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Data Storage Science

Paper Stronger Than Cast Iron 327

Posted by kdawson
from the write-on dept.
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."
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Paper Stronger Than Cast Iron

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  • Milli-pascal? (Score:5, Informative)

    by dascandy (869781) <> on Monday June 09, 2008 @11:26PM (#23719397)
    > 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:First! (Score:3, Informative)

    by icebike (68054) on Monday June 09, 2008 @11:29PM (#23719445)
    This is hardly surprising given that the source for most paper is wood, and wood has the highest tensile strength of any building material known to man based either on weight or cross sectional area.

    Not a lot of our building techniques rely primarily on tensile strength, most rely on spanning gaps with weight bearing members. But if you have to hang something heavy, Wood is your friend.

    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. Firefighters really dislike entering steel framed buildings, when fighting active fires because steel softens and collapses without warning, where as wood groans and snaps and gives ample warning that it is about to collapse.
  • by Garridan (597129) on Monday June 09, 2008 @11:34PM (#23719501)
    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.
  • by dbIII (701233) on Monday June 09, 2008 @11:37PM (#23719531)
    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.

  • Re:Milli-pascal? (Score:5, Informative)

    by Anonymous Coward on Monday June 09, 2008 @11:40PM (#23719579)
    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.
  • cast iron? (Score:5, Informative)

    by Tmack (593755) on Monday June 09, 2008 @11:41PM (#23719583) Homepage Journal
    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


  • by Anonymous Coward on Monday June 09, 2008 @11:42PM (#23719599)
    There's actually an anime with a paper-powered superhero.
  • Re:First! (Score:5, Informative)

    by serviscope_minor (664417) on Monday June 09, 2008 @11:47PM (#23719675) Journal
    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.

  • by solitas (916005) on Monday June 09, 2008 @11:51PM (#23719721)
    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?
  • by Jeff DeMaagd (2015) on Monday June 09, 2008 @11:51PM (#23719725) Homepage Journal
    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.
  • next time (Score:2, Informative)

    by Anonymous Coward on Monday June 09, 2008 @11:56PM (#23719787)
    it's "*badum-psht*"
  • Re:First! (Score:5, Informative)

    by mrcaseyj (902945) on Tuesday June 10, 2008 @12:01AM (#23719827)
    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 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
  • by Iamthecheese (1264298) on Tuesday June 10, 2008 @12:21AM (#23720015)
    If nothing else, it will revolutionize the packaging industry. Strong cardboard boxes are a holy grail of packaging.

    Other uses? Paper airplanes, coat it with plastic and make a really cheap fishing boat, tape that won't break, temporary floor, single-use knife, non-toxic circuit board for cheap toys... This is a breakthrough in the highest meaning of the word.
  • by mrcaseyj (902945) on Tuesday June 10, 2008 @12:36AM (#23720165)
    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! (Score:5, Informative)

    by fabs64 (657132) <beaufabry+slashdot,org&gmail,com> on Tuesday June 10, 2008 @12:39AM (#23720183)
    The same weight of wood would be stronger.
    But not the same cross-sectional size.
  • Also, why would they use the tensile strength of CAST iron? The tensile strength of rolled red steel is 350 MPa, and that's what is used for tensile applications, like.... almost everything. Cast iron is used for compressive purposes, because of it's ease of manufacture, and strength in compression only.
  • Re:cast iron? (Score:5, Informative)

    by plover (150551) * on Tuesday June 10, 2008 @01:07AM (#23720373) Homepage Journal
    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! (Score:5, Informative)

    by rrkap (634128) on Tuesday June 10, 2008 @03:04AM (#23721137) Homepage
    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.
  • by gweihir (88907) on Tuesday June 10, 2008 @03:41AM (#23721343)
    This comparison is highly suspicuous. You do not use cast iron for anything that needs tensile strenght, as it breaks too easily. Wrought iron is a whole different matter and is what is used in construction of cars, ships, girders, and the like. Cast iron in the shape of a pice of paper could easily broken by hand without tools.

    It seems aluminum alloy has about twice the tensile strength of cast iron. Ever tried to rip tinfoil? Not that difficult.

    Side note: mPA is milipascals, not megapascals.
  • 122 years earlier... (Score:2, Informative)

    by Anonymous Coward on Tuesday June 10, 2008 @03:55AM (#23721433)
    ...Jules Verne wrote about a heavier-than-air airship that was made from paper, treated with glue and pressed into shape. the resulting material was "as strong as the best steels, and much lighter", to quote the author.

    the novel is called Robur-le-Conquerant (Robur the Conqueror) (1886)
  • by (805246) <.mike. .at.> on Tuesday June 10, 2008 @05:53AM (#23722187) Homepage
    You'd be surprised...

    In the UK at least half of all domestic construction uses timber frame for the load-bearing structure with simple block and render for the outer skin which provides none of the structural support. Come up to Scotland and practically every building less than 5 storeys high is made using a timber frame.

    The trick in making a building fireproof isn't in making the structure fireproof, but in stopping the fire from getting to the structure in the first place. That's the why every wall and ceiling is made from plasterboard of some kind, because they provide the 30 and 60 mins of fire resistance, not the studs or the joists.

    I'd provide figures to back my assertions, but my books and magazines are in another office.
  • Re:Milli-pascal? (Score:3, Informative)

    by smchris (464899) on Tuesday June 10, 2008 @08:38AM (#23723683)
    I can testify that cast iron is brittle from experience. I had a summer job many, many years ago drilling and tapping cast iron foot pedals for industrial equipment. We weren't allowed to toss them into the finished bin. They had to be _laid_ in the bin (a very significant fraction of the time of a unit cycle) because it was quite common for them to shatter if you tossed them four or five feet. Nonetheless, there would be many uses for this product. Perhaps cast iron wasn't the best comparison the PR guy/reporter could have used.
  • by greyhueofdoubt (1159527) on Tuesday June 10, 2008 @10:09AM (#23725217) Homepage Journal
    On the other hand, aluminum foil is basically pure aluminum, while aluminum alloys contain up to around 10% of either copper, zinc, tin, etc. Some special 7000-series alloys have tensile strengths surpassing some of the softer steels; they are however shockingly expensive and brittle (and they ring like glass when struck).

    The aluminum found in aluminum foil would never be used in aircraft construction or anything else requiring strength. While I love materials science, TFA or the researchers (whoever chose this comparison w/ cast iron) are way off base here. Anyone who has worked with thin materials including cast iron knows that tensile and shear strengths do not scale and are not compatible among different metals (example: you can't replace thick aluminum with thinner steel because although the tensile strength may be higher, the shear strength will be lower. This is important in aircraft repair, as some members endure one or both stresses).

    Also, tearing a sheet of foil constitutes shear stress, not tensile. A sheet of aluminum foil perfectly supported somehow on both ends so that the force was equal along its length would be stronger than you might imagine. Think of it this way:

    12 inch sheet X .005 inch thick= .060" total cross-sectional area

    That gives you a wire with diameter of .276". That's a pretty beefy wire even for a soft metal.

  • Re:First! (Score:3, Informative)

    by Hognoxious (631665) on Tuesday June 10, 2008 @10:56AM (#23726171) Homepage Journal

    With wood, the direction of the grains matter, where with steel it doesn't matter.
    Steel that has been worked by rolling or drawing can have anisitropic properties.

Great spirits have always encountered violent opposition from mediocre minds. -- Albert Einstein