模具设计外文翻译--注射／压缩流体组合模塑的数值模拟

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1、附录二：外文翻译原件及翻译稿 Numerical simulation of injection/compression liquid composite molding Part 1. Mesh generation K.M. Pillaia, C.L. Tucker III, F.Ra. Phelan Jrb aDepartment of Mechanical and Industrial Engineering, University of Illinois, 1206 W. Green Street, Urbana, IL61801, USA bPolymer Composites G

2、roup, Polymers Division, Building 224, Room B108, National Institute of Standards and Technology, Gaithersburg, MD20899, USA Accepted 14 June 1999 Abstract This paper presents a numerical simulation of injection/compression liquid composite molding, where the fiber preform is compressed to a desired

3、 degree after an initial charge of resin has been injected into the mold. Due to the possibility of an initial gap at the top of the preform and out-of-plane heterogeneity in the multi-layered fiber preform, a full three-dimensional (3D) flow simulation is essential. We propose an algorithm to gener

4、ate a suitable 3D finite element mesh, starting from a two-dimensional shell mesh representing the geometry of the mold cavity. Since different layers of the preform have different compressibility, and since properties such as permeability are a strong function of the degree of compression, a simult

5、aneous prediction of preform compression along with the resin flow is necessary for accurate mold filling simulation. The algorithm creates a coarser mechanical mesh to simulate compression of the preform, and a finer flow mesh to simulate the motion of the resin in the preform and gap. Lines connec

6、ted to the top and bottom plates of the mold, called spines, are used as conduits for the nodes. A method to generate a surface parallel to a given surface, thereby maintaining the thickness of the intermediate space, is used to construct the layers of the preform in the mechanical mesh. The mechani

7、cal mesh is further subdivided along the spines to create the flow mesh. Examples of the three-dimensional meshes generated by the algorithm are presented. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Liquid composite molding (LCM)； E. Resin transfer molding (RTM) 1. Introduction Liquid

8、 composite molding (LCM) is emerging as an important technology to make net-shape parts of polymer-matrix composites. In any LCM process, a preform of reinforcing fibers is placed in a closed mold, then a liquid polymer resin is injected into the mold to infiltrate the preform. When the mold is full

9、, the polymer is cured by a crosslinking reaction to become a rigid solid. Then the mold is opened to remove the part. LCM processes offer a way to produce high-performance composite parts using a rapid process with low labor requirement. This paper deals with a particular type of LCM process called

10、 injection/compression liquid composite molding (I/C-LCM). In I/C-LCM, unlike other types of LCM processes, the mold is only partially closed when resin injection begins. This increases the cross-sectional area available for the resin flow, and decreases flow resistance by providing high porosity in

11、 the reinforcement. Often, the presence of a gap at the top of the preform further facilitates the flow. After all of the resin has been injected, the mold is slowly closed to its final height, causing additional resin flow and saturating all portions of the preform. The I/CLCM process fills the mol

12、d more rapidly, and at a lower pressure than the other LCM processes that use injection alone. Complete filling of the mold with adequate wetting of the fibers is the primary objective of any LCM mold designer； incomplete filling in the mold leads to production of defective parts with dry spots. The

13、re are many factors which affect the filling of the mold: permeability of the preform, presence of gaps in the mold to facilitate resin flow, arrangement of inlet and outlet gates, injection rates of resin from different inlet ports, etc. Often it is not possible for the mold designer to visualize a

14、nd design an adequate system for resin infusion by intuition alone, and mold filling simulations are used to optimize mold performance. The situation in I/C-LCM is more complex than ordinary LCM because of compression of the mold during the filling operation. As a result, numerical simulation of the

15、 mold filling process in I/C-LCM becomes all the more important. I/C-LCM fiber preforms frequently comprise layers of different reinforcing materials such as biaxial woven fabrics, stitch-bonded uniaxial fibers, random fibers. Each type of material has a unique behavior as it is compressed in the mo

16、ld. When such different materials are layered to form the preform, each of them will compress by different amounts as the mold is closed. This behavior is illustrated in Fig. 1, which shows a small piece of a mold. Here the lighter center layer deforms much more than the darker outer layer as the mo

17、ld is closed. (B) After compression (A) Before compression Fig. 1. Uneven deformation of preform layers under compression. Capturing this deformation behavior during compression is critical to the accuracy of any I/C-LCM process model. Resin flows through the preform at all stages of compression, an

18、d the porosity and permeability of the preform are critical in determining the resin flow. The ratio of deformed volume to initial volume determines the porosity of each preform layer, and from this one can determine the layers permeability, either from a theoretical prediction or a correlation of e

19、xperimental data. Because of this strong coupling between the state of compression in a preform layer and its permeability, computations for fluid flow and preform compression have to be done simultaneously for mold filling simulations in I/C-LCM. Significant steps have already been taken to computa

20、tionally model the mold filling in the I/C-LCM process. A computer program called crimson, is capable of isothermal mold filling simulation which involves simultaneous fluid flow and preform compression computations in the flow domain. But the initial capacity of crimson is limited to two-dimensiona

21、l (2D) planar geometries where prediction of preform compression is straightforward. Deformation of the preform is modeled using the incremental linearized theory of elasticity； the mathematics simplifies due to reduction in the number of degrees of freedom (DOF) associated with displacement from th

22、e usual three to one along the thickness direction. However parts made by the I/C-LCM process typically have complicated three-dimensional shapes and this reduction of the mathematical complexity is no longer possible. The present paper describes our effort to expand the capability of crimson by ena

23、bling it to tackle any arbitrary non-planar three dimensional (3D) mold geometry. Most injection molding simulation programs read for the mold geometry in the form of a shell mesh. Even if it were possible to transmit the full geometrical information about the mold through a 3D mesh, it still is dif

24、ficult to incorporate all the information of relevance to the process engineer. The latter needs to know the thicknesses of various layers of fiber mats and their corresponding porosities at each time step. As a result, it is very important that elements representing different layers of preform in t

25、he 3D finite element mesh fall within separate layered regions. Overlap of an element onto more than one region is not acceptable as the element has to carry the material properties, such as porosity, permeability, of only one fiber mat. Mesh-generators in state-of-the-art commercial software such a

26、s PATRAN are not designed to generate such a 3D mesh. Consequently, we decided to create a preprocessor suitable for I/C-LCM mold filling simulation. The objectives of this paper are to introduce basic ideas about modeling mold filling in 3D I/C-LCM parts, and to introduce an algorithm to generate a

27、 3D finite element mesh from a given 2D shell mesh for preform and flow computations. In subsequent papers, we will model finite deformation of preform using the non-linear theory of elasticity, and use this information to model resin flow in an I/C-LCM mold. 2. Generating a 3D mesh from the given 2

28、D shell mesh Our aim is to develop a preprocessor that can generate 3D finite element meshes for flow computations starting from a 2D shell mesh. We wish to allow the I/C-LCM process engineer to include all relevant information such as thicknesses of the layers of the preform, thickness of the gap, into the mesh. A - open gap everywhere C - just touching / partly compressed D - fully compressed everywhere B - open gap / just touching