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MIT Aluminum Bicycle Project 1974 (2016)

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Re: MIT Aluminum Bicycle Project 1974 (2016)

#71

Post by ndsipa_pomu »

fnord77 wrote: post #18

I'm convinced titanium is a pretty optimal bike material. I hate aluminum frames, too stiff, some amount of flex makes a bike so much nicer. Hate carbon, too. Steel is nice. I've have a lite ghisallo frame which I think was under 2lbs. The whole bike is under 15lbs and still manages to carry my 200lbs of weight.

> I'm convinced titanium is a pretty optimal bike material.

I'm less convinced. Firstly, I'm not convinced by the frame flex theory of ride comfort - I believe that the tyres are by far the biggest contribution to ride comfort due to the amount that they can flex which is far more than the tiny amount that the frame can.

Secondly, aerodynamics is far more important (if you care about speed/effort) and titanium is tricky to get into highly tailored shapes unless you resort to fancy 3d-printed frames.

Carbon would be my choice due to the design flexibility - by orienting the carbon fibres differently, components can provide strength/stiffness in one direction whilst allowing for compliance in other directions. Also the shape can be relatively easily changed - no need to always use circular tubes.

It'd be interesting to see a 3d-printed titanium frame that uses some kind of honeycomb internal structure to provide super strong/light frames, but I suspect it would be exorbitantly expensive.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#72

Post by briansm »

I find the obsession minimizing bicycle weight funny. It's not the bicycle weight that matters, it's the combined weight of bicycle and rider that counts.

Rider weight massively outweighs the relevance of bike frame material, especially in the West where obesity epidemic has biased BMI upwards over the last half century.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#73

Post by ginko »

xpe wrote: post #23

> Use larger diameter tubular components - Strength goes up as the cube of the diameter so unless there are geometric constraints, use larger diameter tubes with thinner walls to get a lighter structure with increased strength and stiffness. This trend has continued -- it is very noticeable in road and mountain bikes. But this trades off against impact resistance, aerodynamics, and the can-it-fit-between-your-legs-me…

My main gripe with those large diameter tube frames is that they're just ugly.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#74

Post by benj111 »

What was the patent for?

I remember seeing an old aluminium bike in the Manchester industrial museum

This is from 1896 https://collection.sciencemuseumgroup.org.uk/objects/co84092...

And theres this https://collection.sciencemuseumgroup.org.uk/objects/co25722...

Doesn't give a date, but this is the one I remember, and seem to recall it being 1901

Re: MIT Aluminum Bicycle Project 1974 (2016)

#75

Post by rjsw »

3eb7988a1663 wrote: post #6
A_D_E_P_T wrote: post #3

> 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 stif…

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?

Computational materials science is a current research area.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#76

Post by _yb2s »

A_D_E_P_T wrote: post #13
twic wrote: post #7

Earlier quoted context omitted.

There was a magnesium bike frame back in the '90s, made by Kirk: https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolu... https://www.bikeforums.net/classic-vintage/1279777-kirk-prec... https://www.independent.co.uk/news/uk/magnesium-in-frame-to-... https://www.flickr.com/photos/11521783@N05/albums/7215764801... A friend had one. It cracked.

> 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.

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.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#77

Post by ndsipa_pomu »

A_D_E_P_T wrote: post #13
twic wrote: post #7

Earlier quoted context omitted.

There was a magnesium bike frame back in the '90s, made by Kirk: https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolu... https://www.bikeforums.net/classic-vintage/1279777-kirk-prec... https://www.independent.co.uk/news/uk/magnesium-in-frame-to-... https://www.flickr.com/photos/11521783@N05/albums/7215764801... A friend had one. It cracked.

> 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.

If you're thinking of wrapping a material in carbon fibre, why not just use carbon fibre composite in the first place? Is magnesium stronger than CF for a given weight?

Re: MIT Aluminum Bicycle Project 1974 (2016)

#78

Post by tomaskafka »

briansm wrote: post #72

I find the obsession minimizing bicycle weight funny. It's not the bicycle weight that matters, it's the combined weight of bicycle and rider that counts. Rider weight massively outweighs the relevance of bike frame material, especially in the West where obesity epidemic has biased BMI upwards over the last half century.

That’s what I tell myself when picking the bike - just get a competent basic $700-ish bike, and if you want it 2 kg lighter, lose those 2 kg instead of paying thousands.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#79

Post by A_D_E_P_T »

_yb2s wrote: post #76
A_D_E_P_T wrote: post #13

Earlier quoted context omitted.

> 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.

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.

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.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#80

Post by A_D_E_P_T »

ndsipa_pomu wrote: post #77
A_D_E_P_T wrote: post #13

Earlier quoted context omitted.

> 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.

If you're thinking of wrapping a material in carbon fibre, why not just use carbon fibre composite in the first place? Is magnesium stronger than CF for a given weight?

Magnesium, especially a casting, can be something like an order of magnitude cheaper. Carbon fiber is an intrinsically more expensive material, and manufacturing complex engineering parts solely with CF, to high quality standards, is almost an artisanal process.
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