William Ros

Fibre-scale Modeling of C/C Processing by Chemical Vapour Infiltration Using Xray CMT Images and Random Walkers

We present a computational tool for the modeling of Chemical Vapor Infiltration of carbon/carbon composites, which is based on 3D images acquired by X-ray Computerized Micro-Tomography with a very fine resolution, such that the fibers are clearly distinguishable from each other. Preliminary image processing is necessary in order to perform segmentation between solid and void phases. Then, morphological and transport properties are computed in the images. Random walkers are used for the simulation of gas transport in continuum and rarefied regimes. The image modification under chemical deposition is handled by a specific surface discretization technique and a pseudo-VOF method. Results are presented and discussed: the notion of infiltrability is introduced as a design tool for the CVI engineer.

Modelling Infiltration of Fibre Preforms From X-Ray Tomography Data

The production of high-quality Ceramic-Matrix Composites often includes matrix deposition by Chemical Vapour Infiltration (CVI), a process which involves many phenomena such as gas transport, chemical reactions, and structural evolution of the preform. Control and optimization of this high-tech process are demanding for modelling tools. In this context, a numerical simulation of CVI in complex 3D images, acquired e.g. by X-ray Computerized Microtomography, has been developed. The approach addresses the two length scales which are inherent to a composite with woven textile reinforcement (i.e. inter- and intra-bundle), with two numerical tools. The small-scale program allows direct simulation of CVI in small intra-bundle pores. Effective laws for porosity, internal surface area and transport properties as infiltration proceeds are produced by averaging. They are an input for the next modelling step. The second code is a large-scale solver which accounts for the locally heterogeneous and anisotropic character of the pore space. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed.

An X‐Ray Tomography Based Modeling Solution For Chemical Vapor Infiltration Of Ceramic Matrix Composites

A numerical tool for the simulation of Chemical Vapor Infiltration of carbon/carbon composites is introduced. The structure of the fibrous medium can be studied by high resolution X‐Ray Computed Micro Tomography. Gas transport in various regimes is simulated by a random walk technique whilst the morphological evolution of the fluid/solid interface is handled by a Marching Cube technique. The program can be used to evaluate effective diffusivity and first order reaction rate. The numerical tool is validated by comparing computed effective properties of a straight slit pore with reactive walls to their analytical expression. Simulation of CVI processing of a real complex media is then presented.