US Breakthrough Could Build Hypersonic Shields, Rocket Parts In A Fraction Of The Time

Authored by Christopher McFadden via Interesting Engineering,

John Hopkins APL researchers have found a way to dramatically speed up the way that carbon-carbon composites can be created. The new approach, the research team explains, could replace the current slow, labor-intensive process, ultimately slashing the cost of production.

"That speed is what makes FAST CAR² so compelling," said Sal Nimer, assistant manager of APL's Science of Extreme and Multifunctional Materials program. "It has the potential to enable faster and more efficient production of advanced materials for high-performance applications, whether for rocket nozzles or hypersonic vehicles," he added.

Carbon-carbon, in case you are unaware, is basically carbon fiber embedded in a solid carbon matrix. Imagine carbon-fiber reinforced plastic, except instead of the fibers being surrounded by epoxy/resin, they're surrounded by more carbon.

That gives you something that is simultaneously very light, mechanically strong and astonishingly tolerant of heat. It's why you see it in things like rocket nozzles, re-entry systems, missile nose cones, aircraft brakes and hypersonic thermal protection.

Making carbon-carbon composites easier to make

"Carbon-carbon is one of the most important materials available for the thermal protection systems that help high-speed flight vehicles survive extreme heat," said William Fahy, an APL materials engineer who co-led the FAST CAR2 project.

"It was crucial for the heat shield on NASA's Parker Solar Probe - the spacecraft flying closer to the Sun than any human-made object. It's indispensable," he added. However, at present, making it is a painfully slow process.

Traditionally, you start with a porous carbon-fiber structure. You then need to fill all the tiny gaps between the fibers with additional carbon.

There are two main ways of doing that: repeatedly force carbon-rich gas through the material and deposit carbon inside it, or soak it with a resin and heat the resin until almost everything except the carbon burns/pyrolyses away.

The problem is that one pass doesn't fill everything. FAST CAR2, on the other hand, makes this much simpler and faster. In fact, similar materials that take months to produce can be created in just days.

Instead of slowly growing or depositing the carbon matrix inside the fiber structure, they put a carbon-bearing material directly into the fiber preform and then squash and heat the whole thing extremely rapidly using a technique called field-assisted sintering.

Looking ahead

The electrical current produces very rapid heating, while the press simultaneously forces everything together. The actual densification apparently happens in minutes, although preparing the piece and completing the whole manufacturing process still takes days.

"We're aiming for something revolutionary - to change the mechanism itself so we can get there orders of magnitude faster," Chapkin said. "When we started, the theory was there, but we didn't even know if the material would hold together," Chapkin said. "We've been surprised every step of the way," he added.

Looking ahead, the team is now working with external partners to access larger presses that will allow them to scale the process to even larger sample production and open the door to more applications.

"Scaling is always the hard part," Fahy acknowledged, "but seeing how quickly this all came together and how successful it has already been, we feel optimistic about where it can go," he added.