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Dave Palmer
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Platinum
Re: "The modulus of rupture is zero"
Dave Palmer   1/18/2013 5:22:53 PM
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@Ann: Okay, apparently you learned some highly non-standard definitions.  According to Instron's glossary of materials testing, modulus of rupture is synonymous with flexural strength.  If you Google "modulus of rupture," you'll see that this is the most commonly used definition.  Clearly, "the flexural strength is zero" would not be a correct statement.

The derivation of the most widely-used modulus of rupture formula assumes that the material deforms in a linear and elastic way, so the formula no longer applies after the yield point.  However, this doesn't mean that "the modulus of rupture is zero"; it just means that the formula no longer correctly predicts the stress.

As far as "catastrophic failure" goes, the most common definition seems to be "(sudden) failure from which recovery is impossible."

Give me any material, and I guarantee I can find a way to make it fail such that you'll never get it back into its original shape.  Hit it hard enough, and it will fail catastrophically.

Ann R. Thryft
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Blogger
Re: Better wood than wood
Ann R. Thryft   1/18/2013 4:56:25 PM
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I've also noticed that some earlier ideas and technologies are being revived,and given another chance. Some may have been inventions that were in advance of their time.

Ann R. Thryft
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Blogger
Re: "The modulus of rupture is zero"
Ann R. Thryft   1/18/2013 4:53:51 PM
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Dave, I disagree. That's simply not the way I learned those definitions.

Dave Palmer
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Platinum
Re: "The modulus of rupture is zero"
Dave Palmer   1/18/2013 4:01:17 PM
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@Ann: The fact that something bends before it breaks doesn't mean that it doesn't have a catastrophic failure mode -- it just means that it bends first.  If you continue to load it, it will fail catastrophically, sooner or later. (Steel bends before it breaks, too, but you can point to any number of catastrophic failures of steel structures).

And "the modulus of rupture is zero" is just plain wrong.  As I said, modulus of rupture is a measure of the load-carrying capacity of a beam.  If the load-carrying capacity were zero, it would be useless.

Modulus of rupture just isn't a useful number for something that yields before it breaks, since the equation assumes no yielding. 

Ann R. Thryft
User Rank
Blogger
Re: Better wood than wood
Ann R. Thryft   1/4/2013 2:51:28 PM
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Scott, this was originally developed at Dow but never commercialized, so I suspect it was not aimed at specific applications, at least originally.

Ann R. Thryft
User Rank
Blogger
Re: "The modulus of rupture is zero"
Ann R. Thryft   1/4/2013 12:38:58 PM
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TJ, thanks for the clarification. Determining that would probably take a detailed lifecycle analysis. Although these are now voluntary, and not nearly as common as many of us would like, I hope that someday they'll be required as an item on the data sheet.

TJ McDermott
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Blogger
Re: "The modulus of rupture is zero"
TJ McDermott   1/3/2013 9:13:23 PM
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The original question was worse for the environment - structural members made from wood or the composites described in the article.

The lumber industry sells itself as renewable because the companies plant trees to replace the ones harvested, and the renewal process is pretty straight forward - Cut down a forest, make lumber, plant seedlings in the now-cleared area, come back in 20 years or so and repeat.

IF the composites are made from organic feedstocks, they may be the equal of wood's impact on the environment.  If they're made from petrochemicals, one would probably have to say they have a larger impact.

Ann R. Thryft
User Rank
Blogger
Re: "The modulus of rupture is zero"
Ann R. Thryft   1/3/2013 8:10:22 PM
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TJ, I'm still not getting your point. Organic feedstocks are at least potentially renewable, whether they're based on trees or on other plants.

Ann R. Thryft
User Rank
Blogger
Re: Better wood than wood
Ann R. Thryft   1/2/2013 12:05:48 PM
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Lou, I thought the hurricane-resistance use was one of the most intriguing and unique about this material, aside from the more mundane uses like deck replacement. Chuck, this is not aimed at high load-bearing structural components such as bridge beams: as we state, it's for lighter construction uses such as decks and pontoons.



Scott Orlosky
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Platinum
Re: Better wood than wood
Scott Orlosky   12/30/2012 5:28:48 PM
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Interesting development.  Nice to see these sort of efforts moving forward.  They may not always be the most cost effective, but it's a step in the right direction.  I wonder if this is one of those "we can do it in the lab, so let's see if we can sell it" sort of things or if they actually had a specific market in mind.

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