Abstract: In the current work,flow fields in both straight and divergent dies were analyzed,and the circumferential stretch rate in the divergent channel was derived. The glass fiber orientation and distribution across the thickness of samples extruded from both dies at two flow rates were studied.  The formation mechanism of aforementioned glass fiber orientation and distribution was explained by using the distribution of shear and stretch strain rates. The results showed that most of the glass fibers were aligned in the flow direction in the samples extruded from the straight die. A five-layered structure, including two skin layers, two sub-skin layers,and a core layer,formed across the thickness of the samples extruded from the divergent die. It was first found that the fibers exhibited a “W” type alignment in the core layer. It was also demonstrated that the glass fiber alignments were affected more remarkably by the strain rate than the strain.In the current work,flow fields in both straight and divergent dies were analyzed,and the circumferential stretch rate in the divergent channel was derived. The glass fiber orientation and distribution across the thickness of samples extruded from both dies at two flow rates were studied.  The formation mechanism of aforementioned glass fiber orientation and distribution was explained by using the distribution of shear and stretch strain rates. The results showed that most of the glass fibers were aligned in the flow direction in the samples extruded from the straight die. A five-layered structure, including two skin layers, two sub-skin layers,and a core layer,formed across the thickness of the samples extruded from the divergent die. It was first found that the fibers exhibited a “W” type alignment in the core layer. It was also demonstrated that the glass fiber alignments were affected more remarkably by the strain rate than the strain.

Key words: polymer composites, glass fiber orientation, straight die, divergent die, flow field

摘要： 本文分析了平直和发散两种挤出机头内的流场，推得发散流道内熔体周向拉伸应变速率的表达式；研究了两种挤出流率下由这两种机头挤出的制品壁内玻纤的取向和分布，并通过流道内的剪切和周向拉伸应变速率，对玻纤取向和分布的形成机理进行解释。结果表明：经平直机头挤出的制品内，玻纤在剪切作用下基本沿流动方向排列。发散机头内熔体受剪切和周向拉伸的共同作用，使制品壁厚方向形成了“表层-次表层-芯层-次表层-表层”的五层结构，并首次发现芯层呈“W”形排列。玻纤的排列不仅受流动过程中的应变影响，更取决于应变速率的大小。

关键词: 聚合物复合材料, 玻纤取向, 平直机头, 发散机头, 流场