RMI Answers Your Questions: Autocomposites

"Dashboard"On Thursday, February 7, RMI hosted a Google Hangout focused on lightweight, ultra-strong carbon fiber composites as a key enabler of dramatically increased fuel efficiency and vehicle electrification. Today Greg Rucks, RMI consultant, answers your questions from the Hangout.

As we introduce ultralight autos onto America’s roads—which will still have millions of older, heavier vehicles—what sorts of safety concerns emerge? For example, how do we address acceleration injuries associated with light vs. heavy auto collisions?

Weight is a factor in safety, but size is the more significant factor. Large vehicles need not be heavy. A light, large vehicle with lots of crush space can decelerate and dissipate crash energy in a controlled fashion, even in an encounter with a much more massive vehicle. The higher crash energy absorption potential of carbon fiber composite, in combination with its potential to produce lightweight yet strong structure, make it an ideal candidate to manage this crash energy and protect the driver.

How do lighter vehicles handle and perform compared to heavier vehicles? Do they corner as well?

Cornering and handling characteristics can be fine-tuned to suit the weight of the vehicle. Cornering is a form of acceleration. The force, and therefore the energy, required for acceleration is driven by the mass, so a lighter vehicle will actually corner more easily (in the sense that it will corner with less force and energy input).

What are the carbon emissions/capture issues associated with carbon fiber? Does carbon fiber manufacturing emit or capture carbon? What happens when a carbon fiber vehicle is wrecked?

Making carbon fiber is energy intensive, requiring high-temperature ovens to carbonize the fibers from acrylic precursors. Pound for pound, carbon fiber contains more embodied energy and emits more CO2 per lb of produced material than the steel it would replace, and is currently less recyclable than steel, nearly all of which is recycled in the automotive sector.

Comparing materials on a pound-for-pound basis, however, misses the bigger picture: carbon-fiber-intensive vehicles can be well under half the weight of their steel counterparts.

The fuel not burned in these lighter vehicles far outweighs the increased energy and emissions intensity of producing the lighter materials, and that’s even with today’s relatively immature production processes. Work is underway by several major producers such as Harper International and by scientists at Oak Ridge National Laboratory to reduce the energy consumption associated with carbon fiber production. Energy intensity will continue to decrease as adoption increases, because energy cost is a significant portion of producers’ cost basis and competition will compel them to further optimize their processes.

When a carbon fiber vehicle is wrecked, it is repaired via several emerging processes (see www.rmi.org/autocomposites and download the pre-read for more detail) or the fiber can be reclaimed and recycled. Several means of recycling carbon fiber are already available and in use by manufacturers and continue to improve as use of recycled fiber can offset carbon fiber’s relatively high cost.

What are some of the environmental lifecycle costs associated with carbon fiber autocomposites? For example, as researchers work on improving carbon fiber recycling, how does the interim use of non-recyclable materials (or immature carbon fiber recycling pathways) contribute to waste streams?

The lifecycle costs (from both an energy and emissions standpoint) are much lower with carbon fiber composite than they are with steel. That’s because the fuel savings, imparted by the lighter weight, of carbon fiber composite relative to steel far outweighs the higher emissions and energy intensity of producing the carbon fiber.

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Inside image courtesy of Shutterstock.