7075 nanotech welding: any news?

Discuss light weight issues concerning road bikes & parts.
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C36
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by C36

Stolensteel wrote:Pros are riding with 7075 bars since years, every hi-quality stem is made of 7075. The notorious ultra-thin tubes of CAAD do not turn it into a noodle, it´s just a matter of design... I don´t see why this should be a problem. Take the same design of Caad12 and make it out of 7075, my guess it would weight around 900g, the material would be stronger (less possibility of failure?*), the welds would be way stronger, potentially at about the same price.
Would you buy it? I would. Like tomorrow.

*I´m not an expert, it´s a serious question.
So when you dimension a frame you need 2 basic things:
- solid enough not to break
- desired level of stiffness
7075 is stronger than most other aluminium alloys meaning you can use thinner walls —> less material for the same strength = lighter
7075 is as stiff as other alloys (it is a property independant of strength), then if you used thinner wall (since the high strength allow you to) you necessarily end up with flexure frame. If you want the same stiffness... then you need the same amount of material than more classical alloys.

Cannondale example is a good one, 6061 alloy they historically used, is far from being the strongest, but since they designed their frames for a specific stiffness, it largely exceeded the strength needed... using a stronger alloy would just make it... stronger, not stiffer.

Now where would it bring value? In pieces where sufficient strength is more difficult to achieve than stiffness, a stem is an example.


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by Weenie


Stolensteel
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Joined: Mon Sep 30, 2019 5:05 pm

by Stolensteel

Attermann wrote:
Sat Oct 12, 2019 2:54 pm
I can see now that your are right they were made in 7020, the frame weigh 1050 grams in a 56, but they rode really really well, I have owned one of the last they made, the revolution d2s
that looks like a pretty cool bike. Rare to find but it could be a pretty good deal on the 2nd hand market.

Stolensteel
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by Stolensteel

alanyu wrote:
Sat Oct 12, 2019 4:53 pm
A lightweight metal frame close to a carbon one is as fragile as or even fragiler than a carbon frame in a crash. What's more, the cost of repairing that metal frame can be expensiver than a carbon frame.
there must be a reason why crit-vampires ride alloy, and they definitely know something about crashing

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C36
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by C36

alanyu wrote:
A lightweight metal frame close to a carbon one is as fragile as or even fragiler than a carbon frame in a crash. What's more, the cost of repairing that metal frame can be expensiver than a carbon frame.
That global statement is totally inaccurate. Making a light, strong frame is fairly easy.
Achieving the proper stiffness level is more complex.


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XCProMD
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by XCProMD

Problem is stiffness, as pointed out previously, and fatigue.

It is true that stiffness depends not only on Young modulus but also on moment of inertial of the cross section. But to compensate for a Young modulus as low as 0,3 times that of steel, a big cross section in the direction of the stress to counteract is needed.

A big cross section means much material. Unless walls are very thin. All fine until here. But then welding the tubes together is needed. (Let’s let buckling out of the picture this time, we can always add kinks)

The fatigue strength of aluminium is nothing extraordinary and on top of that it hasn’t a clear “knee” in the S/N (Stress/Number of cycles) graph. To exploit the high strength of Al7075 we will need to control the surface toughness to a high extent. Every micrometre of Rz will mean decrease fatigue strength and a bicycle frame is, well, cyclical in its stress range.

That’s doable, no problem. But then we will need to weld the tubes together. And a weld toe is by definition a huge defect (considering we have perfect penetration and therefore no possibility of root cracks). So much that no matter the strength of the aluminium used, its fatigue strength will be exactly the same.

What actually means that the design criteria in nowadays alu frames is not the strength of the alloy but the FAT class of the welds against the stress range. Of course high strength alu allows for thinner walls that will not be dented so easily and that actually allows butting the tubes quite heavily ( or alternatively reduce their moment of inertia away from welds). But 7075 will only add a very marginal weight gain using those strategies against a still very complicated weld, a less workable (ductile) material and much higher costs.


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alanyu
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by alanyu

Stolensteel wrote:
Sat Oct 12, 2019 6:46 pm
there must be a reason why crit-vampires ride alloy, and they definitely know something about crashing
Nothing wrong with alloy frames. "Normal" weight alloy frames nowadays, such as allez sprint, can be stiff and strong. However, how many percentage of crit-vampires ride alloy frame less than 1000g?
C36 wrote:
Sat Oct 12, 2019 6:46 pm
alanyu wrote:
A lightweight metal frame close to a carbon one is as fragile as or even fragiler than a carbon frame in a crash. What's more, the cost of repairing that metal frame can be expensiver than a carbon frame.
That global statement is totally inaccurate. Making a light, strong frame is fairly easy.
Achieving the proper stiffness level is more complex.


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Considering strength to weight, alu has no advantage to carbon in a frame. A lightweight metal frame close to a carbon frame, let's say alu 950g frame, requires the tube wall as thin as a can. The welding area even has a lower strength. In a crash it's just no less fragiler than a carbon frame.

Also here is a link of the industry simulation:
http://www.dexcraft.com/articles/carbon ... _to_weight

Hexsense
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by Hexsense

Just thinking out loud. Feel free to correct me on any of my thought.
1.)Make the tube larger diameter and thinner can increase stiffness for the same weight right?
2.)What stop people from making huge cross section but very thin tube? -> because it'll be too fragile and not enough strength to prevent damage?
3.)Then higher strength allow thinner wall to be used therefore push the limit of how large the tube diameter can be for the same weight?

4.) Stem is a simple structure that doesn't need any weld, so it benefit from better aluminum. Frame suffer from weld joint. Can the entire bike cast in a mold without welding too? Would that be a large gain in stiffness to weight?

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C36
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by C36

You will hit few problems
- making the tubes, hard alloys are more difficult to stretch in ultra thin tubes (few years ago, hydroforming was not possible for those alloys for bike industry (did a project for airbus but that was not for tubes).
- welding, will have challenges to control the temperature of the tube.




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Butcher
Shop Owner
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by Butcher

If you build it, they will not come. You'll be bankrupt. Carbon has this market covered pretty well.

XCProMD
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by XCProMD

Some good points all there. But you forget fatigue and a bicycle frame has to be mainly dimensioned against fatigue, especially talking about metals.


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LouisN
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by LouisN

I can see a potential for custom fit frames. 7075 material is dirt cheap compared to titanium.
That would bring custom made to low budgets niche. If the frames are under 1K g, then you will get customers.

Louis :)

XCProMD
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by XCProMD

LouisN wrote:I can see a potential for custom fit frames. 7075 material is dirt cheap compared to titanium.
That would bring custom made to low budgets niche. If the frames are under 1K g, then you will get customers.

Louis :)
Problem is 7075 tubes are not going to be cheap, if they’ll ever get produced


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bremerradkurier
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by bremerradkurier

How does 7075 compare in strength to some of the newer scandium based alloys?

bm0p700f
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by bm0p700f

7075 is used for hardness as well as strength. For extruded tubes it's not the best choice. To expensive for little gain.

by Weenie


robertbb
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by robertbb

2014 is the highest quality for bars/stems.

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