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A New Computationally Effective Approach for Handling Mass Conservation During 3D Rolling of Strips

出版	Ohio State University, 2000
URL	http://books.google.com.hk/books?id=KqRMywAACAAJ&hl=&source=gbs_api

註釋Rolling process occupies the most important position of all deformation processes. Over 90% of all metals that are ever deformed are subjected to rolling [Schey, 2000]. Rolling of strips is the process of making sheet metal, which is the starting material for various secondary metal working processes. The application of sheet metal requires uniform thickness in length and width direction, a flat shape, a controlled and uniform surface finish, and reproducible mechanical properties. Satisfying these requirements needs a close control of strip rolling process. The traditional control of strip rolling process is based on a trial and error procedure. Finite element modeling of strip rolling process helps reduce this trial and error process, and provides prediction of rolled strip properties. Strip rolling involves extreme material thinning; therefore it is almost impossible to simulate a multi-pass strip rolling process using finite element method (FEM) without remeshing. Shear strain near the strip edges causes FEM mesh distortion and consequently negative Jacobian, which prevents FEM simulation from proceeding further. The element stretching introduced by extreme material thinning cannot be solved by remeshing alone, which tremendously increases the number of elements and wastes computer resources. Fortunately, plane strain prevails in strip during rolling along the width except at the edges. Since the strain state does not change in width direction, the entire width need not to be simulated. This characteristic originated the idea of material dropping. In this technique, the regions with known strain state are not simulated. This technique together with remeshing then provides good mesh quality through out all the rolling passes and yet keeps the number of elements low. In this study, a unique remeshing method based on the characteristics of metal flow and the material dropping scheme are integrated with a 3D FEM rolling simulation program named ROLPAS. The simulation of thermo-mechanical microstructure phenomena during hot rolling of strips is very important to the accurate prediction of roll force, grain size, metal flow and mechanical properties of strips. In this study, static recrystallization, dynamic recrystallization, and metadynamic recrystallization are simulated and their effects on roll force, microstructural evolution and metal flow are discussed. The results of the simulation are validated by comparing with data published in literature.