3 ms·

> High compressive strengths are not very useful. I mean, it depends on the use case right? Modern tall buildings/skyscrapers with metal framing use metal pill

by lnenad 3mo ago

> High compressive strengths are not very useful. I mean, it depends on the use case right? Modern tall buildings/skyscrapers with metal framing use metal pillars where high compressive strength is very useful.

A_D_E_P_T 3mo ago
Absolutely nobody is using an expensive novel alloy for 2GPa compressive strength. A 2GPa tensile strength, depending on various other factors such as corrosion resistance and thermal properties, could however be very interesting. (The strongest bulk steel alloys generally peak at ~3.6GPa tensile, which is approximately their theoretical maximum, but there are a lot of applications where steel simply can't be used. Nickel superalloys are typically 0.9 to 1.1GPa UTS.)
- lnenad 3mo ago
  That's true, but it's still factor and if price comes down having that much compressive strength at your disposal could be an interesting choice for supertall skyscrapers.
  - A_D_E_P_T 3mo ago
    2GPa isn't a super-high value for compressive strength. Regular tool steels can exceed it. Technical ceramics routinely exceed it. If you normalize to weight, various cement/concrete formulations can also surpass it. Also, the price of a Ta-Hf-Zr-Nb-Ti alloy isn't especially elastic. Tantalum in particular is an unavoidably expensive element. I'll grant that what would be exceptional is a metal with a >2GPa compressive strength, a >2GPa tensile strength, and decent damage tolerance and ductility. I don't think that this paper describes a material with that outstanding combination of properties, though -- it's much more likely to describe a simple brittle material.
lazide 3mo ago
Interestingly, the design of beams and the like (used for columns) still means tensile strength is the limiting factor, not compressive strength. For compressive strength alone to matter, you’d essentially need a solid steel column - which is so prohibitively heavy, it would often end up collapsing under it’s own weight (in tensile failure, most likely) before it got up to a useful height.
- lnenad 3mo ago
  Yeah, nothing exists in a vacuum :), even for concrete columns rebar is added.
- max51 3mo ago
  I'm a structural engineer, and this is incorrect. For structural steel (e.g., A992, 350W, etc.), the tensile strength is the same as the compressive strength. That's why we only need one value for both. And yes, when we design beams, we check the stresses in both tension and compression. For a symmetrical shape like an I-shaped beam, both verification will be the exact same formula so we don't need to calculate both explicitly. For columns, we do check the compressive stress, and it is the controlling failure mode for short columns. Long, slender columns will buckle before the compressive stress exceeds the allowable limit.
  - lazide 3mo ago
    It depends on the geometric stability of the column shape, which is why I said what I said. The reality is that compressive stress limits are much lower in steel than tensile, as you’re noting. They are only the same in an abstract theoretical sense, not an actual one. And bucking within the column (and/or the resistance too it) is primarily resisted by tensile strength.
    - max51 3mo ago
      >It depends on the geometric stability of the column shape, which is why I said what I said. What you said was like 99% completely false. >that compressive stress limits are much lower in steel than tensile No they are not. > as you’re noting I never acknowledge that. Your lack of understanding in what column buckling is doesn't change anything. Unironically, you should ask chatgpt, it can probably give you a high level explanation that is more compatible with your understanding of physics than what I can give you. Buckling is a stability problem, not a resistance problem. The compressive stress resistance is literally not part of the formulas that we use to verify it. The column could have 100 MPa, 350 MPA, or 359918 MPa compressive resistance and it would change nothing when it comes to buckling. Only the elastic modulus and the physical shape of the column (length, inertia, etc.) is relevant for buckling verification. >And bucking within the column (and/or the resistance too it) is primarily resisted by tensile strength. Than please explain to me why we don't need the tensile (or compressive) resistance of the material to know the buckling resistance of the column. I really want to hear that one.

by lnenad 3mo ago

A_D_E_P_T 3mo ago

Absolutely nobody is using an expensive novel alloy for 2GPa compressive strength. A 2GPa tensile strength, depending on various other factors such as corrosion resistance and thermal properties, could however be very interesting. (The strongest bulk steel alloys generally peak at ~3.6GPa tensile, which is approximately their theoretical maximum, but there are a lot of applications where steel simply can't be used. Nickel superalloys are typically 0.9 to 1.1GPa UTS.)

lnenad 3mo ago
That's true, but it's still factor and if price comes down having that much compressive strength at your disposal could be an interesting choice for supertall skyscrapers.
- A_D_E_P_T 3mo ago
  2GPa isn't a super-high value for compressive strength. Regular tool steels can exceed it. Technical ceramics routinely exceed it. If you normalize to weight, various cement/concrete formulations can also surpass it. Also, the price of a Ta-Hf-Zr-Nb-Ti alloy isn't especially elastic. Tantalum in particular is an unavoidably expensive element. I'll grant that what would be exceptional is a metal with a >2GPa compressive strength, a >2GPa tensile strength, and decent damage tolerance and ductility. I don't think that this paper describes a material with that outstanding combination of properties, though -- it's much more likely to describe a simple brittle material.

lazide 3mo ago

Interestingly, the design of beams and the like (used for columns) still means tensile strength is the limiting factor, not compressive strength. For compressive strength alone to matter, you’d essentially need a solid steel column - which is so prohibitively heavy, it would often end up collapsing under it’s own weight (in tensile failure, most likely) before it got up to a useful height.

lnenad 3mo ago
Yeah, nothing exists in a vacuum :), even for concrete columns rebar is added.
max51 3mo ago
I'm a structural engineer, and this is incorrect. For structural steel (e.g., A992, 350W, etc.), the tensile strength is the same as the compressive strength. That's why we only need one value for both. And yes, when we design beams, we check the stresses in both tension and compression. For a symmetrical shape like an I-shaped beam, both verification will be the exact same formula so we don't need to calculate both explicitly. For columns, we do check the compressive stress, and it is the controlling failure mode for short columns. Long, slender columns will buckle before the compressive stress exceeds the allowable limit.
- lazide 3mo ago
  It depends on the geometric stability of the column shape, which is why I said what I said. The reality is that compressive stress limits are much lower in steel than tensile, as you’re noting. They are only the same in an abstract theoretical sense, not an actual one. And bucking within the column (and/or the resistance too it) is primarily resisted by tensile strength.
  - max51 3mo ago
    >It depends on the geometric stability of the column shape, which is why I said what I said. What you said was like 99% completely false. >that compressive stress limits are much lower in steel than tensile No they are not. > as you’re noting I never acknowledge that. Your lack of understanding in what column buckling is doesn't change anything. Unironically, you should ask chatgpt, it can probably give you a high level explanation that is more compatible with your understanding of physics than what I can give you. Buckling is a stability problem, not a resistance problem. The compressive stress resistance is literally not part of the formulas that we use to verify it. The column could have 100 MPa, 350 MPA, or 359918 MPa compressive resistance and it would change nothing when it comes to buckling. Only the elastic modulus and the physical shape of the column (length, inertia, etc.) is relevant for buckling verification. >And bucking within the column (and/or the resistance too it) is primarily resisted by tensile strength. Than please explain to me why we don't need the tensile (or compressive) resistance of the material to know the buckling resistance of the column. I really want to hear that one.