非弹性流体模口膨化的原因及切力变稀(或增稠)性对模口膨化比的影响

THE MECHANISM OF DIE SWELL OF NON-ELASTIC FLUID AND THE EFFECT OF STRAIN THINNING (OR STRAIN THICKENING) ON DIE SWELL RATIO

本文首先按照流体通过狭缝挤出后横向拉伸应变的不同把流场分成皮层和芯层两部分,然后通过分析它们的应变和受力情况证明非弹性流体的模口膨化是由于芯层流体在皮层施加的纵向拖力和横向拉力及狭缝出口横截面上的剪切应力的作用下产生的横向拉伸应变。按照这一理论的推测,非弹性流体的模口膨化比随流体切稀性的增强而减小,随流体增稠性的增强而增大.这一推测与实验结果及有限元计算结果相符合。本文的理论发展和完善了 Tanner 的“皮层一芯层”理论.

In this paper the extrusion flow field is divided into two——the“skin”and the“core”accordingto whether the elongational strain in the transversal direction is positive.The origin of the die swell ofviscous fluid is that the core fluid produces larger transverse elongationai strain than that of skin fluidunder the interaction between skin and core and the action of the shear force acting on the exit crosssection of the die.According to this theory the die swell ratio increases with the gradient of viscositywith respect to the second invariant of strain rate tensor,therefore,the die swell ratio of“powerlaw”fluid increases with non-Newtonian index,and that of Powell-Eyring fluid increases with η_∞/η_oif B remains constant(see eq.(32))but goes through a maximum as the η_∞/η_o remains constant andB grows from zero to infinite.This inference tallies with available results of experiment and finite ele-ment calculation.Tanner's“skin-core”theory is thus developed.