DEC 2018


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DECEMBER 2018 46 CompositesWorld FOCUS ON DESIGN FIG. 1 Forming-study results for residual mold travel and filling Extensive simulation work that was subsequently verified by small- and large-part testing was done on all major aspects of the rear floor module's design, processability and performance. For example, several forming studies looked at the impact of mold travel (top) and filling (bottom). Source | Fraunhofer Institute for Chemical Technology Forming-study results for residual mold travel (top) and filling (bottom) a b c Mold travel of (a) 70 mm, (b) 40 mm and (c) 24 mm a b c AP3 Demostration: Rear Composite Floor Structure One-shot hybrid thermoplastic composite part Aluminum profiles D-LFT including metallic insets UD tape laminate FIG. 2 Rear composite floor structure The final rear floor module demonstrator featured a thin-shell, near-net-shape structure produced from UD tapes preconsolidated into a laminate (gray) as well as D-LFT ribs (green) in X-shaped lattice structures with select use of integral metallic inserts and aluminum profiles (blue) on the axial side of the part. D-LFT ribs are 2.5-3.8 cm tall. Source | Fraunhofer Institute for Chemical Technology by selectively using discontinuous/chopped direct-long ber thermoplastic (D-LFT) compos- ites, which are •owable, allow high levels of func- tional integration/parts consolidation and are far easier to form into complex ribs without ber bridging, yet can absorb signicant crash energy. With D-LFT, it also is easier to insert metallic attachments, especially if inserts are predrilled so holes permit composite to •ow through and around the metal, creating a strong bond via mechanical interlocking. Further, D-LFT is less costly than tapes or organosheet and far easier to mold in thick sections. Compounded at press side, D-LFT simplies materials inventory manage- ment and o-ers high •exibility on development programs to quickly change material features — ber length and type, ber-volume-fraction (FVF) and matrix — as parts are made and evaluated. During production, material/process settings are controllable to achieve high levels of repeatability and reproducibility, which is why automotive has used the process for medium-to-high-volume production for almost two decades. Because researchers wanted to keep the rear load •oor thin and light and able to resist buckling while absorbing high impact loads, they conducted simulations and initial development through small-part testing with glass and carbon ber-reinforced tapes and D-LFT at di-erent ber- weight fractions (FWFs) to evaluate mechanical performance vs. lling behavior. Although carbon ber composites produced thinner, lighter, sti-er structures than did glass ber, because cost also was a concern and the front load •oor already used carbon ber reinforcement, researchers selected glass ber to reinforce the rear load •oor during scale-up to full-size parts. Ultramid BˆK PA‹ D-LFT with ŒŽ-wt% berglass and eight layers of Ultratape BˆWG"" PA‹ with ‹Ž-wt% berglass, both from BASF, were used. After much simulation work, the ".ˆ-by-".ˆm rear load •oor's nal design comprises a thin-shell, near-net-shape structure produced from UD tapes preconsolidated into a laminate overmolded with a thicker D-LFT crush zone (Fig. "). Large corrugations, also made of UD tape, with deep troughs (—Ž mm high by ""— mm wide) were molded along the part's longitudinal axis for high sti-ness at low mass and thickness. Addition- ally, two windows were formed during tape layup to allow D-LFT to penetrate through the laminate to where it was needed. Because deep corruga- tions are di˜cult to form in large laminates, it was

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