【作者】 杨金水；

【导师】 肖加余； 杨军；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2012， 博士

【摘要】 真空导入模塑工艺（Vacuum Infusion Molding Process, VIMP）是大型复合材料构件的常用制备工艺。本文系统开展了VIMP工艺整体成型大尺寸厚截面碳纤维复合材料的相关基础研究。重点考察了厚截面碳纤维预成型体中碳纤维/树脂的浸润机理、树脂体系的流变行为和固化动力学行为、多层纤维织物预成型体的压缩响应行为、多层纤维织物预成型体的面内（x-y平面内）和面外（即z向）渗透特性、厚截面复合材料固化过程中的热化学效应和残余热应力、以及尺度效应对碳纤维复合材料静态力学性能的影响规律。主要研究工作包括：开展了碳纤维/环氧树脂的界面性能研究。采用偶联剂直接加入树脂中的迁移法来改善碳纤维/树脂的界面性能，确定偶联剂的最佳含量，优选出纤维/树脂界面粘接性能最佳的胺基硅烷偶联剂改性环氧树脂体系为VIMP工艺整体成型厚截面碳纤维复合材料的基体树脂体系。开展了基体树脂体系的VIMP工艺特性研究。考察了基体树脂体系的等温和非等温流变特性。结果表明，基体树脂体系具有VIMP工艺整体成型厚截面碳纤维复合材料的低黏度流变特性，及其适宜的低黏度保持时间。针对单一黏度模型难以准确预测宽黏度范围内树脂体系黏度变化的问题，提出了联合黏度模型来预测树脂体系的流变行为。结果表明，在0~5000mPa·s黏度范围内联合黏度模型预测黏度结果与实验值具有良好的一致性。开展了基体树脂体系的固化动力学研究。采用DSC热分析法确定了基体树脂体系的最佳预固化温度、固化温度和后固化温度。建立了基体树脂体系的固化动力学模型。结果表明，树脂体系的动态和等温固化动力学行为可分别采用自催化模型和修正自催化模型来描述，最大固化度与等温固化温度呈良好的线性关系。开展了真空负压下多层纤维织物预成型体的压缩响应研究。采用数值模拟方法分析了VIMP工艺注射过程中纤维预成型体压实应力状态随树脂渗流进程的变化规律，以及预成型体厚度（层数）变化对其渗透率、纤维体积分数和流体压力的影响。考察了材料参数和工艺参数对干态纤维预成型体压缩响应的影响。结果表明，纤维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。纤维预成型体的压缩响应行为与纤维种类、织物形态、铺层方式和混杂方式等因素密切相关。考察了VIMP工艺参数对湿态纤维预成型体压缩响应、复合材料制品厚度和纤维体积分数的影响。结果表明，预注射阶段、注射阶段和后注射阶段，纤维预成型体的厚度变化规律遵循不同的压缩响应模型。沿注射口至抽气口方向，VIMP工艺成型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。开展了多层纤维织物预成型体的面内（x-y平面内）渗透特性研究。考察了导流介质对纤维预成型体面内渗透率及树脂流动行为的影响，以及预成型体面内渗透率随其厚度（层数）的变化规律和厚度效应。结果表明，VIMP工艺中导流介质的提速机理可用渗漏模型和Lead-lag效应来描述。导流介质的提速作用随纤维预成型体厚度（层数）的增加而逐渐减弱。纤维预成型体的面内表观渗透率随其厚度（层数）的增加而降低。开展了多层纤维织物预成型体的面外（即z向）渗透特性研究。提出了一种新的面外渗透率测试方法，考察了纤维预成型体面外渗透率随其厚度（层数）的变化规律，以及穿层缝合对预成型体面外渗透率的影响。结果表明，纤维预成型体的面外渗透率比其面内渗透率低1~2个数量级。纤维预成型体的面外渗透率随其厚度（层数）的增加而降低。穿层缝合能够显著提高纤维预成型体的面外渗透率，且缝合因子随厚度（层数）的增加而增大。采用Lead-lag效应表征多层纤维织物预成型体中树脂液体的面内和面外耦合流动行为。结果表明，随着纤维预成型体厚度（层数）的增加，耦合流动行为的影响作用增大。开展了厚截面碳纤维复合材料固化过程中的热化学效应和残余热应力研究。考察了单面非对称加热条件下，固化过程中厚截面碳纤维复合材料构件内部的温度和固化度分布，以及厚度变化对温度和固化度分布的影响。结果表明，厚截面复合材料构件中存在明显的温度突变。构件内部温度和固化度呈梯度分布，温度差别最大可达30℃，而固化度差别最大可达10%。温度突变幅度、最大峰值温度、温度梯度和固化度梯度均随着复合材料构件的厚度和体积的增加而增大。考察了厚度变化对厚截面碳纤维复合材料残余热应力的影响。结果表明，厚截面复合材料横向残余热应变的绝对值明显大于纵向残余热应变。厚截面复合材料残余热应力随着构件厚度的增加呈现增大趋势。开展了厚截面碳纤维复合材料静态力学性能的尺寸效应研究。结果表明，厚截面碳纤维复合材料弯曲强度、短梁剪切强度和压缩强度均随着厚度的增加而降低，而弯曲模量和压缩模量的测试结果则与试样厚度基本无关。厚截面复合材料的弯曲强度、短梁剪切强度和压缩强度具有明显的尺寸效应，且可用Weibull概率模型进行描述。厚截面复合材料弯曲强度和短梁剪切强度的尺寸效应不仅与“最弱链”数目有关，而且与试样的三维应力状态有关，而压缩强度的尺寸效应仅取决于“最弱链”的分布和数目。更多还原

【Abstract】 Vacuum infusion molding process (VIMP) is an integral manufacturing techniquefor large-scale composite structures. The basic research related to the VIMPmanufacturing process for large-size thick-section carbon fiber composite structures issystematically carried out in this paper. The research focuses on carbon-fiber/resininfiltration mechanism, rheological behavior and curing kinetics behavior of resinsystem, compaction response of multilayer fabric preform, in-plane (x-y plane) andout-plane (z direction) permeability characteristics of multilayer fabric preform, thethermochemistry effects and thermal residual stress in thick-section composite duringcuring, as well as the scale effects on mechanical properties of the thick-section carbonfiber composites. The main work includes:To improve carbon-fiber/resin interfacial adhesion, epoxy resin is modified byincorporation of amino-silane coupling agent. Based on the determined optimalsilane-coupling-agent and its content, an epoxy resin modified by silane coupling agentis chosen as the matrix resin for thick-section carbon fiber composite manufacturedintegrally by VIMP.Isothermal and non-isothermal rheological behavior of the epoxy resin isinvestigated by viscosity experiments. The results show that the low-viscosityrheological properties and low-viscosity maintain time of the epoxy resin is appropriatefor VIMP manufacturing of thick-section carbon fiber composites. In order to improvethe prediction accuracy of a single viscosity model, an empirical combined viscositymodel is proposed to predict the rheological behavior of the epoxy resin in a wideviscosity range. The results show that the viscosity predicted by the combined model isin good agreement with the experimental data in the viscosity range of0~5000mPa s.DSC analysis is employed to determine the optimal pre-curing, curing andpost-curing temperatures of the epoxy resin. Based on the DSC analysis, the curingkinetics model is established to predict the curing degree of the epoxy resin. The resultsshow that the dynamic and isothermal curing behavior of the epoxy resin can beexpressed by autocatalytic model and modified autocatalytic model, respectively. Themaximum curing degree increases linearly with the isothermal curing temperatures.Compaction response behavior of multilayer fabric preform under vacuum pressureis systematically investigated. Numerical simulation is used to analyze the compactionstress variation of the fiber preform and the effects of thickness variation on liquidpressure, permeability as well as fiber volume fraction of the fabric preform during resininfiltration process. Effects of material configurations and processing parameters on thecompaction response behavior of the dry fabric preform are experimentally investigated. The results show that a hysteresis phenomenon can be obviously observed in thecompaction and relaxation process of the fabric preform. The relationship between fibervolume fraction, thickness and vacuum compaction stress, compaction time as well ascyclic times can be expressed by two or three-parameters power law models for thefabric preform. The fiber volume fraction and relaxation factor of the fabric preformincreases with the increasing thickness (layers). Fabric form, fiber types, the way oflayup and hybrid modes have remarkable effects on the compaction response behaviorof the fabric preform. Effects of VIMP processing parameters on the compactionbehavior of wet fabric preform, the thickness and fiber volume fraction of the compositestructures are investigated by experiments. The results show that the thickness variationof the fabric preform follows different compaction response models during pre-filling,filling and post-filling process in VIMP. Thickness of the composite structuremanufactured by VIMP decreases gradually along direction from the injection gate tothe vent, while the fiber volume fraction increases along the direction.Flowing experiments are conducted to investigate the in-plane (x-y plane)permeability characteristics of the multilayer fabric preform, including the effects ofdistribution medium on the in-plane permeability and the resin flowing behavior, thevariation rule of in-plane permeability as thickness increasing and thickness effects. Theresults show that the leakage model and Lead-lag effect can be used to describe theaccelerating mechanism of distribution medium on the resin filling flow velocity. Theaccelerating function of distribution medium reduces gradually with the increasingthickness (layers) of the fabric preform. The in-plane permeability of the fabric preformdecreases with the increasing thickness (layers) following two-parameter power lawmodel. It indicates that the accelerating function of the distribution medium and thein-plane permeability of the multilayer fabric preform would be significantly affectedby the thickness of the fabric preform.An innovative measuring methods is proposed to investigate the out-plane (zdirection) permeability characteristics of the multilayer fabric prefrom, including theeffects of puncture stitching on the out-plane permeability and the variation rule ofout-plane permeability as thickness increasing. The results show that the out-planepermeability of the fabric preform is1~2orders of magnitude less than that of thein-plane permeability. The out-plane permeability of the fabric preform decreases withthe increasing thickness (layers) following three-parameter power law model. Theout-plane permeability of the fabric preform can be significantly improved by puncturestitching. The stitched factor increases with the increasing thickness (layers) followingthree-parameter power law model. Flow coupling behavior of the in-plane (x-y plane)and the out-plane (z direction) flow is investigated by using Lead-lag effect. The resultsshow that the effect of the flow coupling behavior increases with the increasingthickness (layers). Considering single-sided asymmetric heating condition during curing process ofthe thick-section carbon fiber composite manufactured by VIMP, distribution oftemperatures and curing degree as well as the effect of thickness variation areinvestigated by experimental and finite element methods. The results show thattemperature overshoot is observed clearly in the temperature variation history of thethick-section composite during curing process. Along thickness direction, thetemperature and curing degree of the composite are of gradient distributions. Internalmaximum temperature and curing-degree difference of the composite is up to30℃and10%, respectively. The temperature overshoot, maximum peak temperature, temperaturegradient and curing degree gradient increase linearly with the thickness and volume ofthe composite. Effects of thickness variation on the thermal residual stress of thethick-section carbon fiber composite are investigated by experimental and finite elementmethods. The results show that the transverse residual thermal-strain is significantlygreater than the longitudinal residual thermal-strain of the thick-section carbon fibercomposite. And the thermal residual stress of the thick-section composite increases withthe increasing thickness.Size effects of static mechanical properties of the thick-section carbon fibercomposite are investigated by experiments and finite element simulation. The resultsshow that flexural strength, short-beam shear strength and compression strength of thecomposite decrease with the increasing thickness following logarithmic model, whilethe flexural and compression modulus basically remain a constant as thicknessincreasing. The size effects of flexural strength, short-beam strength and compressionstrength of the thick-section composite can be expressed by Weibull probability model.The size effects of flexural and short-beam shear strength depend on not only thenumber of the “weakest link” but also the three-dimensional stress states of thespecimen. While the size effects of compression strength only depends on the numberand distribution of the “weakest link”.更多还原