The aim of this study is to gain knowledge concerning the process and its physics, as well as to become able to optimize the fabrication of large and complex composite parts in aeronautics appli- cations. Composite materials have many advantages and the use of this technology is increasing in the aeronautic industry. In the L.R.I. process, dry textile preforms are impregnated by a thermoset liquid resin. All the elements are enclosed in a vacuum bag of known pressure. Once preforms are totally impregnated, the resin system begins the curing reaction to obtain the composite part. This study contains two major sections. Firstly, numerical modeling was done with the Pam- Rtm nite element code to determine the evolution of the ow front during the infusion. Simulations were performed to analyse the infusion of sandwich composite parts with a perforate foam, which allows the inferior skin to be impregnated in the same operation. Secondly, experimental work was conducted to conrm the numerical results.