| Polymer is one of the most widely used materials due to its quality performance, and injection molding is one of the most widely employed methods of polymer processing. There is a complex, unsteady and non-isothermal process for polymer melts in injection molding, which has an important effect on the mechanical and optical performance of the molded part since the viscoelastic nature of the polymer results in development of shear and normal stresses and large elastic deformation during the filling stage and subsequent incomplete relaxation during the cooling stage. The paper is trying to investigate the development and relaxation of flow stress during injection process, and to predict the effects of molding conditions on residual stresses and molecule orientation.It has presented those viscous and viscoelastic constitutive models that are commonly used in the numerical simulation of injection molding, especially the Leonov model. Based on different hypotheses, Leonov models in different conditions have been obtained.The steady and dynamic experiments of PS-666D, PP-J640, LDPE-2100TNOO and PE are conducted. According to their results, the theological parameters in Leonov model of 1 till 4 nodes are evaluated using least square method.Appling Leonov model to the numerical simulation of injection modeling of polymers, this paper calculates the evolvement of the shear stress, shear strain velocity and the normal stress. Besides, the effects of mould temperature, melt temperature, injection velocity and so on have been investigated in the paper.
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