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。      

二步法三维编织变截面薄壁壳体RTM 工艺数值模拟与试验研究

采用分段-集合计算方法, 对二步法三维编织变厚度变截面薄壁壳体RTM 充模工艺过程进行了较深入的理论研究。提出了较准确的树脂流动速度、树脂充模时间和树脂流动压力计算方程。数值预测值与充模试验结果具有良好的一致性, 所推导理论方程为合理设计RTM 充模工艺参数提供了理论依据。      

RTM工艺树脂流动过程数值模拟及实验比较

树脂充模是RTM工艺成型过程中的重要一环。研究了RTM工艺树脂流动过程的特点,建立了树脂渗流控制方程。采用贴体坐标/有限差分法模拟了树脂渗流过程,给出了不同时刻树脂流动前沿曲线及终止时刻压力场分布,计算结果与试验结果吻合良好。     

视窗化RTM工艺充模过程模拟仿真技术研究

根据RTM工艺树脂流动充模模型,研究和开发了基于FEM/CV算法的RTM工艺复杂渗流充模过程数值模拟软件平台-BHRTM-2。BHRTM-2在视窗系统下运行,带有FEM网格捕捉器窗口可直观方便地设置注射口、溢料口和工艺参数,操作简单,能够模拟复杂边界制件的树脂流动充模过程、显示充模过程中任意时刻模腔内压力的分布场、流动前峰和预测充模时间及可能的干斑缺陷位置,为RTM工艺设计与优化提供了有效技术手段。文中对BHRTM-2的模拟结果的正确性和可靠性进行了理论与实验验证,并给出了具体算例。      

RTM成型复合材料T型接头工艺参数优化与力学性能实验研究

对树脂传递模塑(RTM)成型的复合材料T型接头进行了工艺参数优化、制备及力学性能实验研究。应用流动模拟软件,对RTM成型的复合材料T型接头进行了基体流动数值模拟,确定模具最佳注射方式和出胶口位置,并优化了影响树脂充模时间的工艺参数,显著提高了RTM接头的工艺性能。根据优化工艺参数结果,制备了RTM成型的复合材料T型接头试样,并进行了拉伸和压缩试验,分析了其破坏机制。根据拉伸和压缩试验现象和结果,发现RTM成型的复合材料T型接头拉伸破坏模式主要为富树脂三角区的树脂与纤维布界面分层,其拉伸破坏主要取决于树脂基体抗剥离分层的拉伸强度;压缩破坏模式为底板中央部位的弯曲分层与折断,其压缩破坏由接头底板中的纤维布抗拉强度决定;T型接头的压缩破坏强度高于拉伸破坏强度。     

树脂膜熔渗工艺充模过程的模拟与分析

树脂膜熔渗工艺(RFI)是一种新型的复合材料成型工艺.为了更深入了解树脂膜熔渗工艺过程中充模阶段的控制参数对制品质量的影响,避免制品出现空斑、充模不完全等问题,针对该工艺过程中树脂在复杂形状预制件中的流动行为进行了分析,在达西定律基础上建立了二维等温流动控制方程,利用有限元/控制体方法建立了数值分析模型,编制了FORTRAN程序进行模拟运算,并讨论了流动过程中施加的压力对充模时间的影响.由计算实例可见,所编制程序能够很好地预测树脂膜熔渗工艺过程中充模时间、各个时刻树脂的流动前沿位置及模腔中的压力分布.     

树脂传递模塑过程的数学描述和数值模拟进展

树脂传递模塑(resin transfer molding,RTM)过程的数值模拟对于优化工艺参数和模具设计、控制制品质量等具有重要意义.本文简述了RTM工艺的流体流动特点,介绍了RTM工艺过程数值模拟的理论基础,综述了RTM工艺过程数值模拟的发展历程,并展望了其发展趋势.     

RTM工艺参数对树脂充模过程影响 的模拟与实验研究

通过开发计算机程序与有限元/控制体积分析软件,能够实现对任意复杂三维形状复合材料构件的造型和RTM工艺充模过程的模拟。研究了改变工艺参数时工字孔平板的RTM工艺模拟结果和实验结果,两者基本保持一致;证明了恒压注射情况下,充模时间与注射压力、渗透率成反比,与树脂粘度成正比;也证实了该模拟软件确实可用于预测树脂流动模式以及成型效率,为RTM实际工艺设计与优化提供了有效的技术手段。      

RTM工艺树脂流动过程数值模拟

RTM工艺过程数值模拟对模具设计、工艺过程控制及参数优化非常重要。本文作者介绍了RTM工艺过程及特点,给出了树脂渗流控制方程,阐述了RTM工艺过程数值模拟存在的主要问题,采用贴体坐标/有限差分法和网格分区划分法模拟了模具内有插入物情形下的RTM工艺树脂渗流过程,给出了不同时刻树脂流动前沿曲线、计算网格及终止时刻压力场分布,确定了排气孔位置,计算结果与其它研究结果吻合良好。结果表明:贴体坐标/有限差分法和网格分区划分法适合解决复杂边界及可移动边界问题。     

缝合夹层结构复合材料树脂传递模塑成型工艺充模仿真

对复合材料与金属经缝合连接形成的夹层结构板的树脂传递模塑成型（RTM）工艺进行了充模模拟研究。首先通过实验和数值计算的方法,分别获得缝合夹层结构织物和芯层孔洞的渗透率;随后,建立能够反映缝孔内流动情况的二维和三维简化模型,进行RTM充模仿真,讨论不同工艺参数对成型流动的影响;最后通过成型实验验证工艺的可行性。缝线与孔洞直径之比为0.3~0.8时,孔洞渗透率随缝线直径的增大而减小,预制体织物渗透率与孔洞渗透率相差两个数量级;缝孔内容易产生缺陷,没有缺陷的区域随着注射压力的增加、孔洞密度和芯层厚度的减小而增大,在芯层表面沿每排孔洞单向开槽能够改善树脂在孔洞内的浸润;线注射时,树脂整体流动情况优于点注射,而点注射时,将进胶口设置在一角,能够减少表面干斑。     

A coupled SDPH–FVM method for gas‐particle multiphase flow: Methodology

This paper describes a novel methodology that combines smoothed discrete particle hydrodynamics (SDPH) and finite volume method (FVM) to enhance the effective performance in solving the problems of gas‐particle multiphase flow. To describe the collision and fluctuation of particles, this method also increases a new parameter, namely, granular temperature, according to the kinetic theory of granular flow. The coupled framework of SDPH–FVM has been established, in which the drag force and pressure gradient act on the SDPH particles and the momentum sources of drag force are added back onto the FVM mesh. The proposed technique is a coupled discrete‐continuum method based on the two‐fluid model. To compute for the discrete phase, its SDPH is developed from smoothed particle hydrodynamics (SPH), in which the properties of SPH are redefined with some new physical quantities added into the traditional SPH parameters, so that it is more beneficial for SDPH in representing the particle characteristics. For the continuum phase, FVM is employed to discretize the continuum flow field on a stationary grid by capturing fluid characteristics. The coupled method exhibits strong efficiency and accuracy in several two‐dimensional numerical simulations. Copyright © 2016 John Wiley & Sons, Ltd.     

A localized collocation meshless method (LCMM) for incompressible flows CFD modeling with applications to transient hemodynamics

The current paper reports on the development and validation of a localized collocation meshless method (LCMM) to model laminar incompressible flows. A high order upwinding scheme was devised to dampen the numerical oscillations arising in convection-dominated flows. Subsequently, the LCMM was analytically validated and demonstrated to yield third-order accurate solutions when compared to a benchmark analytical decaying vortex solution. Numerical validations are provided by comparison with the finite volume commercial (FVM) solver Fluent 6.2. The flow geometry for the numerical validation arises from a biomedical application that consists of modeling blood flow in the inter-connection between a bypass graft and an artery. Very good agreement was found between the LCMM and the FVM.     

基于多相流的LCM工艺气泡生成仿真

分析了液体模塑成型工艺（LCM）下织物预成型体中双尺度流动以及由此造成的空气裹入,进而产生细观及微观气泡的现象。基于多相流（VOF）方法建立了树脂空气两相流体在单胞内部流动的数学模型,并确定了该模型中多孔介质阻力源项和毛细力源项的具体形式。基于Fluent软件的UDF功能实现了上述两相流模型的数值求解,研究了平纹织物单胞中的两相流动以及2种气泡的生成过程。对Rovcloth 2454织物的气泡生成仿真结果显示,毛细数 Ca 对气泡的产生有决定性作用：当毛细数接近临界毛细数 Ca^c时,气泡产生量最低,而当Ca小于Ca^c时,容易产生细观气泡,反之容易产生微观气泡。通过与文献中的理论预测和实验数据对比,验证了本文算法的正确性。     

湍流边界层中三维山丘地形风场大涡模拟

利用谐波合成法生成粗网格的脉动风速时程,通过双线性插值得到入口节点时程数据,考虑时程互相关性对时程进行修正得到大涡模拟湍流入口。采用谱元法对两种不同坡度的三维山丘地形进行大涡数值模拟,将结果与风洞试验及有限体积法数值模拟进行对比。结果表明:大涡模拟能较准确地预测山丘地形的风场及湍流特性;与有限体积法相比,谱元法的计算效率更高,在复杂山地地形的风场预测上有较好的应用前景。     

Compressible flow analysis of filling and postfilling in injection molding with phase-change effect

In order to predict the shrinkage, warpage and mechanical properties of the injection molded parts, it is necessary to know the history of the flow field during injection-molding processes. In the present investigation a numerical simulation program was developed to predict the flow field in filling and post-filling stages of injection molding. To simulate the real molding conditions more accurately, a generalized Hele-Shaw model for a non-Newtonian fluid was assumed considering the effects of phase change and compressibility of the resin. A finite-element-finite-difference (FEM-FDM) hybrid scheme with control volume approach was employed as the solving technique. For modeling the viscosity of the resin, a modified Cross model was used with a double-domain Tait equation of state being employed in describing the compressibility of the resin during molding. The energy balance equation, including latent-heat dissipation for semicrystalline materials, was solved in order to predict the solidified layer and temperature profile in detail. For verification of the numerical results obtained from the developed program, the simulation results were compared with the experimental results obtained from the test mold set designed in the current study using commercial-grade PP and the data available in the literature. Based on a comparison between experiments and simulations, it was found that the currently developed program was useful in unified simulations of filling and post-filling in injection-molding processes when considering the phase-change effect.     

Mass conservation in numerical simulation of resin flow

The finite element/control volume (FE/CV) approach is commonly used for numerical simulation of resin flow in many composites manufacturing processes. The law of mass conservation is sometimes violated with the use of this approach. Especially, when the Galerkin formulation is used with isoparametric finite elements to obtain the pressure field, the balance of resin mass cannot be achieved.In this paper, reasons leading to such mass imbalance are investigated. A numerical model based on material incompressibility is developed to eliminate the problem. A few isothermal flow simulation examples are presented to demonstrate the application of the model. The results obtained are in excellent agreement with the analytical solutions.     

烟草专用标准恒流孔的研究

为了更好地测量卷烟吸阻和滤棒压降,基于计算流体动力学的角度对烟草专用恒流孔进行了研究,采用有限体积法和Realizable k-ε的湍流模型进行三维数值仿真,能够模拟烟草专用恒流孔的内部流动情况,并进行了理论、数值仿真和实验研究。实验数据和在浙江中烟标准化实验室测得的标准恒流孔入口端的体积流量的实验数据对比,综合分析后发现标准恒流孔能在其前端保持恒定的体积流量。     

Simulation of coupling filtration and flow in a dual scale fibrous media

In this article, numerical simulation of suspension (particles filled-resin) flow through a fibrous media taking into account dual scale porosity in LCM (Liquid Composite Molding) processes is presented. During the flow, a strong interaction between the particle motion and the fluid flow takes place at the porous media wall (the fiber bundle surface). In this study, the Stokes–Darcy coupling is used to describe the resin flow at mesoscopic scale to treat the particles in suspension. A “fluid” model to describe the suspension flow, a “filtration” model to describe the particle capture and a “solid” model dedicated to the modeling of mass particles dynamics was used. The “solid” model is also operated to identify the particles retention.For validation, the numerical results of proposed model were compared with the experimental results from the literature and found in good agreement. Then, other numerical results studying the suspension’s rheological behavior are presented.     

微型车室内三维空气流动与传热的数值模拟

建立微型车室内三维空气流动与传热计算的物理模型和数学模型,应用κ-ε紊流模型、非结构化网格及有限体积法对微型车室内两种回风方式的三维空气流场与温度场进行数值模拟仿真计算与对比分析,为微型车的空调环境优化研究提供有益的参考.     

Simulation of the three-dimensional non-isothermal mold filling process in resin transfer molding

Numerical simulation of resin transfer molding (RTM) is known as a useful method to analyze the process before the mold is actually built. In thick parts, the resin flow is no longer two-dimensional and must be simulated in a fully three-dimensional space. This article presents numerical simulations of three-dimensional non-isothermal mold filling of the RTM process. The control volume/finite element method (CV/FEM) is used in this study. Numerical formulation for resin flow is based on the concept of nodal partial saturation at the flow front. This approach permits to include a transient term in the working equation, removing the need for calculation of time step to track the flow front in conventional scheme. In order to compare the results of the nodal partial saturation concept with the conventional method, a numerical scheme based on the quasi-steady state formulation is also presented. The computer codes developed based on both numerical formulations, allow the prediction of flow front positions; and pressure, temperature and conversion distributions in three-dimensional molds with complicated geometries. The validity of the two schemes is evaluated by comparison with analytical solutions of simple geometries. In all instances excellent agreement is observed. Numerical case studies are provided to demonstrate the effectiveness of the developed computer codes. The results show that the numerical procedure based on the nodal partial saturation concept, developed in this study, provides numerically valid and reasonably accurate predictions.