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Materials & Assembly

Strong, Flexible Composite Combines Minerals, Thermoplastic

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TJ McDermott
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Re: "The modulus of rupture is zero"
TJ McDermott   12/23/2012 9:12:40 PM
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Cabe, you asked a very interesting question -

"Which is worse for the environment, manufacturing these composite materials or logging the equivelent amount of wood?" 

 

Logging industry is careful to point out the renewable resource that is lumber, and that they plant a large number of trees every year to replace what was cut.  I don't think it's as easy to make that statement with regard to polypropylene.

Ann R. Thryft
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Re: "The modulus of rupture is zero"
Ann R. Thryft   12/27/2012 1:20:54 PM
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Dave, the absence of a catastrophic failure mode (the modulus of rupture is zero) typically doesn't mean the material doesn't fail: it means it doesn't fail catastrophically, or, it bends before it breaks as you said. TJ, I agree about your comparison with plastic--anyone planted any plastic trees lately?



TJ McDermott
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Re: "The modulus of rupture is zero"
TJ McDermott   12/28/2012 10:52:43 PM
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Ann, I wasn't talking about plastic trees; I was thinking about the renewable feedstocks we'd discussed several months ago.  You mentioned that such feedstocks are no longer food-based such as corn, but still organic based.

Scott Orlosky
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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.

Ann R. Thryft
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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.



Ann R. Thryft
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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.

TJ McDermott
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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
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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.

Ann R. Thryft
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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.

Dave Palmer
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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. 

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