8 ms·

Have we invented a material that is resistant to these thermal cycles indefinitely, or at least within a range of temperatures of several thousand degrees? I'm

Have we invented a material that is resistant to these thermal cycles indefinitely, or at least within a range of temperatures of several thousand degrees? I'm never going to have my own Star Destroyer if we continue to use subpar materials.

coryrc 6y ago
Steel, below a certain loading (err, ~20% of max fatigue?) does have indefinite life.
- chaboud 6y ago
  Climbers and riggers should all be familiar with fatigue limits. It can be as high as 50% max tensile strength for steel, but I use 30% as my working figure when rigging, and I regularly re-inspect and age-retire gear (at least use annualized color coded markings). When I’ve rigged circus in the past I’ve taken to replacing aluminum gear I find with steel, especially if it’s going to be installed for a while. That said, I climb on aluminum. I just age out my equipment. I’d hate for my last thought to be “huh... I guess aluminum really does degrade with repeated stress.”
  - lanstin 6y ago
    I had an aluminum bicycle where the front fork failed suddenly. Not instantly but in maybe one or two seconds (just slowly enough to let me not have a terrible fall). My next bike was chrome/steel.
    - HPsquared 6y ago
      This solves something I'd wondered for a while - why my aluminium bike has a steel fork.
      - robryk 6y ago
        I was told once that the reason for that was stiffness: apparently aluminum forks are stiffer, so unsuspended ones are way less comfortable (in terms of vibrations being transmitted to the frame and handlebars) than steel unsuspended forks.
      - chaboud 6y ago
        Years ago I totaled a mountain bike in a strange pinched-wheel-in-crack accident that bent the frame in two places but left me uninjured. When I commented to a bike designer/engineer that it was a strange failure, he said that it was intentional, at least on hardtail mountain bikes like mine. A bent frame is ruined but doesn't lead to a catastrophic loss of control. A detached wheel or twisted fork would be next to impossible to control to a stop. He looked at my frame and explained that that the two bends were in exactly the place they'd been designed to be, just behind the last butting. It's an impressive bit of forethought. My guess on road bikes with steel forks, though, is that it's a matter of aerodynamic performance calling for compactness to reduce frontal area, something that would be harder to do in aluminum, and for far less weight savings than the longer tubes on the frame. There's always titanium... The only big drawback is the cost...
- bregma 6y ago
  Even burning jet fuel can't melt such steel beams?
namibj 6y ago
Carbon-Carbon composite has a cycle life in the millions when cyclically loaded between 0% and 85% of ultimate tensile strength. Furthermore, that material has a very low thermal expansion coefficient and remains structurally sound at high temperatures. It does oxidize at high temperature, so you'll have to coat it with something. It's also fairly brittle, basically a strong ceramic (it caused us to loose Columbia during re-entry).
- mycall 6y ago
  What is the difference between "Carbon" and "Carbon-Carbon"? It seems incongruous.
  - ygra 6y ago
    I think this is this: https://en.wikipedia.org/wiki/Reinforced_carbon%E2%80%93carbon https://en.wikipedia.org/wiki/Reinforced_carbon%E2%80%93carb... which is carbon-fiber in graphite, apparently, so the name is apt in that it's a composite of two different forms of carbon with different properties.
    - namibj 6y ago
      Yes. It's a heterogeneous allotrope made from typically pyrolyzing the matrix, followed by slowly decomposing Acetylene inside the porous structure until the porosity is gone. Other ways are to just infuse the porous matrix with more resin, before pyrolyzing again. Then loop a (few) dozen times.
  - HPsquared 6y ago
    There's plain old "carbon fiber" which is short for carbon fiber reinforced polymer/plastic (CFRP). This is the much more common type, and is a polymer matrix reinforced by carbon fibers. This is very strong and light, but not terribly heat-resistant. In a carbon-carbon composite, on the other hand, the plastic component is also replaced by graphite. This gives a very strong and heat-resistant, though somewhat more brittle, material.
wahern 6y ago
https://en.wikipedia.org/wiki/Fatigue_limit https://en.wikipedia.org/wiki/Fatigue_limit
blackrock 6y ago
But won’t anybody think of the souls of millions of people, snuffed from existence, and vaporized from the heat of a death laser from your Star Destroyer. As if millions of voices suddenly cried out in terror and were suddenly silenced.
normaljoe 6y ago
As the other posts point out it's not just a matter of material, but a trade off. As you increase the ductile strength you end up with something that is more brittle and the same is true in reverse. Brittle materials are more temperature sensitive and can rapidly fail. Brittle fracture is no joke look for WWII Liberty ships split in two as an example. We didn't really understand why at that point in time. The answer though is actually pretty simple and why you can't get a perfect material. The lattice structure of the molecules connected to each other can be soft (plastic) or hard (steel). In the plastic example just take a milk jug and poor boiling water into it. Don't actually do this without protective gear (oven mit should be fine). The molecules holding everything together get excited from the energy (heat) move around and since they are not closely bonded end up in a different configuration. Your milk jug at this point does not look the same and is deformed. In the hard example just boil the water you are using for the plastic test. The pot you used does not change because the molecules are tightly bonded. It turns out the the tighter the molecules are bonded there is still a point where that bond will break. Hence the brittle fracture, which is every molecule mic dropping and going home at the same time. While I could go down another rabbit hole to the atomic, subatomic, level of how those lattice structures work. I won't as I think this example gives you what you need. Finally in this case we have a very old, by modern space technology, structure that is made of material that was most likely never expected to last this long. If you want a space ship to last you just have to make sure the engineers understand what "last" means. :)
nine_k 6y ago
I would suggest a thin, non-load-bearing, and easy to replace insulation / reflection layer above the pressurized hull. It could reflect much of solar energy back to space, and much of the hull's radiation back to the hull, keeping the difference of temperatures on the hull much lower. I wonder if it's already implemented.
- exporectomy 6y ago
  Yes, it already uses a reflective blanket. https://www.scienceabc.com/nature/universe/is-it-hot-or-cold-at-the-international-space-station.html#how-does-the-iss-deal-with-the-radiation-in-space https://www.scienceabc.com/nature/universe/is-it-hot-or-cold...
throwaway0a5e 6y ago
>Have we invented a material that is resistant to these thermal cycles indefinitely Yeah. It's called steel and it's too heavy to put in space in the quantities needed for a space station.

coryrc 6y ago

Steel, below a certain loading (err, ~20% of max fatigue?) does have indefinite life.

chaboud 6y ago
Climbers and riggers should all be familiar with fatigue limits. It can be as high as 50% max tensile strength for steel, but I use 30% as my working figure when rigging, and I regularly re-inspect and age-retire gear (at least use annualized color coded markings). When I’ve rigged circus in the past I’ve taken to replacing aluminum gear I find with steel, especially if it’s going to be installed for a while. That said, I climb on aluminum. I just age out my equipment. I’d hate for my last thought to be “huh... I guess aluminum really does degrade with repeated stress.”
- lanstin 6y ago
  I had an aluminum bicycle where the front fork failed suddenly. Not instantly but in maybe one or two seconds (just slowly enough to let me not have a terrible fall). My next bike was chrome/steel.
  - HPsquared 6y ago
    This solves something I'd wondered for a while - why my aluminium bike has a steel fork.
    - robryk 6y ago
      I was told once that the reason for that was stiffness: apparently aluminum forks are stiffer, so unsuspended ones are way less comfortable (in terms of vibrations being transmitted to the frame and handlebars) than steel unsuspended forks.
    - chaboud 6y ago
      Years ago I totaled a mountain bike in a strange pinched-wheel-in-crack accident that bent the frame in two places but left me uninjured. When I commented to a bike designer/engineer that it was a strange failure, he said that it was intentional, at least on hardtail mountain bikes like mine. A bent frame is ruined but doesn't lead to a catastrophic loss of control. A detached wheel or twisted fork would be next to impossible to control to a stop. He looked at my frame and explained that that the two bends were in exactly the place they'd been designed to be, just behind the last butting. It's an impressive bit of forethought. My guess on road bikes with steel forks, though, is that it's a matter of aerodynamic performance calling for compactness to reduce frontal area, something that would be harder to do in aluminum, and for far less weight savings than the longer tubes on the frame. There's always titanium... The only big drawback is the cost...
bregma 6y ago
Even burning jet fuel can't melt such steel beams?

namibj 6y ago

Carbon-Carbon composite has a cycle life in the millions when cyclically loaded between 0% and 85% of ultimate tensile strength. Furthermore, that material has a very low thermal expansion coefficient and remains structurally sound at high temperatures. It does oxidize at high temperature, so you'll have to coat it with something. It's also fairly brittle, basically a strong ceramic (it caused us to loose Columbia during re-entry).

mycall 6y ago
What is the difference between "Carbon" and "Carbon-Carbon"? It seems incongruous.
- ygra 6y ago
  I think this is this: https://en.wikipedia.org/wiki/Reinforced_carbon%E2%80%93carbon https://en.wikipedia.org/wiki/Reinforced_carbon%E2%80%93carb... which is carbon-fiber in graphite, apparently, so the name is apt in that it's a composite of two different forms of carbon with different properties.
  - namibj 6y ago
    Yes. It's a heterogeneous allotrope made from typically pyrolyzing the matrix, followed by slowly decomposing Acetylene inside the porous structure until the porosity is gone. Other ways are to just infuse the porous matrix with more resin, before pyrolyzing again. Then loop a (few) dozen times.
- HPsquared 6y ago
  There's plain old "carbon fiber" which is short for carbon fiber reinforced polymer/plastic (CFRP). This is the much more common type, and is a polymer matrix reinforced by carbon fibers. This is very strong and light, but not terribly heat-resistant. In a carbon-carbon composite, on the other hand, the plastic component is also replaced by graphite. This gives a very strong and heat-resistant, though somewhat more brittle, material.

wahern 6y ago

https://en.wikipedia.org/wiki/Fatigue_limit https://en.wikipedia.org/wiki/Fatigue_limit

blackrock 6y ago

But won’t anybody think of the souls of millions of people, snuffed from existence, and vaporized from the heat of a death laser from your Star Destroyer. As if millions of voices suddenly cried out in terror and were suddenly silenced.

normaljoe 6y ago

As the other posts point out it's not just a matter of material, but a trade off. As you increase the ductile strength you end up with something that is more brittle and the same is true in reverse. Brittle materials are more temperature sensitive and can rapidly fail. Brittle fracture is no joke look for WWII Liberty ships split in two as an example. We didn't really understand why at that point in time. The answer though is actually pretty simple and why you can't get a perfect material. The lattice structure of the molecules connected to each other can be soft (plastic) or hard (steel). In the plastic example just take a milk jug and poor boiling water into it. Don't actually do this without protective gear (oven mit should be fine). The molecules holding everything together get excited from the energy (heat) move around and since they are not closely bonded end up in a different configuration. Your milk jug at this point does not look the same and is deformed. In the hard example just boil the water you are using for the plastic test. The pot you used does not change because the molecules are tightly bonded. It turns out the the tighter the molecules are bonded there is still a point where that bond will break. Hence the brittle fracture, which is every molecule mic dropping and going home at the same time. While I could go down another rabbit hole to the atomic, subatomic, level of how those lattice structures work. I won't as I think this example gives you what you need. Finally in this case we have a very old, by modern space technology, structure that is made of material that was most likely never expected to last this long. If you want a space ship to last you just have to make sure the engineers understand what "last" means. :)

nine_k 6y ago

I would suggest a thin, non-load-bearing, and easy to replace insulation / reflection layer above the pressurized hull. It could reflect much of solar energy back to space, and much of the hull's radiation back to the hull, keeping the difference of temperatures on the hull much lower. I wonder if it's already implemented.

exporectomy 6y ago
Yes, it already uses a reflective blanket. https://www.scienceabc.com/nature/universe/is-it-hot-or-cold-at-the-international-space-station.html#how-does-the-iss-deal-with-the-radiation-in-space https://www.scienceabc.com/nature/universe/is-it-hot-or-cold...

throwaway0a5e 6y ago

>Have we invented a material that is resistant to these thermal cycles indefinitely Yeah. It's called steel and it's too heavy to put in space in the quantities needed for a space station.