Experiments found that the influence of gas pressure on the melt extrusion was very significant in gas assisted extrusion (GAE).In order to ascertain the influence mechanism of the gas pressure on the melt extrusion,a gas/melt two phase fluid model was established,the non isothermal viscoelastic numerical simulation of the GAE was performed using finite element method,the change discipline of melt extrudate profile,flow velocities,pressure drop and first normal stress difference etc were obtained under different gas pressures.Simulation results demonstrated that gas pressure has a significant effect on the flow distributions and extrudate profile of melt.When the gas pressure is little and stable gas layer can be formed,the flow velocities is uniform, pressure drop and first normal stress difference is little,and no extrudate deformation appears.But with the increase of gas pressure,the flow velocities,pressure drop,first normal stress difference,and the extrudate shrinkage degree of melt all evidently increase.It was demonstrated that the first normal stress difference at the entrance of the gas/melt interface is the main reason for triggering the extrudate deformation and flow distributions changes due to the influence of gas.
