Abstract

In the modern industry Resin Transfer Molding (RTM) is a well-known low cost technique to produce high quality composite materials parts in a relatively short time. The process injects a pressurized resin in a closed mold containing a fiber preform to fill all the empty spaces between fibers and inside fiber tows. Often modeling of infiltration processes is performed treating the material as a homogeneous porous medium. However, engineering reinforcements used in the industry are often dual scale presenting different filling rate for the pores inside the fiber tows and for the regions between the fiber tows. One of the main issues related with the RTM process are flow induced defects and the presence of dual scale flow could potentially lead to meso and microvoid generation and entrapment. Once a part is cured, such voids influence negatively its performance, reducing mechanical properties and, in some cases, representing localized spots for crack initiation and future failure. In this work, the dual scale nature of the process is modeled using Liquid Injection Molding Simulation (LIMS) software. The saturation of the tows is analyzed using a network of one-dimensional elements, which are attached to the mesh that represents the bulk preform. This network is modified to take into account the anisotropic permeability of the fiber tows and the architecture of the reinforcement. Capillary effects deriving from the compacted tows are also included. The model is validated with experiments, in which flow front position and dual scale filled regions are measured optically. Two geometries are investigated, first a flat plate geometry, and second a C-shaped spar. Role of various processing conditions is also included in this study; such as the effect of vacuum conditions on bulk and tow filling during the impregnation of the reinforcement, and on the final quality of the part in terms of void content.