Cette thèse est consacrée à la dérivation des modèles de fracture comme limite de modèles d'endommagement.L'étude est justifiée essentiellement à travers des simulations numériques.On s'intéresse à étudier un modèle d'endommagement initié par Allaire, Jouve et Vangoethem.Nous apportons des améliorations significatives à ce modèle justifiant la cohérence physique de cette approche.D'abord, on ajoute une contrainte sur l'épaisseur minimale de la zone endommagée, puis on ajoute la condition d'irréversibilité forte.Nous considérons en outre un modèle de fracture avec pénalisation de saut obtenu comme limite asymptotique d'un modèle d'endommagement.Nous justifions ce modèle par une étude numérique et asymptotique formelle unidimensionnelle.Ensuite, la généralisation dans le cas 2D est illustrée par des exemples numériques. / This thesis is devoted to the derivation of fracture models as limit damage models.The study is justified mainly through numerical simulations.We are interested in studying a damage model initiated by Allaire, Jouve and Vangoethem.We are making significant improvements to this model justifying the physical consistency of the approach.First, we add a constraint on the minimum thickness of the damaged area and then we add a condition of strong irreversibility.We see also a fracture model with jump penalization obtained as an asymptotic limit of a damage model.We justify this model by a one-dimensional formal asymptotic numerical study.Then, the generalization in the case 2D is illustrated by numerical examples.

La presente tesis aborda problemas de optimización y obtención de desigualdades óptimas dentro de la Geometría Convexa. En concreto, se recogen las propiedades conocidas del anillo mínimo asociado a un cuerpo convexo plano y se estudian algunas propiedades nuevas que ayudan a conocer mejor la relación entre ambos. Se estudian con detalle las desigualdades geométricas existentes entre el anillo mínimo de un cuerpo convexo y las magnitudes geométricas clásicas, a saber, área, perímetro, circunradio, inradio, anchura mínima y diámetro, obteniendo en cada caso los conjuntos extremales. Se estudian con detalle propiedades que relacionan el anillo mínimo de un cuerpo convexo con su circunradio por un lado, y su inradio por otros. Se consideran fijos anillo mínimo y circunradio y se presentan las desigualdades óptimas que realcionan estas magnitudes con las restantes, describiendo los conjuntos extremales. Finalmente se realiza algo similar pero considerando fijos, esta vez, el anillo mínimo y el inradio. / This thesis aims to deal with the optimization problems and how to obtain the optimal inequalities within the Convex Geometry. It aims to treat with the already known properties of the minimal annulus associated to a plane convex body; we are also to study some new properties that help us know the relationship between both of them. The geometrical inequalities existing between the minimal annulus of a convex body and the classical geometrical measures are studied in detail. These measures are the area, the perimeter, the circumradius, the inradius, the minimal width and the diameter, and we will obtain in each case the extremal sets. We will study in detail those properties relating the minimal annulus of a convex body with its circumradius first and its inradius later. We will consider as fixed the minimal annulus and the cicumradius, and the optimal inequalities that relate those measures with the remaining one will be represented by describing the extremal sets. Finally, we will do something similar but considering as fixed the minimal annulus and the inradius.