纤维预成型体弹性回复效应对树脂渗流行为影响研究

Vacuum infusion molding process (VIMP) is a low-cost liquid composite molding (LCM) technique to manufacture large scale composite structures. Fiber preform is placed on a tool surface and covered by a flexible vacuum bag. A vacuum is drawn on the system to compact the fiber preform and infuse the resin. Part thickness varies with flow development during resin injection process due to the flexibility of vacuum bag. This is elastic-recovery effect of fiber preform. Due to the elastic-recovery effect, performance uniformity could be badly damaged in composite part. And the risk of manufacturing failures would greatly increase in large products. The elastic-recovery effect is a result of interaction between preform elastic-deformation and resin movement. The relationship between elastic-recovery effect and compaction response will be investigated to establish the compaction response model and the permeability model for the fiber preform. The relationship between elastic-recovery effect and resin flow behavior will be investigated to reveal the flow mechanism of viscous fluid in the elastic-deformation porous-medium. And the influence of elastic-recovery effect on performance uniformity will be investigated to evaluate the integral performance of composite structures. The aim of this project is to improve the reliability of VIMP technology for large-size composite components manufacturing.

真空导入模塑工艺（Vacuum infusion molding process, VIMP）是一种制备大尺寸复合材料构件的低成本液体模塑成型技术。其采用单面刚性模具和柔性真空袋膜包覆纤维预成型体，抽真空压实纤维预成型体和注入树脂。由于真空袋膜为柔性体，注射过程中复合材料构件的厚度会随着树脂渗流进程的发展而变化，此现象称为纤维预成型体弹性回复效应。弹性回复效应严重损害复合材料性能的均一性和增大大尺寸复合材料构件VIMP工艺成型失败的风险。纤维预成型体弹性回复效应是预成型体弹性回复变形与树脂运动相互作用的结果，本项目拟研究纤维预成型体弹性回复效应与压缩响应之间的关系并揭示其内在科学规律；研究纤维预成型体弹性回复效应与树脂渗流行为之间的关系，揭示粘性流体在弹性变形多孔介质中的渗流机理；研究弹性回复效应对复合材料性能均一性的影响，为VIMP工艺成功制备性能均一的大尺寸复合材料构件提供理论依据。

本项目开展纤维预成型体弹性回复效应对树脂渗流行为影响研究，主要考察纤维预成型体弹性回复效应与压缩响应关系、纤维预成型体弹性回复效应与树脂渗流行为关系，以及纤维预成型体弹性回复效应对复合材料性能均一性的影响。主要研究结论如下：.采用实验方法研究真空负压下多层纤维织物预成型体的压缩响应行为，考察材料参数和工艺参数对预成型体压缩响应行为的影响规律，建立了考虑弹性回复效应的三参数幂律压缩响应模型和渗透率模型。结果表明：多层纤维织物预成型体的压实和松弛过程存在明显的滞后现象；预成型体纤维体积分数和厚度随真空压实应力、压实时间和循环加载次数的变化关系遵循双参数或三参数幂律模型；预成型体纤维体积分数和松弛因子均随其厚度（层数）的增加而增大，但增幅较小；多层纤维织物预成型体的压缩响应行为与织物形态、纤维种类、铺层方式和混杂方式等因素密切相关。.设计渗流实验考察了树脂面内渗流、Z向渗流、耦合渗流（A和B两种模型）时纤维预成型体的弹性回复效应规律，建立了考虑弹性回复效应的树脂渗流模型，揭示了纤维预成型体弹性回复效应与树脂渗流行为之间的关系，及其相应的渗流机理。结果表明：弹性回复对厚度的影响程度、平均织物单层厚度增量和预成型体纤维体积分数具有内在一致性，其变化与铺层层数的趋势基本一致，三种参量均可用来表征纤维预成型体的回弹能力；面内一维渗流时的弹性回复幅度较小，Z向渗流时回弹幅度较大，且两种模型呈现不同的弹性回复规律；耦合渗流模型（A和B）同时受到面内渗流和Z向渗流的影响，受影响程度与预成型体的厚度密切相关。.考察了弹性回复效应对复合材料性能均一性的影响。结果表明，沿注射口至抽气口方向，复合材料制品的厚度呈现逐渐减小的趋势，纤维体积分数则逐渐增大，制品的拉伸强度、弯曲强度、短梁剪切强度依次增大；树脂面外渗流时弹性回复效应对制品力学性能的影响明显大于面内渗流。