تحليل تغيير شكل ويسكوپلاستيك فلزات در فرآيندهاي شكل دهي

چكيده انگليسي :

Analysis of Viscoplastic Metal Deformation in Forming Processes Bardia Nezamzadeh b nezamzadeh@me iut ac ir Date of submission January 25th 2014 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc language Farsi Supervisor Prof A R Pishevar apishe@cc iut ac ir Abstract The behavior of most high temperature metals polymers concrete and wide range of composite materialsare described as viscoplastic flows The mathematical theory of plasticity adequately describes the time independent aspect of the behavior of materials but is inadequate for analysis of time dependent behavior Anapproach to achieve a satisfactory formulation for time dependent behavior has been generalized plasticity tocases within the strain rate sensitive range One such generalization has been provided by the theory ofviscoplasticity On the other hand when large progressive deformation occurs under plastic or viscoplasticconditions elastic deformations are negligible and the material flows in a viscous manner In this study a novelEulerian method based on solution algorithm for incompressible flows is developed for simulation of viscoplasticflows of materials In order to develop a tool for modeling metal forming process we implemented in the flowformulation based on Eulerian finite difference method In the extrusion and forming of solids the plastic orviscoplastic deformations are so large that the elastic strain is negligible So in our work the viscoplastic materialsare treated as incompressible non Newtonian viscous fluids By doing this we obtained a reliable and efficientEulerian formulation for modeling steady and transient metal forming problems Finally some cases were analyzedin order to test performance of the formulation The governing equations consist of conservation of mass andmomentum together with viscoplastic constitutive equation Since both material and die are assumed to be at thesame temperature the energy equation and momentum equation become identical and it is not necessary to solveenergy equation An important advantage of the proposed method is its ability to simulate large deformations and longtimetransient solutions Despite of the classic Lagrangian methods due to the Eulerian viewpoint of our method thegrid remains unchanged and therefore the mesh quality always remains suitable Fractional step method isemployed for the numerical method and the governing equations are decomposed into the separated portions andeach part is treated differently The transport part of governing equations is discretized by fifth order explicitWENO method while the contribution of stress terms are taken into account using an implicit method FinallyProjection method is used for the pressure velocity coupling To avoid spurious oscillation and checkerboard ofvelocity field equations are discretized on a full staggered grid The third order TVD Rung Kutta method is usedfor time integration One of the key feature of this work is employment of level set field to sharply describing theinterfaces Using Eulerian viewpoint together with level set function provide us with a powerful tool to simulateunsteady problems with moving boundaries and large deformations such as die forming without any further needof remeshing The ability of the proposed method is tested with different numerical examples including dieforming and low velocity impact The examples of application include steady state and transient extrusionproblems for which other numerical solutions and analytical solutions are available This example demonstratedthe free surface solution for a large deformation process Another example of transient process is upset forging While being capable of dealing with any viscoplastic model the Perzyna model is employed in simulations andthe results are compared with those available in literature and a very good behavior agreement is observed Keywords Viscoplastic forming Perzyna ghost fluid method level set fifth order WENO T

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تحليل تغيير شكل ويسكوپلاستيك فلزات در فرآيندهاي شكل دهي

مدل پرزينا , سيال مجازي , سطح مبنا , ونو مرتبه پنج , تفاضل محدود