At first glance, this may seem like a familiar school child’s arithmetic problem, but it’s actually a highly sophisticated physics problem. Common sense and experience, of course, tell us that the new car is the better bet. A true scientific explanation, however, lies at the molecular level, beyond the perceptions of the naked eye—but not beyond the reach of researchers at Mississippi State University’s Center for Advanced Vehicular Systems (CAVS).

Understanding how automobiles age
CAVS is an interdisciplinary research and development facility that provides the automotive industry with engineering, design, and manufacturing innovations. Among its goals, it seeks to provide the auto industry with research and technology that will improve automotive performance, lower production costs, and shorten production times. In keeping with these goals, the center is studying automotive materials and creating multi-scale crash simulations to give engineers a new edge in designing better vehicles.

“Currently, research on car crashes treat a one-day-old car the same as a 10-year-old car,” points out Dr. Mark Horstemeyer, CAVS chair professor in mechanical engineering, “but clearly that can’t really be accurate.”

To understand fully why a new bumper might dent while an older one may crack, or why one hood mildly crinkles and another dramatically folds, CAVS researchers are studying specific automotive materials at the molecular level. Their work is exploring exactly how materials—mainly metals—behave, given the stress and strain of use. This knowledge will help auto manufacturers to develop safer and more durable vehicles.

The main phenomena CAVS researchers are looking at are metal fatigue and fracture. Every time a car owner slams the door, or loads and unloads weight—whether it’s the kids in the SUV or a load of bricks in the pickup—various parts in the vehicle undergo invisible but cumulative damage, known as fatigue, that affects performance and durability over time. The other phenomenon, fracture, is a one-time event where a material breaks. While CAVS’ research on metal fatigue and fracture is focused on the automotive industry, it is certainly important to more than just commercial auto manufacturers.

Horstemeyer explains that CAVS’ metal fatigue and fracture research “looks at any impact or absorption of energy, from the bumping and denting of commercial automobiles, to the incidents of bullet penetration and mine detonation that military vehicles are subject to.” In addition, the research can easily be extended to other materials—such as glass, plastic, stone, and just about anything else—and can benefit numerous engineering tasks, including construction and product design.

Visualizations reveal the realities of metal fatigue and fracture To explain how a material’s history affects its behavior, CAVS researchers have devised computational techniques for the atomistic modeling of metal fatigue and fracture. Although research in this particular area is nothing new in and of itself, CAVS’ work takes the study further than ever before. Researchers at CAVS believe that they are the first to study the phenomena at the nanoscale level, where cracks as short as a single nanometer are being studied.

To understand exactly what’s going on at this level in their experiments, CAVS researchers have developed their own specialized software that they use to gather data in their experiments on various metals. The computations from this software are then fed into EnSight, a software program from Computational Engineering International (CEI), to produce visualizations. EnSight visualizations give researchers the opportunity to observe the formation of shear bands and cracks, as if the researchers were watching these same phenomena take place in larger objects.

“Since we’re looking at these mechanisms at the small scale, visualization is key for us to be able to accurately see and identify the mechanisms for deterioration,” explains Dr. Horstemeyer. “Visualization is so effective in this process because the human eye can instantly identify and distinguish these different phenomena, and EnSight provides the best post-processing capabilities for what we’re doing.”

Visualizations have also proven essential to CAVS researchers when it comes to communicating their findings.

“It’s important to have a tool that can communicate visually what’s happening at the small scale—whether it’s for grad students, undergraduates, or even K–12 students—to show them what happens to material in a crash,” says Dr. Horstemeyer. “It’s very important for them to identify what’s going on there. After all, they all do—or one day will—drive cars.”

The ability to communicate their findings through visualizations has also been crucial when addressing another audience: funding agents.

“To receive and maintain proper funding, we really have to show our funders why the work we’re doing here is important, and visualizations have been an important part of that process.”

Redefining materials science
CAVS’ use of visualizations to understand exactly how materials react and behave at the atomic level is not only helping to explain what goes on in car crashes, but it is also helping to change what will happen in future crashes.

Researchers have already applied what they’ve learned about current materials and are using computational simulations to help develop new alloys that will lead to stronger and more resilient automobiles. For that matter, their work could quite feasibly result in new materials for use in a wide variety of applications—not just automobiles—giving their research far-reaching importance for the entire field of materials science.

“We’re raising the next generation of materials scientists—computational materials scientists,” declares Horstemeyer. While it’s a tall claim to say that the research facility is the source of a new kind of materials scientist altogether, CAVS has already produced very convincing evidence that backs up the statement. One strong argument in the researchers’ favor is the 2006 Corvette, which exhibits improved performance thanks to computational simulations and CAVS researchers.

The 2006 Corvette was the first car to feature a cradle—the structure that supports the engine—made of a new magnesium-based alloy developed by a team that partnered with CAVS scientists to apply their technology. Researchers used computational simulations and EnSight visualizations to find a material that was superior to the aluminum alloy used for the old cradle. By studying the properties and behavior of various metals—such as their stiffness and how they corroded and broke—the researchers found that magnesium had an excellent stiffness-to-weight ratio that would outperform the previously used alloy.

While developing new alloys has always been an important area of materials science, what makes CAVS’ work so revolutionary is its computational approach. Until now, developing new alloys has mainly been a science of trial and error, where different elements are combined until a suitable material is achieved.

This trial and error method leaves much to be desired in a number of areas, particularly when it comes to understanding how a metal part will fatigue or fracture with use. That’s why designing a new cradle was previously a fairly risky endeavor. A new alloy developed by old methods might look suitable at first, but could actually prove to be a poor choice after a few years of use.

CAVS, however, was able to use visualizations of computational modeling to study the new magnesium alloy and predict how it would behave with use—all before a cradle prototype was ever made.

“The computational design of materials is a new realm—it really hasn’t been done at all before. Trial and error was the only method, but now we’re trying to do physics-based modeling to develop a new material. This is really a paradigm shift, a change in the culture,” Horstemeyer says of CAVS’ work in alloy development.

Work in this area has great potential for the automotive industry and well beyond, but CAVS researchers won’t stop there. In addition to their work with metals, they are considering using computational methods and visualizations to expand the scope of their work to new areas, such as polymers. This would include not only the plastics used in cars but would also include the human body. So one day, EnSight visualizations may be used to show how human tissue responds to a crash, displacing conventional crash dummies and helping scientists to answer the kinds of questions they’re ultimately looking for: if an eastbound and westbound car collide, how well will the drivers survive?

Plastic slip at the crack tip in the case of fatigue loading of a copper single crystal along the axis after nine loading cycles .