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Tracking the Cracks
Roland Piquepaille writes "Israeli physicists from the Weizmann Institute have used a new approach to study how materials break. In a short news release, brilliantly titled "Breaking news", they explain their new method for analyzing the progression of a forming crack. The news release even says that it could have help engineers predict 'exactly how much pressure the levees protecting New Orleans could withstand before giving way.' This method could be used by engineers and material scientists in a vast variety of applications."
never design something so it will hold exactly what it needs to stand up against. Unless you're building for suicidal adventurers, people will appreciate headroom. Especially people behind levees...
Plumbers should especially pay attention.
No existe.
In the article they say taht they have applied their method to a variety of materials, namely plastic, glass and metal. There is a common thread there though, in that all three are higly regular materials. In an earthen levee, or even a contcrete one, the materials used to make are way more irregular than what they have tested their methods with. It sounds like the connection to New Orleans levees is really premature to me.
Another Roland "story"...
I'm currently involved in the making of 3D nano devices. One of the steps involved in the making of these things is the breaking of a silicon wafer. This is currently the least reliable step in our process, and we sure are very interested in ways to improve this.
-- Cheers!
I nominate this discovery for the title of highest ratio of actual importance to perceived importance.
You have tried to support your argument with faulty reasoning! Go directly to jail; do not pass Go, do not collect $200!
The news release even says that it could have help engineers predict 'exactly how much pressure the levees protecting New Orleans could withstand before giving way.'
No, it doesn't. That's a rhetorical question in the first paragraph.
There was a program about the Orleans aftermath over here in the UK (it was an edition of 'Horizon' on the BBC), which showed not only that the levvies had only been built for a smaller scale hurricane (not surprisingly...), but also that the designers/builders hadn't taken into account the clay-like consistency of the soil they were being laid into and so they literally just got ripped straight out of the ground.
Talk about missing out engineering 101. Idiots.
The question was not *IF* a hurricane would flood New Orleans, just *WHEN*.
Experts had been warning for this for years but somehow the levees were not reinforced.
This will just give manufacturers of various products another excuse to keep using plastics for high-stress and load-bearing components, which fail at about 1% the lifespan of metal parts, just to increase the profit margin a few cents.
"Scientists all over the world have experimented with crack(ing)"
God spoke to me.
I've found that a good way to stop a crack from spreading is to drill a hole at the leading edge. Then use epoxy or whatever on the crack itself.
Maybe a bit off topic, but could be useful.
Be heard || Be herd
These people crack me up.
I hope the title was meant to be punny, because a model on cracking is nothing new. There are currently many models that work for crack propagation in composites (of metal, polymers and amorphous materials). Every research groups CLAIMS that their model allows them to gain the best insight, because saying anything else:
forfeits further research dollars.
Until the model is explained in further detail and some source code is released, rather than the typical hand-waving, hype and money generating BS, this "breaking news" is nothing but hype.
-PhD student. Metallurgical Sciences.
... for they let in the light." - Spike Milligan
"All you have to do is be fragile and grateful. So stay the underdog." Chuck Palahniuk, Choke
There is one thing about your post that just makes the whole topic much more annoying. Katrina was a level three hurricane by the time it could do any damage. The levees were rated for a level three hurricane. Thus they should not have been breached. Unfortunately, we are talking about engineers here and they usually have to argue about everything.
Ooo man the floppy drive is broken. No wait. The computer is just upside down.
You should patent that.
It's not like it has any more prior art than many other brilliant recent patented "discoveries."
Why is this article posted on /.? At best this is a report of a minor advance in a well established field. Hundreds of such advances are made in every field every week. Yes, PR department at Weitzmann Inst called it a breakthrough but that doesn't make it into one.
Is it possible to limit the science postings to real science news? Maybe have editors who know the field evaluate the postings before hand.
2000 years too late, the veil split already.
If my call is important, why am I talking to a recording?
This article was a disappointment - the science of fracture mechanics is at least a half century old, and quite well developed. It *is* a reasonably hard problem to predict crack growth, direction, speed etc in metals (say in an aeroplane structure) but there is software that'll do it, given a big computer, a good FE model, plenty of time, and lots of good material data (usually at least one of these is missing, in my experience...)
However, my quick read of the aricle did not enlighten me at all as to what these guys claim to have done differently. To be honest it wasn't even that clear what specific fracture mechanics problem they had set out to solve.
Or maybe I've drunk too much Sunday night scotch - I dunno...
The engineers had taken into account the soft soil and the levees were designed to go through this and into more stable soil. However they were not set as deep as the design called for. This is not a design issue, it's an issue with the contractor and inspectors. It is possible that there were also design issues that compounded the problem but I have not heard of any major ones. Incidently you say "clay-like soil consistency" like it's a bad thing. Stable clay soils are exactly the type of earth you want to construct earthen levees, damns, subgrade, etc. out of since it compacts so well and won't move once it is compacted. This as opposed to the material the levees were built in that had a lot of biological material in it and was very unstable.
So when do we in the rest of the world get to kick ours out? It's been 50 years, and I'm still waiting.
All I can say is, thank god for Khatami.
I thought this was going to be about tracking people who crack software.
This is only true if your engineers are completely incompetent and mix the concrete incorrectly in places. Otherwise, concrete is much more regular at microscopic level than glass or plastic, which are both amorphous solids. And if your engineers are that incompetent, a good model for cracking is not going to save you. As to larger-scale irregularities, they're generally irrelevant if you know the structures of the component grains or regions.
:-P
We already know the strengths of the materials we use to build things, because we test them beforehand. The reason new models are important is that they give us a better understanding of _why_ the strengths turn out the way they do.
P.S. A +5 insightful attached to an assertion that a mostly crystalline solid is less ordered than an amorphous solid makes me cry inside. Everyone makes mistakes, but moderators aren't supposed to encourage it
...it's really a sad day for America when we require a goddamn ACT OF CONGRESS to make our DVD players work properly. ~
It used to be the running joke that any scientific research would claim to possibly be leading to a cure for cancer. Now I guess the new paradigm is that it can be fixing the New Orleans problem instead.
Brackets contain world's first nanosig, highly magnified:[.]
Yes, because the problem in New Orleans was the precision of measuring the inadequate levees. It couldn't possibly be that the Federal Corps of Engineers built levees that , then claimed they failed because they weren't designed to stand a category 5 hurricane.
--
make install -not war
The people designing pants should also be wary of plumbers. The force of their cracks cannot be denied!
They failed due to base erosion caused by overtopping and/or poor 'transition points' where embankments went from natural earthen mounds to man-made concrete slabs. Has there been something more authoritative (that included cracking) since the ASCE's report?
Maybe have editors who know the field...
That's a good one! Hahahaha....
They don't exactly carry the May issue of "Physical Review E" on the local newsstands, and the press release came out this month, so nobody knew about it... so no, it couldn't have helped to predict anything.
Plus they already knew how much the levees could hold. Katrina exceeded that.
(Yes, it weakened to a Cat 3 as it made landfall, but it was for all intents and purposes a Cat 4 storm as it approached, storm surge and all.)
"Win treats sysadmins better than users. Mac treats users better than sysadmins. Linux treats everyone like sysadmins."
Well, I heard the rumor that the Israelis had taken over the dealing in XTC, but hey, now that I heard it confirmed on slashdot that they're now taking over the crack trade as well, my, gosh.
I'm still trying to figure out what people mean by 'social skills' here.
This is only true if your engineers are completely incompetent and mix the concrete incorrectly in places.
That's the norm here. Welcome to NOLA!So if you build a chair that's supposed to be safe for a 400-pound person, you should design it so it will stand up to being run over by a 2-ton truck? Yeah, that makes a lot of sense.
Gimme a break (pun intended):
The news release even says that it could have help engineers predict 'exactly how much pressure the levees protecting New Orleans could withstand before giving way.'
Come on. That's ridiculous. If only... Pffff!!! Besides the fact that it doesn't matter when those levees would have broken, because they would have anyway, this is nothing more than FUD to drum up money.
Janine Gordon Associates specializes in placing favorable PR pieces, rather than direct advertising. See their case histories page, where they boast about how they plant stories. (Note: annoying all-Flash site.)
This is a Roland the Plogger story, of course. But, for once, none of the links benefit his search engine ranking. So one wonders if Janine Gordon Associates uses Roland the Plogger.
Besides not giving any detail about the computation process (wich is not a real problem, since the article is not a scintific paper), I doubt a novel approach would solve all of our problems at once. In such cases the problem lies usually not in the computaional model, but in determining the input data (in this case: the material properties) for the calculations.
Even if a model works - there are even some analytical solutions for a very few (~50) mechanical problems to determine the stress distribution near a crack tip - it is always based on an ideal material. Metals, plastics, glas are usually modeled as isotropic, ideally elastic materials, but in the reality they are never so perfect, so altough the models work on a computer, their results can never be directly used for real-world problems, such as crack propagation in the so-called heat affected zone of a welded steel structure or in any part of a reinforced concrete beam or column, not to mention wood.
We just do not now what exactly there is in the material.
It's the Palestinians that have taken over the crack market, Crackpot!
I believe the factor of safety for stell structures is in the order of 1.5. As for earthworks the factor of safety can be up to 3. A factor of safety of 10 is not needed. But you DO have to maintain the structures so they are still at their designed capacity.
I don't have the details about the New Orleans levees, but I honestly doubt cracking had anything to do with it. Such huge works are rarely made of expensive materials such as concrete. It's just too huge. Usually only the sections of levees protecting the most "critical" areas would be expected to be made of concrete. Most of it would be made of earth. This seems to be validated by some info that can be found on the levee failures
http://www.csmonitor.com/2005/1103/p02s02-ussc.htm l
One thing that you need to do when building any kind of water retaining structure is to have your impermeable cutoff wall deep enough to prevent percolation of water when the water is at its maximum. Either the water level was maintained higher than the levee height (which would have been difficult since the water would just have overtopped the levee... unless the whole area beyond the levee was already flooded, but then the water on the other side would have prevented that kind of percolation and resulting erosion) or the original design assumed the water would never reach the top of the levee. Either that or the flow properties of the underlying soil were compeltely erroneously estimated
In any event, cracking had nothing to do with any of the described failures. The comment in the article was pure "buzzword". I think it's the kind of research that will be of more use to mechanical and structural engineers than to geotechnical engineers.
In summary, the factor of safety was probably good enough to resist the forces applied to the levees. At least in terms of strength it probably was. Where the design seems to have been lacking is in terms of erosion protection. Erosion will weaken an earth structure.
I like my dinosaurs feathery, and my pterosaurs hairy (or is it pycnofibery?)
Where the heck are you getting this idea that concrete is more regular than glass? You seem to be talking of a laboratory prepared CEMENT mixture. Yes, certainly if you prepare glass and cement in a laboratory condition, your hardened cement is likely to be more regular. There are, many considerations that makes this untrue for real life construction.
The first thing to understand is that concrete is NOT cement. Concrete is a MIXTURE of cement and agregate. You can use all kinds of things for agregate, gravel and sand being the most common. Sometimes some fly ash from blast furnaces is added. Engineers normally use lower factors of safety for concrete than steel because the uncertainties are greater. When you test concrete to failure, sometimes the fractuers cut across the agregate grains where the cement bond was stronger than the agregate, other times it will follow a path around strong agregate particles.
The other thing to know about concrete is that is it NOT made in a factory, under controlled industrial conditions and unit testing. Sure, you may get your concrete mixed at a concrete plant and the trucks, but eventually it has to get to the field. Then it must be placed... and the experience and professionalism of the workers is very variable. Furthermore, concrete needs to cure in place. The water content of the concrete during this stage is important since it needs water for the chemical reactions to harden the concrete. But then again there is an optimum value. The chemical reaction is also helped by high temperatures. So weather conditions and placement conditions will affect the final product.
And of course, portland cement is a strong alkali. It can actually react with the agregates themselves which can build up stresses and cause cracks inside the concrete independently of external stresses. You may have witnessed this alkali-aggregate reactivity in concrete if you see cracks in concrete that seem to be humid, even what it hasn't been raining, and somtimes oozing a bit of white foam.
In final analysis concrete is a highly nonuniform construction material.
It can also added that most of your levees, and most likely the sections that failed, are probably earthworks. Therefore whatever the uniformity or lack thereof of the concrete, it would have done nothing for the leveees. Cracks are only meaningful in materials that need resist tensile or bending stresses. Needless to say, that is NOT how earthworks are desined.
I like my dinosaurs feathery, and my pterosaurs hairy (or is it pycnofibery?)
This is great! Now if only they could help me keep tabs on my glass pipe, too. After the first couple of twenty rocks I always seem to lose track of the pipe and then I end up having to smoke out of an old lightbulb.
when you work at a hammer factory, every problem looks like a nail
Don't build a goddamned city below sea level!
Anti-US ramblings aside, I am fascinated by this very topic and have pondered upon the science behind destruction, especially with regards to tensile strength. Why do things smash when we hit them ? Why does wood split when you drive a screw/nail through it ? I think this research will not only give us very advanced insight for future building projects, but it might also trickle down to everyday uses like fasteners and glues, or maybe a better wood axe.
The best type of scientific breakthrough is the one that can benefit everyday people in great numbers.
-Billco, Fnarg.com
Perhaps you're crying inside because you're wrong...
Concrete is a mixture of cement and aggregate (sand/gravel/etc.), and is neither uniform in microstructure, nor chemical composition. At least the amorphous solids you speak of (glass & plastic) have a nominally uniform chemical composition.
I do, however, agree with your opinion of the moderators. They've labelled you as "informative", something that should most certainly be discouraged.
Hugs and Kisses,
AC
to torture Palestinians I guess.
to the untrained eye .The energy passing through a solid travels in a spiral motion.since all forces can be disected into three diferent properties ,the crack in 3d would look like a hexagon when looking at it from one view.Another view of the same crack would look like a wave.This may not be true .It is only my observation.
The old saying is:
Cement is to concrete as flour is to fruitcake.
You wouldn't consider fruitcake very homogenous, would you?
Just wanted to point out that lower factor of safety is used for STEEL than for concrete because steel is more reliably produced. Sorry about the typo.
I like my dinosaurs feathery, and my pterosaurs hairy (or is it pycnofibery?)
>Latest information is that the pilings driven by the contractors hired were less than HALF the required depth in several key locations.
WRONG. They were the EXACT lenght spec'ed.
>The COE specs were quite adequate.
WRONG. They wall was built as speced and it failed.
>If you want to blame the COE for anything it's not exerting proper oversight on contractors, but how do you know they have driven X feet of piling and not X+1 if you are not watching and measuring every one.
Ummmm. Wrong. Agian the piles were the length the corps speced.
>If you have a COE Engineer monitoring each piling that adds money as he/she could be doing other work. If you hire contractors to monitor the other contractors that is even more expensive, so you get less levvees built with the same $$$.
blah blah blah blah
>The COE trusted the piling contractor and got ripped off. The contractor should be sued but I imagine the statute of limitations has passed.
You are a complety uninformed moron. Before spounting off about things you know nothing about why not use this thing called google.
They even dug undamaged sections of the floodwall out and measured the length... 17 feet 6 inches. 6 inches more than the Corps specs.
Clueless. Just clueless.