DEC 2018


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45 Multi-material autocomposites Illustration / Karl Reque SMiLE Hybrid Composite Rear Load Floor for Battery-Electric Vehicle › Unidirectional fiberglass- reinforced PA6 tapes form thin, near-net-shape floor structure that resists buckling during rear impact With goals to absorb higher impact energy while reducing mass and cost for both the rear and front load oors as well the larger BIW structure of which they were a part, the decision was made to produce the rear load oor using thermoplastic composites with metallic inserts. e team wanted to add trunk features and second-row seatbelt-attachment structures, but they also wanted to use the load oor to absorb signicant crash energies. Normally, carmakers rely primarily on metallic proles on the sides of metallic load oors to manage rear-crash energies on passenger vehicles. However, given the impact strength of thermoplastic composites, researchers wondered if the entire width and length of a composite load oor could be used to manage crash loads. ey also wondered if higher crash energies could be absorbed. Researchers reviewed common automotive thermoplastic composites. Polypropylene (PP) and polyamide - (PA-) matrices were considered but PP was eliminated for temperature reasons since the rear load oor travels with the BIW through the high-temperature electrophoretic coating (e-coat) rust-prevention process. Continuous ber reinforcement was needed to achieve the highest stiƒness and strength, so pretrial work focused on fabric- reinforced organosheet (a form of glass-mat thermoplastic (GMT) composite) and unidirectional (UD) prepreg tapes. For many reasons, tapes were selected for further prototyping. Researchers knew the geometry of the rear load oor would be complex. Use of automated tape-laying (ATL) machines — which place UD tapes in any orientation and make windows/holes with less material than organosheet — would reduce scrap, mass and cost, and permit the most e'cient use of bers locally and globally across the part. Also, since bers placed via ATL lie at and parallel in each layer of the ply stack and are not woven like fabrics, there is no undulation and consequent loss of stiƒness and strength. UD tapes do have limitations, however: ey are relatively expensive and have poor drapeability with almost no ow, making it di'cult to ll complex geometries. ese issues were overcome › Fiberglass-reinforced PA6 D-LFT strategically over- molded to form X-shaped ribbed lattice structure › Insert-molded aluminum profiles provide additional sti€ening, facilitate mounting load floor to surrounding structure, control crushing and transfer load to D-LFT rear crush zone › Additional metallic inserts and plates permit second-row safety belts to attach to load floor Large aluminum rocker panels PA6/60-wt% fiberglass tape laminate Hybrid rear (thermoplastic composite/aluminum) load floor Metallic hardware Insert-molded aluminum profiles Hybrid front (ther- moset composite/ aluminum) load floor Complete composite floor module PA6/40-wt% fiberglass D-LFT Insert-molded aluminum profiles Hybrid rear load floor

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