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.

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.

Study on Numerical Simulation of Mold Filling and Heat Transfer in Die Casting Process

A 3-D mathematical model considering turbulence phenomena has been established based on a computational fluid dynamics technique, so called 3-D SOLA-VOF (Solution Algorithm-Volume of Fluid), to simulate the fluid flow of mold filling process of die casting. In addition, the mathematical model for simulating the heat transfer in die casting process has also been established. The computation program has been developed by the authors with the finite difference method (FDM) recently. As verification, the mold filling process of a S-shaped die casting has been simulated and the simulation results coincide with that of the benchmark test. Finally, as a practical application, the gating design of a motorcycle component was modified by the mold filling simulation and the dies design of another motorcycle component was optimized by the heat transfer simulation. All the optimized designs were verified by the production practice.

Rheological Behaviors and Processing Windows of Low Viscosity Epoxy Resin for VIMP

The chemorheological behaviors of a low viscosity epoxy resin system （Huntsman 1564/3486） for vacuum infusion moulding process （VIMP） were studied with viscosity experiments.The dual-Arrhenius rheological model and the engineering viscosity model were established and compared with the experimental data.The result showed that the viscosity in the earlier stage calculated by dual-Arrhenius model were smaller than the experimental data,while the data calculated by the engineering model were larger.Combining the two models together can predict the rheological behaviors of the resin system in a more credible manner.The processing windows of the resin system for VIMP were determined based on the two models.The optimum processing temperature is 30-45 ℃.

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.

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。

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。

3D Numerical Simulation of Non-isothermal Resin Transfer Molding Filling Process Using Unstructured Tetrahedron Mesh

We present a numerical formulation for resin flow based on the concept of quasi-steady state situation at the flow front. To be fit for complicated product shapes,we use the four-node unstructured tetrahedron mesh based on which the numerical formulation of temperature and degree of cure is developed. The validity of our method is established in the case where ffexible meshes are used. The results show that the numerical procedure,tested on known data,provides numerically valid and reasonably accurate predictions.

RTM专用双马来酰亚胺树脂体系化学流变特性

进行了RTM工艺专用双马来酰亚胺(BMI)树脂体系的化学流变特性及工艺过程研究。采用DSC热分析技术和粘度测量手段,研究了该树脂体系固化特性以及固化过程中粘度与温度的关系,根据对等温粘度曲线的分析,建立了双阿累尼乌斯粘度模型和工程粘度模型。对比所建立的两种粘度模型,结果显示两种模型都可以适用于RTM工艺注射阶段,工程模型在粘度转折点附近的预测精度要优于双阿累尼乌斯粘度方程。同时建立了恒温温度-凝胶时间之间的数学关系。验证了所建立的工程模型在工程中的实用性,并指出了工程粘度模型的使用范围在固化体系交联结构形成之前,所建立的工程粘度模型能够有效地预测体系RTM工艺的粘度变化和工艺过程,为复合材料成型工艺模拟分析以及工艺参数的准确制定奠定了基础。

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工艺及其在我国航空工业的应用前景

本文介绍了树脂传递模塑即ＲＴＭ工艺方法及其特点，并将其与手糊和ＳＭＣ成形工艺进行了对比；概括了ＲＴＭ在国外航空工业上的应用，进而提出我国航空工业迅速发展ＲＴＭ工艺的必要性和重要性。

RTM酚醛树脂研究进展

根据国内外酚醛树脂的研究现状 ,从树脂的合成、主要特征、工艺和性能等方面介绍了几种RTM酚醛树脂酚三嗪树脂、苯并嗪树脂、双马改性酚醛树脂和PAA树脂 ,同时指出了各种树脂的优缺点。

RTM用低黏度树脂体系的工艺窗口预测

为有效预测低黏度环氧树脂体系TQ-50的流变黏度变化规律并确定其在树脂传递模塑(RTM)工艺中的适宜工艺窗口,本文采用差示扫描量热仪(DSC)、黏度计、流变仪和凝胶时间测试仪对TQ-50树脂体系的固化反应特性、静态黏度、动态黏度和凝胶时间等性能进行了系统的研究.在实验结果的基础上,利用双阿累尼乌斯方程(Arrhenius)建立该树脂体系的静态流变模型,该流变模型与实验结果具有良好的拟合一致性,能够准确地描述TQ-50环氧树脂在较低黏度范围内的化学流变行为.利用该流变模型建立温度、时间和黏度三维预测图谱和温度、时间等黏度曲线,并对工艺窗口进行预测,为工艺参数的优化提供科学依据.研究结果表明:TQ-50低黏度环氧树脂体系的黏度低于500 mPa·s时,工艺窗口的温度可选范围为50~70℃,保持时间约为150~180 min,黏度低于200 mPa·s时,工艺窗口温度的可选范围为55~70℃,保持时间约为56~96 min,该树脂体系具有较宽的适宜注射温度范围和较长的注射时间,满足RTM工艺成型的基本要求.

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。

大型高性能复合材料构件RTM工艺进展

航空航天工业的飞速发展对大型、高性能先进树脂基复合材料构件的高效、低成本制造提出了迫切需求。树脂转移模塑成型(Resin transfer molding,RTM)是一种制造先进纤维增强体树脂基复合材料的工艺技术,与现有的热压罐技术相比具有设备结构简单、生产效率高及制造成本低等优点。本文综述了两种典型的RTM工艺:真空辅助树脂转移模塑成型(Vacuum assisted resin transfer molding,VA RTM)与轻质树脂转移模型成型(Light resin transfer molding,L RTM)的技术研究与应用现状,指出了这两种工艺在制造大型高性能构件时存在的问题,并对RTM工艺过程多场耦合数值仿真、仿真新方法及多功能仿真的研究现状及技术难点进行了总结,基于此对RTM工艺发展趋势进行了探讨,旨在为实现快速工艺优化,获得高效、高性能和大型构件的RTM工艺应用提供参考。

复合材料传动轴RTM工艺仿真与模具设计

为提高直升机尾翼传动轴的性能和降低其质量,提出了利用RTM树脂传递成型技术制造传动轴的工艺方法及其模具设计。根据直升机尾翼传动轴的设计要求设计了装配型的复合材料传动轴,并在RTM模拟软件中模拟传动轴的注射过程,经分析得到合理注射压力、注胶口和溢胶口的位置等工艺参数。然后,根据模拟的结果设计了传动轴的模具,对模具的基本结构和设计过程进行了较详细的阐述。最后,进行了模具制造和实验验证,实验结果与模拟结果基本吻合,对制备出的传动轴进行了性能测试,结果满足设计要求。