BigMac on Steel

Metallurgy and cycling, the party animal topic of the cycling world!! Well, not quite but it's a facinating subject. I will include other posts from very knowledgable people here. This turns into a very technical thread thanks to Germanboxers and MadRocketSci. Great reading on Metallurgy and cycling.

William
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Posted by William:

Frames of today vs Yesteryear...
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What do you think of the thought that the thinner walled tubes of many frames made today just won’t stand the test of time over the long run? They may be able to be made stiffer by OS-ing the tube diameter, but what about longevity? Is the quest for lighter & stiffer frames sacrificing the longevity of frame performance? One would think that thicker tube sets would last longer. Someone mentioned one manufacturer saying that their frames had an average life of 5 years. I’ve heard people say replace every couple of years. If this is true, then it appears that some manufacturers are moving to disposable products like so much of what graces the shelves of stores today. Is this just a by-product of consumer demand? Technological advances? Everyone wanting lighter bikes? Or is it possible that “planned obsolescence” has reared its ugly head once again?


Just the kind of dribbling thoughts that flow through William’s mind as the caffeine is starting to kick in early in the morning.

William

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Posted by dbrk:

I remember in Cyclesport the chairman of Cinelli saying that their new aluminum frames _should not_ be ridden everyday or for more than a year or two, anymore than a Ferrari should be taken out on the road for everyday driving. The modern race bike as a specific, limited tool for a job is the obvious ratonale. Bikes are more "fragile" because roads and wheels are better but they can tolerate less. It's a throw-away world, after all. Why build something to last?

Most of my bikes will undoubtedly last far longer than I will at this point. My '72 Mondia Special, purchased new when I was a lad, still rides beautifully and I have three or four bikes made in the last five years of NOS 531 and they ride as well or better than anything else I own, imo. Still, I am not averse to modernity or to trying on some zooty stuff. The Hampsten Z1 has been a particular pleasure though I think I shall never get used to the difference between carbon and metal (my take is that carbon quiets the road as soon as possible and steel lets it diffuse over the whole of the frame, hence steel's soothing tuning fork-like quality, it's liveliness.)

But more honestly, I'd bet that the vast majority of aluminum, carbon, and ultra thin steel bikes last years and years and without much, if any, deteriorization in the quality of their ride. Unless the welds are corrupt or the glue comes undone or other reasons that would equally apply to more stalwart tubing, they will neither fall apart nor change. Of course, I am adamantly of the view that the quality of a ride does not change over the years due to metal/material changes.

Most of my favorite bikes will be no more obsolete tomorrow then they were the day I bought them just like most modern bikes will ride no worse tomorrow then they already do today.

dbrk
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Posted by OldDog:

I think all aluminum frames have a limited life (short) when used on a regular basis, and steel frames will last as expected for a very long time due to the longevity of the material. I don't know for sure but would expect todays steels to have better inherent anti-corosive properties and with coatings such as Frame Saver, should remain rust free at least as long as the tubesets back in the day, that is the the thinner tubes should not rust through. (any frame builders can chime in here) It will be interesting to see 10 - 15 years down the road if todays carbon layups are still going strong, with regular riding, barring crashes.
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Posted by BigMac:

William:

Your inquiry does not identify a single material but I assume you were primarily inquiring about steel frames as the alternatives have only been primarily produced in bike frames for 20-odd years. As for the "other" materials, the various aluminum alloy frames and plastics will have very finite service cycles, perhaps assisted by OS tubing and improved construction techniques but certainly not a 10+ year service life if used on a regular basis -- say 6k miles/yr. I suspect Ti frames, especially something with shapely OS tubes like a Legend, may in fact still provide servicable duty to your grandchildren...if they are so inclined to ride such a "dinosaur-era" contraption .

Specific to steel, yes tubes are drawn thinner but larger diameter than in 70's and prior to. Be aware however that vendors have made quantum leaps in steel alloys. The defacto 70's steel was Reynolds 531, a manganese-molybedenum alloy with tensile strength of maybe 125-130ksi. In mid-late 70's, Reynolds introduced 753, a specially heat-treated 531 that increased tensile strength to a claimed 175ksi. Now OS diameter tubing for bicycles was still a few years away but this increase in tensile strength allowed very thin walled tubing. For example a butted 531DT had typical wall thickness of 1.0/0.7/1.0mm or a lighter weight 0.9/0.6/0.9mm. The 753 was available as thin as 0.7/0.4/0.7mm. All being made of steel, the density is same but obviously far less material was required to acheive similar strength/safety/performance with 753 thus a lighter frame resulted. The thinner wall tubing was more prone to denting and rust damage because there was so much less material. 753 was available in very limited quantities and only to select builders who had to be certifed by Reynolds before they could purchase the tubes.

If we leap forward to today, 175ksi tubes are commonplace, in fact I believe every steel tubing vendor has at least 1 tubeset in their stable claiming over 200ksi! The belly of butted tubes is not really any thinner as most are unable to draw tubing thinner than 0.4mm (Columbus claims 0.385mm in at least 2 tubesets) but the ends are often thinner guage than even that legendary 753 tube. More importantly, the larger diameter tubes offer considerably higher torsional stiffness. Even in 753 frame construction, a 531 DT or specially drawn thicker guage 753 DT would often be employed in larger frames, that was an era of 28mm OD DT's. Today, a tube of similar tensile strength may be 32mmOD at HT and 35mmOD at BB offering higher torsional stiffness but can be lighter guage thus no added mass.

Back to your original inquiry, I do believe the "modern" steel frames with lighter guage OS tubes are certainly more prone to denting, they are also more susceptable to rust failure because the thinner guage has removed much of that 'margin of safety' the heavy guage allowed. These are only concerns to those who may neglect and/or abuse their frames. Don't bash around you frame, treat inside of tubes every 5 years or so with Boeshield..."problem" solved. I would personally be a bit reticent about the longterm durability of TIG'd steel frames. I know some builders consider this somewhat over cautious but somehow these super-thin walled tubes being melted together causes some consternation with 20 year service cycles. With all of the above said, I have personally owned MANY lugged steel frames during the past 35 years and have never had one last more than 25k miles w/o some failure. Yes they are in most cases easily repaired, but never-the-less that is my experience.

Ride on!

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Posted by zap:

This is a complicated question.

1-Materials (steel, carbon, al) are superior today than what was available even 5 years ago.

2-Designs are more sophisticated to better withstand forces and fatigue.

3-Build quality. This is still the most important aspect to longevity.

Metal tubing is thinner today, but it's oversized and shapped. Oversizing tubes increase strength quite a bit. Double the diameter of a tube, strength goes up 4x, if wall thickness stays the same.

But wall thickness is a problem. It's easy to dent thin steel and al tubes, so crash worthiness isn't what it used to be. Ti will hold up better in this regard.

I think most people will sell frames before useful life expires.

By the way, high tech even allows todays Ferrari's to be driven every day.

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Posted by MadRocketSci:

maybe a metallurgist can say for sure, but, i don't think that yield strength and fatigue resistance are the same thing. more material = more margin for microcracks (are these called "dislocations"?) that develop over time...

disclaimer: took this class a long time ago and my engineering materials book is at my parent's house so correct me if i'm wrong....

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Posted by Andreu:

we live in a throw away society. Even if it is not true, the notion of being able to change your belongings after 5 years because the manufacturers have built in obsolescence is appealing to alot of people.
A

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Posted by climb1742:

i may be superficial but i honestly doubt in ten years i'll want to ride the bikes i'm riding now. there may be one or two, but as zap said, i'll tire of them before they fatigue. sorry, here i guess i'm part of the problem, not part of the solution.

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Posted by Germanboxers:

Quote:
Originally Posted by MadRocketSci
maybe a metallurgist can say for sure, but, i don't think that yield strength and fatigue resistance are the same thing. more material = more margin for microcracks (are these called "dislocations"?) that develop over time...

disclaimer: took this class a long time ago and my engineering materials book is at my parent's house so correct me if i'm wrong....



Yield strength and fatigue resistance are two very different things and so very unfortunate for Aluminum that they are. This is the primary reason many Al-tubed frames have massive diameter tubes...fatigue resistance. With steel there is a fatigue limit, a stress level that if not exceeded will NOT contribute to the eventual failure of the material through repeated loadings. Aluminum does not have this limit. With Aluminum every single stress applied eventually contributes to the failure of the material. Small loads contribute a little, big loads much more, but eventually it will fail if ridden enough.

The "more material = more margin for microcracks" is... how can I say... WRONG! MadRocketSci, I think you've confused a couple different metallurgy terms. "Microcracks" may be used sometimes in the place of "stress risers", but it's pretty uncommonly used among Mets. There is no reason to believe that more material = more margin for stress risers, certainly not the small additional material we are talking about. Stress risers are often created by extreme geometries (we're not talking "crit geo" versus touring geo here) and/or bad assembly/machining, etc.

Dislocations are missing planes of atoms within the crystal structure of the metal. They are highly valuable to the metallurgist for without them, there is little to do to control the strength of materials. Dislocations cause a stress field within the crystal (for just a few atomic spacings). As external stresses are applied and slip begins, dislocations move. To strengthen (raise the yield strength) of a material, we introduce other stress fields by alloying (makes crystal bulge out just a little), precipitates (a small, coherent with the crystal "rock" will create a stress field), reducing grain size (grain boundaries create stress fields), etc. These stress fields react with and impede the movement of dislocations. By controlling these, we control the strength of the material.

Sorry for going off on a tangent, but as I've said before on this board, I've so few things I really know that when the topic comes up I tend to go off. I'm a metalllurgical engineer by training, but I play a mechanical engineer in "Days of our Steel Rolling Lives". Have a great night everyone!

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Posted by MadRocketSci:

Thanks Germanboxers for the clarifications!

Like I said, it's been a LONG time...materials engineering was a 2-unit class in the aerospace curriculum, and a crappy class at that...the prof made us read some soft cover orange book called "Engineering Materials I" and then regurgitate it on the final. Now that it's barely coming back to me, I did use the wrong term. Dislocations are those things that you're trying to move around when you cold roll something to increase yield strength, right?

The picture I have in the brain is little cracks in steel propagating...i recall that the stress at the tip of a crack is 3x larger than without the crack. The crack slowly grows as stress is applied until the material fails. Is the assumption that more material gives it more room to grow before failure occurs wrong?

I guess the point I was trying to make was that everybody equates strength of the material with fatigue resistance. I'm still not sure this is the case. If you have a steel tube that has higher yield strength but less wall diameter than another steel tube, does it lower or roughly the same fatigue resistance?

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Posted by Germanboxers:

>>>Quote:
Originally Posted by MadRocketSci

Dislocations are those things that you're trying to move around when you cold roll something to increase yield strength, right?>>>



Correct! Just as alloying elements, grain boundaries, etc have stress fields that interact with and impede dislocations, dislocations interact with and impede other dislocations. Cold rolling introduces massive quantities of dislocations and dramatically strengthens the material. It also makes it very brittle.


>>Quote:
Originally Posted by MadRocketSci

The picture I have in the brain is little cracks in steel propagating...i recall that the stress at the tip of a crack is 3x larger than without the crack. The crack slowly grows as stress is applied until the material fails. Is the assumption that more material gives it more room to grow before failure occurs wrong?>>>



Correct. I must have misunderstood you. I thought you were suggesting that more material = higher probability for stress risers and the microcracks they form. Yes, more material buys you some time, I suppose.


>>Quote:
Originally Posted by MadRocketSci

I guess the point I was trying to make was that everybody equates strength of the material with fatigue resistance. I'm still not sure this is the case.>>



There are many factors to consider. Most associate the strength of the material with yield strength. This is, of course, different from stiffness. In fact, stiffness is roughly the same for all grades of steel from soft/ductile steels to the strongest more brittle steels. Stiffness relates to the elastic portion of the stress/strain curve, whereas yield strength relates to the stress at which the material begins to plastically deform.


>>Quote:
Originally Posted by MadRocketSci

If you have a steel tube that has higher yield strength but less wall diameter than another steel tube, does it lower or roughly the same fatigue resistance?>>



I wish I could answer this intelligently, but my education/experience in this area is over 15 years removed. I would guess though, in the context of bicycles frames, that you can't really frame (no pun intended) the question in this way. It's probably more appropriate to discuss fatigue by discussing the strains, rather than the stresses. A larger diameter tube is stiffer and would therefore deflect/strain less. I would imagine that this is one reason Al frames are usually made with large dia tubing, usually much larger than what would be needed to make a reasonably stiff frame. It's likely a safety margin that also allows for greater life of the frame since the strains are less. Is the move toward smaller diameter tubing with Al frames the reason some say they are only good for x-years now? It probably plays a role.

With steel, the limit is probably never exceeded with normal riding/racing unless an accident occurs. Even then, you still have a great deal of life left in most cases. I would bet that most steel frame designers don't give too much attention to fatigue failures? Maybe someone with more knowledge (paging all you frame-makers of fame) could answer this question?

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Posted by Andreu:

Out of interest and further along the tangent..
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how homogenous is metal....does it have a grain (like wood)? I presume the atoms are lined up in a certain way and can be manipulated to line up through processing? How do they make tubes for bikes (and where are the biggest stresses introduced into the tube)?
Thanks for info.
A
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Posted by Germanboxers:

>>Quote:
Originally Posted by Andreu

how homogenous is metal....does it have a grain (like wood)? I presume the atoms are lined up in a certain way and can be manipulated to line up through processing? How do they make tubes for bikes (and where are the biggest stresses introduced into the tube)?>>



Most metals have a "texture", an anisotropy. In otherwords, the strength and ductility in one direction is somewhat different from another direction. Most of this is due to the forming processes used, not an intrinsic property of the material. They do not have a grain in the sense that wood does, unless it is cold worked and not fully annealed. We speak of "grains" in that each grain is a collection of crystals that are oriented in a certain way. Adjacent grains are oriented differently. All, however, have the same crystal structure.

For most steel alloys, the atoms are arranged in what is called a body-centered-cubic structure (imagine a cube with an 1/8 Fe atom at each corner and another stuffed in the middle of the cube). There are some grades of stainless (high Ni varieties) that are called "Austenitic Stainless" that are arranged in a face-centered-cubic structure (imagine a cube with an 1/8 Fe atom at each corner and 1/2 Fe atom on each face of the cube).

I believe that tubes for bicycles frames are seamless tubes, basically solid steel rods that are pierced and then drawn to make the tube?? If they are indeed seamless tubes, then the stresses are fairly uniform. Of course joined ends are subject to higher stresses. I would love to see bicycle tubes drawn...anyone have access for a field trip???!!!

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Posted by William:

Great feedback everyone!!! Just the kind of information I was hoping the fine group of Serottaians here would contribute.

I got to thinking about it looking over my bikes as well as lurking on the frame builders’ list. The 25-year-old Raleigh Super Course is in great shape and no rust. I foresee this one living for many more years. My Serotta is a solid, stalwart frame that I’m sure will match the Raleigh for longevity. My aluminum Bianchi on the other hand, though very light and fun to ride will die long before the other two. It’s by far the lightest bike I have ever owned, but it will die if I continue to ride it as I do now.

My original question was really about comparing older steel tubing to newer steel/alloy tubing (which I didn’t make real clear ). But please feel free to add info about the other materials where appropriate.

From a strictly non-engineering POV, it seemed logical to think that the thicker walled tubing of old, though not as stiff as the thinner OS grade tubes of today, would handle stresses over a longer period of time. A longer cycle life? Thinner walled OS tubes though stronger, lighter, and stiffer in the short run end up having a shorter cycle life?

Now, whether a “cycle life” means anything to the individual is another question. If you like to upgrade every few years then it’s really a moot point. Sell it and let others worry about it. But, if you tend to keep things and use them till they die, it may be more of a concern. One should reasonably expect that if you pay $2,000 - $7,000+ on a frame/bike, it would last for quite a few years of regular use.


>>Quote:
as I've said before on this board, I've so few things I really know that when the topic comes up I tend to go off. I'm a metalllurgical engineer by training >>

Germanboxers…....I WANT TO PARTY WITH YOU!!


William
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Posted by zap:

Germanboxers-great posts.

Regarding stiffness (tube) and tensile strength, I had an interesting discusion with CoMotion when specing our tandem 12 years ago.

My wife and I tested a CoMo which was very much to our liking. Great ride with very good lateral stiffness which is very important in a tandem frame. I was informed that CoMotion had just started building the Double Espresso with Tange Super Prestige tubset which has significantly higher tensile strength than the True Temper tubed bike we tested. The Tange Prestige tubed tandem frameset would be 2-3 lbs lighter. Boy did my ears perk up

I knew that anything lighter would have less material, so I thought the Super Presige would create a wippier frame. I also did not believe tensile strength contributed to the stiffness of the tube. Additionally, tubing diameter between the two was virtually indentical.

Not wanting to sacrifice lateral stiffness, I asked CoMotion about this and they did confirm that thicker walls and/or larger diameter contributes to frame stiffness, not tensile strength. Larger diameter Super Prestige tubing was not available at the time.

So we got the heavier, stiffer bike and have been happy with our choice for 12+ years.

The amount of material also affects fatigue. As William points out, thicker tubes will last longer. But, larger diameter tubes will be put under less stress for a given amount of force extending fatigue life even with thinner tubing.

Higher material strength (tensile) improves fatigue life as well.

Whats different about Al alloys is that the fatigue cycle to failure is different from steel alloys. Under repeated "full" loading, steel will constantly slope downwards with each cycle until failure occurs at around a million cycles.* Aluminum on the other hand decreases slowly past a million cycles until it fails at around 500 million cycles*!

But we know that most aluminum alloys are weaker and less ellastic than steel alloys. So it takes less force for aluminum to begin the fatigue cycle. So designers that use aluminum need to limit the amount of movement if fatigue life is important. So a designer increases tubing diameter or adds more material to acheive this. Remember, aluminum is 3 x lighter than steel.

I know some steel builders think this analogy is stupid, but look at airplanes and how those aluminum wings flex. Some suspension designs use aluminum chain stays (Castellano & Klein) with great success. But they all limit the amount of movement (flex) to increase fatigue life.

As cyclists, I think pretty hard sprints (Pot hole or two ) will introduce fatigue cycles on many bicycle frames. Especially big boys like TooTall and William.

Fatigue cycle tests conducted by EFBe in Germany appear to confirm this. Trek OCLV and Cannondale frames (I don't own either) repeatedly come out on top against steel and Ti frames (and other carbon and Al).

By the way, I'm not an engineer and no one paid me. It's a hobby.

Enough of this, get out and ride.

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Posted by William:

Here is a short but interesting article on how "NOT" to test a frame for failure.

http://hea-www.harvard.edu/~fine/op...frame-test.html

Study up BillyBear, quiz on Monday!


William
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Posted by zap:

William,

Good link. Thanks. I see Anvil are big fans

The plot deepens.

What I can't figure out is how long some (note some) of those Vitus Al noodle frames are still in use. I have a friend that still rides his 16 year old Vitus hard.