【摘要】 采用PTT黏弹模型,对聚合物熔体在T型异型材挤出口模内的三维等温流动进行数值模拟,得出口模内外速度、剪切速率、压力和应力分布。结果表明:由于出口效应,在口模出口处,速度、剪切速率、压力分布均发生突变。这种突变有可能造成负压,从而引发熔体破裂。口模内二次流动产生的剪切应力甚至会超过因挤出流动产生的剪切应力。应力易集中发生在口模截面的拐角处,随着挤出流量的增加,口模内最大剪切应力和最大第一法向应力差几乎线性地增加,而不会急剧增大。更多还原

【Abstract】 By means of the viscoelastic PTT constitutive model,numerical simulation was implemented for the three dimensional isothermal flow through the die for extrusion of the product with a T-shaped cross section.The distributions of velocity,shear rate,pressure and stress under various conditions were worked out.Because of the exit effect,all of the distributions of velocity,shear rate,pressure and stress had sudden change,which could cause negative pressure and result in melt fracture.The shear stress caused by the second flow could exceed that caused by the extrusion flow.The stress usually reached its maximum around the corner of the cross section of the die,the maximum of shear stress and the first normal stress difference within the die grew almost linearly but not drastically along with the increasing of the flow rate.更多还原