static compression. The results of the these experiments are used to characterize the tissues as hyper elastic, visco elastic and hyper visco elastic materials in the form of Ogden, Mooney Rivlin and Maxwell materials. These material models are further used to develop the finite element model of organs for human and pigs. The developed models are validated by performing in vivo dynamic tests on pigs, whereas using dynamic tests data from the literature on human liver and reproducing the same with the numerical approach in the LS Dyna explicit solver. The developed models are observed to be robust and can be used for accident reconstruction as well for biomedical applications viz., to develop virtual surgical environments & to plan surgeries or train surgeons.

Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2015-10-27T18:16:56Z No. of bitstreams: 2 Dissertação - Renato de Sousa e Silva - 2015.pdf: 7212801 bytes, checksum: 41d5a93b0ae749a6418b871cd4fea683 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-10-28T14:29:10Z (GMT) No. of bitstreams: 2 Dissertação - Renato de Sousa e Silva - 2015.pdf: 7212801 bytes, checksum: 41d5a93b0ae749a6418b871cd4fea683 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-10-28T14:29:10Z (GMT). No. of bitstreams: 2 Dissertação - Renato de Sousa e Silva - 2015.pdf: 7212801 bytes, checksum: 41d5a93b0ae749a6418b871cd4fea683 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-06-12 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / Structural elements with large deformation capacity as hyperelastic membranes are gaining prominence in several engineering branches and have applications in biomechanics, thus the study of the dynamic behavior of hyperelastic structures is very important to minimize effects as the loss of the stability and undesirable vibrations. In this paper the elasticity theory for large deformations in the development of membrane theory, in order to investigate the linear and nonlinear dynamic behavior of hyperelastic membrane is used. A rectangular membrane composed of an elastomeric material, isotropic, homogeneous, incompressible and consisting of neo-Hookeano, Mooney-Rivlin and Yeoh models is considered. To model the membrane, the energy and work of external forces are used together with the application of the Hamilton on the Lagrange function. The Galerkin method is applied to obtain a discretized system of nonlinear Partial Differential Equations (PDE) and the Runge-Kutta method of 4th order is used to obtain its time response. Finally, the Brute Force and Continuation methods are applied to investigate the nonlinear dynamic behavior of the membrane. A parametric analysis is carried out looking to evaluate the influence of the material, geometry and initial tensions on the natural frequencies of the membrane. It is noted that increasing the size of a tensioned membrane, it is also increased the natural frequency for a given amplitude, and increasing the strength of a pre-tensioned membrane, the smaller the value of the frequency in relation to a range. Small differences are perceived in the behavior of the membrane for the three constitutive models of material, which are calibrated to represent the same material. Moreover, the main bifurcations of the analyzed membranes are of cyclic bending type, known as saddle-node bifurcation. / Elementos estruturais com grande capacidade de deformação como membranas hiperelásticas vêm ganhando destaque em diversas áreas da engenharia e têm várias aplicações na biomecânica, assim, o estudo do comportamento dinâmico de estruturas hiperelásticas é de grande importância visando minimizar os efeitos, como à perda de estabilidade e vibrações indesejáveis. No presente trabalho é utilizada a teoria da elasticidade para grandes deformações no desenvolvimento da teoria de membranas com o objetivo de investigar o comportamento dinâmico linear e não linear de membranas hiperelásticas. Considera-se a membrana retangular composta por um material elastomérico, isotrópico, homogêneo, incompressível e descrito pelos modelos constitutivos de neo-Hookeano, Mooney-Rivlin e Yeoh. Para obter as equações de equilíbrio estático e dinâmico da estrutura são utilizadas as energias e trabalhos atuantes, bem como o princípio de Hamilton aplicado na função de Lagrange. O Método de Galerkin é utilizado para discretizar as Equações Diferenciais Parciais (EDP) em um sistema de Equações Diferenciais Ordinárias (EDO). Para resolver esse sistema, utiliza-se o Método de Runge-Kutta de quarta ordem e utiliza-se o Método da Força Bruta e o Método da Continuação para investigar o comportamento dinâmico da membrana. É realizada uma análise paramétrica visando avaliar a influência do material e da geometria da membrana nas frequências naturais e nas tensões inicias. Constata-se que as bifurcações das membranas analisadas são do tipo Dobra Cíclica, conhecida como Nó-Sela. Além de verificar que quanto menor o nível de tração, maior será a não linearidade da curva de frequênciaamplitude da membrana e que há leves divergências no comportamento da membrana em relação aos três modelos constitutivos do material adotados.