Visualization and numerical analysis of fiber orientation on weld line in processing for fiber-reinforced composite materials

测量了浓缩纤维悬浮液(CFS)和稀纤维悬浮液(DFS)中流动诱导纤维的取向和浓度分布。在以前的工作中，许多研究人员定性地研究了纤维增强塑料注射成型产品中的纤维取向和浓度分布。然而，在目前的工作中，通过直接观察浓悬浮流中的纤维来定量地估计它们。对于CFS，一些纤维在通道壁和圆柱体之间的膨胀部分旋转，纤维取向几乎成为随机状态。另一方面，由于圆筒下游中心线附近的拉长流动，纤维沿流动方向完全排列。纤维浓度除在通道壁和中心线附近外均呈平坦分布，DFS的纤维浓度分布在中心线上有一个明显的极小值，并在中心线附近和通道壁附近出现两个峰值。这种特征分布是由纤维-壁面和纤维-圆柱体相互作用引起的。研究发现，流道中的圆柱体等障碍物对CFD障碍物下游的纤维取向有显著影响，而对DFS的纤维浓度分布影响较大。

Flow-induced fiber orientation and concentration distributions were measured in a concentrated fiber suspension (CFS) and a dilute one (DFS). The channel has a thin slit geometry containing a circular cylinder.In the previous work, many researchers have qualitatively studied fiber orientation and concentration distributions in injection-molded products of fiber-reinforced plastics. In the present work, however, they are quantitatively estimated by direct observation of fibers in the concentrated suspension flow.For the CFS, some fibers rotate in an expansion part between the channel wall and the circular cylinder, and the fiber orientation becomes almost random state. On the other hand, fibers are perfectly aligned along the flow direction owing to the elongational flow near the centerline downstream of the cylinder. The fiber concentration has a flat distribution except near the channel wall and the centerline.For the DFS a minimum in the fiber concentration distribution was clearly observed on the centerline, and two peaks beside the centerline and near the channel wall. This characteristic distribution is caused by the fiber-wall and fiber-cylinder interactions. It is found that the obstacle such as the circular cylinder in the channel significantly affects the fiber orientation downstream of the obstacle for the CFD, while it affects the fiber concentration distribution for the DFS.