复合材料RTM工艺充模过程数值仿真与缺陷预测研究

发布时间：2018-05-04 00:40

本文选题：复合材料 + RTM工艺　；参考：《哈尔滨工业大学》2015年博士论文

【摘要】：树脂转移模塑(Resin Transfer Molding,RTM)已经发展成为纤维增强树脂基复合材料的主导工艺技术之一,该工艺的成型质量很大程度上取决于充模阶段树脂对预成型体的浸润程度。为解决目前RTM模具和充模工艺参数的设计需要进行大量试验而带来的高成本、低效率以及质量难以保证的问题,本文在分析国内外有关RTM工艺数字化技术及相关领域研究成果的基础上,对影响RTM工艺的预成型体几何结构、渗透率、充摸过程和缺陷形成进行了深入研究,并针对计算机辅助工艺过程分析的实际需要,将本文的研究成果应用于开发的RTMSimu系统中。预成型体的几何结构是影响RTM工艺参数的主要因素,建立预成型体几何模型是进行工艺仿真和成型缺陷预测的基础。本文在详细分析RTM织物预成型体多尺度结构特性的基础上,建立了三个尺度下的几何模型。在微观尺度,基于Monte Carlo随机运动法获得了纤维束前后两个截面不同的单丝分布,通过拉伸操作建立了纤维束初步模型,采用Bezier曲线理论对单丝中心线进行校正后,建立了同时包含轴向和径向随机性的微观纤维束模型。在细观尺度,分析了单胞内纱线的截面及弯曲状态,采用最小势能原理求解了单胞的几何参数,分析了单胞剪切和压缩变形过程,建立了预成型体单胞不同变形状态的几何模型。在宏观尺度,提出了基于几何信息的铺覆仿真算法,基于曲面切向量、法曲率等几何信息进行织物节点位置的求解,建立了二维织物在复杂曲面上的铺覆模型。预成型体渗透率是RTM充模过程仿真的关键参数,表达树脂在预成型体内流动的难易程度。本文以上述预成型体多尺度几何模型为基础,研究了微观纤维束和细观单胞的渗透率仿真预报方法。通过对纤维单丝间树脂流动进行仿真,预报了纤维束渗透率,结果表明,单丝的随机性分布对微观渗透率有一定的影响。建立了单胞内树脂双尺度流动的数学模型,研究了纱线卷曲和相互挤压对微观渗透率分布的影响,基于有限差分法建立了树脂流动控制方程的数值求解方法,求得了单胞内树脂流动压强和速度场,进而获得了单胞渗透率预测值。在正交单胞渗透率预测方法的基础上,采用贴体坐标法完成了剪切变形后流动控制方程从物理域到计算域的转换,实现了剪切单胞渗透率的预报。研究了单胞渗透率随剪切和压缩变形的变化规律。通过与文献预测数据和实验值对比,证明了本文预测模型和求解方法的正确性。针对树脂空气两相流难以直接求解的问题,研究了基于VOF(Volume of Fluid)多相流技术的RTM工艺充模过程仿真算法。通过在Navier-Stokes方程中增加流固阻力项的方式建立了RTM充模过程树脂流动的数学模型,基于VOF技术实现了上述模型的数值求解,算例表明上述算法具有较高的精度。针对带有预成型体变形的RTM工艺,为了避免对树脂流动/预成型体变形耦合方程的直接求解,建立了基于动态网格模型和主从单元法的充模过程全三维仿真算法,实现了基于黏弹性模型的预成型体变形计算,提高了仿真精度。算例表明上述算法能够实现充模过程中流场区域的动态更新和顺序注射策略的仿真。对RTM成型缺陷进行预测是充模过程仿真的一个重要任务。干斑是RTM工艺的主要缺陷之一,本文对干斑的形成以及演变过程进行了分析,基于VOF方法仿真了干斑的形成过程。研究了充模过程中的气泡产生机理,建立了气泡预测模型,该模型通过对比纱线内外的树脂流动速度来判断空气裹入的位置及其尺寸。重点分析了树脂流动方向和织物剪切变形对单胞浸润的影响,研究了气泡位置和尺寸随流动方向和剪切角的变化规律。通过实验验证了上述模型的正确性。基于本文的研究成果,开发了RTM充模过程数值仿真系统(RTMSimu)。在数据库系统的基础上利用面向对象编程语言完成了原型系统的开发,实现了RTM工艺预成型体几何建模、渗透率预测、充模过程仿真以及充模缺陷预测等功能的参数化驱动和各模块的集成。通过某型号汽车引擎盖的建模与仿真过程为例,展示了RTMSimu系统的主要界面和操作流程,并综合分析了系统的技术指标,初步验证了上述系统的可行性。
[Abstract]:Resin Transfer Molding (RTM) has developed into one of the leading technology of fiber reinforced resin matrix composites. The molding quality of the process depends largely on the infiltration degree of the resin to the preformed body during the mold filling stage. A large number of tests are needed to solve the current design of the RTM mold and mold filling process parameters. The problem of high cost, low efficiency and inability to guarantee the quality is difficult. On the basis of analyzing the domestic and foreign research achievements in the digital technology of RTM technology and related fields, this paper deeply studies the geometry structure, permeability, filling process and defect formation of the preformed body which affects the RTM process, and aims at the computer aided process. The actual needs of the process analysis are applied to the developed RTMSimu system. The geometric structure of the preformed body is the main factor affecting the parameters of the RTM process. The establishment of the preformed geometric model is the basis for the process simulation and the prediction of the forming defects. In this paper, the multi-scale structure characteristics of the RTM fabric preform are analyzed in detail. On the basis of this, a geometric model under three scales is established. On the microscale, the distribution of monofilament in two sections of the fiber bundle before and after the fiber bundle is obtained on the basis of the Monte Carlo random motion method. The initial model of the fiber bundle is established through the stretching operation. The axial and diameter of the single filament is established by using the theory of Bezier curve to correct the single wire center line. On the microscale, the cross section and bending state of the single cell yarn are analyzed on the meso scale. The geometric parameters of the single cell are solved by the principle of minimum potential energy. The process of the single cell shear and compression deformation is analyzed, and the geometric model of the different deformation state of the preformed single cell is established. The geometry based on the macroscopic scale is based on the geometry. The embedding simulation algorithm of information is based on the geometric information such as curved surface tangent vector, normal curvature and other geometric information to solve the location of fabric nodes. The overlay model of two-dimensional fabric on complex surfaces is established. The permeability of the preformed body is the key parameter of the simulation of RTM filling process, and the difficulty of the flow of the resin in the preformed body is expressed. On the basis of the multi-scale geometric model of the body, the permeability simulation prediction method of the micro fiber bundle and the meso cell is studied. The fiber beam permeability is predicted by the simulation of the flow of the fiber monofilament resin. The results show that the random distribution of the monofilament has a definite effect on the microscopic permeability. The double scale flow of the single cell resin is established. In the mathematical model, the effect of the yarn crimp and mutual extrusion on the micropermeability distribution is studied. Based on the finite difference method, the numerical solution of the flow control equation of the resin is established. The flow pressure and velocity field of the resin in the single cell are obtained. Then the prediction value of the single cell permeability is obtained. On the basis of the orthogonal cell permeability prediction method, the method of predicting the permeability of the single cell is obtained. The transfer of the flow control equation from the physical domain to the computational domain after the shear deformation is completed by the body fitted coordinate method, and the prediction of the shear single cell permeability is realized. The variation of the single cell permeability with the shear and compression deformation is studied. The accuracy of the prediction model and the solution method is proved by comparison with the predicted data and the experimental data. In view of the problem that the resin air two phase flow is difficult to be solved directly, the simulation algorithm of the mold filling process of the RTM process based on the VOF (Volume of Fluid) multiphase flow technology is studied. The mathematical model of the resin flow in the RTM filling process is established by adding the fluid solid resistance term in the Navier-Stokes equation, and the above model is realized based on the VOF technology. Numerical calculation shows that the above algorithm has high accuracy. In order to avoid direct solution to the deformation coupling equation of resin flow / preformed body, a full three dimension simulation algorithm based on dynamic mesh model and master slave unit method is established for the RTM process with preformed body deformation, and the viscoelastic model is realized. The calculation of the deformation of the preformed body improves the simulation accuracy. The calculation example shows that the algorithm can realize the dynamic updating of the flow field and the simulation of the sequential injection strategy during the filling process. It is an important task for the simulation of the mold filling process to predict the defects of the RTM molding. The dry spot is one of the main defects of the RTM process. The evolution process is analyzed. The formation process of the dry spot is simulated based on the VOF method. The bubble generation mechanism in the mold filling process is studied. The bubble prediction model is established. The model determines the position and size of the air wrapped by comparing the flow velocity of the resin inside and outside the yarn. The direction of the resin flow and the shear deformation of the fabric are analyzed. For the influence of the single cell infiltration, the change of the position and size of the bubble with the flow direction and the shear angle is studied. The correctness of the model is verified by the experiment. Based on the research results of this paper, the numerical simulation system of the RTM filling process (RTMSimu) is developed. The prototype is built on the base of the database system and the prototype is used to complete the prototype. With the development of the system, the parameterized driving of the functions of the RTM preform, the permeability prediction, the simulation of the mold filling process and the prediction of the mold filling defect, and the integration of each module are realized. The main interface and operation process of the RTMSimu system are demonstrated by an example of the modeling and Simulation of a type of automobile engine hood, and the comprehensive analysis is made. The technical indicators of the system preliminarily verify the feasibility of the above system.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB33

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