1.Bagging Film 6.Inlet Tubing 2.Distribution Tubing 7.Tool Plate 3.Release Cloth 8.Coated Tool 4.Woven Perform 9.Vacuum Tubing 5.Sealant Tape 10.Distribution Media FIGURE 3.9 VARTM process.(Courtesy of B.Grimsley,NASA Langley Research Center,2001.) transfer phenomena must be managed for successful RTM processes.Heat transfer between the polymer and the fiber preform,and between tool, preform,and polymer,as well as exothermic heat generation during the cure of the polymer,are three such phenomena that influence the process [12]. 3.1.2.1 Vacuum-Assisted Resin Transfer Molding (VARTM)Processing Both open-mold approaches,where one surface is bagged with a flexible film,and closed-mold approaches to resin transfer molding are practiced. An example of open-mold RTM,vacuum-assisted resin transfer molding (VARTM)is a common method employed as an alternative to autoclave use In VARTM,atmospheric pressure is utilized to achieve consolidation and impregnation by vacuum bagging the laminate in the same way as discussed in Section 3.1.1.An inlet for the polymer is located at one or more points in the tool or bag,and vacuum outlets are located some distance away.The vacuum pump creates a pressure gradient of approximately 1 atm within the bag,which is sufficient for the impregnation of laminates large in size and complex in geometry.For processes in which final cure occurs after the mold is filled,completion of the cure can be carried out in an oven while atmospheric pressure is maintained on the impregnated laminate. The VARTM procedure for a representative flat 61.0x 30.5 x0.64 cm panel (Figure 3.9)is described in the following steps: 1.Tool surface.The tool is a flat aluminum plate with planar dimen- sions sufficient to accommodate the proposed composite panel. First,clean the metal tool surface using sandpaper and acetone.On the cleaned surface,create a 71 x 30.5 cm picture frame using masking tape.Apply several coats of release agent to the metal surface inside of the masked frame.Remove the masking tape. ©2003 by CRC Press LLCtransfer phenomena must be managed for successful RTM processes. Heat transfer between the polymer and the fiber preform, and between tool, preform, and polymer, as well as exothermic heat generation during the cure of the polymer, are three such phenomena that influence the process [12]. 3.1.2.1 Vacuum-Assisted Resin Transfer Molding (VARTM) Processing Both open-mold approaches, where one surface is bagged with a flexible film, and closed-mold approaches to resin transfer molding are practiced. An example of open-mold RTM, vacuum-assisted resin transfer molding (VARTM) is a common method employed as an alternative to autoclave use. In VARTM, atmospheric pressure is utilized to achieve consolidation and impregnation by vacuum bagging the laminate in the same way as discussed in Section 3.1.1. An inlet for the polymer is located at one or more points in the tool or bag, and vacuum outlets are located some distance away. The vacuum pump creates a pressure gradient of approximately 1 atm within the bag, which is sufficient for the impregnation of laminates large in size and complex in geometry. For processes in which final cure occurs after the mold is filled, completion of the cure can be carried out in an oven while atmospheric pressure is maintained on the impregnated laminate. The VARTM procedure for a representative flat 61.0 × 30.5 × 0.64 cm panel (Figure 3.9) is described in the following steps: 1. Tool surface. The tool is a flat aluminum plate with planar dimen￾sions sufficient to accommodate the proposed composite panel. First, clean the metal tool surface using sandpaper and acetone. On the cleaned surface, create a 71 × 30.5 cm picture frame using masking tape. Apply several coats of release agent to the metal surface inside of the masked frame. Remove the masking tape. FIGURE 3.9 VARTM process. (Courtesy of B. Grimsley, NASA Langley Research Center, 2001.) TX001_ch03_Frame Page 45 Saturday, September 21, 2002 4:51 AM © 2003 by CRC Press LLC