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

在浓纤维悬浮液（CFS）和稀纤维悬浮液（DFS）中测量了流动诱导的纤维取向和浓度分布。该通道具有包含圆柱体的细狭缝几何形状。在以往的工作中，许多研究者定性地研究了纤维增强塑料注塑制品中的纤维取向和浓度分布。然而，在目前的工作中，它们是通过直接观察集中悬浮流中的纤维来定量估计的。对于CFS，一些纤维在通道壁和圆柱之间的膨胀部分旋转，纤维的取向几乎变为随机状态。另一方面，由于圆柱体下游中心线附近的拉长流动，纤维沿着流动方向完美排列。除通道壁和中心线附近外，光纤浓度基本呈平坦分布。对于DFS，光纤浓度分布在中心线处有明显的最小值，在中心线附近和通道壁附近有两个峰。这种特征分布是由纤维-壁和纤维-筒相互作用引起的。研究发现，对于CFD而言，通道内的圆柱等障碍物会显著影响障碍物下游的纤维取向，而对于DFS而言，则会影响纤维浓度分布。

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.