Carbon-fiber reinforced plastics (CFRPs) are responsible for more than 50 percent of materials by weight in new aircraft such as the Boeing 787 Dreamliner and the Airbus A350. Yet polymer composites on average constitute less than 2 percent of an automobile's total weight. Kozarsky said:
It will take awhile before the average plane has as much carbon fiber as the 787 and the A350. The motivation now for using CFRP is more for long-distance flights. In larger volume, smaller planes for regional use, such as the B787, one trend to watch will be whether aircraft makers choose Alcoa's next-generation aluminum-lithium alloys, or go with CFRP for the skin.
Historically, carbon fiber has been well suited for an aircraft's flat skin, due to the nature of carbon's long fibers. But 3D components involve a more complicated, expensive molding technology. Kozarsky said:
Primary structures like fuselage and wings, and the landing gear and pylons, also have different structural requirements from each other. Secondary structures also have different requirements, further motivating why it's important to look at these structures on a component level while evaluating their ideal materials.
CFRPs are not only more expensive, but using them is also a step change difference, which is much greater than transitioning from using one metal to another metal. "When we talk to builders of wind turbines, automobiles, and aircraft, they're equally interested in advanced metals like aluminum, titanium, magnesium, and AHSS," said Kozarsky.
The lightest structural metal, magnesium, is not widely available, and has drawbacks in its material properties, including brittleness, susceptibility to corrosion, and sourcing difficulty. Despite these difficulties, automotive manufacturers are as interested in magnesium as they are in CFRP. Aircraft manufacturers are looking at titanium more because of its high strength-to-weight properties, but its high cost has limited its adoption outside of a few high-end applications. Some new processing technologies are emerging that may help to reduce costs.
It has been interesting to see steel fight back against new materials. Legacy materials and systems benefit from technology as well as new materials. Another example is the internal combustion engine. It may get so efficient that it edges out hybrids and EVs for consumers wanting to go green.
@Ann: Thank you, thank you, thank you for this article. There are some people who think that "lightweighting" means "make it out of plastic." This tends to go hand in hand with an idea that aluminum and steel are "old materials," while plastics and composites are "new materials."
The fact is that aluminum and steel technologies are hardly standing still. If you want evidence, just look at the new carburizing steels which QuesTek has developed. These alloys were developed from the ground up, starting with computational models. This is an exciting approach, which I think will bear even more fruit in the future.
Dave, thanks for the feedback. I was impressed with the thorough, detailed approach this study took to the materials decision making process. There's been a lot more news about composites than about metals and, in fact, many of the R&D efforts I've reported on are new materials. Also, I've had a tough time getting many metals companies to talk to me about lightweighting, especially in the steel industry, especially for automotive applications. So thanks for the info about carburized steel. What I'm especially interested in is structural applications and AHSS, as well as titanium and magnesium in aerospace and/or automotive apps.
Ann, is there an industry component to whether new composites or legacy metals tend to win the lightweight argument? Seems that aerospace likes components. In the auto industry is there more bias toward steel? Or am I reading this incorrectly?
Rob, there are definitely industry differences. Generally speaking, aerospace has been using composites, both glass and carbon fiber-based, for decades, first in military planes and more recently in commercial aircraft (as well as in spacecraft). Whereas in cars it's more recent and confined primarily to race or specialty cars. Regarding metals, steel doesn't figure much in aircraft because of its weight; the primo metal there is aluminum. Metals in most commercial planes still average over 50%. In Detroit cars, metals are a much higher proportion, primarily because of the cost of composites and the difficulty in adapting their manufacturing to highly automated, high-volume automotive production. All of this is a moving target.
The question still comes down to HOW STRONG IS IT? Researching a homebuilt car and the material requirements for structural strength and the weight savings aren't always there for lighter materials as you need more of the lighter material for the same strength. Cars and trucks need the strength to protect the passenger and deal with environmental factors (salt on the roads in the winter, accidents with other vehicles) while aircraft have used aluminum (and tubing ans cloth) and much more sophisticatd design to save weight ans still be strong. Imagine the cost of a Semi-Monoque car body built by riveting the layers together, but that is the approach aircraft use because weight is a controlling factor. In Automobiles weight is less of a concern, and durability and passenger protection as cars are more likely to be involved in an accident.
And how well would carbon fiber stand up to something trying to pierce it in an acceident? Steel, on the other hand, can deform and contain an object trying to piece the passenger compartment.
Smaller aircraft have used some of the composites, but a small savings on a 2000lb aircraft doesn't make much of a difference as compared to a 200,000lb aircraft so the savings does not always scale very well.
Another question is the repair of the vehicle - Stell is easy to cut and weld and repaint. Aluminum to cut and rivet ans paint. Would composites require a whole new section, and would it be available in 2 or 4 years?
And some of the chemicals rused in composites require special handling and present a whole new set of hazards to those handling them.
Rob, good point. One of the "features" missing from the article is the fabrication difficulty. In aerospace and some high end applications, where the systems will last a long time, it is worth paying up front for more difficult fabrication. I think it was on this site that a new technique for welding titanium was discussed. This is just one example. Aluminum is also more difficult to weld than steel. Recall that most aircraft, which have used aluminum for a long time, are riveted. Jaguar started making the bodies of their high end XJs of aluminum. When they did that they save 500 pounds (on a 4,000+ pound vehicle). Many wondered if they would ever recover the cost of the production line changes that had to be made. As you mention, steel may end up getting better before price or process technology catches up for the other materials. In addition, steel and aluminum are eaisly recyclable.
The limitation of Carbon and Aramid and Glass reinforced materials - as well as nano-materials - is a lack of awareness of the ability to use zirconate and titanate and aluminate coupling agents to bond the interface of the fiber reinforcement to the polymer resin. Silanes - the material that made the Corvette possible (fiberglass reinforced peroxide cured unsaturated polyester) - have severe interfacial reaction and environmental aging issues due to the nature of their molecular bond formation.
I'm not sure what composites you're researching, but they sound like glass fiber. Carbon fiber is another story and answers your strength questions: the strength-to-weight ratio is higher for carbon fiber than steel and even higher than aluminum. Also, I'd bet that any carbon fiber materials you're likely to be able to purchase as a home user are not the ones you can get for building military or commercial aircraft.
NIST's new five-year strategic plan for its Material Measurement Laboratory lists additive manufacturing materials development as one of the main areas it will support by developing measurements, data, techniques, and models.
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