Détermination des mécanismes de dégradation de poumons humains sous chargement de blast et critères lésionnels associés

Lung damage is the leading cause of death in the face of a blast. For protection purposes, it is essential to understand the causes of this damage. For the moment, the effects of this shock wave on the lungs are poorly described. Indeed, in the literature, the lung models used for the evaluation of lung injuries in the face of an explosion rely on global indicators such as the intra-pulmonary pressure or the velocity of the front of the rib cage. However, these global indicators are not associated with physical mechanisms of injury. The work of this thesis is interested in the study of the mechanisms of pulmonary degradations in front of a blast as well as the lesion criteria which are associated with it. Moreover, this study allows a first approach to define the important parameters for the representation of the behavior of the thorax in front of the blast to design a representative simulant.Due to the lack of understanding of the mechanisms of lung degradation, a two-scale modeling is proposed. First, a study of the loads and their effects at the macroscopic scale, on simple models, allows a better understanding of the effects involved face of the blast and validation of the hypotheses that will be used in the establishment of a more accurate simulation. In addition, autopsies from IRBA tests will be studied to determine the location of these injuries, in particular their initiation zone. In a second step, the possible degradation mechanisms, at the microscopic scale, in front of the blast will be studied. At the microscopic scale, an analysis of the effects of all the mechanical accidents impacting the lungs is performed to understand the mechanisms of lung degradation. A sorting is proposed on the loads inducing bleeding. By coupling these data to some observations of the literature at the scale of collagen fibrils, a mechanism of over-elongation of the alveolar wall reinforcements is retained and a macroscopic criterion in maximum principal deformation is associated with it. Finally, a coupling between the macroscopic loadings and the criteria drawn from this study at the microscopic scale is carried out by a simulation of the effects of the blast on a Finite Element model representing the geometry and the mechanical properties of the thorax organs. For this purpose, the THUMS model was modified to implement a lung behavior more representative of the real one. This coupling allowed us to highlight the presence of elongation in the part of the lungs where the degradations are located during the compression of the thoracic cage.