OVERVIEW OF TEXTILES
Figure 2-7. Types of stitching used for through-thickness reinforcement.
Another process is called resin film infusion (RFI) (Fig. 2-8b). In this process,
solid sheets of resin material are placed next to the fiber preform. At cure temperatures, the
viscosity of the resin drops dramatically and the resin flows through the thickness of the
preform, wetting the fibers. Since the resin starts inside the tool, RFI allows the use of
tooling methods developed for prepreg materials (single-sided tooling and vacuum
bagging). The amount of resin is controlled by the number of sheets of resin used in a
given area. The distance the resin needs to flow is usually less than in an RTM tool, which
simplifies the problem of obtaining full wetting.
The RTM and RFI processes are both suitable for thermoset resin. Additional
techniques are being developed for thermoplastic materials (Fig. 2-9, [2.5]). Thermoplastic
materials can be spun into fibers. This offers the possibility of commingling the
thermoplastic and reinforcing fibers to produce a hybrid yarn. The hybrid yarn is woven
into a preform and placed into a tool. When heated, the thermoplastic fibers melt and form
the matrix. Alternatively, the thermoplastic thread can be spun over the outside of the
