The team believes the latest technology can significantly extend the lifespan of structural components such as wind-turbine blades and aircraft wings. Their findings are detailed in Nature Communications.
In a statement, Jason Patrick, corresponding author of the research paper and an assistant professor of civil, construction and environmental engineering at North Carolina State University, said: “Researchers have developed a variety of self-healing materials, but previous strategies for self-healing composites have faced two practical challenges.
“First, the materials often need to be removed from service in order to heal. For instance, some require heating in an oven, which can’t be done for large components or while a given part is in use. Second, the self-healing only works for a limited period. For example, the material might be able to heal a few times, after which its self-repairing properties would significantly diminish. We’ve come up with an approach that addresses both of those challenges in a meaningful way, while retaining the strength and other performance characteristics of structural fibre-composites.”
Laminated composites are made from layers of fibrous reinforcement, such as glass and carbon-fibre, and bonded together. Damage most often occurs when the ‘glue’ that binds these layers together begins to delaminate. The research team addressed this by 3D printing a pattern of thermoplastic healing agent onto the reinforcement material. The researchers also embedded thin ‘heater’ layers in the composite. When an electrical current is applied, the heater layers warm up. This melts the healing agent, which flows into any cracks or microfractures within the composite and repairs them.
“We’ve found that this process can be repeated at least 100 times while maintaining the effectiveness of the self-healing,” said Patrick. “We don’t know what the upper limit is, if there is one.”
The printed thermoplastic is claimed to enhance inherent resistance to fracture by up to 500 per cent, and the healing agent and heater layers are made of readily available materials.
If incorporated into aircraft wings, the internal heating elements would allow airlines to stop using chemical agents to remove ice from wings when aircraft are on the ground, and also to de-ice in flight.
“We’ve demonstrated that this multi-functional technology works,” said Patrick. “We’re now looking for government and industry partners to help us tailor these polymer-based composites for use in specific applications.”