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Reynolds Steel - is it overkill?(9 posts)

Reynolds Steel - is it overkill?phlegm
Aug 6, 2002 10:19 AM
I've been thinking about getting a nice steel road bike, so I go over to http://www.reynoldsusa.com to learn about the different types of steel tubing they make. This is what confounds me. Reynolds 853 is said to have a strength of 1350 MPa. So I convert it to units I'm more aware of. 1350 MPa is equivalent to 196,000 psi. That's a lot!!!

Here's how strength is described on their website:

Strength (UTS): This indicates force per unit area required in MegaPascals (MPa) tested by pulling apart the material until it fractures . The higher the number, the more force that has to be applied to make it break. Reynolds prefer to quote "typical" numbers rather than the maximum possible in ideal condtions.

So my question becomes when will a bike frame ever experience anywhere near that kind of pressure? Even Reynolds 631 (a lower grade) has strength rating of 850 MPa (123,000 psi).
re: Reynolds Steel - is it overkill?Andreas_Illesch
Aug 6, 2002 10:31 AM
steel with such strenght allows tubes with very thin walls.
the columbus foco and ultrafoco steel has similar strenghts.
the thickness off the tube walls goes down to 0.4 mm for foco tubes

theorie:
if you make the tube walls thinner and thinner you will get such tensions of 1350 MPa.
but there are limits coming from welding capability and dent sensitivity
re: Reynolds Steel - is it overkill?phlegm
Aug 6, 2002 11:03 AM
OK, so say we have a 1 inch outer diameter tube with 0.4 mm walls. The cross sectional area is roughly 126 mm^2. 1350 MPa is rougly 303 lbs/mm^2 So that 1 inch diameter tube of 853 can withstand 38,000 lbs? That still seems like a lot.
re: Reynolds Steel - is it overkill?Andreas_Illesch
Aug 6, 2002 12:50 PM
it is a lot.
but your calculation and this value 1350 MPa are only for a pure axial load or tension.
but on all tubes and seatstays in a frame there are torsional and bending stresses and to make it more complicated these stresses are all dynamic not static.
there are formulas to get the maximal allowed torsional and bending stresses. it is still not fully clear where and how these stresses work. so a lot of safety factors are used in a calculation, they bring the 1350 MPa down to a much lower value.
as i said before you need some wall thickness for welding and to avoid dents.
modern FEM softwares and a lot of experience enables the frame builder too build these butted tubes with very thin walls.
re: Reynolds Steel - is it overkill?eoceneman
Aug 6, 2002 10:02 PM
Is is overkill? -> what do you mean? the better the properties of the steel, the lighter the resulting frame (in rough terms), and lighter frame = better (assuming the other properties are acceptable)

Are frames with Reynolds 853 overdesigned? -> no.
Add a saftey factors, shock loading factors etc to a maximum weight limit, and consider the mode in which the frame is actually likely to fail (not pure tension) and all the numbers will work out.

Maths??

1 inch OD tube with wall thickness of 0.4mm = 31.4mm^2 cross section

1350 MPa = 1350 x 10^6 kg/m^2 = 1350 kg/mm^2 = 2976.24 lb/mm^2

2976.24 lb/mm^2 * 31.4mm^2 = 93453lb (in tension)

The frame won't fail in tension though, so your calculations (apart from all being incorrect) mean nothing...

Oh, and sorry for being so harsh (wasn't really my intention)
re: Reynolds Steel - is it overkill?phlegm
Aug 7, 2002 8:41 AM
Yeah, I hosed the calculation for cross sectional area. I think we have different lb calculations because you're using lbm, and I used lbf. Pesky English units.
Fatigue....julio
Aug 7, 2002 9:23 AM
A road frame is more likely to fail from fatigue than a catastrophic failure (unless you crash really hard). Fatigue is caused by cyclic loading, ie. being flexed back and forth or twisted, for example you could pull on a paper clip all day and not break it but fold it a few times and it snaps. I'm not going to get into the metallury of it but if you're interested any materials engineering book should have plenty of info. Fatigue strength is usually 1/2 the ultimate strength but it is greatly affected by eveything from loading to temperature and manufacturing method (and more!).

Good Fatigue Strength data is kind of hard to come by, most engineering books don't have much detail and data obtained by testing a square coupon in bending won't be exactly the same as a tube in torsion. All big aerospace companies do their own testing and have their own proprietary data that eventually tricles down to the rest of us. Bike companies do some testing on their own products but don't really have the budget or time the aero guys do to dedicate to it. The best source I've found is Military Handbook 5, it lists everything about the tests and is a wealth of data.
It's all relativegrzy
Aug 8, 2002 3:23 PM
You can go millions and millions of cycles and never have a failure of a properly designed steel frame. A steel frame is much more like to fail from neglect - as in the owner wants something new. Come to think of it when was the last time you saw a steel frame fail due to fatigue - anyone. Nope - much more likely it was run into a car.
For that matter, how about aluminum?Spoke Wrench
Aug 9, 2002 5:18 AM
There's a gazillion of them out there, and I don't hear a lot of talk about fatigue failures. The most frequent complaint I hear is that 12 year old frames with 126mm dropouts can't be upgraded to modern 9-speed drivetrains.

I've never had a bicycle frame that didn't last way longer than I wanted it to.