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Lighter Cars, More Efficient Cars

By Antonio Villareal

Exploring how lightweight structural materials may help cars run more efficiently

Most of the time, when we think of ways to make new cars more efficient and environmentally friendly, our ideas focus on advanced battery technologies, fuel cells or new hybrid power systems.

Jyhwen Wang thinks about steel.

These aren’t just idle daydreams. In 2010, the federal Department of Transportation and the Environmental Protection Agency have issued new rules calling for improved fuel economy and, for the first time, national standards for greenhouse gas emissions. Automakers will be required to raise the average gas mileage their vehicles get from 27 miles per gallon to 34 miles per gallon by 2016.

Electric or hybrid cars offer promising routes to lower emissions and higher gas mileage, but they’re not the only way to get there, says Wang, an associate professor in Texas A&M’s Department of Engineering Technology and Industrial Distribution.

“Another way is to reduce the vehicle weight,” says Wang, a mechanical engineer by training and a specialist in manufacturing processes and material response to those processes. “In this case, we have different alternatives.”

Much of his research is centered on the steel that automakers use to build automobile bodies and the interaction between the properties of the metal and the processes used to form it into auto body parts. One of the major challenges in using new materials, especially advanced varieties of steel, to build automobile body parts is that the properties of the steel that allow for lightweight auto bodies often make it difficult to process. Advanced steels also are often more expensive than conventional steel.

"Electric or hybrid cars offer promising routes to lower emissions and higher gas mileage, but they’re not the only way to get there. Another way is to reduce the vehicle weight."

From his former experience as a research engineer in the steel industry, Wang acknowledges that materials have to be strong and ductile, but more important, the price must be reasonable.

Wang is taking a two-pronged approach to achieve this goal. On one side, materials scientists are trying to develop materials that are formable, strong and cheap, Wang says. On the other, manufacturing engineers are trying to develop techniques to make products that use these materials.

The first approach would require improving advanced steels while making the new material affordable for mass production. The alliance of advanced steel with other metals is a key part of this process.

To reduce the vehicle weight, a great deal of the research is focused on aluminum, which seems like a perfect partner for advanced steels. From an economic standpoint, the price is competitive and stable. From a material standpoint, aluminum is resistant and three times lighter than steel. And it has an environmental asset: It can be 100 percent recycled with a low energy demand and without losing any quality in the process.

Again, many ways exist of reducing the weight of a car’s body, and Wang’s team is currently following a more experimental line of research. It consists of attaching polymer foam to the sheets of metal in order to increase their stiffness: “a metal–polymer sandwich,” as Wang defines it. His preliminary results suggest that, in several years, this metal–polymer sandwich could also be feeding the industry’s voracious appetite for new materials.

The second approach is equally challenging and focuses on the industrial process of making the parts of the car. In Wang’s words, “We can replace components with different types of material, but we also need to look into how to produce these components.”

Once they have created the right material to turn their brightest idea into a real product, they next develop the best process to give the product a shape without damaging the material.

“In the past, this has been done by stamping,” Wang says.

In fact, researchers are using hydroforming to shape their materials into different parts, either sheets or tubes of metal. Hydroforming consists of a die in which the material is formed inside a negative mold after the injection of a high-pressure hydraulic fluid, thus allowing more complex shapes and producing lighter and stronger products.

The use of this process also involves predicting the formability of the material, Wang says.

“We want to know how far we can stretch the material, but we also want to know what could happen if we change the material,” he says, and whether that change would also require modifying the manufacturing process.