NC State, Houston University develops self-healing composite that repairs damage 1,000 times

3D printed thermoplastic healing agent (blue overlay) on glass fiber reinforcement (left); infrared thermograph during in situ self-healing of a fractured fiber composite (middle); 3D printed healing agent (blue) on carbon fiber reinforcement (right). Sources | Jason Patrick, NC State University.

Researchers from North Carolina State University (NC State, Raleigh, U.S.) and the University of Houston (Texas, U.S.) have developed a self-healing composite that has been shown to outperforms materials currently used in aircraft wings, turbine blades and similar applications, while retaining the ability to repair itself more than 1,000 times.

“This would significantly drive down costs and labor associated with replacing damaged composite components and reduce the amount of energy consumed and waste produced by many industrial sectors because they’ll have fewer broken parts to manually inspect, repair or throw away,” says corresponding author Jason Patrick, an associate professor of civil, construction and environmental engineering at NC State.

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The self-healing technique developed by NC State researchers targets interlaminar delamination, which occurs when cracks within the composite form and cause the fiber layers to separate from the matrix.

“Delamination has been a challenge for FRP composites since the 1930s,” Patrick explains. “We believe the self-healing technology that we’ve developed could be a long-term solution for delamination, allowing components to last for centuries. That’s far beyond the typical lifespan of conventional FRP composites, which ranges from 15-40 years.”

The self-healing material resembles conventional FRP composites, but with additional features. First, the researchers 3D printed a thermoplastic healing agent onto the fiber reinforcement, creating a polymer-patterned interlayer that makes the laminate two to four times more resistant to delamination.

Next, they embedded thin, carbon-based heater layers into the material that warm up when an electrical current is applied. The heat melts the healing agent, which then flows into cracks and microfractures and rebonds delaminated interfaces, thereby restoring structural performance.

To evaluate long-term healing performance, the teams built an automated testing system that repeatedly applied tensile force to an FRP composite producing a 50-millimeter-long delamination, then triggered thermal remending. The experimental setup ran 1,000 fracture-and-heal cycles continuously over 40 days, measuring resistance to delamination after each repair.

“We found the fracture resistance of the self-healing material starts out well above unmodified composites,” says Jack Turicek, lead author of the paper and a graduate student at NC State. “Because our composite starts off significantly tougher than conventional composites, this self-healing material resists cracking better than the laminated composites currently out there for at least 500 cycles. And while its interlaminar toughness does decline after repeated healing, it does so very slowly.”

In real-world scenarios, healing would only be triggered after the material is damaged by hail, bird strikes or other events, or during scheduled maintenance. Researchers estimate the material could last 125 years with quarterly healing or 500 years with annual healing.

“This provides obvious value for large-scale and expensive technologies such as aircraft and wind turbines,” adds Patrick. “But it could be exceptionally important for technologies such as spacecraft, which operate in largely inaccessible environments that would be difficult or impossible to repair via conventional methods on-site.”

Patrick has patented and licensed the technology through his startup company, Structeryx Inc.

The paper, “Self-healing for the Long Haul: In situ Automation Delivers Century-scale Fracture Recovery in Structural Composites,” is published in the Proceedings of the National Academy of Sciences. First author of the paper is Turicek. The paper was co-authored by Zach Phillips, a Ph.D. student at NC State, and Kalyana Nakshatrala, the Carl F. Gauss professor of civil and environmental engineering at the University of Houston.

This work was done with support from the Strategic Environmental Research and Development Program (SERDP) through grant W912HQ21C0044 and from the National Science Foundation, under grant 2137100.