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.     

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。      

热压工艺参数对单向复合材料层板密实状态的影响

为了提高复合材料的质量稳定性并降低成本, 需要研究纤维密实状态的变化规律及其影响因素。采用密实指数I_c表征单向复合材料层板中纤维的密实程度, 进而研究了热压工艺下压力、加压时机及铺层层数对密实指数的影响规律。结果表明, 密实指数随压力的增大呈非线性增大, 随加压点树脂粘度的增大而减小, 随铺层层数的增大呈线性减小。该研究结果为优化热压成型工艺窗口和短程流动模型的建立提供了重要的实验依据。      

L 形复合材料层板热压工艺密实变形过程的数值模拟

基于 Biot 固结原理和达西定律 , 建立了二维树脂流动与纤维密实模型 , 采用有限元方法实现了 L 形层板热压成型过程树脂压力分布、 层板变形的预测。通过对 AS4 炭纤维/环氧 350126 等厚层板厚度变化的模拟结果与实验数据的对比分析 , 证明了数学模型和有限元程序的可靠性。以阳模成型 90° 铺层 S22玻璃纤维/环氧 648L 形层板为例 , 对工艺过程层板厚度变化进行了分析。模拟结果表明 : 剪切模量对拐角以及拐角与平板过渡区域的变形影响较大 ; 平板长度对拐角区域变形影响较明显 , 对平板区的变形影响较小。采用热压罐制备了 90° 铺层S22玻璃纤维/环氧 648阳模成型 L 形层板 , 实验数据表明 , 固化后层板呈现拐角区厚、 平板区薄的厚度不均现象 , 并且平板长度对拐角区厚度变化影响较显著 , 这与数值预测结果具有较好的一致性。     

热压罐零吸胶工艺树脂压力在线测试及其变化规律

针对碳纤维缎纹布/环氧914预浸料热压罐零吸胶工艺,采用热压成型过程树脂压力在线测试系统监测树脂压力的大小与分布,分析了真空、外加气压对树脂压力的作用规律,通过显微观察研究了真空及外加气压对孔隙缺陷的影响。实验结果表明,所采用的在线测试系统可以定量分析真空在铺层内的作用程度和树脂压力的变化;零吸胶工艺树脂承担了大部分外压且沿层板厚度及面内方向分布均匀;真空通过铺层内的气路通道排出夹杂空气,其作用程度受到树脂黏流状态和铺层密实程度的影响;不同压力条件下复合材料层板孔隙状况与树脂压力的测试结果相吻合。     

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。      

光纤微弯压力测试系统实时监测复合材料热压成型过程

利用自行研制的光纤微弯压力测试系统, 对树脂基复合材料热压成型过程进行实时监测。实验结果表明, 该系统除了能较好地反映垂直层板方向压力变化外, 还能提供加压过程树脂流动状态及层板密实达到稳态均匀时间的相关信息。这些结果对确定合理加压点及保压时间、优化工艺参数、控制复合材料成型构件质量具有十分重要的意义。      

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。     

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。      

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。     

Numerical and Experimental Study on the Effect of Lay-Up Type and Structural Elements on Thickness Uniformity of L-Shaped Laminates

Based on the two-dimensional resin flow and fiber compaction model developed by our group, we studied the cured laminate thickness uniformity of the L-shaped CF/BMI resin laminates and the effects of lay-up type and structural elements on it. Both the simulated and experimental data showed that the quasi-isotropic laminate thickness was more uniform than that of the [90°]_n laminates and the cured thickness of laminates molded by rigid convex tool was more uniform than that molded by the rigid concave tool. Lay-up type has a great influence on the cured laminate thickness uniformity. For the quasi-isotropic laminates, the structural elements, such as curvature radius, flat part length, and the number of plies, did not have much influence on the cured laminate thickness uniformity in the studied scope. For the [90°]_n laminates, the corner radius has a larger effect on the corner consolidation in comparison with the flat part length and the number of plies. According to the simulated results, resin pressure and consolidation time were largely affected by the lay-up type, due to the different permeability and compressibility. The rich resin defect was observed in the metallographic photos of the corner region of the [90°]_n laminates fabricated with the rigid concave tool, which demonstrated that the resin flow in the laminates played an important rule and validated the numerical prediction. Good agreement between the simulated results and experimental data demonstrated the reliability and universality of the numerical simulation method. These results are greatly helpful for the control of defects in angle-bended laminates and the optimization of cure cycle in autoclave process.     

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.     

基于材料性能时变特性的复合材料固化过程多场耦合数值模拟

针对热固性树脂基复合材料固化过程中各种复杂的物理化学变化之间的相互影响,建立了基于材料性能时变特性的复合材料固化过程的二维多场耦合计算模型。该模型由已知的3个经典复合材料固化过程子模型构成,包括热-化学模型、树脂黏度模型和树脂流动模型。在此基础上,将固化过程中材料性能的时变特性引入多场耦合计算模型中。通过与文献中实验结果的比较,证明了所建立的模型具有较高的可靠性。对AS4/3501-6复合材料层合平板的固化过程进行了数值模拟,重点研究了固化过程中纤维体积分数变化及材料参数的时变特性对固化过程中温度、固化度和树脂压力等参量的影响。分析结果表明:考虑纤维体积分数变化和材料性能的时变特性后,固化过程中复合材料层合板中心温度峰值明显减小,树脂压力随时间的变化将有所滞后。     

复合材料热压工艺多物理场耦合数学模型

针对热压工艺特点 , 将预浸料视为可变形的多孔介质 , 通过体积平均 , 建立了固化过程中温度、 纤维应力和树脂流动多物理场耦合的数学模型。该模型考虑了纤维变形和体积分数变化的影响 , 反映了渗透率和纤维体积分数的关系。对于复合材料层合平板热压工艺 , 通过进一步简化 , 给出了一维固化方程 , 并进行了有限元数值分析。数值模拟中采用 AL E移动网格方法来处理动边界问题。计算结果表明 , 与非耦合的经典模型相比 , 该模型给出的结果能更好地与实验吻合 , 层合板逐层压缩现象也和实验结果一致。而且该模型能预测树脂的排出量和纤维层间纤维体积分数的变化。     

Effect of room-temperature out-time on tow impregnation in an out-of-autoclave prepreg

Tow impregnation as a function of material out-time was investigated for an out-of-autoclave carbon fiber–epoxy prepreg. Prepreg was aged at ambient temperature for 56 days. Every 7 days, laminates were laid up and cured using vacuum bag only processing. Void content was calculated through image analysis of polished sections. Experimental results were used to validate an analytical model for tow impregnation. Model predictions were based on flow kinetics during processing conditions, taking into account increasing degree of cure and evolution of resin viscosity as a function of ambient aging time. The study found that no significant tow porosity occurred within the material’s stated out-life, that tow porosity increased once this out-life was exceeded and eventually stabilized due to the room-temperature vitrification of the resin. The model’s predicted trends were consistent with experimental results, suggesting that an increase in resin viscosity is indeed the main cause of out-time induced tow porosity and providing a means of predicting laminate quality as a function of room temperature aging time.     

基于纤维束/环氧树脂复合材料试验的单向层合板横向拉伸强度预测方法

实验研究表明,纤维束/环氧树脂复合材料试件的横向拉伸强度与工程上常用的单向层合板横向拉伸强度在趋势上具有很好的相关性,但是数值上存在一定差距。本文使用两种碳纤维和两种环氧树脂制备了三种纤维束/环氧树脂复合材料和单向层合板,并分别测量了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度,以及环氧基体的拉伸强度。在实验基础上,应用Griffith断裂强度理论建立了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度的关系模型,通过两种复合材料实验的结果拟合了该模型中的参数。利用第三种复合材料实验进行校验,发现该模型预测的单向层合板横向拉伸强度与实测强度之间达到很好的一致性,相对偏差为9%。采用本文提出的方法,可以用较为简单的纤维束/环氧树脂复合材料和环氧基体拉伸试验预测单向层合板的横向拉伸强度。     

Mechanical Properties of Date Palm Fiber Reinforced Composites

Mechanical properties of several laminates of date palm leave (DPL) reinforced composites are investigated. Three different processes to construct these composite laminates are assessed. These are wet lay-up with simple vacuum bagging, autoclaving with vacuum bagging and Vulcan press moulding. Several fiber orientation and dimensions are tested. Two types of resins are selected. The first is a high temperature curing Phenolic (phenol formaldehyde) resin. The second is a two-component Bisphenol resin with amine-based slow curing agent. The average tensile strength ranged between 127.4 and 152.3 MPa for long unidirectional fibers and 8.4 to 62.6 MPa for short and medium length fibers respectively (depending on process and resin type). The Bisphenol laminates have better mechanical properties. These laminates have consistently 25 to 50% higher tensile strength than Phenolic laminates. The bending strength ranged between 120.6 and 342.3 MPa (at 500 mm/min loading speed) depending on fiber length. Short fiber Bisphenol laminates have excellent fatigue life characteristics (over 466,000 and 653,000 cycles at 70% and 60% of maximum stress loads respectively). The process parameters and resin types have significant effects on the laminate properties. The water absorption of the laminates ranged between 2.3 to 5.8% for the Phenolic laminates (depending on the test method and manufacturing process used). The water absorption of Bisphenol laminates ranged between 10 and 40%. The produced laminates were very stable to handle all required machining processes as construction panels. They were successfully subjected to several machining processes such as milling, end milling, hack sawing and drilling.