硅橡胶热膨胀工艺预浸料铺层内树脂压力变化规律

采用硅橡胶热膨胀工艺制备了碳纤维/双马树脂复合材料层板, 通过自行设计的成型模具及树脂压力在线测试系统测试并分析了成型过程中热胀压力和预浸料铺层内树脂压力的变化规律, 考察了工艺间隙和温度分布的影响, 并通过显微观察分析了不同工艺条件下层板的密实状况。结果表明: 采用树脂压力在线测试系统, 可实现热膨胀工艺预浸料铺层内树脂压力的测试; 工艺间隙和硅橡胶内的温度分布对树脂压力及硅橡胶的热胀压力有重要影响, 在零吸胶工艺条件下, 当工艺间隙设计合理时, 凝胶前热胀压力和树脂压力的变化趋势及变化程度基本一致, 固化层板纤维密实并且厚度均匀; 通过增加恒温平台减小硅橡胶内部温差, 可使热胀压力的增加速度减小。      

热压罐工艺树脂压力测试系统适用性实验研究

采用玻璃纤维织物/环氧树脂E51预浸料研究热压罐工艺树脂压力在线测试系统适用性,分析了树脂黏度对测试系统动态反应特性的影响,进而测试了热压罐工艺零吸胶条件下等厚、非等厚及L形预浸料铺层内部的树脂压力,并与理论模型计算树脂压力对比,以分析测试系统的准确性。结果表明: 树脂黏度明显影响系统的动态反应特性,当树脂黏度低于25 Pa·s时树脂压力测试系统具有较高的动态反应特性,满足复合材料内部树脂压力测试需求; 对于所研究的各种形式的预浸料铺层,树脂压力测试值与理论值有很好的一致性,当热压罐压力达到0.5 MPa,相对误差约为2%,验证了系统的准确性。     

复合材料层板热压工艺参数的分析与优化

在热固性树脂基复合材料热压成型过程中,外加压力和加压时机是决定层板厚度、纤维含量以及孔隙含量的两个主要因素.基于复合材料热压成型过程树脂流动模型,采用遗传算法,根据固化层板纤维体积分数的要求,对单向和正交两种铺层形式的T700/5228和T700/5224层板加压时机进行了分析.以航空航天应用的典型纤维含量为准,对优化得到的加压时机以及不同工艺条件下固化层板内纤维分布特点进行了分析.结果表明,纤维、树脂种类相同,铺层方式不同,加压时机差别很大;纤维种类、铺层方式以及初始和优化目标相同的条件下,不同树脂体系,加压时刻树脂粘度基本相同;层板内纤维分布均匀性主要由纤维层压缩特性决定.采用本文建立优化方法,可以快速地得到满足目标纤维含量要求的加压时机,具有重要的学术价值和工程应用意义,有助于降低成本,缩短复合材料研制周期.     

采用薄膜传感器的树脂基复合材料热压罐工艺密实压力测试方法

针对树脂基复合材料层板热压罐成型工艺,采用薄膜压力传感器建立了密实压力在线测试系统,用于监测成型过程中复合材料所受密实压力的大小和分布。研究了密实压力测试系统在热压罐工艺条件下的适用性,在此基础上以该系统为测试手段,研究了热压罐工艺下L形碳纤维/环氧树脂复合材料层板的密实压力变化规律及模具形式的影响。结果表明: 所建立的密实压力测试系统具有较高的准确性和动态响应性,能够测试高温条件及曲面位置的密实压力,满足复合材料热压罐成型过程中密实压力的在线测试要求; L形复合材料层板成型过程中拐角区与平板区的密实压力随热压罐压力增大而增加,但增加速度和最终大小不同,阳模成型时拐角区密实压力高于平板区,阴模成型时拐角区密实压力小于平板区和外加压力,表明曲面结构与平板结构的密实行为具有差异性。     

变厚度复合材料热压罐工艺层板厚度控制的实验研究

针对2种碳纤维织物/环氧预浸料,采用热压罐工艺在不同条件下制备了变厚度层板,并通过层板内部形貌、层板厚度、纤维含量、吸胶量、织物渗透率的测试分析,研究了变厚度层板的密实过程和纤维分布的影响因素。结果表明：密实过程中树脂的二维流动导致2种织物变厚度层板厚板区的纤维含量高于薄板区;G0827单向织物的面内渗透率与厚度方向渗透率比值大于G0803缎纹织物,造成G0827织物变厚度层板的纤维分布不均匀性更大;无吸胶材料的条件下层板内纤维分布均匀,说明吸胶材料内树脂的面内流动对层板的纤维分布有很大影响。     

复合材料等厚层板热压成型中树脂流动过程数值模拟

树脂基复合材料热压成型过程中树脂流动在很大程度上决定着层板纤维含量、 孔隙含量以及层板尺寸 , 根据有效应力原理与达西渗流定律建立了描述复合材料等厚层板热压成型过程树脂流动与纤维密实的数学模型 , 采用有限单元方法实现了热压成型中纤维密实均匀状况的预报。分析了温度边界条件、 铺层方式对树脂流动过程的影响。结果表明: 温度边界条件对计算结果影响比较大 ; 铺层方式对层板厚度以及纤维体积分数分布规律影响非常大 ; 边界条件以及材料参数的准确性直接影响计算结果的可靠性。以 T700S/环氧 5228单向层板为例进行了实验验证 , 结果表明计算与实验结果的一致性非常好。      

环氧复合材料层板热压成型孔隙缺陷影响因素

针对玻璃纤维/环氧复合材料, 采用真空袋和热压机工艺, 研究了层板中孔隙含量、 形态及其分布规律, 考察了成型温度、 工艺压力、 预浸料吸湿量、 铺层方式等因素对孔隙缺陷的影响, 并应用Kardos气泡模型对实验结果进行了理论分析。结果表明: 孔隙缺陷的主要影响因素随工艺方法而变化, 单向层板中孔隙率的分布规律有着很好的一致性; 同时Kardos气泡模型可用于判断孔隙缺陷的形成状况。      

L形层板真空袋成型缺陷的实验研究

采用真空袋阳模成型法在不同条件下制备了90°的L形玻纤单向布/环氧树脂层板, 对层板不同位置处纤维密实和缺陷状况进行了研究, 考察了成型过程主要工艺条件对缺陷的影响规律。结果表明, 富树脂、 孔隙、 厚度分布不均和纤维屈曲变形是L形层板中主要的缺陷类型, 加压时机、 层板尺寸、 铺层方式以及边界条件对纤维密实和缺陷的形成都有重要的影响。对以上各种缺陷的产生机制进行了初步分析: 剪切流动的存在导致层板厚度分布不均匀而且出现富树脂区; 纤维的屈曲变形是由于轴向受压缩力; 本文实验条件下孔隙的主要来源是夹杂空气。研究结果对热压工艺中缺陷的预测与控制以及工艺参数的优化具有重要的指导意义。      

复合材料变厚层板热压成型缺陷类型与成因实验研究

采用热压机工艺与热压罐工艺两种成型方法制备了玻璃纤维/环氧 648 变厚度层板 , 研究了两种工艺下缺陷的形成机制及铺层方式和变厚梯度对缺陷程度和分布的影响。结果表明 : 纤维分布不均、 富树脂、 分层是主要缺陷类型 , 其中纤维分布不均由树脂二维流动引起 , 并与纤维不连续区、 纤维层渗透特性以及外压的均匀性有关; 富树脂主要是纤维的不连续性造成的 ; 而分层缺陷与纤维分布和热膨胀各向异性紧密相关。研究结果对变厚度复合材料层板的缺陷消除和成型质量控制有重要的指导意义。      

碳纳米管-玻璃纤维/环氧层板双真空灌注工艺及性能

针对碳纳米管(CNT)-玻璃纤维/环氧树脂体系, 采用传统的真空灌注工艺(VARIM)和双真空灌注工艺(DVARIM)制备复合材料层板, 分析了不同工艺方法下层板缺陷状况, 测试了层板的弯曲性能和层间剪切性能, 并结合树脂性能和纤维/树脂界面粘结状况观察, 探讨了DVARIM对CNT分布的影响及碳管的增强机制。结果表明: 与传统的VARIM相比, DVARIM能增加纤维的间距, 提高树脂对纤维的浸润能力, 减小纤维束内的孔隙缺陷; 添加质量分数为0.05％的酸化CNT后层板性能提高, 而且采用DVARIM性能提高更明显; 不同灌注工艺对CNT的分布产生影响, 从而改变了CNT对纤维/树脂界面粘接的影响, 同时这种影响与织物结构的紧密程度有关。      

Effects of Processing Parameters on the Forming Quality of C-Shaped Thermosetting Composite Laminates in Hot Diaphragm Forming Process

In this study, the effects of processing temperature and vacuum applying rate on the forming quality of C-shaped carbon fiber reinforced epoxy resin matrix composite laminates during hot diaphragm forming process were investigated. C-shaped prepreg preforms were produced using a home-made hot diaphragm forming equipment. The thickness variations of the preforms and the manufacturing defects after diaphragm forming process, including fiber wrinkling and voids, were evaluated to understand the forming mechanism. Furthermore, both interlaminar slipping friction and compaction behavior of the prepreg stacks were experimentally analyzed for showing the importance of the processing parameters. In addition, autoclave processing was used to cure the C-shaped preforms to investigate the changes of the defects before and after cure process. The results show that the C-shaped prepreg preforms with good forming quality can be achieved through increasing processing temperature and reducing vacuum applying rate, which obviously promote prepreg interlaminar slipping process. The process temperature and forming rate in hot diaphragm forming process strongly influence prepreg interply frictional force, and the maximum interlaminar frictional force can be taken as a key parameter for processing parameter optimization. Autoclave process is effective in eliminating voids in the preforms and can alleviate fiber wrinkles to a certain extent.     

VARI工艺成型纤维增强树脂复合材料层合板厚度和纤维体积分数的影响因素

分析了影响真空辅助成型技术（VARI）工艺成型复合材料的纤维体积分数和厚度均匀性的关键因素,即VARI成型工艺的树脂流动控制形式、纤维预制体状态、织物状态、树脂黏度,通过试验分析了各因素对VARI成型复合材料厚度和纤维体积分数的影响。试验结果表明,采用HFVI（high fiber-volume vacuum infusion）工艺、BA9914树脂及真空处理后的U3160单向机织物成型的纤维增强树脂复合材料层合板,其纤维体积分数和厚度均匀性能够接近预浸料/热压罐成型的复合材料制件的水平。     

Void formation in composite prepregs – Effect of dissolved moisture

Void formation as a function of resin moisture content was investigated to better understand and control process defects in composite parts made from prepreg. In this study, uncured prepreg was conditioned at 70%, 80% and 90% relative humidity and at 35 °C. Conditioned prepreg was laid up into quasi-isotropic laminates and cured using vacuum bag only (VBO) processing (low-pressure), and autoclave processing. Moisture uptake in the resin was measured using coulometric Fischer titration. Void content was measured by image analysis of polished sections of cured laminates. Void fractions increased substantially with increasing moisture content in VBO processed laminates, while autoclave-processed parts remained void-free. Experimental results were consistent with trends predicted using a diffusion-based analytical model. The findings are discussed in the context of causes of voids in prepreg composites.     

Numerical and Experimental Study of the Bleeder Flow in Autoclave Process

In the autoclave process, resin flow is a primary mechanics for the removing of excess resin and voids entrapped in the laminate and obtaining a uniform and void free composite part. A numerical method was developed to simulate the resin flow in the laminate and the bleeder, and the effects of ‘bleeder flow’ on the resin flow and fiber compaction were conducted. At the same time, fiber distribution in the cured laminates was investigated by both experiments and simulations for the CF/Epoxy and CF/BMI composites. The data of the experiments and simulations demonstrated that fibers consolidated and reconsolidated in the laminate and it was impacted by the viscosity and gel time of the resin system. Compared to the post study in which only resin flow in the laminate are considered, these results will deepen the understanding of the consolidation process, resin pressure variation and void control during the autoclave process, which is valuable for the study of the performance of composite parts, provided that fiber distribution does affect some properties of composite material.     

碳纤维增强双马来酰亚胺树脂预浸料铺覆黏性及其储存老化行为

将碳纤维增强双马来酰亚胺树脂预浸料CCM40J/HT-280分别置于4种储存环境（真空、N₂、O₂、空气）进行室温老化实验,研究了预浸料铺覆黏性与储存环境和老化时间的关系,对不同环境下黏性失效前后的样品进行了DSC、流变、红外光谱分析。针对不同黏性级别的预浸料,采用热压罐成型工艺制备了复合材料层合板,对层合板内部成型质量及复合材料力学性能进行了研究。结果表明,真空和N₂环境储存下的CCM40J/HT-280预浸料黏性失效周期相比于O₂与空气中的样品延长约40%。DSC和流变测试结果表明,老化后树脂的交联程度大于新鲜树脂,树脂最低黏度也显著增大,O₂环境下的样品表现的更为明显;对红外光谱特征峰分析表明,O₂环境储存条件下树脂交联反应程度高于真空环境,说明O₂对双马来酰亚胺树脂室温下的老化具有促进作用。黏性失效的预浸料制备的CCM40J/HT-280复合材料内部多为层间或层内的密集孔隙,其弯曲强度下降约13.0%、弯曲模量下降约6.5%,层间剪切强度下降约10.7%。      

热固性树脂中孔隙形成条件的定量测试方法与影响因素

根据热固性树脂基复合材料的热压成型特点和扩散形成孔隙机制 , 建立了一种离线的孔隙形成条件量测试方法 , 可实现孔隙率2树脂压力变化关系的定量测定。采用该方法研究了两类环氧树脂体系固化过程中胶温度、 相对湿度、 树脂压力等条件对孔隙形态和分布的影响 , 并与修正的 Kardos气泡模型的理论计算结果进了对比分析。结果表明: 所建立的测试方法可以模拟热压工艺条件离线测定水汽形成孔隙情况 , 结果重复性好不同条件下树脂压力与孔隙率的关系均呈指数衰减的变化规律 ; 凝胶温度和相对湿度对孔隙率影响显著; 树脂类明显影响孔隙率大小和形态分布。研究结果为热压工艺复合材料孔隙缺陷的控制提供了重要的测试方法和验依据。      

Experimental characterization of voids in high fibre volume fraction composites processed by high injection pressure RTM

Replacing autoclave processes is a well-known industry drive in the composites community. One of the most recognized candidates for this replacement is high injection pressure resin transfer moulding (HIPRTM), because it is both an out of autoclave process and because the high processing pressures can, hypothetically, reduce the size of voids, thereby reducing void content. In order to clarify this issue, this paper presents our results on the size distribution and total void fraction of composites containing high fibre volume fractions (>60%) composites produced by HIPRTM. To substantiate this work we present a comparative study considering both autoclave and RTM at lower pressure/fibre volume fractions. Results show that HIPRTM is able to produce high fibre volume fraction parts at very low void content (<0.05%) and is comparable to autoclave results. Future work should study the mechanical properties of these laminates in order to clarify further the limits of HIPRTM.     

Out-of-autoclave cure cycle study of a resin film infusion process using in situ process monitoring

Liquid resin infusion (LRI) of textile tailored reinforcements (TRs) is increasingly applied in new processing technologies for manufacturing carbon fibre composites. This work presents a cure cycle study of an out-of-autoclave toughened resin film infusion (RFI) process as part of the examination of an alternative manufacturing process for composites. To successfully produce laminates using resin film infusion in combination with a fast-curing process, the flow behaviour of the selected resin material under changed processing conditions was investigated. The effect of processing parameters, specifically heating rates and dwell times, on resin viscosity and laminate infiltration was evaluated through experimental work and supported by in situ process monitoring. A DC-resistance sensor system was applied to track the change in resin viscosity during cure. Results showed that cure cycles with a relatively short dwell time and higher heating rate compared to an autoclave cure led to enhanced flow properties of the toughened resin system. High quality laminates, comparable to autoclave panels, were manufactured with vacuum pressure only by modifying the original vacuum bagging arrangement.