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ADVANCED AUTOMOTIVE MATERIALS

THE VEHICLE Technologies Office of the U.S. Department of Energy has worked with the Lightweight Materials National Laboratory Consortium in optimizing advanced automotive materials. The March 2018 issue of Tech Briefs summarizes aspects of this work. Here are tidbits from its article, “Pros & Cons of Advanced Lightweighting Materials.”

VTO and LightMAT Efforts. The Lightweight Materials National Laboratory Consortium links ten national labs, including Argonne, Lawrence Livermore, Oak Ridge, and Sandia.

DOE’s Vehicle Technologies Office works with them in activities of lightweight materials development and application. Studies involve advanced material sourcing, cost, engineering, and safety. Other aspects include modeling through computational material science and optimizing end-of-use recycling.

Light Weight = Fuel Efficiency. According to Tech Briefs, a ten-percent reduction in overall vehicle weight can result in a 6 to 8 percent fuel economy benefit: “Replacing traditional steel components with lightweight materials such as high-strength steel, magnesium alloys, aluminum, carbon fibers, and polymer composites can directly reduce the weigh of a vehicle’s body and chassis by up to 50 percent, and therefore reduce a vehicle’s fuel consumption.”

The payoff is particularly beneficial in hybrid electric, plug-in hybrids, and battery electric vehicles. The first two categories inherently add weight and complexity in their dual propulsion. Pure electric vehicles are challenged by battery weight, cost, and range limitations.

The Audi A8 L features a unibody of varied materials, including steels, aluminum, polymers, and magnesium. This and the following image from Tech Briefs, March 2018.

High-Strength Steel, as its name suggests, offers more strength and stiffness than traditional varieties of steel. Compared with aluminum, it has advantages of cost, formability, and corrosion protection.

On the other hand, its stamping equipment is more costly and wears out more quickly than those used with conventional steels. Also, there’s an inherent tradeoff of high-strength steel’s ductility and strength that complicates its forming and joining.

Aluminum is a familiar material that has had years of use in aerospace. Its light weight offers as much as a 60-percent savings compared to an equivalent steel component. Aluminum alloys exhibit good stiffness, strength, and energy absorption.

The Ford Escape features machined-aluminum wheels.

Tradeoffs include complex joining with other materials, possible electrolytic corrosion, and a higher cost than steels.

Magnesium is a special-application star of lightweight metals, offering as much as a 70-percent weight savings. It has high stiffness and strength; it’s also amenable to thin-wall casting of components such as sub-assembly closures, bracing, and brackets.

Magnesium is expensive, however, and has challenges in manufacturing, repair, and recycling. If ignited, for example, its transformation to magnesium oxide is extremely difficult to extinguish. Tech Briefs also notes a “lack of availability from U.S. manufacturers in large quantities to meet automotive needs.”

Carbon Fiber Composites offer high strength and stiffness. Half the weight of steel, they’re four times stronger. What’s more, fiber directionality can be optimized specifically for applications.

The carbon-fiber roof of a production BMW M3 coupe.

These materials appear in high-performance cars, however, according to Tech Briefs, cost and fabrication complexities are “generally too high for use in popular models.”

Titanium is cited by Tech Briefs for its use in “powertrain systems to reduce weight by up to 55 percent” It offers an excellent strength-to-weight ratio, can withstand high temperatures, and is used in engine valves, springs, and other specialized applications.

Tradeoffs include high material costs and formability challenges, neither of which hamper titanium’s widespread use in Formula One and in high-end eyeglass frames. ds

© Dennis Simanaitis, SimanaitisSays.com, 2018

12 comments on “ADVANCED AUTOMOTIVE MATERIALS

  1. sabresoftware
    March 24, 2018

    “Half the strength of steel, they’re four times stronger. ”

    I think that was supposed to be half the weight …

    • simanaitissays
      March 24, 2018

      Agg; a typo! Of course, you’re correct and I shall fix post-haste.

      • sabresoftware
        March 24, 2018

        I was also going to ask about high strength steel stiffness, thinking that Young’s Modulus for steel is generally around 200 GPa, but found a paper from research in Australia indicating that thinner sections of higher strength steels (550 MPa yield) demonstrate E values closer to 240 GPa. Interesting. I suspect that the alloys required for higher strengths fundamentally make this steel a different material from normal steels that are currently used for structural work (250-350 MPa).

  2. carmacarcounselor
    March 26, 2018

    I was under the impression that structural aluminum is more vulnerable to fatigue than steel, making it necessary to specify sections that are initially over-designed for strength.

    • simanaitissays
      March 26, 2018

      Another interesting aspect not addressed in the “Tech Briefs” item.

  3. Brian Paul Wiegand
    March 26, 2018

    Material substitution (aluminum for steel, etc.) is just one of many methods used by professional mass properties engineers (members of the SAWE) to reduce the weight of vehicles. Generally such substitutions come with detrimental consequences such as increased cost, difficulty in manufacture, increased physical risk, etc. A true professional mass properties engineer incurs such detrimental consequences only as a last resort, preferring to optimize the structure by paring away unstressed mass, making one component serve more than one function, deleting unnecessary features, simplifying load paths, etc. It’s amazing that, with all the emphasis on reduced weight in the automotive world, so little use is made of the resources and members of SAWE.

  4. carmacarcounselor
    March 26, 2018

    Titanium was also used for the frame of my Breitling Avenger Sea Wolf, which I could wear without fear of damage to visit the Lexington, recently discovered in 3,000 meters at the bottom of the Coral Sea. Of course I would have been dead long before we reached that depth. I chose it specifically because of that ridiculous specification, and it’s size. It would be suitable as brass knuckles, the use for which James Bond chose a Rolex in On Her Majesty’s Secret Service.

    • sabresoftware
      March 26, 2018

      My Sinn UX dive watch also has ridiculous specifications. The watch is made from tegimented (specially hardened) high-strength seawater-resistant German Submarine Steel. The watch is filled with a silicone oil so that there is no void space and therefore no possibility of fogging. The case is rated to 12000 metres but the thermocompensated quartz movement inside is “only” good to 5000 metres. There is a special variant of the watch, which is the official

      The movement is a COSC certified chronometer (accurate to +/- 25.5 seconds per year). Mine runs about +20 seconds per year. Not the best of my thermocompensated watches, but not too shabby. Most quartz watches are in the +/- 10-15 seconds per month range. And the best automatics meet COSC requirements at +7/-3 seconds per day (if I remember correctly).

      The one downside is that the watch has to go back to Sinn for a battery replacement due to the oil fill. Fortunately they put in an 8 year battery (so mine will have to go back soon).

  5. sabresoftware
    March 26, 2018

    Correction: official service watch of the German GSG9 special services.

  6. carmacarcounselor
    March 26, 2018

    5000 meters will do in a pinch. Mine just has a bank vault-like case and a stem that screws in. Accuracy? It says chronometre officielment certifie on the face and the back, but if that is supposed to mean it meets some standard, it must be a lose one. In the last few months I’d had to adjust it every time I took a shift as Vault Docent at the Petersen, to know if I was finishing my Tours on time. It’s my only “good” watch, and that frequent use of the stem might be why it went into the shop for the first time in 7 years – the stem pulled out. Now its good for about five seconds a day. My old Seiko Five could do that when it was new.

    • sabresoftware
      March 26, 2018

      Yeah 5000 metres is not bad. Watch would survive the diver by about 4500 metres.

      All Breitlings are COSC certified chronometers. The +7/-3 per day for mechanicals (or better), and +/- 25.5 per year (or better) for their quartz. My Breitling Airwolf Raven started at about -4 SPY when I first got it, and has shown aging creep, now running about +8 SPY. These calibers can be adjusted and I will get the watch adjusted the next time I replace the battery.

      COSC is Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute, which is the institute responsible for certifying the accuracy and precision of wristwatches in Switzerland.

      • carmacarcounselor
        April 11, 2018

        Now that I have had my Sea Wolf repaired by a local shop, any deviation from nominal is pretty much gone, so I guess it’s living up to its certification.

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