5 ms·

> He ruled out magnesium, which is best per unit weight in compressive buckling but is brittle and difficult to extrude. There's a fascinating, and very new, c

> He ruled out magnesium, which is best per unit weight in compressive buckling but is brittle and difficult to extrude. There's a fascinating, and very new, class of nano-laminate magnesium alloys called Long Period Stacking-Ordered (LPSO) alloys. These are very lean -- the standard version is 97% Mg + 1% Zn + 2% Y -- and they have outstanding mechanical properties. At an equal weight, they're much stronger and stiffer than 6061 aluminum, and the kicker is that this is generally true only if they're extruded. If they're not extruded, the laminate-like grain structure doesn't form properly. Could make excellent bike frames. Magnesium corrosion would still be a problem, though. I got some LPSO-Mg samples from Fuji Light Metals, in Japan, and they were quite badly degraded within weeks.

3eb7988a1663 2y ago
Can modern material science model this computationally, or does everything have to be observed experimentally? This kind of insane just-so recipe - are researchers just iterating on hundreds of thousands of different alloy compositions and production techniques or are there strong theoretical principles on which some of this can be derived?
- choilive 2y ago
  Its been some time detached from the mat sci folks deeply involved in the space but its both. There is a bunch of theoretical underpinnings but ultimately a lot of throwing darts on the board as well.
  - A_D_E_P_T 2y ago
    Yeah. It depends a lot on the type of material, too. Conventional metal alloys -- like LPSO-Mg -- are the toughest to model. Too many variables. Ceramics and intermetallics are a lot easier to model in principle, but they can have surprising properties on an atomic level, and there's really no predictive method for that sort of thing. Modeling does get you pretty far with high-entropy alloys -- because to a substantial extent their properties hinge on how a bunch of different atoms might fit together randomly, and that's something that can be computationally predicted. A lot of the recent interest in HEAs is because they're relatively easy to model.
- rjsw 2y ago
  Computational materials science is a current research area.
twic 2y ago
There was a magnesium bike frame back in the '90s, made by Kirk: https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolution-200 https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolu... https://www.bikeforums.net/classic-vintage/1279777-kirk-precision-magnesium-frames.html https://www.bikeforums.net/classic-vintage/1279777-kirk-prec... https://www.independent.co.uk/news/uk/magnesium-in-frame-to-be-cycling-s-metal-of-the-future-1538389.html https://www.independent.co.uk/news/uk/magnesium-in-frame-to-... https://www.flickr.com/photos/11521783@N05/albums/72157648018071533/with/16116502239 https://www.flickr.com/photos/11521783@N05/albums/7215764801... A friend had one. It cracked.
- A_D_E_P_T 2y ago
  > It cracked. > "Kirk Revolution cast magnesium" Cast magnesium is really weak/brittle compared to forgings and extrusions. Its use was not a great design decision on Kirk's part. I suppose they could have wrapped the casting in carbon fiber or something like that, to give it extra bending strength and spread out loads that might cause fractures, but then it would get expensive.
  - _yb2s 2y ago
    Carbon would cause galvinic corrosion in contact with magnesium, and would also visually hide dangerous cracks- I don’t think a carbon wrapped magnesium bicycle would be safe.
    - A_D_E_P_T 2y ago
      I was just spitballing, but it's possible: First you coat or anodize the magnesium, which I imagine needs to be done in any case. Then you apply a layer of epoxy. Then you wrap in carbon/epoxy. Done properly, there's no direct contact between carbon and magnesium, and you're probably less likely to see corrosion in the Mg-CF composite than you are with magnesium by itself.
      - _yb2s 2y ago
        The epoxy barrier might work, but in general encapsulated metals are risky because they are impossible to inspect for corrosion and cracking so fail without warning, and the encapsulation can block surface oxide formation which causes crevice corrosion- especially if small amounts of salt and water get in there, which they will over time, even in epoxy. I’m sure what you are saying could be done- especially to basically add stiffness to key regions of a carbon racing bicycle, but it would be experimental and I would not trust it to last a long time
genter 2y ago
How would you fabricate a frame from extruded tubing? Welding would destroy the grain structure.
- A_D_E_P_T 2y ago
  That looks like it's an active research problem: https://www.sciencedirect.com/science/article/pii/S2666330924000372 https://www.sciencedirect.com/science/article/pii/S266633092... At a glance, though, the problem doesn't seem insurmountable. FSW appears to work.
- le-mark 2y ago
  Brazing has a long tradition in building bicycle frames.
  - deleted 2y ago
    [deleted]
  - Scoundreller 2y ago
    And lugs
- etrautmann 2y ago
  Aren’t truck chassis increasingly made with epoxy or other adhesive bonds?
alanbernstein 2y ago
I learned about this company's magnesium frames recently: https://www.vaastbikes.com/company/ https://www.vaastbikes.com/company/
metal_am 2y ago
Interesting. I haven’t heard of them. Joining would still be a problem for a bike frame. Any idea on how well they work with other severe plastic deformation processes?
- A_D_E_P_T 2y ago
  They appear to benefit from ECAP, if that's what you mean. For e.g.: https://www.sciencedirect.com/science/article/abs/pii/S0921509314008661 https://www.sciencedirect.com/science/article/abs/pii/S09215... Presumably they'd also benefit from SMAT and other forms of surface modification. That said, they're really good as extruded, and they don't appear to benefit as much from SPD as some steel and aluminum alloys do.
rich_sasha 2y ago
I'm looking forward to a sleugh of articles telling me carbon frames have a really harsh ride quality and lack a certain "je ne said quoi" compared to magnesium frames.
- philjohn 2y ago
  Quite - the grass is always greener. With modern understanding of composites, and complex layups with UD fibre, the "not comfortable, too stiff" is less and less true. The reduction in road buzz I got when I finally moved to CF handlebars was noticeable.
rfmoz 2y ago
Magnesium is common in suspension forks lower legs.
m463 2y ago
I thought stiff was a problem with aluminum - stronger is better but is stiffer better? That said, I wonder if there is a way to make frames more comfortable without having the flex absorb pedaling energy.
- ndsipa_pomu 2y ago
  I don't believe that the frame material makes much difference to comfort. The part that can deflect/absorb bumps and vibration the best is the tyre. So the answer to your question is bigger tyres at lower pressures.
  - david-gpu 2y ago
    Yeah, whenever I hear people talk of the properties of bike frame materials it reminds me of audiophiles: plenty of strong opinions backed by a remarkable absence of data. A typical bike frame follows a truss structure: stiff and unyielding by design. Vertical compliance is going to be found elsewhere: tires, exposed seatpost, chamois/saddle, fork, handlebar, tape. Yet, how many roadies do you find talking about suspension seatposts? It's all because in that subculture emulating present and past pro racers is seen as cool, and anything else isn't. If you are curious, a few people like CYCLINGABOUT [0] and Overbiked Randonneuring [1] have done some measurements and the data suggests that suspension seatposts provide even more reduction in vibrations than wide tires. [0] https://www.youtube.com/watch?v=u1e3g8uqrJU https://www.youtube.com/watch?v=u1e3g8uqrJU [1] https://www.youtube.com/watch?v=rAkDaHlZQow https://www.youtube.com/watch?v=rAkDaHlZQow
    - ndsipa_pomu 2y ago
      Yeah, suspension seatposts can provide 20mm of vertical compliance (varies for different models) which is more than you'd get with 28mm width tyres. I have tried a split stem suspension seatpost, but found that that particular design wasn't great as it was difficult to set the saddle up so that it didn't end up tilting as the two parts of the seatpost moved within the frame. I currently use just a standard carbon fibre seatpost that provides some compliance, but isn't a "suspension" type.
mikeryan 2y ago
How’s it compare to carbon which is the most common high end, lightweight bike material these days?
- A_D_E_P_T 2y ago
  As of right now, nobody makes LPSO alloys in commercial quantities. Fuji Light Metals has a pilot plant that does small-scale production of extruded strips and plates, but their customers are all researchers and R&D labs. That said, we can extrapolate from mechanical properties. If we assume that both materials are tubes with the same wall thickness, and that we're looking at T300 carbon fiber (by far the most common type) in epoxy resin vs a standard research grade of LPSO, then: - The CF will be stiffer - The CF composite will be slightly less dense (1.6 gm/cc vs. ~1.8 gm/cc) - The CF composite will have a slightly higher tensile strength, but the difference is very small and could be nonexistent in practice. - LPSO-Mg will be more damage tolerant -- with better resistance to abrasion and better capacity to flex in a recoverable way in response to extreme mechanical stress. (Cast Mg alloys are undoubtedly worse than CF, but LPSO-Mg is a lot more like an aluminum alloy in this respect. It's a pretty ductile material.) - LPSO-Mg should in principle be cheaper, though this is likely not going to be the case for a long time. - LPSO-Mg will have better mechanical damping properties, so might transmit fewer vibrations to the rider.

3eb7988a1663 2y ago

Can modern material science model this computationally, or does everything have to be observed experimentally? This kind of insane just-so recipe - are researchers just iterating on hundreds of thousands of different alloy compositions and production techniques or are there strong theoretical principles on which some of this can be derived?

choilive 2y ago
Its been some time detached from the mat sci folks deeply involved in the space but its both. There is a bunch of theoretical underpinnings but ultimately a lot of throwing darts on the board as well.
- A_D_E_P_T 2y ago
  Yeah. It depends a lot on the type of material, too. Conventional metal alloys -- like LPSO-Mg -- are the toughest to model. Too many variables. Ceramics and intermetallics are a lot easier to model in principle, but they can have surprising properties on an atomic level, and there's really no predictive method for that sort of thing. Modeling does get you pretty far with high-entropy alloys -- because to a substantial extent their properties hinge on how a bunch of different atoms might fit together randomly, and that's something that can be computationally predicted. A lot of the recent interest in HEAs is because they're relatively easy to model.
rjsw 2y ago
Computational materials science is a current research area.

twic 2y ago

There was a magnesium bike frame back in the '90s, made by Kirk: https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolution-200 https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolu... https://www.bikeforums.net/classic-vintage/1279777-kirk-precision-magnesium-frames.html https://www.bikeforums.net/classic-vintage/1279777-kirk-prec... https://www.independent.co.uk/news/uk/magnesium-in-frame-to-be-cycling-s-metal-of-the-future-1538389.html https://www.independent.co.uk/news/uk/magnesium-in-frame-to-... https://www.flickr.com/photos/11521783@N05/albums/72157648018071533/with/16116502239 https://www.flickr.com/photos/11521783@N05/albums/7215764801... A friend had one. It cracked.

A_D_E_P_T 2y ago
> It cracked. > "Kirk Revolution cast magnesium" Cast magnesium is really weak/brittle compared to forgings and extrusions. Its use was not a great design decision on Kirk's part. I suppose they could have wrapped the casting in carbon fiber or something like that, to give it extra bending strength and spread out loads that might cause fractures, but then it would get expensive.
- _yb2s 2y ago
  Carbon would cause galvinic corrosion in contact with magnesium, and would also visually hide dangerous cracks- I don’t think a carbon wrapped magnesium bicycle would be safe.
  - A_D_E_P_T 2y ago
    I was just spitballing, but it's possible: First you coat or anodize the magnesium, which I imagine needs to be done in any case. Then you apply a layer of epoxy. Then you wrap in carbon/epoxy. Done properly, there's no direct contact between carbon and magnesium, and you're probably less likely to see corrosion in the Mg-CF composite than you are with magnesium by itself.
    - _yb2s 2y ago
      The epoxy barrier might work, but in general encapsulated metals are risky because they are impossible to inspect for corrosion and cracking so fail without warning, and the encapsulation can block surface oxide formation which causes crevice corrosion- especially if small amounts of salt and water get in there, which they will over time, even in epoxy. I’m sure what you are saying could be done- especially to basically add stiffness to key regions of a carbon racing bicycle, but it would be experimental and I would not trust it to last a long time

genter 2y ago

How would you fabricate a frame from extruded tubing? Welding would destroy the grain structure.

A_D_E_P_T 2y ago
That looks like it's an active research problem: https://www.sciencedirect.com/science/article/pii/S2666330924000372 https://www.sciencedirect.com/science/article/pii/S266633092... At a glance, though, the problem doesn't seem insurmountable. FSW appears to work.
le-mark 2y ago
Brazing has a long tradition in building bicycle frames.
- deleted 2y ago
  [deleted]
- Scoundreller 2y ago
  And lugs
etrautmann 2y ago
Aren’t truck chassis increasingly made with epoxy or other adhesive bonds?

alanbernstein 2y ago

I learned about this company's magnesium frames recently: https://www.vaastbikes.com/company/ https://www.vaastbikes.com/company/

metal_am 2y ago

Interesting. I haven’t heard of them. Joining would still be a problem for a bike frame. Any idea on how well they work with other severe plastic deformation processes?

A_D_E_P_T 2y ago
They appear to benefit from ECAP, if that's what you mean. For e.g.: https://www.sciencedirect.com/science/article/abs/pii/S0921509314008661 https://www.sciencedirect.com/science/article/abs/pii/S09215... Presumably they'd also benefit from SMAT and other forms of surface modification. That said, they're really good as extruded, and they don't appear to benefit as much from SPD as some steel and aluminum alloys do.

rich_sasha 2y ago

I'm looking forward to a sleugh of articles telling me carbon frames have a really harsh ride quality and lack a certain "je ne said quoi" compared to magnesium frames.

philjohn 2y ago
Quite - the grass is always greener. With modern understanding of composites, and complex layups with UD fibre, the "not comfortable, too stiff" is less and less true. The reduction in road buzz I got when I finally moved to CF handlebars was noticeable.

rfmoz 2y ago

Magnesium is common in suspension forks lower legs.

m463 2y ago

I thought stiff was a problem with aluminum - stronger is better but is stiffer better? That said, I wonder if there is a way to make frames more comfortable without having the flex absorb pedaling energy.

ndsipa_pomu 2y ago
I don't believe that the frame material makes much difference to comfort. The part that can deflect/absorb bumps and vibration the best is the tyre. So the answer to your question is bigger tyres at lower pressures.
- david-gpu 2y ago
  Yeah, whenever I hear people talk of the properties of bike frame materials it reminds me of audiophiles: plenty of strong opinions backed by a remarkable absence of data. A typical bike frame follows a truss structure: stiff and unyielding by design. Vertical compliance is going to be found elsewhere: tires, exposed seatpost, chamois/saddle, fork, handlebar, tape. Yet, how many roadies do you find talking about suspension seatposts? It's all because in that subculture emulating present and past pro racers is seen as cool, and anything else isn't. If you are curious, a few people like CYCLINGABOUT [0] and Overbiked Randonneuring [1] have done some measurements and the data suggests that suspension seatposts provide even more reduction in vibrations than wide tires. [0] https://www.youtube.com/watch?v=u1e3g8uqrJU https://www.youtube.com/watch?v=u1e3g8uqrJU [1] https://www.youtube.com/watch?v=rAkDaHlZQow https://www.youtube.com/watch?v=rAkDaHlZQow
  - ndsipa_pomu 2y ago
    Yeah, suspension seatposts can provide 20mm of vertical compliance (varies for different models) which is more than you'd get with 28mm width tyres. I have tried a split stem suspension seatpost, but found that that particular design wasn't great as it was difficult to set the saddle up so that it didn't end up tilting as the two parts of the seatpost moved within the frame. I currently use just a standard carbon fibre seatpost that provides some compliance, but isn't a "suspension" type.

mikeryan 2y ago

How’s it compare to carbon which is the most common high end, lightweight bike material these days?

A_D_E_P_T 2y ago
As of right now, nobody makes LPSO alloys in commercial quantities. Fuji Light Metals has a pilot plant that does small-scale production of extruded strips and plates, but their customers are all researchers and R&D labs. That said, we can extrapolate from mechanical properties. If we assume that both materials are tubes with the same wall thickness, and that we're looking at T300 carbon fiber (by far the most common type) in epoxy resin vs a standard research grade of LPSO, then: - The CF will be stiffer - The CF composite will be slightly less dense (1.6 gm/cc vs. ~1.8 gm/cc) - The CF composite will have a slightly higher tensile strength, but the difference is very small and could be nonexistent in practice. - LPSO-Mg will be more damage tolerant -- with better resistance to abrasion and better capacity to flex in a recoverable way in response to extreme mechanical stress. (Cast Mg alloys are undoubtedly worse than CF, but LPSO-Mg is a lot more like an aluminum alloy in this respect. It's a pretty ductile material.) - LPSO-Mg should in principle be cheaper, though this is likely not going to be the case for a long time. - LPSO-Mg will have better mechanical damping properties, so might transmit fewer vibrations to the rider.