DEC 2018


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DECEMBER 2018 6 CompositesWorld COMPOSITES: PAST, PRESENT & FUTURE » CW's August 2018 article, "Teaming to dene what CFRP could be," on the CFRP front subframe developed by Ford Motor Co. (Dearborn, MI, US) and Magna International (Aurora, ON, Canada), illustrates innovation in sheet molding compound (SMC) — specically, overmolding noncrimp carbon ber fabric SMC with chopped carbon ber SMC. Šis idea of using a contin- uous ber SMC comolded with conventional chopped ber SMC, and the use of chopped carbon ber SMC, may seem new, but these innovations actually go back more than 30 years to the GMC Astro Class 8 truck door using SMC developed by Premix/ EMS. Several other projects contributed further developments over the years. Še history of SMC development shows how far the industry has come, but also that the future belongs to those who understand the big picture, and thus, are willing to take risks. Še GMC Astro Class • vehicle door was one of the parts that impressed me the most when I joined the industry in –—•˜ as a technical sales representative for Premix/EMS (North Kingsville, OH, US). A heavy truck ›eet owner even remarked that the SMC door was the best thing about that truck. Še three-piece assembly had inner and outer structural parts with a decorative cover panel. But I was most impressed with the addition of continuous unidi- rectional material in the window frame area. It was an example that I used often when talking with vehicle design engineers who needed higher tensile strength than what our conventional discontinuous ber materials oŸered. My lesson learned: A vehicle designer considering development of a comolded part must have enough condence in all phases of part development to know whether he or she is creating a break- through or just another science experiment. The next step In 2003, the Dodge Viper represented the rst use of carbon ber SMC in a production vehicle 1 . Še vehicle manufacturer, Chrysler, and the SMC supplier, Quantum Composites (Bay City, MI, US), developed breakthrough solutions in three structural systems: • Thin-walled sections in fender supports, • Carbon fiber SMC and low-density glass fiber SMC in door panels, • Comolded unidirectional carbon fiber with structural SMC on the windshield surround. In a £¤¤£ paper published by the Society of Plastics Engineers (SPE, Bethel, CT, US), the development engineers at Chrysler and Quantum cite lack of understanding carbon ber as one of the key factors limiting prior use of it in SMC. I think another key issue was the need to understand how randomly oriented bers behave in structural applications. Material suppliers, molders and design engineers had decades of experience in making thermoset berglass composite structural parts. Šey were accustomed to these being stronger than thermoplastics, using materials with clear data sheet values, and if you needed more strength, you could just add material. Še parts were characterized by long-term resistance to creep, which insured that structures remained in place under stress. But the SMC industry was not ready for the examination that Boeing would conduct into discontinuous bers. New challenges As the Boeing Co. (Chicago, IL, US) developed its 787 Dreamliner commercial aircraft, it began looking at a variety of new materials, including Hexcel's (Stamford, CT, US) HexMC chopped carbon ber/ epoxy material. Še push at Boeing to use this material for primary structure created a need for a deeper characterization of discon- tinuous ber performance, including understanding the variation and predictability of SMC. Šis was the type of data and analysis the industry was ill-prepared to provide. To understand the answers to Boeing's questions, I went to Dr. Paolo Feraboli at the Automobili Lamborghini Advanced Composite Structures Laboratory (ACSL), which was created with the University of Washington (Seattle, WA, US). Feraboli's work, summarized in the £¤¤— paper "Notched behavior of prepreg-based discontinuous carbon ber epoxy systems," £ helped the industry understand the underlying principles of coupon and part testing, and provided insight into why parts worked and the limits to assumptions from coupon test values alone. A summary of similar work was presented at the £¤–ª SPE Automotive Composites Conference & Exhibition (ACCE) by Matt Kaczmarczyk and Tim Langschwager of Quantum Composites ª . Šis gave Quantum the data and condence that we not only understood our materials but could explain their performance to others. Performance at the next level As head of the ACSL, Feraboli had performed testing and development work on the Sesto Elemento, the rst Lamborghini model to use CFRP not only in its monocoque, but also in its suspension control arms. Še Sesto Elemento also pioneered application of carbon ber SMC in both of these applications. Šis development was in parallel with Callaway Golf Co.'s (Carlsbad, CA, US) use of the material for driver crowns (golf club heads) and Quantum Composites's AMC 8500 family of chopped 12K carbon ber/vinyl ester resin products. Both Lamborghini and Callaway were seeking to expand the limits of performance and practical part size. Še Sesto Elemento's suspension arm actually used unidirectional carbon ber overmolded with carbon ber SMC, one of the rst commercial applications of the material 4 . The future of SMC development belongs to those willing to take risks. Innovation in SMC: A long history and great potential

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