La compréhension des mécanismes d'endommagement, notamment intergranulaires des polycristaux passe par la connaissance précise des champs mécaniques (contraintes, déformations) à l'échelle mésoscopique. Le but de cette étude est de les déterminer par simulation numérique. Pour cela nous considérerons un motif multicristallin inclus dans un milieu homogène équivalent. Ce milieu obéit au comportement expérimental du matériau (ici du 316 L(N) à chaud) à l'échelle macroscopique; le comportement cristallin microscopique est lui aussi connu. Une simulation par un code de calcul pa.r éléments finis prenant en compte l'aspect cristallin du motif et celui continu de la matrice nous donnera les champs mécaniques dans le motif. Nous définirons le cadre théorique de ce "mésoscope numérique", en insistant sur le concept de relocalisation et sur sa position vis à vis des modèles de passage micro-macro. Puis, nous aborderons les difficultés du choix du motif multicristallin et de la cohérence entre la loi de comportement du milieu homogène équivalent et celle des cristaux. Nous donnerons ensuite les résultats de l'identification des paramètres de la loi macroscopique. Enfin, le traitement numérique par éléments finis du problème sera abordé, et nous discuterons des premiers résultats. Nous 'conclurons sur les évolutions et les possibilités de ce nouvel outil, notamment pour la description du comportement des joints de grains.

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made his exit from Paris in October 1665. He left behind three imbuih schemes for the eastern fagade of the Louvre, a disappointed King and court, and little hope that the strained relationship between the French Monarchy and the Italian Papacy could be repaired. Bernini's trip to France had been orchestrated in the name of political and architectural expediency; to the double problem of a palace without a proper facjade and a diplomacy without real amicability, Bernini's talents potentially offered a single solution. One of his schemes, despite his departure, was still in the works. As it turned out, Louis XIV's ambivalence about Bernini's proposals was eventually matched by Colbert's distaste for his grandiloquence -and the extensive demolition required by the Italian's designs was seen by both as an affront to French sovereign power.' Colbert's response to this vexing sequence of events was, ultimately, to relieve Bernini of his obligations and to resume the search for a French solution that had, since January 1664, already yielded several different proposals. In the spring of 1667 he appointed a committee that brought together the premier architecte Francois Le Vau, the premier peintre Charles Le Brun, and the physician Claude Perrault, to propose new designs. By ail accounts, this petit conseil executed its mandate swiftly and without much difficulty; within three months, the scheme for a colonnade with coupled columns had been proposed, authorized, and finalized. In light of the controversy that had surrounded the commission, and of the debates that the fafade's coupled columns would continue to provoke long after its completion, the decisions of the petit conseil appear in the historical record as a rare moment of conceptual clarity in an otherwise endlessly contorted and highly politicized process. When poet Nicolas Boileau gave Le Vau sole credit for the fa(;ade in 1694 -disputing the rumor that it was Perrault alone who deserved it -he triggered a centurieslong debate over the design's credits and merits.' By the end of the eighteenth century, Perrault had been canonized as both the most vocal defender of the facade and the most eager contender for its authorship, causing the faf ade's origins and originality to emerge as inextricably linked.' Still today, the debate over attribution continues to animate art historical scholarship -most notably that of Robert W. Berger. who recently launched a new search to determine, with absolute certainty, whose hand was responsible for the design for the eastern facade of the Louvre -as if a controversy that had begun with Bernini's fall into disfavor needed to culminate in the naming of an alternative, yet equally singular, individual. " Although this search has unearthed a considerable amount of archival material, no definitive authorship has been established, and today Perrault remains a ghost figure, the not-Bernini of the Louvre.There is little doubt that, if the attribution of the unorthodox facade to Perrault seems attractive to us moderns, it is because Perr...