Automakers Reducing CO2 Emissions With Composites
As the world scrambles to address the challenge of climate change, governments are setting aggressive new targets for reducing carbon dioxide (CO2) emissions. In the U.S., the Corporate Average Fuel Efficiency (CAFE) standards require individual automakers to raise the fleet-average fuel efficiency of their new cars and trucks to 54.5 miles per gallon by 20251. The European Union’s 2021 target2 requires a fleet average of 95 grams of CO2 per kilometer, which means fuel consumption of around 4.1liters/100 kilometer (3.6 l/100 km for diesel). The 2021 target represents a reduction of 40% from the 2007 fleet average of 158.7g/km.
In general, the opportunities for increasing vehicle fuel efficiency, and correspondingly, reducing CO2 emissions, fall into a few well-explored categories, including improved aerodynamics, powertrain advances, and reduced rolling resistance. Recently, however, a fourth strategy has been getting more and more attention: the practice of reducing overall vehicle weights, better known as “lightweighting.”
Lightweighting represents a tremendous opportunity for efficiency gains. Consider that in 2010, in the U.S. the average fleet vehicle weighed a bruising 4,000 pounds3. Research by the U.S. Environmental Protection Agency shows that for every 100 pounds shed, vehicles enjoy a corresponding 1% gain in fuel efficiency4. The science is fairly direct: The less a vehicle weighs, the less power it takes to get and keep it moving.
Traditionally, the automotive industry has reduced weight by making vehicles smaller, a strategy that works well—up to a point. Going forward, though, if vehicles are to retain the comfort and utility consumers expect, substantial gains will be possible only through a materials-based approach, namely replacing carbon steel with compounds that have the same structural and performance properties but weigh a great deal less.
The challenge for automakers now is to exchange steel for materials that are lighter but retain the same—or offer better—safety and durability characteristics. Aluminum, magnesium, and advanced steels5 are a few of the materials seeing expanded use, but recent activity has focused more and more on thermoplastic composites.
Why Thermoplastic Composites?
First, let’s define exactly what thermoplastic composites are. Thermoplastics are polymer materials that become pliable when they reach a certain temperature and solidify when they are allowed to cool. In general, a composite is a combination of two or more materials in which the constituents retain their identities rather than dissolving or merging into each other to form a homogenous material.
Continuous-fiber reinforced thermoplastics are a combination of a fiber textile, generally glass, and a polymer matrix material, with the matrix material wetting, or impregnating, nearly all of the fibers. The fiber textiles used also can take the form of unidirectional tapes or multi-axial, non-crimped fabrics. (Multi-axial fabrics are notably useful for chassis and structural parts in high-performance vehicles.)
Advanced composites are an important subcategory within thermoplastic composites. These materials are suitable for crash or load-bearing applications, and ultimately for applications in the body-in-white (BIW) stage. Advanced composites typically rely on glass or carbon fibers combined with a matrix material chosen from engineering plastics, starting with polyamides and working upward in the performance pyramid.
Thermoplastic Composites are Becoming More Available
If you’ve read many press releases or trade articles in recent years, you’re probably aware that several large global players including DuPont have become active in the field of advanced thermoplastic composites for automotive use. Producers of thermoplastic materials have extended their short-fiber resin portfolios to include composites, and some carbon fiber manufacturers have proposed adding thermoplastic composite solutions to their current menus. What’s more, a few traditional composite players, whose main production activities until now have been confined to thermoset composites, are enlarging their thermoplastic composite offerings.
Given this evolution, it’s all but certain that in the coming years thermoplastic composites for auto use will become more and more available on a global basis. They’ll be produced on a larger scale, too, which should lead to greater product consistency across the board. All of us should welcome this trend toward standardization, as materials compatibility will be a chief factor driving the success of lightweighting as it pertains to reducing CO2 emissions. It is reasonable to assume that all of these companies will continue to innovate in the material space and make new products with features and different cost/performance balances to address the auto industry’s evolving needs.
Advances in Simulation with Thermoplastic Composites
Along with increased production capacity, DuPont and others have made great strides recently in the simulation of thermoplastic composites. DuPont especially has devoted a good deal of resources to understanding its materials’ behavior at the constituent level, which in turn allows manufacturers to choose the most appropriate materials model based on commercially available codes like Abaqus, Pam-Crash, and Radios.
DuPont thermoplastic composite beams can be tested in many different formats and orientations: stamped only or with overmolded ribs, quasistatic or dynamic, fixed on each side or free. DuPont is now able to simulate the behavior of such components under nearly any imaginable circumstance based on the fundamental work done in our labs. As a consequence, we can help our automotive partners integrate these material models into their simulation approaches and successfully model a thermoplastic composite part not only in a vehicle’s subsystem, but in full-car crash scenarios.
A good example of this has been published as part of the DuPont partnership with PSA Peugeot Citroën, where we integrated a side-intrusion beam made of DuPont™ Vizilon® thermoplastic composite (TPC) into a car door and reliably modeled the effect of a crash on the door. In tests, the Vizilon® TPC beam demonstrated the kind of step change in energy absoprtion that can be achieved when using thermoplastic composites in lieu of normal, short fiber resins. Those properties, along with its very high weight-specific strength, make Vizilon® TPC very suitable for crash applications.
Moreover, glass-reinforced thermoplastic composites are compatible with steel in terms of thermal expansion, making them ideal for multimaterial construction using standard bonding techniques like riveting or glueing. They also demonstrate significantly less creep than short-fiber thermoplastics. Additionally, their long-term thermal aging behavior recommends their use in the engine compartment.
Advances in Processing and Processing Support for Thermoplastic Composites
Automation is a critical factor in the successful adoption of any material for mass production. The good news is that a number of players in the supply chain are now developing thermoplastic composite processing technology that will allow these materials to become dependable agents for reducing CO2 emissions. In 2010, DuPont invested in a state-of-the-art processing equipment for stamping, trimming, and overmolding of thermoplastic composite sheets. Other material suppliers have since announced similar investments. In academia, too, more and more institutions are developing processing know-how and refining their early prototyping work. A prime example is the Fraunhofer Project Center at Western University in Ontario, Canada. And recently, the U.S. Department of Energy announced a major grant for the Institute for Advanced Composite Manufacturing Innovation, headquartered at the University of Tennessee. In short, a lot of investment is occurring downstream that will enable the use of thermoplastic composites in mass production.
Given the advances outlined above, automakers can feel confident when considering thermoplastic composites as part of their strategies for improving fuel efficiency and reducing CO2 emissions. Materials like DuPont™ Vizilon® TPC offer a number of advantages over steel, not only from a performance point of view, but more importantly, in their suitability for mass production.
Worldwide, the trend for thermoplastic composites is toward greater availability, parts and systems that can be simulated reliably, and new processing technology that allows for a high degree of automation and lower production costs. When freedom of design, performance, and potential for reducing CO2 emissions are factored in, thermoplastic composites represent a uniquely attractive option that should be on every automaker’s materials list.