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Caractérisation et modélisation de la rupture des tissus hépatiques

Abstract : In the field of road safety, internal injuries including abdominal injuries cannot be predicted through crash-tests using dummies. Numerical simulation is a promising tool to evaluate the risk of injury of a given impact configuration by descripting the loadings on the organs. Quantifying the risk of failure requires knowledge about the mechanical behaviour and the failure properties of the tissues of the human body. As the liver injuries account for a large amount of the serious injuries, the present study is focused on this organ and more specifically on the surface laceration. The aim of this study is to characterize and model the failure behaviour of the two tissues involved in the surface laceration : the parenchyma and the hepatic capsule. The experimental study includes three protocols which range from the organ scale to the tissue scale. Compression tests on whole perfused porcine and human livers enhanced the failure mechanism of the liver surface ; surface laceration seems to be caused by multiaxial tension. Uniaxial tensile tests on parenchyma and capsule samples from human and porcine livers allowed the determination of the failure properties of these two tissues. Independent characterization of the human liver capsule was conducted through inflation tests, which correspond to a more realistic loading than uniaxial tension. Full-strain fields were computed by digital image correlation and stereocorrelation on the second and third protocols ; local phenomena such as the localization of the strain field before failure or material heterogeneities were observed. The linear modulus of the parenchyma was determined. The capsule behaviour was modeled as linear first, then as hyperelastic. Statistical tests based on the results of the uniaxial tests assessed the influence of the biological origin of the tissues - porcine or human - and the preservation method - keeping fresh of freezing. The modeling part of this study is focused on the damage and rupture of an isotropic fibrous membrane. The fibers are linear elastic and brittle. The failure of the fibers at the microscopic scale creates macroscopic damage in the tissue which can be described by two scalars. The homogenization of the behaviour is conducted through two methods available in the literature ; they can therefore be compared. Several phenomena observed on biological fibrous tissues - damageable fibers, crimped fibers, random mechanical properties of the fibers - have been included in the model. This damage model is finally identified on the inflation tests of the capsule which are simulated using the experimental boundary conditions catched by stereocorrelation. The elastic modulus as well as the ultimate strain of the fibers are determined by an optimization algorithm. The material and failure properties as well as the damage model determined in this study can be included in a liver model to simulate a crash. The occurence of surface laceration could then be predicted.
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  • HAL Id : tel-00701532, version 1

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Aline Brunon. Caractérisation et modélisation de la rupture des tissus hépatiques. Sciences agricoles. INSA de Lyon, 2011. Français. ⟨NNT : 2011ISAL0105⟩. ⟨tel-00701532⟩

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