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Self-Healing Composites
Nick pointed us to this AP story about self-healing composites, fibrous materials with integrated, fungible glue capsules - so that each stress which breaks fibers also breaks the glue capsules to repair those fibers. Very cool stuff, especially if they could make the glue set fast enough to repair in "real time". The Washington Post has another article about the same thing with a bit more detail.
>A self-healing material sounds marvellous, but the fact is, as in real life, things need to
>break, as part of the natural cycle - if not, there is a potentially greater risk to us.
You're assuming that the material will wear out more slowly. In some cases that may happen, but in many cases it won't- a lot of wearing out is caused by surface effects, and the glue won't help there much.
This technology mainly reduces the chance that the part will catastophically fail- it will not usually increase the life; but it may increase the production yield, which tends to cut product costs without materially affecting manpower levels.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Of course, with the great strides we are making with placing computers in cars and crude AI systems, how long will it be before our car says, "Daddy, I have a booboo on my tailpipe. Can you kiss it and make it better?"
Mas vale cholo, que mal acompañado.
This is somewhat offtopic, but ...
Still further, people often don't realize the extent to which obsolescence is important to the economy - without it, after a few years an industry would become almost obsolete, since all the old equipment would still be in use.
This kind of economy should become obsolent, since it is a waste of resources and does harm to our environment.
By having things break, however, jobs are created,
I'm really tired of this "jobs" argument. If you don't have to buy new things because the old ones do not break, you need less money, thus you can take a part time job without a loss of life-qualitiy, and the number of jobs is preserved.
and improvements are made
I'm very sure, they are made anyway. But these days you have to buy the new things because the old ones breake. With things not breaking, your freedom increases, - your freedom, not to buy.
There are many, many things to do in this world, think of the irrigation of deserts, decreasing hunger and poverty, making software bug-free. - We sure need no industry that relies on things breaking to sell new products.
The idea of embedded glue as a composite repair mechanism has been around since the '60s (Courtaulds, UK, in reference to some early carbon fibre laminates, back when the UK had an aerospace industry).
The tricky aspect is that most cure mechanisms also involve a volume change. Get it right and you glue the crack shut. Get it wrong and you've driven a wedge in to make it bigger.
Of course in your meteorite shield, the macroscopic strength (structural) is less important than the microscopic scale (impact resistance), so the idea could still work well.
As someone how works with composites I would like to take this time to point out of few things to the less experienced and therefore point out why a "self-healing" composite of this type is not really that advantageous.
Composites are used mostly because they have superior specific strengths and stiffnesses to more conventional materials like metals. This means that you can make something out of composites do the same job as something out of steel but have it be significantly lighter. This is usually a big advantage.
Composites also have superior fatigue characteristics to most metals. Fatigue occurs because cracks grow in a material as it is loaded cyclicly. Except steel most metals to not have infinite fatigue life. If you have an aluminum bar that takes 10000 lbs to break in one shot, but you load it cyclically at 2000 lbs, eventually this bar will break. Composites don't have much of a problem in fatigue however because cracks end up hitting material interfaces as they try to grow. A crack can only grow so far before it hits a fiber and to move on it has to break this fiber which is pretty difficult. In short if you put a composite sample into a machine to do fatigue tests on it, it is not uncommon for the metal fatigue machine to break before the composite sample does.
Why is all this important? Because this "self-healing" ability is only good for small cracks and it has inferior material properties to a non-healing composite. It helps stop fatigue which is not a big problem in composites anyway. What composites need is a self-healing ability that can cure delaminations and other large scale failures in the composite. This will be important an big news because it is the introduction of large scale problems within a composite that causes the most damage in composites.
So far I've gotten all my Karma from telling people they are wrong... :)
Just think -- self-healing condoms! No longer worry about dying from ripping one of those little bastards.
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Do daemons dream of electric sleep()?
I hope you aren't a structural engineer. It seems obvious to me that lattices are going be be stronger against some kinds of stress than solid blocks. A material that needs to be able to tolerate some amount of tourque (sp?) or provide flexibility (like the joints of a space suit) or that by design you would rather have develope small cracks that heal rather than hold inflexible until it shattered (rails, perhaps?) is going to have the potential for improvement by this process.
rigidity and strength are not always synonymous. Nor, for that matter are absolute strength and suitablity for a job.
Kahuna Burger
...will work for Chick tracts...
Yes, you're right. Yes, that goes at least as far back as Henry Ford, but you're also right that it's for a completely different reason.
There's nothing wrong with a company selling products that are planned to fail after a certain time, because another company can come along and sell one that won't. If you're the kind of person who wants to keep something a long time, you can usually find a product that will last longer... of course it might cost a little more.
That's why I buy Hondas. I plan to drive my one-year-old off to college in the Odyssey I have now.
You are in a maze of twisty little passages, all alike.
As a post-graduate working on dwindling research grants from the American, Canadian and Australian government, I can only say this breakthrough is really a great relief to both me and my team.
It is my belief that while the interest and funding for our project was thriving in the beginning - our lack of working prototype has really set us back. I can only hope this sets us in the right direction again.
The security level of many areas of our research has steadily decreased from eyes only to 'round'-filed. So I can share atleast a few examples of our failed attempts with you.
But failed almost every stress test:
Many top brass exhibited concerns over human rights issues with our stress-tests; Combining biological matter with computer equipment and our flex-resin technology should orginally have been done with primates (They tell us now!) - but we opted for volunteers; which angered the US officials to no end. In the end, many prototypes were actually taken home by the staff and used as ashtrays
Ace
As i see it, i buy things (say a TV) to use them for personal gain (easier work, entertainment, aestetic pleasure), not to stimulate the economy. If a new product comes out with an improvement that i consider worth my hard earned bucks (for TVs: color TV; remote control; 3D imagery) i will buy a new one. Otherwise i'll stick to the old one (why ditch my money for a new TV just because it now comes in a semi-transparent purple plastic model???). Actualy, durability is one of my top criteria when buying new equipment.
Beyond this, there's also the fact that a whole class of things cannot have built-in obsolescence:
"Ladies and gentleman, this is the captain. I regret to inform you that our airplane has reached it's built-in obsolescence deadline of 10 years. The engines are falling-off so we will have a slight delay."
I would think that it would be easy enough to color the repairing resin a contracting color to the original material so that as more and more of it is used the object would slowly change in appearance. This would also help in the inspection/evaluation function to tell when something is weakened too much for continued use
This is similar to an idea, some fiends and I played around with at Univerity. I admit we stole the idea from canoeist/kayekers, who use two part foam for wilderness repairs. The idea was for self healing hull's to protect space craft from micro-meteors.
The best way to describe it is layers of "bubble wrap", alternating with layers of woven Carbon-Kevlar, the bubble's in the bubble wrap would contain a binary (two part) foam or resin. When the two or more 'bubble wrap' layers are breeched the binary components interacts and forms foam or resin, which cloggs up the fissues or holes.
Near real time would be useful but, as seen with superglue, you need a bit of time before you want it to heal. Keep in mind that the stress crack will open and separate and you want the reair to happen aftre the stress cycle so the repair is in the unstressed position. We don't need a material whee the stress cracks fill in and hold the material in the stressed position
Well it's good to know that Science is getting all the physical stuff out of the way BEFORE making AI, so any rouge AI can just build a robot made out of self-repairing laser-deflecting EMP-proof armor.
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ADVENTURERS! - ANTIHERO FOR HIRE - CARDMASTER CONFLICT
Saving space in the material for glue capsules takes away from the soundness of the material. Why not just put something stronger in the glue's place from the beginning so that the material doesn't break at all?
Another simple composite, concrete, is wellknown long lifespan.
It also self-heals. When it has set, a significant fraction of the material is still unreacted. Microcracks admit water and restart the setting process, reenforcing them somewhat. You can even grind it up and cast it a second time (though the second-cast will be a LOT weaker).
The phenomenon has been known for a while. I wonder if it was the inspiration for this work?
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
I'm reminded of the "Acme Inescapable Rope" used to tie up Roger and Jessica Rabbit.
Think of spider-silk adhesive as the inclusion. Cut it and you end up with the scissors stuck in the rope and the layers of rope bonded to each other, etc.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
The composite can only fix the crack once, and the forces that caused the crack are still there, so the composite WILL break again. The only solution is a better design that won't put so much stress on that composite or replacing the composite with a new one. Further, the glue is only a quick fix, a hack, that should only last until an engineer is available to fix the material with a new one. Someone mentioned earlier that the glue should be colored so that it indicates cracks (though it would be very disconcerting to go over an older bridge and see bright green spots on all the girders). While the technology is cool, it's a wrong step in terms of safety and in terms of proper design in engineering applications.
I remember watching a show where an airplaine's skin was fitted with glue capsules, so it actually "bruised", making a clear indication to mechanics where the plane's been hit.
A self-healing Vette would be just great for someone who live where it was a rather constant temperature all year.
But what if you live in say, the Midwest, or in south central Texas (or anywhere else that applies) where temperatures can reach extremes? Will my Vette stop healing itself in February when it's -10 degrees F outside? Or will it never 'set' properly if it's 130 in the shade? How about on an airliner that takes off from Phoenix in August and climbs to 40k feet where the temperature is possibly well (read VERY MUCH) below freezing? Will this extreme change in temperature affect these materials?
These are just temperatures, what about vibration during the drying of the resin. What about humidity or rain? Then consider the combinations of these.
This is an amazing technology, and I realize these questions will be answered with more research and further testing, but the article never really metioned these possible limitations.
I suffer from apathy, but I just don't care.
They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.-Franklin
Adding glue will not necessarily make them more fragile, it will in fact make probably make them tougher in the material science and engineering sense of damage resistance. It will make them weaker (lower specific strength) and probably more flexible (lower specific stiffness).
So far I've gotten all my Karma from telling people they are wrong... :)
The compound retained 75 percent of its original strength after the cracks had healed for 48 hours, the researchers reported.
So how much difference is there compared to cracks in conventional materials? Does anybody have a number on that so that I can appreciate the usefulness of this?
EagerEyes.org: Visualization and Visual Communication
That most of the repairs that this type of material will fix/solve are hidden within the layers of the composite and just weaken the material gradually until a catastrophic failure takes place. I'm sure they'll get the curing time and temperature problems solved now that they have an initial test material to start from. This will be very important in composite propellers and fan blades. It would be interesting to know if you can tell the difference between a fixed and unfixed defect in X-ray inspections.
Hmm.
A self-healing material sounds marvellous, but the fact is, as in real life, things need to break, as part of the natural cycle - if not, there is a potentially greater risk to us.
The potential that this gives is that machinery will be kept for many years - and since it won't break, it will be kept far past the point where it is safe to use.
There will be a lot of obsolete technology in use as a result in future, which will, at best, mean the users of the technology will be disadvantaged, and, at worst, subjected to inferior safety standards compared to modern machinery.
The fact is that much of the improvements made in society come through built-in obsolescence; without things breaking, we would be stuck using the technology of the 1940s - and no-one would want that.
Still further, people often don't realize the extent to which obsolescence is important to the economy - without it, after a few years an industry would become almost obsolete, since all the old equipment would still be in use.
By having things break, however, jobs are created, and improvements are made - it is far better overall to have a rolling replacement cycle than to persist with the same crappy machinery forever.
What happens when you come to demolish the structure? Is this going to be like throwing away a boomerang?
Excuse me if this sounds somewhat foolish, but wouldn't 'real-time' be somewhat useless? A force that is breaking something may be continuous.
Also, this is limited use. Like the articles say, the capsules will eventually be used up. Before this is useful, we'll need to find how much damage this can take (host material, depth, strength, width, number of times?).
We won't be able know how long it will last in a real situation. Testing can only do so much, and we may come to depend on it.
Glad to see that you finally got a chance to make a comment that ties in with your sig.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
No mention of how much strength is lost by adding the glue. So, is this going to make the materials more fragile (for the same section/volume/mass)? Anyway retaining 75% of the original strength is no great shakes, especially in safety critical applications.
Frankly, we'd be better coming up with a composite that highlighted damage (glowglue?), rather than trying to paper over the cracks.
If you were blocking sigs, you wouldn't have to read this.
The same goes for fully composite aircraft.
Case in point - the Aerotek / Atlas developed 'ACE' all composite turboprop trainer
(very similar to the Pilatus PC9), had an effectively unlimited fatigue life.
Not too common, though, because very few aerospace mfgs are willing to commit to
pure composite airframes - they merely use composite panels on conventional structures
or complete composite components, such as fins, ailerons, etc.
The only others around are homebuilts, and (with all due respect to their builders),
these are not always the best designed or built structures around!
Ah! there is one notable exception I almost missed: See here
You can even repair a broken pixel in a TFT Flat-Panel display by putting into an oven at 350degrees Fahrenheit. I don't recommend this, of course, because all the other components of your laptop will melt!
... the main color of your car is Bondo.
- Jeff Foxworthy
Il'l never forget when a friend was shopping for a Saturn: The Salesguy wanted to demonstrate the composite panels around the Saturn sides. He went to the "tried and true" floor model, and kicked in the door [again], but this time, it didn't pop back out. Was his face red!
An odd sidenote about having composite doors is that you can't stick magnets (ie door signs) against the doors or quarter panels, but you can stick them on the hood or trunk, which are still metal. (At least on the SL-2.)
In Nature Magazine.
SIG: TAKE OFF EVERY 'CAPTAIN'!!
So what if a development comes from military R&D?
Just because microwave ovens came from military radar...does that make the food you cooked in there...tainted some how?
Nope, it doesn't. But there is a taint in some people's minds because they have forgotten that the freedom that people in North America, Russian, Western and Eastern Europe enjoy was defended through the force of arms and military technology.
Anyway, self-healing is one thing, these blocks go one further, and the more they take punnishment, the stronger they get.
.. if only.