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Materials that "heal" themselves... and more

"Strong as steel" might be a familiar expression, but Suong Hoa works with materials that are just as strong: composite materials.

Hoa -- who is director of Concordia's Centre for Composites as well as the NSERC Industrial Research Chair in Automated Composites Manufacturing -- first made a bid to bring the "Olympics" of composite materials to Montreal back in 2009. He was successful, and the 19th International Conference on Composite Materials rolled into town on Sunday, July 28, running until August 2. At this gathering of more than 1,500 international academics, 40 per cent of the delegates were students -- evidence of the growing popularity of the field among young engineers.

composites2 A composites braiding machine in Suong Hoa's lab.

Composites, which are made from two or more constituent materials, have become increasingly popular in the aerospace, automotive and boatbuilding industries, in green technologies such as windmills, and in numerous other manufacturing processes.

Strength, rigidity and durability -- plus a far lower weight than many metals -- are the hallmarks of some of the latest composite materials. Yet as Hoa explains, there is even more to them than that. He identifies three major developments in his field that hold huge potential for industry.

1) Multifunctional materials
Composites have in many instances replaced aluminum in the aerospace industry; for example, the brand new Boeing 787 has an airframe built primarily of composites.

However, the materials can serve other purposes, too: Hoa says composites can be designed to conduct electricity or heat and can incorporate nano materials in order to become "intelligent" -- able to sense stimulus such as stress or changes in temperature.

2) Automation of composites
"Traditionally, composites have been made by hand," says Hoa. He recalls how, in the 1990s, making composite structures for his industrial partners took many months.

There can be more than 100 layers in a composite structure. Now, thanks to technology like Concordia's Automated Carbon Fibre Placement Machine, the process has been sped up enormously. "It has very big potential," says Hoa. "Companies like Boeing and Airbus are making the switch."

Automation ensures the repeatability of the manufacturing process, so that numerous structures can be produced identically. Also, automation reduces waste and overall costs. Hoa pushes a carbon-fibre sample tube, just over 30 centimetres long, across his table. "No way you could make this by hand," he says. "You have to make sure every layer is laid down perfectly, otherwise you get wrinkles."

3) Self-healing materials
This is perhaps the most sci-fi-sounding development of them all. Imagine a space shuttle able to self-repair damage done by impacts from, say, space debris.

Hoa makes the analogy of a human's biological capacity to heal a minor cut. A micro capsule -- Hoa compares it to a vitamin pill, but much, much smaller -- is integrated into the composite weave. It has a hard shell and liquid inside. If the bigger structure becomes cracked, the micro capsule shell is punctured and the liquid oozes out, then "cures" and seals the crack.

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