Posting in Aerospace
Henry Sodano is bringing Terminator back into the lab. Researchers at Arizona State University talked to SmartPlanet about their self-healing material.
I'm not ashamed to admit this, I loved watching Terminator. The cyborg assassin (a.k.a Arnold Schwarzenegger) always recovered from damage, no matter what happened. It turns out, the ability for material to really do this, isn't that far-fetched after all.
Engineer Henry Sodano brings a little of James Cameron's science fiction movie into his lab at Arizona State University.
Sodano told me about how his self-healing material can sense when there's trouble.
Essentially, Sodano thinks his polymer should be as smart as our bones. The material must know when it has a problem, know how to stop the crack from causing more damage and be able to fix it.
It's the sensors embedded into the polymer material and external computer system that give the self-healing material the brains to know what's going on.
Sodano talked to SmartPlanet about his self-healing polymer.
SmartPlanet: So what exactly does your material do?
HS: When a crack forms in the material, it can recover the plastic deformation and heal itself. It does that without anyone in the loop.
I am working with shape memory polymers, which have the ability to return to the geometry they are initially cast into. In the particular system, I have devised a network of fiber optic cables which are distributed throughout the material. They are used to sense damage and deliver stimulus to allow it to adapt and heal. For instance, as the damage propagates through the material, the fiber optics fractures allowing the light to be emitted into the polymer directly at the sight of damage. The light gets absorbed by the polymer and creates heat which causes a local reduction of the polymer stiffness causing the cracks to blunt and stop propagating. The thermal energy is then used to induce the shape memory effect to recover the original shape and properties of the material.
SmartPlanet: This material seems cool, but what can it be used for?
HS: I generally perceive its integration into fiber reinforced composites, typically used in aerospace structures, wind turbines and satellites. It can be used essentially in a diverse set of applications. The material without my feedback system is brittle, so it there's a crack moving through, the material readily breaks.
The material essentially acts like bone which can sense a fracture, adapts to try to stop its propagation through a range of mechanisms and then heals.
That's the terminator aspect. He was able to reform his body. This polymer can return to its original geometry. When we take away the heat from it, it will be as strong as it was originally.
It is a complex series of events: sense the crack, stop its propagation, recover any deformation and reload it. The material has 96 percent of its original strength.
SmartPlanet: Can you talk about some of the possible applications?
HS: It can be used in satellites or aircrafts. If a crack starts moving through material, you want to stop it immediately. Or else some accident might occur. We'd like to stop propagation of damage when you don't have access. It can also be used to fix civil infrastructure and be used in prosthetics so a simple crack won't result in another surgery.
These fiber optic cables run through the polymer. One of the biggest challenges is how do you identify where the damage is? You might have a small crack. It's smaller than a dime in a structure the size of an aircraft. How do you identify where the crack is without a human or prior knowledge? How do you find the damage? What do you use for regeneration?
We solved that through this fiber optic network. It needs some interface to perform the sensing [so there's an external computer at work].
SmartPlanet: Aren't other people trying to make self-healing material too?
HS: Self-healing materials have been explored. Ours is the first one that has a sensing component in it thus making it a closed loop system. It can actively heal damage, instead of passively healing it. Existing materials uses a similar concept to epoxy. I'm sure you are familiar with epoxy, mix part A and B such that it polymerizes and acts as glue.
In prior forms, as damage passes through the materials it cause part A and B to come into contact thus reacting and essentially gluing the material back together.
[This technique is] not very advanced. There’s and uncured polymer in the material, so it leads to a reduced of the virgin material’s strength. In our material, we sense where the damage is, then apply controlled levels of energy to heal the damage. There’s a computer doing the brain work.
SmartPlanet: What's the importance of this research?
HS: The failure of structural materials is a huge problem. We couple structural health monitoring with self-healing. No one has combined the two before. We can sense damage and then respond to it. It only takes seconds to stop the damage.
SmartPlanet: Who funded the research?
HS: The research was funded by the National Science Foundation. There's a lot of work to do to find out how we can optimally do this. How do you utilize the system? In terms of demonstrating that it can be used, the material is fairly well demonstrated now. However, the fundamental mechanics of how it returns its strength is less known. It makes sense why it works, although some of the healing mechanisms are a little less known.
We don't actually recreate the polymer bonds that were broken. We believe we are changing the shape of the crack. What happens is when you have a crack, it's very sharp. It has a lot of strain energy at its tips. It tries to fracture the next molecule. If it's a blunt crack, the energy is distributed over a larger area. We think we change the geometry of the tip. This modifies the energy of the tip. But we don't know the exact mechanism and still need to investigate more.
Dec 8, 2010
He needs a better tack than breaking optical cables, to detect damage and deliver the "cure" -- I'm assuming that once a cable breaks, it will stay broken. Even if the ends were "perfectly" lined up once more by the heating, there would be a transmission fault in that location that, presumably, would initiate the healing cycle again -- or necessitate blocking that area from the scheme. I suggest microwave radio heating instead. We (and he) would still have the problem of sorting out sensing signals and delivering healing signals, but wire-borne radio could cycle pairs of wires between sensing, and a self-monitoring signal that would detect and store the normal range of reception, via sensing the EM fields generated by the other wire in the pair. Wires would be tougher than thin glass or plastic light guides, and spreading gaps between "pairs of pairs" would change the collected responses. A trend in that change, or changes that did not coincide with intended flexing of the material, could then be "treated." Heat treatment could consist of the delivery of two half-doses between two criss-crossing layers, that would add up to a full dose at the damage point. That point would then heat up past the recovery point, while "pain" in the area would induced the machine to keep the area static until the temperature was again lowered. Another of radio's strengths is that the hysterisis of the material could change with nearby material density, and with the distance to other wire pairs; a feature not available in the light guides. That could make the material much more sensitive to encroaching stress. With paired and criss-crossed wires, the material might also double as a passive touch sensor matrix. I admit that I'm thinking more in the line of flexible materials on a moving frame, ala robot skins; rather than rigid materials such as turbine blades. The later would also be challenged by the healing process, because they are virtually ALWAYS under stress, and so it would be hard to relax the area. Note that neural nets would likely be the best way to manage this scheme; lots of inputs, but only a few correct responses. Nets are also fabulous at detecting faint or confusing patterns. They could also provide flexibility and redundancy, because of the way the "senses" would overlap with each other, when pair wires switched roles. The inputs could include movement sensors as well, to prevent unneeded "healing" cycles. Also, one would not have to analyse the signals to death to decide. Nets would do that work invisibly. Note also that MY scheme doesn't necessarily lower the strength of the material, nor does it create portions that, once healed, are no longer capable of healing themselves. Finally, note that I'm providing this input voluntarily, for no charge. AND that such provision makes nonsense of the urge corporations have, to always charge for any intellectual capital. WE ARE the intellectual capital of the world, one thought at a time, and the urge to charge for originality will drive such capital into hiding. There will come a day, when this adds up. BTW, the Terminator comparison is bunk. The T-101 was clothed in a suit of LIVING flesh, which healed itself using Life v1.0 technology. The only way it could "mend" its metal skeleton was to pull off broken pieces that inhibited movement. The rest of its "healing" was some form of adaptive programming around broken internal connections. The T-1000 was far beyond any of these ideas.
The Cyberdyne Systems Series 800, Model 101, otherwise known as the T-101 (Arnie) was *NOT* self healing. It had redundant systems and could continue to function depending on the amount of damage sustained, but as more damage occurred, it became less functional. Now, the Model T-1000 is made from a nanomorph mimetic poly alloy substance that can reform from most damage. This terminator, along with the T-1001 and the T-X all have this similar morphing/healing ability. But we need to be clear...the T-101 series 800 terminators could only heal their external skin, not their mechanical skeletal structure. Nor could they heal the skin around their eyes.
Sounds like a great idea, and perhaps could be used in the Boeing Dreamliners. Although I am thinking very old technology, electronics technicians can tell where there is a malformed high frequency transmission cable by simply sending a signal along it, and measuring where the reflection comes back from. No doubt, the same sort of crack detection could be measured using light and fiber-optics.
This is marginally useful for space bound projects. Polymers do not fare well in that environment. What is necessary are nanobot graphene manipulators and re-cross linkers. These tiny bots would walk along the graphene thin films and re-weave broken lattices... those could fix micro-meteor damage, and thus repair tiny air leaks, with a material strong enough to stand up to spacecraft use. The technology as described in this article is more integrated than previous efforts at the same function, but self repairing polymer have, for instance, already been demonstrated for fighter aircraft cowlings, using a Nd:YAG laser with a total internal reflection interferometric crack and occlusion detection system. It works, but again, has limited application for space. Also, both the interferometric (described by me here) and the integrated composite versions (of this article) are ...expensive. Did you ask him how much per square meter his technology would cost to add to some application? Ouch. For robots who do fragile nondurable applications, such as clean room operations, this would work, but then... in that environment, you wouldn't need it.
Wow! Does this mean, in the near future we'll be able to see terminator in our real life !!!??? Rajesh, http://www.unichost.com