Numerical Study on the Resin Transfer Molding Curing Process for Thick Composites Materials

The successful manufacture of thick composites is challenging since the highly exothermic nature of thermoset resins and limited temperature control make avoiding the onset of detrimental thermal gradients within the composite relatively difficult.This phenomenon is mainly caused by exothermic heat reactions.The so-called Michaud's model has been largely used in the literature to reduce the gap between experience and simulation with regard to the effective prediction of the temperature cycle in these processes.In this work,another solution is proposed to simulate the curing process for thick composites,namely preheating the resin to activate the curing reaction before resin injection into the mold.A good agreement between the experiment and the simulation is found.Moreover,in order to minimize the thermal gradient in the final composite,the thermophysical properties of the fiber and the torque(temperature,time)of the Plate have been varied leading to interesting results.

STUDY OF FLOW AND TEMPERATURE IN RESIN TRANSFER MOLDING PROCESS BY NUMERICAL MODEL

A mathematical model of resin flow and temperature variation in the filling stage of the resin transfer molding (RTM) is developed based on the control volume/finite element method (CV/FEM). The effects of the heat transfer and chemical reaction of the resin on the flow and temperature are considered. The numerical algorithm of the resin flow and temperature variation in the process of RTM are studied. Its accuracy and convergence are analyzed. The comparison of temperature variations between experimental results and model predictions is carried out for two RTM cases. Result shows that the model is efficient for evaluating the flow and temperature variation in the filling stage of RTM and there is a good coincidence between theory and experiment.

基于PAM-RTM的CFRP平板RTM工艺及孔隙缺陷仿真

树脂传递模塑(RTM)成型过程中不同工艺参数对碳纤维增强树脂基复合材料(CFRP)构件质量和性能有极大影响。为了精准设计RTM成型参数,降低最终构件的孔隙缺陷含量,分析充模过程中两种尺度孔隙率的变化及在构件中的分布规律,基于PAM-RTM软件对CFRP平板模型RTM成型的充模及双尺度孔隙形成进行了仿真模拟。分析了不同树脂黏度、浇注压力对填充时间及宏观和微观孔隙分布、孔隙率的影响规律;在构件中选取了不同位置的横向轴线并对比轴上宏观/微观孔隙的含量及分布特征,分析随着距离浇注口位置变化孔隙率的变化规律。结果表明,在恒压浇注条件下,浇注压力越大,树脂黏度越小,填充时间越短;树脂黏度为0.1Pa·s、浇注压力为1.5MPa时,充模时间最小,为13.11s。宏观孔隙率随浇注压力升高而减小,微观孔隙率则相反。宏观孔隙在开始填充一段时间后形成,孔隙率最终在出胶口达到最大值;微观孔隙则在填充初始阶段开始形成,孔隙率随着填充距离增加逐渐减小。3条横向轴上两种尺度孔隙率的变化趋势相近;浇注压力影响宏观孔隙开始形成的位置及微观孔隙结束形成的位置,并影响填充结束时的最大宏观孔隙率和填充开始时的最大微观孔隙率。

Filling Simulation of Three-dimension Braided Composite in Resin Transfer Molding

This paper measured permeability of three-dimension braided preform by radial technology. The results show that principal permeability tensor coincided with their braiding axial direction. The software of one dimensional flow filling mold was designed using Visual C++ language. Filling time is predicted and validated. The result showed that the filling time of the mold centerline agrees with the prediction value. The filling time of the mould edge is shorter than that of the prediction. An actual plate of 3D braided preform/ modified polyarylacetylene composite is produced according to prediction value and validation analysis.

Three-dimensional finite element analysis of process-induced residual stress in resin transfer molding process

A three-dimensional finite element analysis of process-induced residual stress in resin transfer molding (RTM) process is presented. The finite element method (FEM) was employed to solve the coupled equations involved in the transient heat transfer and the cure kinetics of the resin, and the distributions of internal temperature and cure degree of the composite at any instant time were obtained. The self-consistent field micro-mechanics model was used to predict the cure-dependent mechanical properties of the composites. Thermal expansion and cure shrinkage were included in the analysis. The thermo-elastic mechanical governing equations were solved using the incremental stress-strain relationship based FEM and the residual stress development was predicted. The present results were validated by the comparisons with the pertinent literature. The numerical example of a half cylinder was presented. The results show that it is necessary to carry out the three-dimensional analysis due to the complex distributions of temperatures, cure degrees and process-induced stress for thick parts, which can be predicted at any point within composite structures in the present analysis.

基于VARTM的碳纤维单向与三维编织混杂织物树脂灌注工艺

为探究碳纤维单向与三维编织混杂增强环氧树脂基复合材料地铁转向架侧梁的树脂灌注成型工艺,首先基于渗透率理论模型采用非饱和径向流法分别测试得到碳纤维单向与三维编织织物的渗透率。通过数值模拟的方法对典型复合材料方形管结构进行缩比建模与网格划分,并利用PAM-RTM软件对树脂灌注成型过程进行仿真分析,预测了制备复合材料方管所需的灌注时间、灌注压力以及树脂流动过程缺陷的产生。最后根据模拟的灌注方案通过真空辅助树脂传递模塑(VARTM)成型工艺制备了碳纤维单向和三维编织混杂织物增强环氧树脂复合材料方管结构件。结果表明,通过PAM-RTM模拟VARTM工艺制备复合材料方管时树脂的流动,预测得到灌注时间为3897 s,VARTM工艺实际制备复合材料方管的灌注时间为4052 s,误差约为3.8%,在合理误差范围内。方管内部灌注压力随着与注胶口距离的增加而逐渐减小。模拟与实验的误差可能是由于实际铺层和灌注过程中树脂流动引起织物的剪切变形以及真空度的差异导致渗透性能产生变化。仿真模拟和实际制备复合材料方管均无明显缺陷产生,证明径向法织物渗透率的理论模型计算测试和仿真结果具有可靠性。

Non-isothermal Mold Filling and Curing Simulation for Resin Transfer Molding

A numerical model of 2.5D non-isothermal resin transfer molding simulation is developed for thin part based on the control volume/finite element method. The non-uniform temperature distribution and the heat generation during the filling stage are modeled with the lumped temperature system and the species balance. Numerical algorithm of the simulation are studied. The molding simulation for a part is performed to show the effectiveness of simulating filling time, temperature distribution and curing degree.

Tackification of textile preforms for resin transfer molding

Tackified textile fiber preforms are used widely in resin transfer molding (RTM) to produce aerospace-grade composite parts. In the present study, a new tackifier was developed to improve RTM laminate performance. The influence of tackifier concentration on spring back, thermal properties and mechanical performance was studied .It has showed that the new tackifier was compatible with the matrix resin and improved the textile handling ability; the ILSS was slightly increased without decreasing of thermal properties, modulus and flexural strength.

Numerical Simulation of Mold Filling in Resin Transfer Molding Using Isoparametric Method

The mold filling of RTM was simulated based on the control volume finite element method (CV/FEM). The formulat ion using isoparametric transformation was discussed in detail and a computation al code based on isoparametric technique was developed. The simulation results w ere compared with experimental data. Different isoparametric elements, quadrilat eral and triangular, were compared in the simulation.It demonstrates that the us e of bilinear quadrilateral isoparametric elements in simulating the process can produce a higher precision and cost a less time than the use of triangular ones .

RTM用耐烧蚀酚醛树脂的合成及性能

通过在合成过程中引入活性较低、反应位点少的酚类制备了一种适用于树脂传递模塑成型(RTM)工艺的高残炭、低黏度、长适用期的酚醛树脂。采用旋转黏度计、热重(TG)分析等方法研究了不同酚类(邻甲酚、萘酚、多环酚)及多环酚添加量对酚醛树脂黏度及其固化物热稳定性的影响,利用差示扫描量热法研究了树脂的固化性能。结果表明,适量多环酚的引入,使得树脂在80℃下具有较低的初始黏度和较长的适用期,以及较高的残炭率(70.15%),且固化温度适中,能够满足RTM工艺要求。另外,通过不同升温速率的TG分析、拉曼光谱、X射线衍射等表征手段对树脂的裂解行为进行研究,发现多环酚由于其多苯环的热稳定结构,能够有效提升酚醛树脂的裂解活化能,减小裂解后树脂碳化物的石墨层间距,增大石墨微晶平面直径,提高酚醛树脂碳化后石墨化程度,使树脂拥有较好的高温热稳定性。根据氧乙炔焰烧蚀测试结果,发现改性后的酚醛树脂基复合材料的耐烧蚀性能也得到了提升,由此得到了性能优良的RTM用耐烧蚀酚醛树脂基复合材料。

RTM工艺过程的缺陷形成分析及边缘效应研究

在树脂传递模塑(Resin transfer molding,RTM)工艺中,边缘效应很容易导致制件产生空隙、干斑等缺陷,其根本原因是在纤维增强体和模具模腔之间的间隙区域树脂的流动阻力小,使得树脂在这一区域流动速度更快。基于达西定律并结合流体体积(Volume of Fluid,VOF)界面追踪方法建立了树脂在纤维增强体中的流动模型,开展RTM工艺边缘效应的数值模拟研究,模型可以准确模拟边缘效应的影响,同时研究树脂粘度及树脂注射压力等工艺参数对于流动时间的影响。研究结果可以对RTM工艺的改善优化提供帮助。

A New Method to Track Resin Flow Fronts in Mold Filling Simulation of RTM Process

A new method to track resin flow fronts, referred to as the topological interpolated method (TIM), which is based onfilling states and topological relations of adjacent nodes was proposed. An experiment on the mould filling process wasconducted. It was compared with exact solutions and the experimental results, and good agreements were observed.Numerical and experimental comparisons with the conventional contour mathod were also carried out, and it showedthat TIM could enhance the local accuracy of flow front solutions with respect to the contour method when mergingflow fronts and resin approaching the mold wall were involved.

Rheological Behavior and Process Prediction of Low Viscosity Epoxy Resin for RTM

The rheological behavior of a low epoxy resin system-SR8100/SD8734 for RTM in aviation industry was studied with viscosity experiments. The dual-Arrhenius rheological model and the improved engineering viscosity model were introduced and compared with the experimental data. The results indicated that the viscosity in the earlier stage calculated by dual-Arrhenius model matched the experimental data. As rising to 400 m.Pas, the viscosity calculated by the improved engineering model was closer to the experimental data. The processing windows of the resin system for RTM were determined by combining the two models, which could predict the theological behavior of the resin system in a more credible way. 30-45 ℃ was the optimum processing temperature.

碳纤维复合材料高压树脂传递模塑(HP-RTM)成型工艺

RTM是指低黏度树脂在密闭模腔中流动、浸润的增强复合材料,在一定温度下固化成型的一种复合材料成型工艺,属于复合材料的半液体成型或织物液体成型技术。其具体方法是在设计好的模具中,预先放入经详细设计、剪裁或经机械化预成型的增强纤维材料,模具周边配备密封件和紧固件,在模具内需达到树脂流动顺畅,合模后注入所需树脂,待树脂充分浸润固化后,即可得到所需产品。RTM工艺起始于20世纪50年代,目前,RTM成型工艺己广泛应用于建筑、交通、电信、卫生、航天航空等领域。2015年以后,碳纤维成本的降低及快速固化环氧树脂的出现,加上针对热固性复合材料快速制造开发的HP-RTM工艺和热塑性复合材料层板热成型自动化设备的研发,到2020年,碳纤维复合材料的综合性价比优于金属,并取代金属材料,用于量产车的底盘制造,并涵盖大多数高端车型和少量中级车。高压树脂传递模塑(HPRTM)是传统树脂传递模塑(RTM)的大规模工业化量产的解决方案,也是使用快速固化的化学原料,文中主要介绍用于医疗器械、新能源汽车、数码电子产品的碳纤维复合材料RTM成型工艺,以及国内外目前RTM成型工艺近况和应用。

Processability of Biobased Thermoset Resins and Flax Fibres Reinforcements Using Vacuum Assisted Resin Transfer Moulding

Biocomposite panels consisting of biobased thermoset resins (EP, PU, UP, and tannin) and flax fibre reinforcements were produced using the vacuum assisted resin transfer moulding process. Panels based on a conventional chemical-based resin matrix were also produced, and investigated comparatively. Rheometric analyses were performed to evaluate the suitability of these resins for liquid composite moulding. Tensile, shear, and impactbending tests have been carried out to assess the quality and mechanical performance of manufactured laminates. The impregnation quality was assessed by means of ultrasonic-C-scanning and microscopy. It turned out that the properties of the biobased composite panels made of biobased epoxy resin and a biobased UP-resin from the company Nuplex in New Zealand were onlay slightly inferior to those produced with a conventional epoxy resin. A biobased PU-resin from the company USSC in the USA developed voids during curing. A tannin-based resin containing of formaldehyde was not processable.

复合材料机身Z形隔框RTM成型方案设计与验证

针对一种典型结构的复合材料机身Z形隔框零件,进行RTM(resin transfer moulding)成型工艺方案的设计与验证。对零件的注射方案进行设计,并结合PAM-RTM进行仿真,仿真结果显示树脂填充率可达到100%;研究注射压力与填充时间之间的关系,得知随着注射压力增加,填充时间先较快速减小后逐步变缓。进行了RTM成型模具的设计及制造,上下模可配合不同的底架完成不同工序的操作,并设计手动液压式升降机构解决了RTM工艺零件脱模困难的问题。对RTM工艺流程进行设计并完成制造验证,结果显示零件无显著内外部缺陷,厚度偏差在±4%范围内,纤维体积含量基本达到55%以上,零件型面基本满足要求,验证了Z形隔框RTM成型工艺方案的有效性。

用于RTM工艺的改性氰酸酯树脂的研究

用环氧树脂改性氰酸酯树脂得到了可用于 RTM工艺的树脂体系 ,借助于红外光谱 (IR)、差示扫描量热 (DSC)、热失重 (TGA)等分析手段 ,研究了改性树脂体系的粘度特性、储存稳定性、反应性以及固化树脂的力学性能、耐热性。

RTM成型石英/苯并噁嗪复合材料的孔隙率研究

采用RTM工艺制备石英/苯并噁嗪复合材料,研究了主要工艺参数对其孔隙率的影响,并和石英/钡酚醛复合材料进行了对比。结果表明,较之纯低压或纯高压的注射方式,先低压后高压的注射方式可显著降低孔隙率;注射温度对孔隙率有一定影响,较佳的注射温度应是树脂黏度达到100～500mPa.s时的温度;孔隙率随着纤维体积含量的增加而减小,而制件厚度对其影响不大。在给定的先1atm后4.5atm的注射压力,50%纤维体积含量,6mm制件厚度,钡酚醛和苯并噁嗪注射温度分别为62℃和96℃的条件下,石英/苯并噁嗪复合材料的孔隙率仅为0.32%,明显低于石英/钡酚醛的3.49%。

RTM充模过程(Ⅰ):数学模型的建立

详细探讨了 RTM成型工艺中树脂流动的充模过程 ,利用多孔介质流体动力学基本理论和达西定律对 RTM充模过程进行了深入的数值分析 ,建立了模拟

RTM工艺充模过程数值模拟及实验比较

树脂传递模塑（ＲＴＭ）工艺越来越成为一种高效的先进纤维增强复合材料的制造方法，其中ＲＴＭ的充模过程是一个很重要的步骤。本文对增强材料各向异性的二维ＲＴＭ充模过程进行数值模拟，并把数值模拟结果和实验结果相比较。