5 ms·

Usually materials that are more hard are also more brittle. I don't read anything about that in this article. Anyone any idea?

fhood 5y ago
See section on "compressive strength".
- jazzyjackson 5y ago
  Diamond has a very high compressive strength, but if you drop one it will shatter, it is brittle. Since this new material has similar hardness & strength, I would assume it is similarly brittle.
  - jacquesm 5y ago
    Brittleness is arbitrarily defined as the ration between tensile and compressive strength so GP has a point (high compressive strength usually indicates a more brittle material), but without knowing the tensile strength it remains to be seen if it is more brittle or less brittle than say diamond.
    - harpiaharpyja 5y ago
      Diamond is quite brittle so I think to the point of the discussion, it's likely a brittle material even if it's somewhat less brittle than diamond.
      - beerandt 5y ago
        Diamonds are actually tricky, because their practical brittleness is mostly due to breaks in the lattice caused by impurities. The lines of weakness are defined as cleavage, and diamonds will typically cleave along those lines when the break. So there's a bit of ambiguity between the actual brittleness of the pure carbon structure and the practical brittleness where breaks in that structure naturally exist.
        zardo 5y ago
        Does that mean diamonds might have ductile fractures if they were flawless? Or just that they would be stronger?
    - beerandt 5y ago
      I don't think a single part of your comment is true. ASCE, ASTM, and other professional orgs have non-arbitrary definitions. They are all versions of some measure of deformation at ultimate strength, but don't correlate to that strength value. Crackers are brittle. Structural steel is not.
      - jacquesm 5y ago
        Yes, but this is an informal discussion, so that ratio actually serves a purpose unless you want to attach a complete course in materials science, it's 'good enough' for this level of discussion and sheds some light on why it is a thing to begin with. Oh, and just to fortify this comment here is a reference: https://subsurfwiki.org/wiki/Brittleness https://subsurfwiki.org/wiki/Brittleness
- deleted 5y ago
  [deleted]
- beerandt 5y ago
  Strength is unrelated to brittleness. Brittleness is a measure of plastic deformation at the (ultimate strength) breaking point. Eg, diamonds, cast iron, and saltine crackers are all very brittle. Resilience and ductility are related technical terms, but not quite opposites.
blix 5y ago
It is probably very brittle. Diamond is a brittle material and this is basically a 'disordered' diamond. It is quite unlikely that any mechanisms of ductile deformation would be active in this material.
- sulam 5y ago
  Hmm, not a materials scientist here, but wouldn't some of diamond's brittleness derive from its crystalline structure, ie that it's easy for it to sheer along a plane? Whereas this material, being "disordered", to use your term, won't have the same sheer planes and therefore potentially be much less brittle?
  - bodhiandphysics 5y ago
    In general disordered materials are more brittle... think glasses, because cracks can propagate in any direction instead of just along crystal faces
  - lcvw 5y ago
    In general if a material is shearing along crystal plains the material is breaking apart. Also I am pretty sure that diamonds are polycrystalline meaning that the a diamond is composed of many crystals with different orientations, so it is generally going to break on the boundaries between those crystals not the crystalline bonds themselves. For an example think of a polycrystal like steel (which I’m a little more familiar with), the atoms in the crystal lattice can be displaced a little (elastic deformation) or the crystalline grains can move or change shape (plastic deformation). Once the crystals (grains) themselves shear that means you’ve applied enough stress to break the crystal’s bonds and the material is going to break. Some materials are different though, and sometimes crystals can slip across grain boundaries. But the bonds between the crystals are generally weaker and more prone to move/change, generally polychrystals break along those boundaries first, before the crystals themselves break apart. This is probably very brittle (and hard) not because there are no shear plains, but because there are no mechanisms for the atoms to move around without breaking chemical bonds.
    - 5y ago

fhood 5y ago

See section on "compressive strength".

jazzyjackson 5y ago
Diamond has a very high compressive strength, but if you drop one it will shatter, it is brittle. Since this new material has similar hardness & strength, I would assume it is similarly brittle.
- jacquesm 5y ago
  Brittleness is arbitrarily defined as the ration between tensile and compressive strength so GP has a point (high compressive strength usually indicates a more brittle material), but without knowing the tensile strength it remains to be seen if it is more brittle or less brittle than say diamond.
  - harpiaharpyja 5y ago
    Diamond is quite brittle so I think to the point of the discussion, it's likely a brittle material even if it's somewhat less brittle than diamond.
    - beerandt 5y ago
      Diamonds are actually tricky, because their practical brittleness is mostly due to breaks in the lattice caused by impurities. The lines of weakness are defined as cleavage, and diamonds will typically cleave along those lines when the break. So there's a bit of ambiguity between the actual brittleness of the pure carbon structure and the practical brittleness where breaks in that structure naturally exist.
      - zardo 5y ago
        Does that mean diamonds might have ductile fractures if they were flawless? Or just that they would be stronger?
  - beerandt 5y ago
    I don't think a single part of your comment is true. ASCE, ASTM, and other professional orgs have non-arbitrary definitions. They are all versions of some measure of deformation at ultimate strength, but don't correlate to that strength value. Crackers are brittle. Structural steel is not.
    - jacquesm 5y ago
      Yes, but this is an informal discussion, so that ratio actually serves a purpose unless you want to attach a complete course in materials science, it's 'good enough' for this level of discussion and sheds some light on why it is a thing to begin with. Oh, and just to fortify this comment here is a reference: https://subsurfwiki.org/wiki/Brittleness https://subsurfwiki.org/wiki/Brittleness
deleted 5y ago
[deleted]
beerandt 5y ago
Strength is unrelated to brittleness. Brittleness is a measure of plastic deformation at the (ultimate strength) breaking point. Eg, diamonds, cast iron, and saltine crackers are all very brittle. Resilience and ductility are related technical terms, but not quite opposites.

blix 5y ago

It is probably very brittle. Diamond is a brittle material and this is basically a 'disordered' diamond. It is quite unlikely that any mechanisms of ductile deformation would be active in this material.

sulam 5y ago
Hmm, not a materials scientist here, but wouldn't some of diamond's brittleness derive from its crystalline structure, ie that it's easy for it to sheer along a plane? Whereas this material, being "disordered", to use your term, won't have the same sheer planes and therefore potentially be much less brittle?
- bodhiandphysics 5y ago
  In general disordered materials are more brittle... think glasses, because cracks can propagate in any direction instead of just along crystal faces
- lcvw 5y ago
  In general if a material is shearing along crystal plains the material is breaking apart. Also I am pretty sure that diamonds are polycrystalline meaning that the a diamond is composed of many crystals with different orientations, so it is generally going to break on the boundaries between those crystals not the crystalline bonds themselves. For an example think of a polycrystal like steel (which I’m a little more familiar with), the atoms in the crystal lattice can be displaced a little (elastic deformation) or the crystalline grains can move or change shape (plastic deformation). Once the crystals (grains) themselves shear that means you’ve applied enough stress to break the crystal’s bonds and the material is going to break. Some materials are different though, and sometimes crystals can slip across grain boundaries. But the bonds between the crystals are generally weaker and more prone to move/change, generally polychrystals break along those boundaries first, before the crystals themselves break apart. This is probably very brittle (and hard) not because there are no shear plains, but because there are no mechanisms for the atoms to move around without breaking chemical bonds.
  - 5y ago