Self-Healing Composite Can Make Airplane, Automobile and Spacecraft Components Last for Centuries
For Immediate Release
Researchers have created a self-healing composite that is tougher than materials currently used in aircraft wings, turbine blades and other applications – and can repair itself more than 1,000 times. The researchers estimate their self-healing strategy can extend the lifetime of conventional fiber-reinforced composite materials by centuries compared to the current decades-long design-life.
“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 Jason Patrick, corresponding author of the paper and an associate professor of civil, construction and environmental engineering at North Carolina State University.
At issue are fiber-reinforced polymer (FRP) composites, which are valued for their high strength-to-weight ratio and are commonly used in aircraft, automobiles, wind-turbines, spacecraft and other modern structural applications. FRP composites consist of layers of fibers, such as glass or carbon fiber, that are bonded together by a polymer matrix, often epoxy. The self-healing technique developed by the 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 says. “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 two additional features. First, the researchers 3D-print 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. Second, the researchers embed 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 re-bonds delaminated interfaces – restoring structural performance.
To evaluate long-term healing performance, the team 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. In other words, the researchers cracked the material in the exact same way, healed it, and then measured how much load the material could handle before delaminating again. And they did that 1,000 times, an order-of-magnitude beyond their prior record.
“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. The 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,” Patrick says. “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.”
The study also shed light on why recovery slowly declines over time. With continued cycling, the brittle reinforcing fibers progressively fracture – creating micro-debris that limits rebonding sites. In addition, chemical reactions where the healing agent interfaces with the fibers and polymer matrix decline over time. Even so, modeling suggests the self-healing will remain viable over extremely long time scales.
“Despite the inherent chemo-physical mechanisms that slowly reduce healing efficacy, we have predicted that perpetual repair is possible through statistical modeling that is well suited for capturing such phenomena,” says Kalyana Nakshatrala, co-author of the paper and the Carl F. Gauss Professor of Civil and Environmental Engineering at the University of Houston.
Patrick has patented and licensed the technology through his startup company, Structeryx Inc.
“We’re excited to work with industry and government partners to explore how this self-healing approach could be incorporated into their technologies, which has been strategically designed to integrate with existing composite manufacturing processes,” Patrick says.
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 Jack Turicek, a Ph.D. student at NC State. 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.
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Note to Editors: The study abstract follows.
“Self-healing for the Long Haul: In situ Automation Delivers Century-scale Fracture Recovery in Structural Composites”
Authors: Jack S. Turicek, Zach J. Phillips, and Jason F. Patrick, North Carolina State University; Kalyana B. Nakshatrala, University of Houston
Published: Jan. 9, Proceedings of the National Academy of Sciences
DOI: 10.1073/pnas.2523447123
Abstract: Nature’s structural composites, such as bone and wood, achieve mechanical performance through hierarchical multi-material design. Though, their real vantage lies in the exceptional ability to repeatedly heal after damage. Synthetic fiber-reinforced polymer (FRP) composites also leverage material hierarchy via fibrous reinforcement encapsulated within a polymer matrix, maximizing stiffness and strength. However, the layered architecture of laminated FRP composites makes them vulnerable to interlaminar delamination—debonding of fibers from the matrix—which significantly compromises structural integrity. Recently, we introduced a self-healing strategy via in situ heating, where soft yet tough thermoplastic inclusions achieve interlaminar fracture recovery via polymer chain re-entanglement, i.e., thermal remending. Here, in our latest embodiment, by automating in situ thermo-mechanical experiments, we achieve an order-of-magnitude enhancement in self-healing repeatability—reaching an unprecedented 1,000 cycles. Healing begins at 175% and slowly declines to 60% of the mode-I fracture resistance of a plain (non-healing) composite, revealing unique chemophysical mechanisms that govern this behavior. Both fiber-debris accumulation in the molten poly(ethylene-co-methacrylic acid) (EMAA) healing agent, and waning interfacial chemical reactions between the EMAA and epoxy matrix, contribute. A Weibull distribution capturing this complex fracture recovery predicts an asymptotic healing limit above 40%, suggesting sustained repair is possible. Translating these newfound thermal remending results into real-world context, a modest quarterly self-healing schedule could maintain interlaminar fracture repair of FRP composites for over 125 years—well beyond the typical design life of many modern structures including aircraft and wind turbines. Thus, this latest self-healing paradigm effectively eliminates delamination as a failure mode.
