柔性导向三维织造复合材料预制体细观结构分析

Mesostructure Analysis of 3D Flexible Woven Preform

针对柔性导向三维织造复合材料预制体的结构表征问题,对预制体的几何结构和纤维束细观形貌进行了研究。基于纤维截面为矩形、纤维处于伸直状态、预制体结构均匀一致、忽略边缘导向套与纤维的缠绕区域等基本假设,建立了预制体几何结构模型,并通过织造实验验证了模型的合理性。通过织造层致密化压实工艺,织造了纤维体积分数分别为44.1%、50.0%和52.5%的预制体,采用树脂转移模塑成型(RTM)技术制备了复合材料试样。将试样研磨抛光后置于显微镜下观测X/Y向纤维束沿Z向和轴向的截面细观形貌变化特征(将纤维与平面内X或Y向纤维之间正交铺设的夹层区域定义为A区域,将X向纤维和Y向纤维正交叠层区域定义为B区域)。结果表明,受不同压实载荷的影响,纤维体积分数高的预制体,A区域的X/Y向纤维束截面形貌更趋于矩形;B区域的X/Y向纤维束,在预制体纤维体积分数达到50%时,呈轻微的反半圆形状,纤维体积分数达到52.5%时,纤维束截面近似呈矩形;X/Y向纤维束沿轴向截面观测结果显示,在A区域和B区域的纤维束轴向截面形貌分别形成反鼓形和鼓形结构,沿着纤维束轴向交替重复出现,且随着压实载荷的增加,制件纤维体积分数提高,该特征更加明显。通过分析碳纤维预制体细观结构特征,得出宏观压实致密化程度对预制体细观结构的影响规律,为预测复合材料性能提供了参考。

Targeting at the problem of structure characterization of 3D flexible woven preform,the macroscopic geometry of preform and the mesostructure of fiber bundle were studied.Based on the basic assumptions that the fiber cross section is rectangular,the fiber is straight,the structure of preform is uniform,and the winding area between edge guide sleeve and fiber is ignored,the macroscopic geometric structure model of the preform was established,and the rationality of the model was verified by the weaving experiment.Through the densification and compaction process of the woven layer,the preforms with fiber volume fractions of 44.1%,50.0%,and 52.5%were woven,and composite material samples were prepared using resin transfer molding(RTM)technology.After grinding and polishing,the mesomorphology of X/Y fiber bundles along Z direction and axial section was observed under microscope,as the sandwich area between Z direction fiber and X direction fiber or between Z direction fiber and Y direction fiber is defined as region A,and the orthogonal stacking region between X direction fiber and Y direction fiber is defined as region B.The results show that,under the influence of different compaction loads,the cross-sectional morphology of the X/Y direction fiber bundle in the A region for the preform with high fiber volume fraction tends to be more rectangular.The cross-sectional morphology of the X/Y direction fiber bundles in the B region shows a slight reverse semicircle shape when the fiber volume fraction of the preform reaches 50%,and it is approximately rectangular when the fiber volume fraction reaches 52.5%.The axial cross-section observation results of the X/Y fiber bundles show that the axial cross-sectional morphology of the fiber bundles in the A and B regions respectively form anti-drum and drum structures,which alternately and repeatedly appear along the fiber bundle axis.With the increase of compaction load,the fiber volume fraction of the part increases,and the above characteristics are more obvious.By analyzing the mesostructure characteristics of carbon fiber preform,the influence of compaction degree on the mesostructure of the preform was obtained,which provides a reference for predicting the performance of the composite materials.