厚度效应对树脂渗流、固化及复合材料性能影响研究

Liquid Composite Molding (LCM) is an advanced technique to manufacture composite materials with the advantage of low cost and good properties, on the basic principle that resin flowing and impregnating fiber materials to make composites after curing. The mechanical properties, as well as the physical and chemical behaviors during manufacturing process, will change regularly along with the composite thickness. This phenomenon is called thickness effect. Thickness effect can not only cause the manufacturing failure of large-scale composite elements but also reduce the integral performance of composite structures. In this research, the relationship between thickness effect and permeability, resin flow behavior, curing characteristics will be investigated to establish the three-dimensional coupling flow model, and the coupling model of resin flow and thermochemistry behavior during resin impregnating process. The relationship between thickness effect and thermochemistry behavior will be investigated to reveal the coupling mechanism of thermochemistry and stress during the composite curing process. The relationship between thickness effect and composite property will be investigated to evaluate the integral performance of composite structures. The results can not only rich flow-mechanics and thermochemistry theories, but also serve as manufacturing and structural optimization for large-scale composite structures.

液相模塑成型技术（Liquid Composite Molding, LCM）是一种具有高性能低成本制造优势的先进复合材料制备技术，其本质是树脂长程渗流浸渍纤维增强材料并固化成型复合材料。采用LCM工艺制备厚截面复合材料过程中的物理化学行为及复合材料性能随其厚度尺寸的变化呈现一定规律的现象，称为厚度效应。厚度效应不仅容易导致超大型复合材料构件制备失败，而且严重损害其整体性能。本项目拟研究厚度效应与纤维预成型体渗透特性、树脂渗流行为和固化特性的关系，建立考虑厚度效应的树脂三维耦合流动模型和树脂渗流-热化学耦合模型；研究厚度效应与固化热化学行为的关系，揭示复合材料固化热化学-应力耦合行为的厚度效应机理，评估厚度效应对复合材料整体性能的影响。研究成果不仅可以丰富渗流力学和热化学理论体系，而且可以为LCM工艺整体成型制备超大型复合材料构件的工艺优化和结构优化提供理论依据，具有重要理论和现实意义。

本项目开展厚度效应对树脂渗流、固化及复合材料性能影响研究，主要考察厚度效应与纤维预成型体渗透特性、树脂渗流行为和固化热化学行为的关系，以及厚度效应对复合材料性能的影响。主要研究结论如下：.采用实验方法研究预成型体面内、面外渗透特性和混合铺层预成型体的等效渗透特性，建立渗透率模型，探讨其厚度效应机理。结果表明：预成型体面内渗透率随其厚度（层数）的增加而呈非线性降低；预成型体面外渗透率比其面内渗透率低1~2个数量级，且随其厚度的增加而降低，变化关系遵循三参数幂律定律；混合铺层预成型体，导流介质的提速作用随着预成型体厚度的增加而逐渐减弱，等效渗透率随其厚度的增加而降低，遵循双参数幂律方程。.采用渗流实验和数值模拟方法考察树脂的耦合渗流行为，探讨Lead-lag、流道、构筑效应与厚度效应的关系，建立渗漏耦合模型，揭示树脂耦合渗流行为的厚度效应机理。结果表明：混合铺层预成型体中的三维渗流行为可用渗漏模型和Lead-lag效应来描述，Lead-lag效应随着厚度的增加而线性增加；面内渗流、面外渗流、渗漏耦合渗流和渗漫耦合渗流的弹性回复，均随着层数增加而增大，呈明显厚度效应规律，且面外渗流的幅度最大；建立渗漏和渗流模型，有限差分法分析表明流体压力分布、渗透率变化和充模时间均呈现明显的厚度效应。.采用实验方法考察厚截面复合材料的固化热化学行为，建立固化动力学模型，揭示固化温度、固化度和残余热应力的厚度效应机理。结果表明，固化温度和固化度呈梯度分布，温差最大达30℃，而固化度差别最大可达10%；温度突变、峰值温度、温度梯度和固化度梯度均随着厚度的增加而增大；残余应力随厚度的增加而逐渐增大，厚度方向分布不均匀，且主要是压缩应力。.考察了复合材料力学性能的厚度效应机理。结果表明，复合材料弯曲强度、短梁剪切强度和压缩强度均随着厚度的增加而降低，具有明显的厚度效应，且可用Weibull概率模型进行描述。