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Boeing's 787 Dreamliner uses composites for various airframe components.  (Source: Boeing)

UV Light Shows Resin Bleeding into Fracture  (Source: Gizmag)
Future composite aircraft could have a circulatory system filled with the resin

Miniscule cracks and flaws in the airframe of commercial and private aircraft can lead to catastrophic failure of the aircraft leading to loss of life and property. Commercial airlines routinely inspect their aircraft for damage and issues that could lead to an accident. The problem is that small cracks and light damage can be difficult to detect and impossible to see with the naked eye.

Aerospace engineers from Bristol University have developed a new method to complement routine visual inspections of commercial aircraft made from composite materials such as the Boeing 787 Dreamliner.

The researchers have devised a way to fill the hollow parts of composite aircraft with a self hardening resin. When the airframe is damaged the resin would bleed out of the hollow spaces into the crack and seal the damaged area with enough strength to maintain flight and safely land. The engineers also say that future aircraft could have the resin moving continuously through a circulatory system built-in to the airframe.

The resin doesn’t return the airframe to 100% of its strength, but the researchers say that the resin would allow the damaged area to regain 80% to 90% of its former strength. The process used by the engineers is likened to the process the human body uses to heal after a cut. In the body, blood leaks into the damage tissue where platelets form clots to stop bleeding and a scab forms to aid in healing and protect the area. In the engineers system the resin is the blood and the hardened resin is like a clot and scab protecting the area.

The resin the engineers propose to use would have a blue color allowing ground crews to readily identify areas where the resin has affected repairs to small areas of damage. Project leader Dr. Ian Bond said, “This approach can deal with small-scale damage that’s not obvious to the naked eye but which might lead to serious failures in structural integrity if it escapes attention. It’s intended to complement rather than replace conventional inspection and maintenance routines, which can readily pick up larger-scale damage, caused by a bird strike, for example.”



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RE: Sounds great, but...
By Keeir on 5/30/2008 3:31:51 PM , Rating: 2
Composite structure is typically a sandwich of high strength layers of graphite fiber "tape" with a middle of a shear carrying layers of honeycomb type foam.

The idea (I think) is to fill the honeycomb with resin. This would significantly increase the wieght of the aircraft and the system to "pump" it or monitor it would only not really save much wieght.

My main concern is that this may repair sections to 80-90% strength, but the actual repair would be invisible to all but fairly sophisticated inspection methods. Therefore, no permanent repair (100%) would be made and potentially this could cause problems since engineers may have originally counted on the structure being at either 100% or 0% (visiblely damaged).


RE: Sounds great, but...
By Solandri on 5/30/2008 5:35:36 PM , Rating: 2
The whole point of using honeycomb is to provide stiffness without weight. If you're filling the honeycomb with material, it defeats the purpose of using honeycomb in the first place.

We covered self-repairing composites when I took courses in it 12 years ago. At the time it was theoretical so I don't know if this stuff works like the theory back then. But the theory goes: Composites are just strong fibers (glass or carbon) held together by a resin matrix. The fibers provide the strength, the resin transfers load between fibers. When it fails, the fibers detach from the the resin, like nails pulling out of wood.

You can repair it by infusing the damaged area with new resin. Most resins (like epoxy) come in two liquid components which solidify when mixed. The theory for self-repairing composites was to imbed bubbles of these two liquids within the resin. When you get a significant fracture, some of these bubbles are burst. The liquids seep out, mix, fill any holes, and solidify, thus re-bonding the fibers to the matrix.


RE: Sounds great, but...
By GTVic on 5/31/2008 12:57:28 PM , Rating: 2
If you fill the entire honeycomb with resin then you defeat the purpose of the honeycomb. So that does not sound correct.

But if the material would have to crack all the way through to the resin before the resin would react then at that point wouldn't you have damage too severe to be repaired?


RE: Sounds great, but...
By jRaskell on 6/2/2008 12:08:20 PM , Rating: 2
quote:
but the actual repair would be invisible to all but fairly sophisticated inspection methods.


From the article:

The resin the engineers propose to use would have a blue color allowing ground crews to readily identify areas where the resin has affected repairs to small areas of damage


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