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Old 04-22-07, 11:34 AM   #1
me thinkst
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steel v. aluminum (denting)

An interesting debate has developed on SSFG forum as to the dent resistance of steel vs. aluminum. Members there are arguing that a steel frame will be easier to dent than an aluminum frame of similar weight and quality. I know this question depends on so many factors, but I believe the steel tubeset would resist denting better than thin walled aluminum would.
Any thoughts on this here?

Example:
a 4130 tubeset-




[whoops]



I have to think a dent of the same impact would put a hole straight through an os aluminum tube even if it is of the same weight (i.e. thicker wall).
And then what about these new hardening "super steels"?
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Old 04-23-07, 01:20 AM   #2
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I'm sure there's correlation between material strength, hardness and wall thickness there somewhere.
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Old 04-23-07, 05:52 AM   #3
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Well, I thought I better get in here quick, before I'm beaten to the punch by anyone who feels the need to question my two penn'orth.... ;-)

This is a very complex issue, as the stripey man pointed out. But it's more complex than that. I think, ages ago, we touched on the mechanics of denting tubing. but I could be wrong....

The energy required to dent a tube has four factors: Materials' initial strength level, materials' work hardening rate, the ratio of wall thickness to external diameter (hence the actual strain involved), and rate of strain application (plays into the strain rate sensitivity). Today, i won't tiouch on them, unless specifically asked, and I'll try to keep this brief....

So, we take an example where we're talking really lightweight frames. This situation will give you the thinnest steel tubing to tube diameter ratio by the largest margin. In this situation it is most likely that the steel tubing will dent first, unless it's Aermet*. Reason is simple. No matter how much stronger the steel (within reason), the strain involved in the denting would force it past it's yield point. It's not stress that takes it to it's yield, its geometric strain. You're shown that strain lags stress when you do basic engineering. Not so. Tensile tests are a bunch o' lies ;-)

Now, we go to the most likely scenario. Moderate weight frames, where the steel tubing thickness is around .55mm at the thinnest. Now we have an interesting issue. The 'denting-firstness' of the steel frame will be governed by the tubing diameter, the larger the lower the dent resistance... Downtubes in steel will dent easiest, but the rear end, and the top tube will be on a par.

Finally, chunky frames. Steel wins.



*Aermet is a very interesting steel. It's strength and toughness figures are just so high by comparison to other frame materials, even other steels, that it woul dhave to be an *extremely* thin steel tubing that would dent before an aluminium alloy, so thin that it would be impractical to draw and/or centreless grind to dimension.
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Old 04-23-07, 06:04 AM   #4
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isn't ox-plat going to be stronger (on it's surface) than it's 6061 or 7075 counterpart? i know that it's stiffer and has less deflection based on http://www.bobbrowncycles.com/eng.htm

edit*
i'm still reading thru Falanx's post and am looking up Aermet
why aren't more builders using Aermet?

Last edited by me thinkst; 04-23-07 at 08:15 AM.
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Old 04-23-07, 11:32 AM   #5
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Quote:
Originally Posted by me thinkst
isn't ox-plat going to be stronger (on it's surface) than it's 6061 or 7075 counterpart? i know that it's stiffer and has less deflection based on http://www.bobbrowncycles.com/eng.htm

edit*
i'm still reading thru Falanx's post and am looking up Aermet
why aren't more builders using Aermet?

I'll answer these in the reverse order.

Because Aermet is what is known in the Greater London borough as a f***in' toilet. It is the very mechanical properties that make it desirable as an engineering material that make it financially unviable as an engineering material. It has 50% higher plain-strain fracture toughness that 4340 (until the USAF accepted Aermet and 300M, far and away the toughest steel they used) at 25% higher strength, previously unheard of properties outside of the maraging steels.

Short and curlies of it? It's impossible for small engineering companies to work and large engineering companies wont make anything smaller than plane parts.


Now, as I said, initial strength of a material is only one of four parameters that control denting. If the geometry - the thickness of the tubing: diameter of the tube ratio is tiny, then the total energy required to dent the tube will be less than a much weaker material.

The easiest way to envisage this is to bend a plastic drain pipe and a coke can in your hands. The can is much, much stronger than the PVC pipe. In fact, the wall of the can is about 10 times stronger than the pipe, but you'll dent the can first. Why? Because it's strength has still been overwhelmed by the substantial bending you've given it with respect to it's thinness of wall.
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Old 04-27-07, 04:54 PM   #6
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Quote:
Originally Posted by Falanx
(until the USAF accepted Aermet and 300M, far and away the toughest steel they used) at 25% higher strength, previously unheard of properties outside of the maraging steels.
What about other miraging steels? Aren't there others that can be (and are being) used in bikes?

953, for example (and some other, similar steels) -- wouldn't the dent resistance be quite high (even with the thinner tubing, but especially with slightly thicker tubing than is currently used)?

Even 853. There are some reviews on mtbr.com that give some empirical evidence of unusual dent resistance for 853 frames, which are favored by certain aggressive riders who put a lot of dents on most frames.

***
How does Aermet compare with 953?
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Old 04-28-07, 05:36 AM   #7
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that's why I brought up ox-platinum. I understand it to be compairable to 853. I think true temper touts it for it's impact resistance and even provides lifetime warranties on the tubing itself. I've even seen BMX frames made from it...

As far as Aermet vs. 953, my brief research I read somewhere that they didn't butt Aermet tubing, so it would be heavier. also it had poorer resistance to fracturing and failure than 953. so save it for the landing gear.

pure conjecture on my part- I'm no framebuilder...

Last edited by me thinkst; 04-28-07 at 05:43 AM.
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Old 04-28-07, 03:18 PM   #8
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Quote:
Originally Posted by Niles H.
What about other maraging steels? Aren't there others that can be (and are being) used in bikes?
At $35,000+ per tonne before any mechanical processing, straight high nickel maraging steels are waaaaay outta the price range. 953 has less than half the nickel of straight maraging steels and this is reflected in it's halved cost. FerroChromium is about as expensive as FerroSilicon these days. It's just not economically practical to work with anything more expensive than 953's starter alloy. In fact, as far as I'm concerned 953's base alloy is not economically feasible in the kind of quantities it will be used in.


Quote:
Originally Posted by Niles H.
Even 853. There are some reviews on mtbr.com that give some empirical evidence of unusual dent resistance for 853 frames, which are favored by certain aggressive riders who put a lot of dents on most frames.
I'm not aware of these tests, so I'm afraid I couldn't comment. Are these specific 853 frames made of custom drawn tubing? It's a very difficult habit to break, but not assuming that a strong material will automatically be more dent resistant, because of the mechanics of dentforming is imperitive. Suffice to say, if these tubes had unusually thick wall:external diameter ratios at the testing zone, then they would demonstrate unusal results.

You need to bear in mind that even in high-end tubesets, tubes are not even close to perfect in shape. Minor inconsistencies in wall thickness, roundness etc will have pronounced effects on the results most severe of mechanical tests - most obviously the impact tests. Do you have a link for these tests? I'd like to see their method.


Quote:
Originally Posted by Niles H.
How does Aermet compare with 953?
Stronger, tougher, easier to weld. Utter b*tch to work.



Quote:
Originally Posted by me thinkst
As far as Aermet vs. 953, my brief research I read somewhere that they didn't butt Aermet tubing, so it would be heavier. also it had poorer resistance to fracturing and failure than 953. so save it for the landing gear.

pure conjecture on my part- I'm no framebuilder...

Actually, both of those peieces of data are wrong. I'm not sure where you got it from? Aermet 100 has 65%, yes, two thirds higher impact toughness than Carpenter Custom 455 (the steel 953 is made from) at 25% greater strength in the unworked condition. After working CC455 to the strength level it has as 953, Aermet has 400% greater impact toughness. Yes, that's right. It's four times tougher.

As an aside, trust me, the reason they make landing gear out of Aermet and 300M is because you want the absolute maximum fracture toughness there. You don't want a MLT shearing off a F-14 on a high sink rate carrier landing....
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Old 04-28-07, 04:56 PM   #9
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Quote:
Originally Posted by Falanx
Actually, both of those peieces of data are wrong. I'm not sure where you got it from? Aermet 100 has 65%, yes, two thirds higher impact toughness than Carpenter Custom 455 (the steel 953 is made from) at 25% greater strength in the unworked condition. After working CC455 to the strength level it has as 953, Aermet has 400% greater impact toughness. Yes, that's right. It's four times tougher.

As an aside, trust me, the reason they make landing gear out of Aermet and 300M is because you want the absolute maximum fracture toughness there. You don't want a MLT shearing off a F-14 on a high sink rate carrier landing....
it was a guy on mtbr, who said he worked at Carpenter, but I think I misinterpreted it and that he was compairing 300M to Aermet:
http://forums.mtbr.com/showpost.php?...3&postcount=49
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Old 04-29-07, 02:04 AM   #10
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Quote:
Originally Posted by me thinkst
it was a guy on mtbr, who said he worked at Carpenter, but I think I misinterpreted it and that he was compairing 300M to Aermet:
http://forums.mtbr.com/showpost.php?...3&postcount=49
Quote:
Originally Posted by Metallurgist At Large
Age Hardenable Alloys
Good question. Precipitation hardenable alloys are alloys that start at one strength level and then after a low temperature "aging" process, they go up dramatically in strength. Examples of age hardenable alloys are the heat treatable aluminums, Ti 6/4, and the Reynolds 953.

At the aging temperature, the atoms in the material start to move around and precipitates forms (on the microscopic level). These precipitates work like glass does in fiberglass. They take a material that is relatively soft and kick the hardness and strength way up. What is neat about these alloys is they can be formed when they are soft (butting, swaging, etc) and then they can be aged to the high strength. Many other steels are hardened using carbon which make them hard to impossible to weld or they require an after weld heat treatment to soften the welds

300M is an age hardenable alloy steel (not stainless). It is similar to our AerMet 100 but has poorer resistance to fracture and worse fatigue (it actually rusts worse, too). I would expect it can't be butted and would then be heavier than the 953 alloy, unless you wanted to weld extremely thin material (AerMet's problem).


You know, I've never heard 6/4 or 300M referred to as age-hardenable before. They are, but it's... it's very little in the way of their stregth that is provided by secondary phases... In fact, in 6/4 it's more titanium alloy that precipitates, but we'll save that for another time...

Bear in mind that that Aermet and C455 are both Carpenter products, so even the scientists there, if theiy're sufficiently corporate men are gonna have a bit of the old 'Our stuffs better' mentality. 300M is an old standard alloy.

He's wrong on the butting. 300M is very, very easy to work as it's strength is developed by first cold work, then quenching, then tempering. After all, it's nothing more than a high molybdenum 4340 steel with vanadium, and 4340 is used everywhere. It's the tempering that produces that little bit of age hardening, but in that case you could say all steels that are tempered so the distinction and importance of the term becomes lost.

300M is a very.... unusual steel. It's composition is designed to be very very resistant to tempering - it contains over 1.5% silicon - yet as pointed out, it's tempered to increase it's strength...

Metallurgist At Large is correct that Aermet has higher fracture toughness and rust resistance at the same strength than 300M, but is way off base on why 300M isn't used. That's just another economics thing. It's no more expensive, materially than 853, which is based off another fairly expensive aerospace alloy...
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Old 04-30-07, 03:21 PM   #11
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Quote:
Originally Posted by Falanx
Do you have a link for these tests? I'd like to see their method.
....
The empirical results I had in mind were given in some of the reviews at mtbr.com.
They were real-world test results, rather than lab tests. Some hard-riding mountain bikers who regularly destroy and replace frames (due to impacts from falls and rocks) were talking about 853 frames. They said that they held up much better than other frames they had gone through. They talked about having them repainted, rather than replaced (--with other frames, they replaced...). They expressed surprise at how dent-resistant these frames were.

These reviews can be found at mtbr.com, among the hardtail reviews. (The Jamis Dragon is one of the 853 bikes reviewed; there are some others as well.)
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Old 05-01-07, 05:43 AM   #12
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Cheers. I'll go have a shufty and report back
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Old 05-02-07, 09:03 AM   #13
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aermet is a composite alloy, not a steel. i met the guy that created it, the smallest application thats mass manufactured are the hooks that the naval jets use landing and a sea carrier. those hooks used to be made out of treated D2 but broke after 5~8 landings. aermet lasts ~5000 landings.

i agree with much of the assessment of what will dent first, it is likely to be steel in bike frame material assuming that the tube diameter and the wall thikness are the same, regardless of steel. when one gets into mixed alloys, then it's a whole differant story and it's no longer steel vs aluminum.

for the record, my opinions are based on machining and working with the automotive industry, namely custom bikes. i recently put together a bicycle frame for a friend going away and kind of got into bicycling and the fabricatiob of.
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Old 05-03-07, 05:51 AM   #14
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Quote:
Originally Posted by rivethead147
aermet is a composite alloy, not a steel. i met the guy that created it, the smallest application thats mass manufactured are the hooks that the naval jets use landing and a sea carrier. those hooks used to be made out of treated D2 but broke after 5~8 landings. aermet lasts ~5000 landings.

i agree with much of the assessment of what will dent first, it is likely to be steel in bike frame material assuming that the tube diameter and the wall thikness are the same, regardless of steel. when one gets into mixed alloys, then it's a whole differant story and it's no longer steel vs aluminum.

for the record, my opinions are based on machining and working with the automotive industry, namely custom bikes. i recently put together a bicycle frame for a friend going away and kind of got into bicycling and the fabricatiob of.
Then the 'guy that created it' failed metallurgy. AERMET 100 and 310 are nickel-cobalt-chromium-molybdenum alloyed secondary hardening ultrafine lath martensite STEELS. If by 'composite' you mean 'multiphase material' then yes, it qualifies. But then so does everything, up to and including custard. It's application history is irrelevant to the statement.

An enormous amount of misinformation on these and other forums is given to the uninitiated by people who either should know better or claim an expertise they don't have.

For the record, my facts are based on two degrees in metallurgy, specialising in ferrous metallurgy, processing and manufacture, and five years of industry experience. I don't think there's a person on here who knows steel like I do....


Oh, and I think you mean D6AC, not D2.

Last edited by Falanx; 05-03-07 at 05:59 AM.
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