Is an aluminium chassis a smart choice?

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Re: Is an aluminium chassis a smart choice?

Postby nbcarey » Tue Jul 26, 2022 2:23 am

gudmund wrote:I 'second' what was just said...... Note, aluminum, 'pound for pound' is more rigid than steel...

Absolutely untrue.

Modulus of elasticity (Young's modulus) for Aluminum is c. 60-70 GPa, depending on alloy.

For mild steel . . . c. 200 GPa

Higher numbers better - so steel is more than 3x stiffer than aluminum.

That's why the tubing used in aluminum bicycle frames is much larger in diameter than steel tubing used in bicycle frames: it has to be.

That requirement for larger sections to achieve the same engineering properties offsets much of the [potential] wraith T savings.
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Re: Is an aluminium chassis a smart choice?

Postby QueticoBill » Tue Jul 26, 2022 6:11 am

So a 10 pound aluminum beam cannot be more rigid than a 10 pound steel beam? I would think that 10 pounds of aluminum could be so much deeper that it would be stiffer. "pound for pound"
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Re: Is an aluminium chassis a smart choice?

Postby John61CT » Thu Aug 04, 2022 3:54 pm

Yes, you need "bigger" members to get the same strength.

So what?

Yes welding to be avoided as much as possible. Stainless steel fittings where steel is required, ideally all materials marine grade if you go anywhere near the coast, or snow country salted roads.

With good design, using the same weight of materials you will get much higher strength.

Yes higher cost, but little to no corrosion, so longevity without as much periodic maintenance.

To me that's worth paying more.

And it looks cool.

Obviously not for those who need cheap and want easy, makes it a much more costly and complex project.
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Re: Is an aluminium chassis a smart choice?

Postby gudmund » Thu Aug 04, 2022 11:12 pm

"gudmund" here - I stand by what I said about the stiffness of aluminum...... this is what was explained to me by some of the Boeing engineers I worked with when I was working there in the late 70's/80's on the B767/B747-400 development in their mock-up department (when there still was mock-up - I never worked on assembling "real" airplanes in their factory, just the 'development work' w/engineers & some flight line 'mod' work/ & 2 'AOG' trips I got to go on). I was 'just' a mechanic, thus = 'not' knowing anything about anything.....and as far as bicycles go, am 'a bit' more versed on them - having ridden upwards of 10thou miles on numerous trips in the 80's with them being of the '6061T6 heat treated' Cannondale/Klien aluminum variation's of frames, which I can say = "Lb for Lb" they were 'no' lighter in weight than "any" of the steel frames I had ever owned or ridden = but YES, they were much "stiffer/rigid" due to the mass amount of aluminum used in their construction. I have just stated my opinion here, from what I had learned over my 68+ years of life so far and if I am "wrong"? = so be it............. take care and stay safe..........
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Re: Is an aluminium chassis a smart choice?

Postby Tom&Shelly » Fri Aug 05, 2022 5:10 am

Speaking strictly as an electrical engineer, I suspect most of the confusion here comes from the materials engineering definitions of concepts like "stiffness", "flexibility", and "rigidity" and the meaning of things like "Young's modulus", vs our intuitive notions of what we need, and our experience.

As my one and only, single semester, survey class in materials was 38 years ago, I won't attempt to un-muddy the waters. But, if anyone cares to post some basic definitions and explanations, it might be interesting reading, and may even help! :D

I mean, I surely don't want a trailer that cracks driving it down bumpy roads. Nor do I want one that avoids cracking by bending like a wet noodle, so that the cabin I've mounted on top cracks. Somehow these things get translated into technical language, and into the relative merits of steel vs aluminum (vs wood, pure gold, copper, etc.)

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