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CityCyclingEdinburgh Forum » Stuff
"Introducing Reynolds 921"
(12 posts)-
Posted 11 years ago #
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Very little info on 921 so far, and nothing on Reynolds' website, but 921 is probably in the 1100MPa range for tensile strength.
931 stainless is about 1300MPa and used in the new Croix de Fer. 953 stainless is up to 2000MPa. Good quality 4130 Cr-Mo steel is anywhere from 500 to 700MPa.
Posted 11 years ago # -
For non stainless Reynolds
520: 700-900 MPa
725: 1080-1280 MPa
853: 1250-1400 MPaPosted 11 years ago # -
For old fashioned types:
531: 700-900 MPa
631: 800-900 MPa
753: 1080-1280 MPaPosted 11 years ago # -
For a stiff yet flexible ride with that undefinable "steel is real" quality about it (laterally stiff yet vertically compliant, etc), is higher better or worse?
Posted 11 years ago # -
"For a stiff yet flexible ride with that undefinable "steel is real" quality about it (laterally stiff yet vertically compliant, etc), is higher better or worse? "
Depends (and dunno). It will depend on frame geometry and other parts (wheels, fork ....). Also the higher strength for more expensive tubes will often mean that thinner (and lighter) tubes are used. Some will argue that the steel feel is a bit of myth and that other factors are more important.
Some more tech stuff at http://reynoldstechnology.biz/assets/pdf/rtl_steel_alloys_extract.pdf
Posted 11 years ago # -
It all depends.
A force on a material will act on the fibres. The intensity of force experienced by the fibres is called stress. Stress results in deformation and can be elastic or plastic, and is called strain. The strength of a material is its ability to withstand the stresses without failing. Failure is measured either at a given amount of deformation or at the point of total failure. Stiffness is not strength, and is a factor of geometry in relation to the applied forces.
'Steel is real' is mainly because aluminium frames must be designed not to flex, because of aluminium's tendency to work harden very easily. When a metal does this, it has experienced plastic deformation and, except for extremely ductile metals, is thus closer to its failure point (tension, bending, etc.) than before.
A stronger steel, that is, one that has a higher ultimate tensile strength, is no lighter than a weaker steel, because the density is very much the same. But the higher UTS allows thinner walls for a given diameter of section, and that means less material and less weight. If you want stiffness, increase the diameter of a tube. The mass increases less than the stiffness does.
Posted 11 years ago # -
This remonds me of the thick tubed Cannondales?? from the early 90's. Do I have the right frame type?
Posted 11 years ago # -
"less than a third of the price of the company's flagship 953 tubing and should be easier to source"
Posted 11 years ago # -
Oh and here's how aluminium alloy compares:
7005 - Al-Zn alloy. UTS: 400 MPa.
6061 - Al-Si-Mg alloy. UTS: 325 MPa,Posted 11 years ago # -
Before everyone gets bogged down quoting tensile strengths it's worth taking a look at a list of other properties for comparing materials. Going by only tensile strength steel is far better than alu but they don't make many downhill bikes out of steel. You can have a material with an extremely high tensile strength that would snap the instant you made a bike frame out of it, or something with a low tensile strength that would be very resilient.
The way in which engineers and designers choose materials is complicated far beyond anything that can really be put across in a forum or a quick PDF from a manufacturer. I've only studied the very basics and it's pretty terrifying when you see the difference 0.1% of an alloy mixture can make. Then you have fatigue, which is a whole other nightmare of complexity, where again shaving a mm or so of metal off a corner or something is the difference between a part lasting 1 year or 100.
Going back to steel vs alu, while alu is indeed 'weaker' in tension and compression, if you can form it into a big fat thin walled square beam that's going to be much stronger than a thin weedy steel tube. Of course it'll also be more rigid which means it might end up being weaker overall if it can't flex. Heck the effect of shape of beam strength is an entire textbook and a half of study in itself.
Posted 11 years ago # -
Re: thick tubed Cannondales - my MTB's aluminium frame is from 1988 or 1989, and according to Sheldonites should have fatigued to bits years ago, even including the decade of stairwell oublié is suffered. Still going strong. He said, tempting fate.
Posted 11 years ago #
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