预成型体渗透率预测及其受压缩变形的影响

建立了织物预成型体单胞内纱线间细观流动和纱线内部微观流动的统一的数学模型。基于最小势能原理建立了织物松弛状态下的单胞几何模型,同时对在模具压缩下的单胞变形进行了分析,并建立了不同压缩状态下的单胞几何模型。通过对单胞内树脂流动数学模型的数值求解,获得了流动速度场及压力场,进而预测了预成型体的渗透率。预测1组不同压缩状态下的单胞渗透率,研究了预成型体压缩变形对渗透率的影响。结果显示:随着压缩量的增加,其渗透率逐渐降低。通过实验测量及数据分析,验证了建模和预测方法的正确性。     

预成形体渗透率预测及剪切变形的影响

准确预测预成型体渗透率对复合材料液态成型工艺过程仿真有重要意义,铺覆过程中织物发生的剪切变形对局部渗透率有很大影响。本工作考虑纱线的可渗透性,对织物单胞内的树脂流动建立了统一的流动控制方程,同时建立了逼真的正交单胞几何模型,基于Adams-Bashforth差分格式和Chorin投影法构造了数值求解树脂流动控制方程的高分辨率TVD格式,利用达西定律预测了单胞的渗透率,算例表明该算法预测值与实验值有较好的吻合,验证了算法的准确性。在正交单胞渗透率求解的基础上,采用贴体坐标法完成了单胞剪切变形后流动控制方程从物理域到计算域的转换,进而实现了剪切单胞渗透率的数值预测,考察了单胞主渗透率比与剪切角的关系,通过与文献中数据对比证明了该剪切单胞渗透率预测算法的合理性。     

无弯曲纤维织物面内渗透率的结构相关性

建立无弯曲纤维织物(Non-crimped fabrics, NCF)的几何结构单胞, 应用树脂在纤维束内与束间耦合流动的模型, 数值模拟树脂的细观流动行为, 结合Darcy定律, 计算单胞的面内等效渗透率, 并对计算方案进行验证。在此基础上, 探讨织物的纤维束间距离、纤维束高度以及束内渗透率等细观结构参数与单胞面内等效渗透率之间的关系。结果表明: 单胞面内等效渗透率随纤维束间距离的增大而增大, 其倒数的对数之间呈正的线性关系; 纤维束高度对单胞面内等效渗透率的影响类似于纤维束间距离对其的影响; 单胞面内等效渗透率随纤维束内渗透率的增加而线性增加。      

基于数字图像技术的纤维织物面内渗透率表征

材料渗透率的表征受其结构空间离散性和求解方式准确性的严重影响。基于数字图像技术,评估了纤维织物渗透率的空间分布,并探讨了阶梯铺层对灌注工艺的影响。首先,从恒压单向注射实验的视频流中动态提取了流动前沿的流速分布和流动前沿角,通过织物渗透率与结构的关系仅一次实验便可求得纤维织物的面内局部渗透率分布;其次,利用正态分布函数拟合,建立了基于数字图像技术的纤维织物面内主方向渗透率张量的求解方法,并利用该方法研究了编织形式对渗透率的影响;最后,研究了阶梯铺层和恒定铺层对灌注过程的影响。结果表明:建立的基于数字图像技术的渗透率表征方法可以通过一次实验同时获取面内主方向上的渗透率及其空间离散型;在恒定铺层下缎纹织物渗透率随着纤维层数增大而增大,从厚铺层向薄铺层的灌注方式可以达到最优的灌注时间。      

树脂传递模塑成型工艺中嵌套效应引起渗透率变异的实验与数值模拟

树脂传递模塑成型工艺(RTM)中最重要的变形模式之一是厚度方向压缩。厚度方向压缩减小了织物预成型体的厚度,使织物预成型体局部结构形式发生改变从而引起嵌套效应。嵌套效应不仅会减少织物预成型体的厚度,增加纤维的体积分数并改变孔隙率,而且相邻织物层嵌套效应具有一定的空间分散性,从而使得织物预成型体渗透率具有变异性。本文针对低黏度树脂设计了一种实验装置用以测量局部渗透率的空间分散性,随后建立了随机嵌套单胞模型,利用ANSYS/CFX有限元软件实现了单胞填充浸润的数值模拟,通过流量分析获得局部渗透率,并研究了渗透率的统计分布。通过实验结果与数值模拟结果相对比,验证数值模拟结果的可靠性。最后,基于渗透率的统计分布建立了随机渗透率场,并进行填充浸润的数值模拟,通过与传统恒定渗透率的方法进行比较,证明该方法具有更高的先进性。研究结果可以对未来RTM工艺的稳健性优化提供依据。      

复合材料液体模塑成型工艺中预成型体渗透率张量的数值预测

结合均匀化理论和计算流体动力学技术, 实现了对复合材料液体模塑工艺中预成型体渗透率张量的预测。首先, 采用均匀化理论分析了流体在多孔介质内的流动问题, 推导出广义达西定律, 证明以施加周期性边界条件的单胞为研究对象, 可以预测预成型体的渗透率张量, 并以单向纤维织物为例, 对该方法进行了验证。对于复杂结构的预成型体, 渗透率的预测分为两步, 首先分别确定预成型体中流道和纤维束的渗透率, 然后计算其整体宏观渗透率。对于二维平面织物, 该方法与其他预测方法及实验的结果吻合较好。本文还考察了单胞的微观结构对渗透率的影响, 微观结构相似的预成型体如果孔隙率相同, 但束间流道的结构不同, 其整体宏观渗透率也存在很大差别。      

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。     

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。     

缝合复合材料弹性性能分析的新方法——流场模型Ⅰ:缝合单层板弹性常数计算

为了求解缝合层合板中单层的弹性常数, 基于单层面内纤维走向与绕流流场中流线形状的相似性, 建立了与缝合单胞相对应的有限空间定常二维无粘性不可压理想流体的无旋绕流流场模型, 流场的几何边界与单胞的边界一致, 绕流物面与缝线截面形状一致。用该流场的速度变化描述单胞面内纤维体积含量的变化, 用流线形状描述缝线周围面内纤维的变形。以流场模型为基础, 用细观力学方法和均匀化方法求得缝合单层的弹性常数,结果与实验值吻合。最后用流场模型分析了缝合参数对缝合单层弹性常数的影响。      

RFI工艺中有关树脂流动监测的研究

渗透率测定是树脂膜熔渗(RFI)工艺在复合材料设计和优化中最关键的技术.基于光导纤维视觉技术,通过纤维视觉传感器测量渗透率,能够在光强度下降的情况下探测出树脂的前进情况,这将易于我们在实际生产中在第一时间内准确地监测树脂的流动.     

The numerical analysis of particle-size distribution of clusters in shear flow at one-dimensional closed system and three-dimensional open system

Aimed at optimizing the resin-molding process, a method for numerically analyzing aggregation and dispersion behavior of the filler in resin composite was proposed. The flow of a resin composite during molding was calculated by using computational fluid dynamics (CFD), and particle-size distribution (PSD) of the cluster in each computational domain of the CFD model was estimated by solving the population balance equation (PBE). The proposed numerical-analysis method is based on the thixotropy model of Usui et al. In the thixotropy model, PSD is calculated by taking into account the aggregation and dispersion rate of the cluster by Brownian coagulation, shear coagulation, and shear breakage. Shear-breakage rate of the cluster is evaluated by solving the energy balance of bonding energy of the primary particles cut at the breakage and the drag applied to the cluster by the flow of the fluid. The composite viscosity was calculated using Krieger and Dougherty’s model based on apparent-solid-volume fraction estimated from the calculated PSD. To solve the PBE at low calculation cost, it was discretized using the fixed-pivot technique of Kumar and Ramkrishna. The proposed method was incorporated into the general-purpose CFD software FLOW-3D®, and its accuracy was proved.     

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.     

基于混合网格方法的VARTM工艺充模仿真与实验验证

针对VARTM工艺的特点,建立了充模过程树脂流动和预成型体变形行为数学模型。提出了基于混合网格方法的VARTM充模仿真算法,在该算法中,模具型腔几何模型进行二维或三维网格划分,在每个真空袋表面单元上增加一个一维附属单元,用于在仿真过程中实时地吸收或挤出因真空袋变形而产生的局部树脂体积变化,形成混合网格仿真模型;求解过程中,对树脂流动和预成型体变形分别进行求解后,基于上述混合网格模型进行两者耦合操作,实现了仿真精度和速度的统一。搭建了VARTM充模实验平台,进行了一维充模实验,通过仿真结果与实验测量结果对比,验证了本文算法的正确性。最后,通过三维仿真算例,验证了算法对三维复杂结构和顺序浇口策略仿真的可行性。     

30 m全回转拖轮舱室噪声预报

基于统计能量法，探讨VA One软件的建模方法，建立拖轮的舱室噪声预报模型，分析了拖轮各个舱室的功率流传递，确定了拖轮激励位置及大小和噪声源的排序。通过将仿真结果与相同船型的测量结果进行对比，计算各个声源对舱室噪声的贡献率，分析会议室、船员室和船长室三个房间仿真值与实验值的误差，验证了基于统计能量法建立30 m全回转拖轮舱室噪声预报模型的可行性，为拖轮的噪声控制措施提供依据。     

Numerical prediction of saturation in dual scale fibrous reinforcements during Liquid Composite Molding

This paper presents a fractional flow model based on two-phase flow, resin and air, through a porous medium to simulate numerically Liquid Composites Molding (LCM) processes. It allows predicting the formation, transport and compression of voids in the modeling of LCM. The equations are derived by combining Darcy’s law and mass conservation for each phase (resin/air). In the model, the relative permeability and capillary pressure depend on saturation. The resin is incompressible and the air slightly compressible. Introducing some simplifications, the fractional flow model consists of a saturation equation coupled with a pressure/velocity equation including the effects of air solubility and compressibility. The introduction of air compressibility in the pressure equation allows for the numerical prediction of the experimental behavior at low constant resin injection flow rate. A good agreement was obtained between the numerical prediction of saturation in a glass fiber reinforcement and the experimental observations during the filling of a test mold by Resin Transfer Molding (RTM).     

树脂流动对气泡运动特性的影响

为了排除复合材料成型过程中的气泡, 建立了气泡运动可视化装置, 研究了树脂流动状态和流动速度对气泡运动速度的影响, 并在此基础上建立了气泡运动模型。研究结果表明: 树脂流动对气泡运动有明显的带动或阻碍作用。当树脂流动方向与气泡运动方向相同时, 随着树脂流速的增加, 气泡的运动速度明显增大; 而流动方向相反时, 随着树脂流速的增加, 气泡的运动速度呈明显下降的趋势。所建立的气泡运动模型与实验结果基本吻合。该研究结果将为热压成型过程中气泡运动模型的建立奠定基础。      

Genetic algorithm-least squares support vector regression based predicting and optimizing model on carbon fiber composite integrated conductivity

Support vector machine (SVM), which is a new technology solving classification and regression, has been widely used in many fields. In this study, based on the integrated conductivity(including conductivity and tensile strength) data obtained by carbon fiber/ABS resin matrix composites experiment, a predicting and optimizing model using genetic algorithm-least squares support vector regression (GA-LSSVR) was developed. In this model, genetic algorithm (GA) was used to select and optimize parameters. The predicting results agreed with the experimental data well. By comparing with principal component analysis-genetic back propagation neural network (PCA-GABPNN) predicting model, it is found that GA-LSSVR model has demonstrated superior prediction and generalization performance in view of small sample size problem. Finally, an optimized district of performance parameters was obtained and verified by experiments. It concludes that GA-LSSVR modeling method provides a new promising theoretical method for material design.     

基于内聚力行为和扩展有限元的砂/树脂复合材料拉伸失效行为的数值计算

基于砂/树脂断裂与砂树脂界面脱粘失效行为的砂/树脂三维微细观单胞模型被构建,用于研究砂/树脂在拉伸载荷作用下的微观应力特征、树脂粘结桥的损伤破坏模式及微观结构（树脂含量、砂粒粒径、砂粒级配及粘结桥有效横截面积比）对其宏观拉伸强度的影响。该三维微细观单胞模型采用内聚力行为方法刻画粘结砂/树脂界面的失效,采用扩展有限元方法（Extented finite element,XFEM）捕捉树脂基体损伤和裂纹扩展。计算结果表明:所构建的三维微细观单胞模型能够显式刻画砂/树脂微细观结构断裂过程,解释微细观结构断裂机制,能够有效地提供树脂含量、砂粒粒径、砂粒级配、粘结桥有效横截面积比等微细观结构对砂/树脂宏观拉伸强度（S_t）影响的信息,可为砂/树脂优化设计提供理论指导。      

液体模塑成型工艺二维径向非饱和流动数值模拟

通过引入沉浸函数建立了双尺度多孔介质非饱和流动模型,并采用有限元/控制体积法实现了恒压及恒流注射条件下液体模塑成型（LCM）工艺二维径向非饱和流动的数值模拟,得到了不同注射条件下纤维织物内的压力场分布及半饱和区域长度随时间的变化规律,并将双尺度非饱和理论结果与单尺度饱和理论结果进行对比。结果表明：非饱和流动过程中,半饱和区域内的压力和压力梯度明显下降;半饱和区域长度随时间逐渐增加随后保持稳定,当流动前沿到达出口后半饱和区域长度开始逐渐减小;当两个主方向渗透率不同时,沿主方向半饱和区域长度也不同,渗透率越大该方向的半饱和区域长度也越大,纤维织物完全浸润时间取决于较小的渗透率。研究结果对合理预测树脂填充过程中压力分布及纤维预制件的浸润具有指导意义。