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."

Comments

The trick is...

[Anonymous Coward]

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

[Mozk]

Plumbers should especially pay attention.

Practically applicable?

[onlysolution]

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.

Interesting

[tsa]

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.

Slightly misleading summary

[gunpowda]

It would be great if submitters of content actually read it, and made it as 'brilliant' as their attempted irony.

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.

Punny

[h nu per lmda]

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.

American Committee for the Weitzman Institute?

[Animats]

This press release comes from the American Committee for the Weitzmann Institute of Science. Who are they? The Weitzmann Institute is a good research school in Israel, but this "American Committee" thing is apparently some kind of a fund raising operation. The return address on the press release is from Janine Gordon Associates, "Where corporate and brand reputations are built, enhanced, and transformed." They also promote "bankrate.com" and Bridal Guide magazine.

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.

Re:My inner Materials scientist just got shot.

[theguyfromsaturn]

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.