By Kevin Wilcox
Researchers are developing a 3-D-printed, closed-cell foam that could lead to lightweight structures and load-bearing insulation and acoustical panels.
The combination of shapes used produces strong vertical, horizontal, and diagonal lines within the foam. © Jonathan Berger
April 21, 2015—Researchers at University of California, Santa Barbara (UCSB) have developed a geometric pattern for 3-D printing that creates precise closed-cell foam materials that approach the theoretical limits of isotropic—or uniform—stiffness. The development holds the promise of developing such lightweight structures as sandwich panels, insulation, or acoustical materials that can also carry structural loads.
"In the end we have a material system that achieves design goals with less material—more than an order of magnitude in some cases," says Jonathan Berger, Ph.D., a postdoctoral researcher at UCSB's mechanical engineering department. "It can potentially have a big impact in reducing the amount of material needed to make all kinds of things, from cars to skyscrapers."
The material is known as Isomax and Berger has formed the company NAMA Development to further the research. The material is composed of alternating three-dimensional diamonds, some hollow on the inside and others supported by interior walls joining all the points on two planes. This combination produces the unique properties of the material.
"The shape of the cells that are formed ...determines the macroscopic properties of the material," Berger says. "Each substructure imparts a specific directional stiffness and strength that can be varied independently to form functionally graded materials."
Berger was inspired to undertake the research by his passion for such gravity-related sports as skiing, snowboarding, and mountain biking. "The human-powered aspect of these sports really drives designs to be more efficient by reducing weight and increasing structural performance. When you don't have an engine, the mass of your vehicle is really apparent," Berger explains. "I was always interested in combining my engineering work with my passion for sports. And while our material is far more widely applicable than just skis and bikes, I'm really happy that one day I might get to see it used that way."
Three-dimensional printing enables the complex cell shapes to be either open or closed. © Jonathan Berger
Berger notes that 3-D printing has made possible the complex material geometries that result in these strong, lightweight foams. "I saw an opportunity to study a class of materials—ordered, closed-cell foams—that had not received much study in comparison to similar materials such as lattices," he says. "While they are quite useful engineering materials, lattices have been shown to achieve only a fraction of the theoretically defined maximum performance, so we went in search of what does actually achieve the bounds."
Berger says that his research team has characterized Isomax successfully through computer modeling and is now focused on making these foams out of such materials as polymers, titanium alloys, and fiber composites. The team is looking forward to then testing the resulting structures. Early tests using polymers in 3-D printing have been promising.
"While 3-D printing is very exciting, it is still in its infancy and there are still many, many issues in getting good microstructures," Berger says. "When you print these things out of aluminum and titanium, it becomes more difficult to get the same kind of microstructure, the same level of strength that you would get out of something that was cast or forged."
Berger believes that the Isomax foam structure will have a wide variety of applications. He foresees the earliest commercial applications in areas in which strong, lightweight materials are especially prized, such as aviation, aerospace, and shipping. Because the international shipping industry is highly focused on volumetric concerns, a material that exceeds the strength-to-weight ratio of balsa wood within a lower volume would be highly prized.
"Combining the structural and multifunctional nature of this material [make it an] interesting material for building fabrication," says Berger, who notes that Isomax can be engineered for a variety of structural, acoustical, and thermal properties. "It has a nice aesthetic quality as well," he adds.
"Cellular materials in general, [such as] lattices, are often used in multifunctional realms where you have heat convection properties that you are after, as well as structural properties," Berger says. "So, in buildings where you perhaps need to insulate as well as carry structural loads, our material can serve that multifunctional purpose, reducing the requirement of other related systems or members."