SAMPE Journal - March/April 2011 - 50

Epoxy/Glass and Polyimide (LaRC™ PETI-8) /Carbon Fiber Metal Laminates Made by the VARTM Process
R.J. Cano NASA Langley Research Center, Hampton, VA A.C. Loos Michigan State University, East Lansing, MI B.J. Jensen and S.M. Britton NASA Langley Research Center, Hampton, VA G. Tuncol and K. Long Michigan State University, East Lansing, MI Abstract Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide resin systems for advanced aerospace applications that can be processed without the use of an autoclave. Polyimide composites are very attractive for applications that require a high strength to weight ratio and thermal stability. Vacuum assisted resin transfer molding (VARTM) has shown the potential to reduce the manufacturing cost of composite structures. Fiber metal laminates (FML) made via this process with aluminum, glass fabric, and epoxy resins have been previously fabricated at LaRC. In this work, the VARTM process has been refined for epoxy/glass FMLs and extended to the fabrication of FMLs with titanium/carbon fabric layers and a polyimide system developed at NASA, LARC™ PETI-8. Resin flow pathways were introduced into the titanium foils to aid the infiltration of the polyimide resin. Injection temperatures in the range of 250-280°C were required to achieve the necessary VARTM viscosities (<10 Poise). Laminate quality and initial mechanical properties will be presented. Introduction Fiber Metal Laminates Fiber metal laminates (FML) are multicomponent materials utilizing metals, fibers and matrix resins. Typical FML are prepared by stacking alternating layers of metal foils and fiber/matrix resin prepreg followed by consolidation in a press or autoclave. FMLs consisting of aluminum sheets and aramid fiber/epoxy prepreg were first developed by Vogelsang et al. at the Technische Universiteit Delft together with ALCOA in the 1980s1 and are known as ARALL (Aramid Reinforced ALuminum Laminate). GLARE (GLAss REinforced FML), which replaces aramid fibers with glass fibers, was introduced in 1991. Fiber metal laminates combine some of the best properties of the metal and the composite making them suitable for aerospace applications. For example, and as shown in Figure 1, GLARE is used in the fuselage of the Airbus A380 and is being evaluated for use as blast resistant cargo containers due to the unique combination of properties. consolidation. Traditionally, composites have also been fabricated by similar methods. A more cost effective process for preparation of composites has been developed2,3 which uses liquid resin infused into dry fabric layers by vacuum pressure only to produce high quality materials. This process, know as vacuum assisted resin transfer molding (VARTM), utilizes a flow distribution media to allow the resin to proceed rapidly on the surface over the length of the part followed by the slower infusion through the thickness of the part, thereby decreasing infusion times. Figure 2 illustrates a typical VARTM set-up. NASA LaRC has developed a VARTM process for FML which utilizes flow pathways (perforations) into metal layers to allow for through the thickness resin infusion4-6. The materials produced by this process will be referred to as VARTMFML.

High Temperature VARTM Polyimide (PI) composites are used in the aerospace industry due to their high strength to weight ratio and excellent Vacuum Assisted Resin Transfer Molding of FML thermal stability. Researchers at LaRC have developed several GLARE is expensive to produce and part size is limited PIs from various aromatic diamines and dianhydrides that can due to the required prepreg and use of an autoclave in be melt processed into coatings, adhesives, composites and films without the use of an autoclave. Controlled molecular weight imide oligomers containing phenylethynyl groups [phenylethynyl terminated imide (PETI), e.g. PETI-8, PETI-330] have exhibited exceptional processability during fabrication of neat resin moldings, bonded panels and composites. LaRC™ PETI-330 was designed specifically for resin transfer molding (RTM) and resin infusion (RI) processing and laminates (a) (b) exhibited excellent properties7-9. LaRC™ PETI-8 Figure 1. Current uses of GLARE: (a) Airbus A380, (b) cargo containers. also produced excellent mechanical properties
50 SAMPE Journal, Volume 47, No. 2, March/April 2011

SAMPE Journal - March/April 2011

Table of Contents for the Digital Edition of SAMPE Journal - March/April 2011