Numerical Simulation And Computational Methods Investigation Of Liquid Composite Molding Process And Behavior

Advanced resin-base composites techniques are extensive used in automotive and aircrafl industries more and more. Mostly industrialized countries in the world all lay a corresponding medium or long term research course to settle the key technique of cost-effective composites. Liquid composite molding (LCM) process is a cost-effective fabrication technique appearing recently. Numeralization and information of composite structures manufacture are effective approach to improve the quality of produce and reduce cost. Therefore, it is one of hot subjects in the field of composite research presently that the simulation, quality evaluation and parameter optimization of liquid composite molding process. The overall success of the manufacturing process depends on the complete impregnation of the fiber perform by the polymer resin, prevention of polymer gelation during filling, and subsequent avoidance of air bubbles and dry spots. In the curing stage, the process parameters of heating and cooling rates, and the temperature level an each element of the curing cycle have direct effects on the development of internal residual stresses. The associated physics of LCM encompasses the multidisciplinary study of mathematics, mechanics, materials and kinetics. The work in this dissertation aims at developing numerical models of LCM process and component behavior to simulate the impregnation stage and curing stage in LCM process and to predict, character residual stress and component behavior, which will help designers in the set-up of the manufacturing process, eliminating costly in trial runs, shortening development time, reducing development cost and controlling quality of produces. The main research works and production of the paper as flow:1) A process model is developed which can be used to describe both flow through dry perform of resin and cure of the resin saturated perform. Approximately isothermal resin flow through the dry fibers is modeled as a Newtonian fluid flow through porous media, where Darcy's Law is employed. The thermo chemical cure submodel is based on a heat transfer analysis coupled with a cure reaction kinetics model. The kinetics model is used to calculate the cure rate, the rate of heat generation due to exothermic chemical reactions, and the degree of resin cure. Resin viscosity can be calculated using a model relating viscosity to temperature and degree of cure.2) Two programs based on control volume/finite element technique (CV/FE) and pure finite element method (FEM) are developed respectively to be used to characterize the flow behavior in LCM of composite structures. The two methods both can be employed to solve for the pressure field and to track the flow front progression of the resin inside the mold cavity. But the pure finite element method is physically accurate and computationally efficient.3) The differential scanning calorimeter (DSC) technique is used to study the polymerization kinetics of the unsaturated polyester resin under dynamic conditions. According dynamic scanning curve, the character temperatures are obtained based on the method of extrapolation and the cure kinetics parameters of the resin are obtained by Kissinger's method.4) Self-programming software and general commercial program are used to simulate the curing of LCM process, respectively. Based on the thermo chemical models, the temperature and cure history are obtained using the finite difference method through a two-dimensional FORTRAN code. Furthermore, a three-dimensional model is build to simulate the temperature field and cure history using the ABAQUS code, writing an internal heat generation (HETVAL) user subroutine in heat transfer analysis of ABAQUS.5) Analytical models are presented for investigation of cure dependent stiffness of woven fiber composites. A linear-like correlation is adopted between the material properties and resin degree of cure. Fiber undulation model takes into account the fiber continuity and undulation and has been adopted for plain weave fiber mats geometry modeling. The analysis is performed on a unit cell, which is a representative of the entire fiber mat lamina. The classical laminate theory (CLT) is applied to determine stiffness constants in the infinitesimal region of the composites unit cell. The theoretical models can prediction the changes of stiffness matrices with the degree of cure. A case studies show that the elements of the stiffness matrices showed exponential increase with the resin degree of cure.6) Processing induced residual stress of LCM is studied. The FE-analysis was carried out using the computer program ABAQUS. Cure stage analysis is proceeded to obtain a result file of the temperature and the degree of cure fields, which will be set as the start conditions of thermal-stress analysis. And user define material's mechanical behavior (UMAT) subroutine is used to define properties of the materials at any time of cure stage. So we can achieve the residual stress situation of curing stage.