Paper Stronger Than Cast Iron

TaeKwonDood writes "All paper is made of cellulose, which at the nanoscale level is quite strong, but paper processing makes large, fragile fibers that break easily. Researchers in Sweden have have come up with a manufacturing process that keeps the fibers small, resulting in 'nanopaper' with over 1.6 times the tensile strength of cast iron (214 megapascals vs. 130 mPa). And since cellulose is the most abundant organic compound on the planet, it's cheap to use compared to other exotic, expensive-to-produce options — such as carbon nanotubes."

Comments

Milli-pascal?

[dascandy]

> 214 megapascals vs. 130 mPa

214 megapascal (singular, it's a unit) is about 1.6*10^9 more than 130 millipascal. Use your units properly.

Re:Milli-pascal?

[Anonymous Coward]

What's he trying to say is that those units should be MPa (capital M and capital P) for both.

Also most steels are above 400 MPa (some as high as 1800) so this isn't that strong, in fact Aluminum alloys can reach into the 400 MPa range.

Cast Iron (in its 2 major forms grey & white cast) is very brittle and therefore does not have good tensile strength. However compressive strength and its good vibration tolerance is why a lot of large machining equipment uses a cast iron base.

Re:Don't they realize...

[Garridan]

Oops, just RTFA'd. They didn't show that paper was as strong as paper. They made paper twice as strong as old "high strength" paper. Which still has very, very little tensile strength. Comparing to cast iron really doesn't help their case.

One point about grey cast iron

[dbIII]

The tensile strength of grey cast iron is fairly low because the carbon comes out in the form of graphite. That's right - the same thing that is in pencils. When you have large flakes of graphite, say a few millimetres in size, you have a fairly low tensile strength (stretch it and it breaks) and low toughness (drop it and it cracks). The compressive strength isn't so bad and cast iron is a lot easier to make than steel which is why it is still used.

With the paper there is the advantage that small particle sizes dramaticly increase strength.

cast iron?

[Tmack]

Really, cast iron is weak in comparison to a lot of metals. 130mPa is also the ultimate strength of human bone, which would have made a much more interesting comparison. Cast iron isnt really used as much for anything anymore since steel is much stronger and is almost as cheap. The article's claim to replacing carbon nano tubes is a bit of an exaderation, as they have a strength of 62GPa

Tm

Re:cast iron?

[plover]

Cast iron's not exactly dead. It's still good for producing relatively intricate parts cheaply. As long as you don't require high accuracy on every surface, you can have a really complex part that's only somewhat more expensive than the scrap iron that goes into it.

Think of a thin stationary engine housing with fins to dissipate heat -- you usually don't care if the fins are within 0.25" of where they're supposed to be; as long as air can pass over them they can do their job. As far as the important surfaces, such as the ones that hold the bearings or that mate with another housing, sure, you'll have to machine those. But if you had to machine all those fins from a solid steel block, or cut a bunch and weld them all on, you'd easily spend three times the money on labor and tooling and have a part that doesn't last as long as a casting.

There are many different alloys of cast iron, and they each have their own set of properties. All are much harder than ordinary steels, and usually have excellent wear resistance. Some alloys allow for more intricate castings. Some are easier to machine. And some, such as white iron, are extremely brittle and almost worthless in tensile strength, but can be treated to crazy levels of hardness. It all depends on your application, and in which properties you require. Steel can't simply be "dropped-in" as a replacement material. Hell, sometimes you can't even substitute ductile cast iron for malleable cast iron.

And I wouldn't count on being able to substitute paper for cast iron, either!

Re:First!

[serviscope_minor]

wood has the highest tensile strength of any building material known to man based either on weight or cross sectional area.

No, steel does. That's why I-beams are steel, not wood. It's also why the cables in suspension bridges are steel, not wood poles.

Not a lot of our building techniques rely primarily on tensile strength, most rely on spanning gaps with weight bearing members.

And what determines how well you can span a gap? A combination of compressive and tensile strength. You need to revise your beam bending...

Tensile strength does come into play on collapsing structures, as weight bearing members are removed, and buildings end up hanging from their walls or rafters.

So what does some in to play? Probably a mixture of tensile and compressive strength, depending on what is failing and why.

Re:Iron Man's nemesis... PAPER MAN

[solitas]

No no no - the girls were the GOOD GUYS, remember? That big trenchcoated mook with the glasses was one of the bad guys. And he dead now.
Awesome anime - did they ever do more?

Re:Don't they realize...

[Jeff DeMaagd]

But... cast iron has the tensile strength on the order of concrete.

I think you might be two orders of magnitude off. Cast iron shows up as having around 130 to 200MPa (depending on your figures), concrete shows up at 3MPa. Having used it, cast iron can be pretty cheesy stuff. But I imagine that strength-to-weight is pretty good.

Re:First!

[mrcaseyj]

Icebike wrote
>...wood has the highest tensile strength of any building material known to man based either on weight or cross sectional area.

I Think your estimate of wood is much too high. Wikipedia's article of tensile strength http://en.wikipedia.org/wiki/Tensile_strength lists pine wood at 40 MPa    I know there are some woods that are significantly stronger but still.

For comparison some other tensile strengths listed in MPa are:

Cast Iron           200
structural steel    400
steel piano wire   2500
Concrete              3
HDPE plastic         37
Aluminum Aloy       455
Glass              4710
Carbon fiber       5650
Carbon nanotubes  63000

What is Tensile Strength

[mrcaseyj]

serviscope_minor wrote:

icebike wrote:

wood has the highest tensile strength of any building material known to man based either on weight or cross sectional area.

No, steel does...

There seems to be some confusion about what tensile strength is. Tensile strength is how well a material can resist pulling, not bending or compression. A rope can show off the tensile strength of a material even though it has no bending strength or compression strength.

Even when adjusting for weight, the tensile strength of wood isn't so great compared to S-glass or carbon fiber. And when adjusting for cross sectional area, the tensile strength of wood fares even worse because it has a lot of air in its pores.

Re:First!

[fabs64]

The same weight of wood would be stronger.
But not the same cross-sectional size.

Re:First!

[rrkap]

If it's loaded in pure tension, you're right, wood is stronger per unit weight. However one thing that you have be careful of with wood beams is that wood has a very low shear strength which makes beams fail at much lower loads than you would expect from the tensile strength alone. It also isn't very strong in tension across the grain which limits your design freedom.