Bubbling Up: Pioneering New Buoyancy Materials

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By Troy Clarke

Engineers dream of a material as strong as steel and light as a feather, but the nature of materials has a way of dashing those dreams. Some of the strongest bulk materials become comparatively weak when engineered to become lighter-weight cellular solids. While it is hard to imagine that fragile glass could meet or exceed the strength of aluminum, titanium, or steel, scientists at Naval Surface Warfare Center (NSWC), Corona Division have patented a method for making such a material: glass foam.

These scientists are transforming millions of microscopic glass bubbles—about the diameter of a human hair—into a new super strong, super light cellular solid material that may one day be used for weapons or equipment. And it can shed more mechanical energy for a given volume than any current cellular material.

The Corona team has discovered that their shock-absorbing foam has additional applications as a strong, buoyant foam. The progress made in designing lightweight, strong cellular solid materials has sparked interest within the special warfare community.

“The new method for fabricating cellular solids from glassy hollow spheres is very versatile,” said Corona physicist and glass foam inventor, Dr. Aaron Wiest. “You can customize the properties of a cellular solid material by using hollow spheres with the necessary initial properties” to create materials that are lightweight, buoyant, or super strong.

Wiest recalls the genesis of this idea came during casual conversations between coworkers. Discussions of physics, materials, engineering, and Navy requirements led to a theory that hollow spheres of glass could be bonded in ways crystalline materials have not been. Materials scientists know that glasses and other materials that lack a crystalline structure are amorphous and soften at a specific temperature to become a highly viscous liquid, thicker than molten tar. At these temperatures, Wiest theorized, hollow spheres should stick to each other and a cellular solid material should be formed upon cooling.

At the time, NSWC Corona didn’t have the testing facilities for this type of project, so Wiest tapped into connections at local universities for proof-of-concept testing. Professor Dale Conner at California State University, Northridge, one of the other inventors of the glass foam, directed graduate students to test the concept and was instrumental in developing the experimental architecture.

Corona has now acquired a material testing laboratory facilitating further development of the foam. This laboratory, which would have cost taxpayers more than $1 million, was pieced together from Defense Logistics Agency excess equipment and repurposed for less than $5,000—the cost of shipping—thanks to leadership from Item Unique Identification Branch Head Jamie Lizarraga and Product Engineering Department Head Doug Sugg.

“Innovation is one of the key ingredients for sustaining a successful organization,” said Corona’s Chief Technology Officer Arman Hovakemian. “In order for NSWC Corona to remain relevant as a scientific organization, we must innovate. We can only accomplish this by fostering an environment where they have the freedom to innovate through experimentation and prototyping. An example of what can be accomplished with this approach is the new foam material being created by Corona scientists and engineers.”

Hovakemian and other senior leaders have used the new cellular solid materials research not only to motivate other scientists at the warfare center, but to spark the interest of new recruits with doctorate degrees and vast experience in academic and industrial research. Corona leadership is looking at possible commercial applications and potential technology transfer agreements.

Capt. Stephen Murray, Corona’s commanding officer, echoes Hovakemian’s view. “We have an entrepreneurial workforce here. Whether you are a young petty officer or a veteran civilian with a doctorate in physics, we are encouraging everybody to push ideas and work toward a truly innovative Navy,” Murray said. “A workforce that thrives on excelling is going to come up with the next innovation that changes the way the Navy operates.”

The innovative glass foam caught the attention of Corona’s executive officer, Capt. Corry Shedd, who quickly saw how a new cellular solid material could potentially save the Navy significant money in the design of undersea combat platforms and other craft. Shedd, whose career has included tours with the Navy’s special warfare community, sees the new material as a potential game changer in the ever-present challenge of gaining maximum combat capacity and capability of a given platform without sacrificing other key performance and design criteria.

“One can easily imagine an incredible range of possible applications for virtually any devise or platform that requires customized buoyancy, strength and density characteristics, especially where the proper trade-offs of those competing factors can result in increased combat capability,” Shedd said. “For instance, incorporating this technology into the design of tactical undersea vehicles, like those utilized by special warfare forces, may allow for a more optimal balance of the vehicle’s internal buoyancy control and stability systems and overall material strength that could result in achieving critical increases in passenger/cargo capacity. In the world of asymmetric operations, delivering even one more Navy SEAL or a few more pounds of combat equipment to the fight is a huge advantage. This technology has the potential to serve as a true force multiplier.”

For his Naval Innovative Science and Engineering project, Wiest explains that glass breaks because it has defects in the bulk material. Fiberglass has much higher strength than window glass partly because the small fiber size minimizes the number of defects that weaken the material. Fiberglass is used today in high-strength composites by weaving cloths of the microscopically thin fibers and bonding them in a resin.

Glass foam uses similar physics for minimizing defects by bonding hollow glass spheres with wall thicknesses similar to fiberglass dimensions–resulting in a cellular solid with ultra-high strength. This novel approach created a significant scientific breakthrough.

Wiest, Conner, and the team showed that processing the glass bubbles at 1,550 degrees Fahrenheit for 30 minutes under vacuum in Pyrex tubes yielded the highest strength materials. This processing bonded them into a super strong material that could dissipate large amounts of mechanical energy. Corona conducted low-speed (low strain-rate) crush tests, while Susan Bartyczak and Dr. Kenneth Jordan at Naval Surface Warfare Center Dahlgren Division and Dr. Vasant Joshi at Naval Surface Warfare Center Indian Head Explosive Ordnance Disposal Technology Division performed high-speed (high strain-rate) testing. The material performed well and dissipated large quantities of mechanical energy at crush rates from 0.0001 m/(m*s) to 4000 m/(m*s). Test results show that Corona’s invented cellular material dissipated more mechanical energy for a given volume than any other cellular material on the planet (14.8 megajoules per cubic meter). For Wiest, the science is challenging and highly rewarding, but it becomes more so because it supports an even greater mission.

“The key to customizing and optimizing the cellular material for lightweight submersible applications will be finding the perfect hollow sphere material and dimensions to bond into a cellular solid so it can withstand the pressures of making a deep dive while being light enough to meet the vehicle requirements,” Wiest said. “We have much work to do and are fortunate to have a great team and strong support from our senior leadership while taking on this exciting project.”

About the author:

Troy Clarke is a public affairs officer with Naval Surface Warfare Center, Corona Division. The command recieved the Navy’s 2014 Thompson-Ravitz Best in Show award for excellence in public affairs for its program, “Better Together: Harnessing a Navy Federal Laboratory for Innovation and Growth.”

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