“Bio-mimetic topology” is a CAE tool that mimics how nature evolves efficient structures (think bones and trees), and is being used by Daimler and Chrysler to holistically engineer body-in-white structures for future vehicles. “We had discussions with Daimler about designing lightweight structures around the time the Chrysler 300C program began,” says Bill Grabowski, director of Body Core Engineering, Chrysler LLC, “and broadened the investigation to include this technology around 2003.” Two years later, the companies formed a partnership with the American Iron and Steel Institute to apply bio-mimetic topology to the use of advanced high-strength steels.
“The CAE tool identifies regions in a structural volume where strain is highest so material can be placed there to increase strength and stiffness,” says Grabowski. “It also identifies low-strain areas where material can be removed without unfavorably affecting the structure.” Starting with a packing volume of the intended vehicle, engineers enter the so-called “holistic forces” associated with safety, refinement, and durability. Once these are calculated, the software creates a topological map that shows a spatial load image for the package volume. This is used to create a beam model—“The former starting point,” says Grabowski—with 45 load paths. From that a complete body-in-white is drawn.
“This can even be used at the component level,” he says. His group looked at the strut tower of the Durango SUV, and removed 1.2 lb. of steel from its design. “The topological map showed there was no need to have a fully enclosed tower, and that allowed us to remove material from its inner face.” The resulting piece looks more like France’s Arc de Triomphe than the typical pyramidal strut tower.
Though current Chrysler vehicles use approximately 30% high-strength steel in their structures, Grabowski says this will increase to more than 60% over the next five years. “By utilizing bio-mimetic topology we are confident that, on average, we can reduce body-in-white weight by 120 lb. or 13%, and increase fuel economy about 1%.” Grabowski says the 2008 minivans are the last Chrysler vehicles that did not fully utilize this technology, and that the 13% weight reduction goal will be reached on vehicles introduced in the 2010-2013 timeframe. “These estimates are based on currently available steel grades,” he says, “and are by no means pie-in-the-sky.”—CAS