Eric Lacoste

Numerical simulation of the infiltration of fibrous preforms by a pure metal

The numerical simulation of the metal-matrix composites (MMCs) elaboration by an injection process is presented. The equations governing the heat and mass transfers through a porous medium are applied to the metal injection process. The bidimensional numerical model is described based on a finite volume formulation. It is shown that two types of metal solidification appear during the injection: (1) a frontal solidification related to the heat balance between the fibrous preform and the metal and (2) a lateral solidification related to the heat losses toward the mold walls. Numerical tests validate the numerical model in the case of theoretical mono-dimensional geometries when analytical solutions exist. The model is then applied to bidimensional geometries. The preform is progressively closed until the channel is obstructed so that injection is achieved to the “impregnation depth.≓ A systematic study determines the influence on the impregnation depth of different parameters, such as thermal properties of fibers and mold walls, injection flow rate, and preform geometry. Finally, the results of the experimental injection of biphenyl resin through the SAFFIL* preform are discussed and compared with the numerical results.

NUMERICAL SIMULATION OF THE LIQUID FLOW INTO A POROUS MEDIUM WITH PHASE CHANGE: APPLICATION TO METAL MATRIX COMPOSITES PROCESSING

A method of metal matrix composites processing consists of injecting a liquid metal through a fibrous preform. The metal flow through the porous preform is associated with phase-change phenomena which imply modifications of the porous medium permeability and disturb the metal flow. A finite-volume model was developed to simulate the injection of a pure metal through a fibrous preform placed between two plane walls of a metal mold. This model is based on the simultaneous resolutions of the heat equation, Darcys law, and an advection equation to follow the evolution of the metal front geometry during the infiltration.

Numerical simulation of the injection moulding of thin parts by liquid metal infiltration of fibrous preforms

Abstract In recent years, many studies have been devoted to the processing of metal matrix composites. The injection moulding process could be a rapid technique for manufacturing near-net thin parts (between 1 and 10 mm thick). A numerical model based on finite volume formulation simulates the flow and the solidification of a liquid metal, aluminium for example, injected within a fibrous preform set between the walls of a metallic mould. This model allowed the influence of different parameters on the impregnation depth to be determined. Thus, the results have shown that the impregnation increases with the injection rate, the initial temperatures of the mould and the preform, and the width of the channel. Furthermore, the study has shown clearly the importance of the fibre thermal conductivity, the fibre volume fraction and the nature of the mould.

Numerical simulation of metal matrix composites and polymer matrix composites processing by infiltration: a review

The injection of a liquid metal through a fibrous preform is one of the techniques used to manufacture metal matrix composites (MMCs). The flow of metal through fibrous preform is a problem of fluid mechanics in porous medium. Numerical simulations of this process were developed in particular for non-isothermal infiltrations which take into account the phenomena of phase change. In addition, numerical models were developed to predict the appearance of defects in the end product and to study the evolution of the deformation of the fibrous preform during metal infiltration. After pointing out the analogous numerical studies devoted to the Resin Transfer Moulding (RTM) process, we give a progress report on the models developed to date for MMCs.

Metal matrix composite processing: numerical study of heat transfer between fibers and metal

Purpose – To study heat transfer kinetics at the fiber scale in order to describe injection of liquid metal through a fibrous perform initially situated in a preheated mould, which is one of the various methods used in order to produce metal matrix composite materials (MMCs).Design/methodology/approach – The first part presents a preliminary study in a static case to describe heat transfer kinetics between a fiber and the matrix in the case of a sudden contact of both components initially set up at different temperatures. This model enables to study the influence of the various parameters of the problem on heat transfer kinetics with phase change. In the second part, we present a modeling which takes into account the metal convection within the pores of the preform.Findings – The numerical results of these two models justify the instantaneous thermal equilibrium assumption classically admitted to describe MMCs manufacturing methods. The results of this dynamic microscopic model are compared with the resul...

Numerical prediction of microporosity formation during the solidification of a pure metal within a porous preform

During the elaboration of metal-matrix composites (MMCs) by infiltration, the appearance of microporosities is more frequent and more difficult to control than in traditional foundry because the fibrous preform slows down the circulation of the liquid metal. With the aim of modelling solidification shrinkage and its prediction, we will present in this paper an algorithm which takes into account : (i) the volume drop due to the solidification shrinkage, (ii) the nucleation of microporosities and (iii) the apparent compressibility of the liquid. It is demonstrated that the apparent compressibility is due to the presence of gas trapped in the liquid during the impregnation of the preform. Secondly, we will present an experimentation with solidification of molten metal infiltrated into a preform. The solidification of the metal in the preform is presented according to various experimental configurations in order to show the influence of the solidification parameters. Lastly, numerical and experimental results will be compared for conditions with and without riser which validates the numerical model.

Correlation between microstructures of SiC-reinforced titanium matrix composite and liquid route processing parameters

A new procedure for filamentary metal matrix composite processing is described here. It consists in running carbon-coated SiC filaments through a liquid titanium bath in levitation. The liquid metal/carbon interaction must be significant enough to enable filament wetting and sufficiently low to avoid composite embrittlement. To insure both requirements, different configurations of the initial ceramic filament can be used: (1) SiC(C) filament free of any other coating, (2) SiC(C) filament coated with a carbide obtained by reactive chemical vapour deposition (R-CVD), or (3) SiC(C) previously coated by a first metal layer. In order to choose the best conditions for developing the process, the different processing configurations were studied through modelling and numerical simulations of the filament/matrix interaction. The microstructure of the interfacial zone between filament and matrix was investigated through SEM and Auger electron spectroscopy (AES) analyses. The microstructure of the interfacial zone between filament and matrix was investigated through SEM and AES analyses. The results show that in comparison to the first processing configuration, the best way to obtain filamentary composite semi-products without excessive fibre/matrix interaction is to use the second configuration. However, the latter requires preliminary R-CVD operations, while the third configuration leads to moderate carbon embrittlement effect without requiring additional equipment.

Heat and Mass Transfer Modeling and Simulation during Liquid Route Processing of SiC/Ti Filamentary Composites

To process SiC/Ti filamentary composites using a liquid route method, it is first necessary to overcome various major difficulties such as, high speed filament/matrix coupling, liquid titanium wetting of filament surfaces, and reduction of filament/matrix interaction. All of these requirements depend mainly on the heat and mass transfer, which occurs as the filament runs through a liquid titanium bath. Consequently, these transfers were modeled and simulated numerically during the different processing steps, particularly the cooling step. The results describe the physical phenomena which occur during the process: the carbon transfer from the carbon coated SiC filament to the liquid titanium, heat exchanges, formation of the TiC interphase at the filament surface, and, finally, the solidification of the titanium coating. Numerical simulation has shown the strong influence of running speed which governs the wettability of the filament by the liquid metal. Furthermore, the effects of an additional specific cooling device have been highlighted.

Numerical Simulation of Segregation Phenomena Coupled with Phase Change and Fluid Flow: Application to Metal Matrix Composites Processing

The injection of a liquid metal through a fibrous preform, located in an initially preheated mold, is one of the techniques used to manufacture metal matrix composites (MMCs). In order to reduce the chemical reactions between the fibers and the metal matrix, the fibrous reinforcement and the mold are commonly preheated up to initial temperatures much lower than the metal solidification temperature. Therefore, local metal solidification instantaneously occurs on fiber during liquid metal infiltration. When infiltrating metal alloy, unlike what happens when infiltrating a pure metal, both temperature and composition may vary within the matrix; this heterogeneity induces segregation within composites. A fiber scale numerical simulation was developed taking into account coupled physical phenomena which occur during the processing: flow of the liquid metal around the fibers, phase change phenomena, solute redistribution at the liquid/solid interface during alloy solidification, and species diffusion. This model predicts the segregation phenomena associated with fibrous preform infiltration by a binary alloy.

Processing of Metal Matrix Composites: Bidimensional Numerical Model of the Infiltration of Fibrous Preform by a Pure Metal

The infiltration process is one of the techniques employed to work out polymer matrix composites (PMC) or metal matrix composites (MMC) and with continuous reinforcement. It consists in injecting the liquid (resin or metal) through a fibrous reinforcement placed in a mould. In the case of the MMC, the fibres and the mould are initially preheated at temperatures lower than the temperature of metal solidification. These thermal conditions induce phenomena of phase change of metal when the metal is in contact with the fibres. These phenomena disturb the flow of metal through the fibrous network. In order to follow the displacement of metal in the preform and take into account of the phase change, a two-dimensional numerical model based on a finite volume formulation was developed, on a very simple geometry.© 2002 ASME