An aircraft that can repair itself is the stuff of science fiction, isn't it? Well, not anymore as work is already dedicated to making science fiction science fact in the not-too-distant future.

Engineers from the University of Bristol in the UK hit the headlines during the summer of 2008 by developing a self-healing composite material. Furthermore, in Portugal, a company is working on putting intelligence into materials to enable a monitoring system to detect faults and fatigue in aircraft material.

Professors behind the project

Two professors, Gustavo Dias and Júlio Viana, working at the University of Minho (UM), which is located in northern Portugal, formed Critical Materials SA in 2008.

Today, Dias and Viana are CEO and product manager, and CFO and product architect of Critical Materials respectively.

Dias, who has been working on research and development at UM with Lockheed Martin, Embraer and others, says that the inspiration for the company came from the work that he and Viana were doing at the university. "We deal with a lot of problems in critical materials; Things connecting materials with software and materials with hardware and the way they react with material. We wanted to put some intelligence into those material systems," he says.

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Dias says the formulation of Critical Materials was more like a process rather than a eureka moment. Through their work with the university, they already had contact with the company Critical Software. "Things appeared naturally and were getting to the point that there were obvious connections between the materials, software knowledge and hardware knowledge," says Dias. Initial conversations took place with Critical Software in mid 2007 and just eight months later Critical Materials with the backing of Critical Software became a reality. "Critical Materials has the same values, the same vision and shares a lot of the same points as Critical Software. It was not so difficult to do," says Dias.

Critical Materials' first project is an aircraft monitoring system capable of detecting problems in materials and reporting them, thus potentially saving on maintenance schedules while enhancing safety. "Materials, even when they are smart, are actually dumb," says Dias. "The way to put intelligence into materials is to have the right combination of materials with some properties that we can work with. Some hardware, some type of saturisation and software that will give the connection between the two worlds and give some kind of intelligence to the system."

“Self-healing materials will not be able to deal with sudden, massive damage, such as an explosion.”

Dias explained that the system under development will have a kind of intelligence that will react with material systems and report their status. "The answer is not only for metals or only for plastics but we starting really with composites, in specific critical applications, in applications that the loss of that part can be catastrophic. That's our definition of critical," says Dias.

Describing the system as like an early warning, he says it was not reasonable to consider that all parts of a working aircraft could be monitored.

However, critical and expensive parts as well as those which are hard to get at and maintain would work well for the system and perhaps allow certain maintenance schedules to be extended.

There is both commercial and military interest in the work that Critical Materials is doing. Dias could not be too specific but says: "We are working now with a company with fixed-wing civil and military aircraft." The company is primarily taking the military route because of the lengthy certification process with agencies such as the Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA). "If this works in a military aircraft like a
transportation aircraft, it will pass easily to a civilian transport aircraft," says Dias.

The company is in early stage talks with EASA but there are no concrete developments yet. For military use of Critical Material's system there are a couple of ways to enter the market. "There are two ways in the military. The first one is to try and integrate this into some kind of new programme that will start in 2009 or 2010. The other way is major reconstructions of aircraft that are in very heavy maintenance. Perhaps we can use those aircraft as platforms just to test the system," says Dias, adding: "That's the way that we are starting to go."

Self-healing material

So, what of the self-healing material itself? Well, the pair already have some self-healing materials in the university lab. "We are starting to work with material that is bio-inspired. It can be a composite or a polymer."

He adds: "We have very small channels that work like veins. Inside those channels you have a special kind of material. If you have a defect that is propagating inside the material within the vascular system, then when that material enters contact with the base material system it will react chemically. It will then try to stop it propagating. That's the concept."

“The first project is an aircraft monitoring system capable of detecting problems in materials and reporting them.”

It is early days yet and of course, self-healing materials will not be able to deal with sudden, massive damage, such as an explosion. However, it is expected that the material will be able to initiate a report to maintenance crews for targeted inspection and heal a small defect in-flight and stop or slow down its progress to a more dangerous state. Dias says that the material should be able to heal an area two or perhaps three times before replacement may become necessary.

In terms of development, Dias says that the system is more software driven and will slot in with self-sensing with the first upgrade. Dias says that COTS sensors would not be part of the self-sensing concept and explained that the company was working with putting some kind of electro conductivity into materials so that any deformation would result in the material itself acting as a sensor.

The monitoring system should be out first with another four or five years needed before the interactivity between monitoring and materials will be able to take place. However, because Critical Materials is not developing new hardware its vision should be a shorter path to military and commercial reality. With the ability to work with avionics that are already in place, science fiction does not seem so far away.