CompositesWorld
Issue link: https://cw.epubxp.com/i/517026
CompositesWorld.com 63 Illustration / Karl Reque PCM Test Case Nissan GT-R Compression Molded Prepreg Decklid › Decklid inner panel's exposed, clearcoated, CFRP fabric weave provides consumer- pleasing trunk aesthetic. › Mass reduction of 40% and lower vehicle center of gravity vs. legacy aluminum part exceeds program goals despite design restrictions. › Class A surfaces on inner and outer achieved without pinholing common to autoclave prepreg processing. inner shell would feature clearcoated/exposed-weave CFRP, the imperfections of which would be readily visible. Tese imperatives posed a challenge: Tis was a running change on the original aluminum part, that is, there was little leeway for signifcant alterations, let alone for a complete system redesign. In fact, no modifcation was permitted on outer panel geometry and only minor adjustments could be made to the inner panel. For example, the aluminum predecessor featured cutouts on the inner panel, but the team decided to leave them solid in the CFRP design because creating cutouts would take longer and complicate preforming. Other small changes were made to enhance stifness and achieve appropriate failure modes during crash testing. Te restrictions eliminated opportunities to consolidate subcompo- nents and integrate attachment hardware (which is bonded during fnal assembly), either of which could have helped reduce fnishing and fnal-part costs. Because geometry couldn't be modifed and the composite panels would be very thin — outer panel, 1.1 mm; inner panel, 0.7 mm — the team anticipated challenges, including handling the thin, preformed prepregs during transfer from preforming station to mold. Another worry was achieving a Class A surface on the inner panel, given its exposed weave and complex contours. It took much trial and error, but the fabric used on the inner panel worked well with minimal resin fow and fber distortion. For the outer panel, fve plies of unidirectional carbon fber rein- forcement (fber areal weight of 250 g/m 2 ; resin content of 30 wt-%) are used in a 0°/90°/0°/90°/0° layup. Te inner panel features just two plies of 3K plain-weave carbon fabric (fber areal weight, 200 g/m 2 ; resin content, 35 wt-%), plus local reinforcement in several locations, using an additional two plies of the same prepreg. The decklid was evaluated frst, via computer-aided analyses and physical tests. For example, Nissan placed a fully assembled/ bonded part in a special test apparatus and compressed it until it broke; this enabled comparison of failure modes for CFRP and aluminum assemblies. Results were used to optimize the design of the decklid's inner panel and the bonding scheme. Durability SPOILER/WING Autoclaved CFRP (possible candidate for PCM in future) OUTER PANEL No modifcation of aluminum geometry permitted Class A surface, pit-free, painted to match body color 5 plies of uni CF prepreg (250 g/m 2 ) [0°/90°/0°/90/0°], 30% resin, by weight INNER PANEL 2 plies, 3K plain-weave CF prepreg (200 g/m 2 ), 35% resin, by weight, plus local reinforcement Cutouts in aluminum design eliminated to simplify preforming "A" surface of inner panel is clearcoated to expose fabric weave Nominal thickness: 1.1 mm Nominal thickness: 0.7 mm