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Old 01-15-08, 10:42 AM   #1
oilman_15106
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Carbon Fiber is 10 times stronger than Steel

Saw something on the TV last night and thought I would stir things up in the New Year.

It was all about carbon and there was a very interesting section on how carbon fiber is made. The guy said carbon fiber is ten times stronger than steel and at least 3 times as light as steel! So for all the posts about fears of carbon fiber failing, and there are many, it seems your fears are misplaced.

I am going to look for a carbon fiber hammer to replace my Estwing!
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Old 01-15-08, 10:49 AM   #2
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Let the war begin!
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Old 01-15-08, 10:54 AM   #3
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You mean, let the war begin again, as it does about every 3-4 months.
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Old 01-15-08, 11:26 AM   #4
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First shot: I've seen a steel fork bend. I've seen a carbon fiber fork shatter.
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Old 01-15-08, 11:29 AM   #5
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I've seen a steel fork break, up close and personal, like when I was riding on it.
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Old 01-15-08, 11:38 AM   #6
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I think the myth/fact issues are around how the two materials fail when they do fail. Steel will bend/flex more allowing it to continue with limited functionality, while carbon fiber tneds to fails catastrophically. Hence, I can drop my steel frame from a second floor window onto the top of a steel fence post, and it might get dented. If I drop my CF frame in the same manner, it might shatter at the point of impact. Well, at least that's what I think will happen, based on no particular scientific evidence.
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Old 01-15-08, 12:08 PM   #7
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It was all about carbon and there was a very interesting section on how carbon fiber is made. The guy said carbon fiber is ten times stronger than steel and at least 3 times as light as steel! So for all the posts about fears of carbon fiber failing, and there are many, it seems your fears are misplaced.

When used in the same size/thickness/density (insert you choice of measurement here)

However.............they are not used in the same size/thickness/density (insert your choice of measurement here)

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Old 01-15-08, 12:11 PM   #8
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if you take a carbon filament and the same diameter steel wire, carbon is 10x stronger.


how you lay up and bond the carbon fiber dictates the ultimate strength of a part
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Old 01-15-08, 12:15 PM   #9
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The guy said carbon fiber is ten times stronger than steel and at least 3 times as light as steel!
What does "strong" mean?
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Old 01-15-08, 12:59 PM   #10
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What does "strong" mean?
It looks like DG's avatar.
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Old 01-15-08, 01:03 PM   #11
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I was out riding Saturday. I ran into a guy on a De Rosa which he had bought in 1983. It is still functional and useable after 24 years. I hear that carbon fiber tends to have problems with little nicks that steel would just shrug off.

Sure CF is the sexy material and you can probably build a lighter bike with it. But I sort of think that a good steel bike is more bullet proof.
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Old 01-15-08, 01:14 PM   #12
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What does "strong" mean?
Best question of the day. And its very important to understand the answer when discussing the properties of dissimilar materials.

Tensile strength
Compressive strength
Shear strength
Yield strength
Ductility
Hardness
Young's modulus

All of these are material properties (and there are many others).

Designers do not use the same dimensions when designing parts from different materials. Steel bicycle tubing is not as thick (wall thickness) as aluminium bicycle tubing because the steel is "stronger" than the aluminium. Thus the harsh ride attributed to aluminium frames. Carbon bikes are not built to the same wall thickness as aluminium or steel (there are many other properties that are different, some due to the direction of the fibre layup) so "strength" and "weight" are difficult to compare (no apples to apples here)

It is possible to design a carbon fibre spring but it will be a much different beast than a steel spring.
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Old 01-15-08, 01:24 PM   #13
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Ok, well the "guy" who said CF was 10x stronger than steel and 3x lighter is a guy who works on and designs parts for race cars, not bikes. Some of the parts are structural, some are not. Many of the structural parts of race cars are re-enforced CF, not a straight up laid weave. They are also engineered far past what bike parts are. The parts the "guy" was referring to are separately designed for different applications. Some are designed to break in a high speed collision, and disperse energy. Others are designed to maintain their integrity, protecting the driver from penetrating objects. Also, the show was about "carbon", not "carbon fiber", they only showed how CF is made and one major use for it.
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Old 01-15-08, 01:30 PM   #14
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I worked as a fibre glass Laminator back in the 70's and at that time- Fibre glass only had an expected life of 10 years before it started to degrade. Some of those boats made then are still going today.

Once I learnt the trade- I was put on the repair team. Boats with holes in them from allsorts of things and I can assure you that Fibre glass is strong- but Very fragile. I saw boats that had hit bridges and knocked chunks out of the bridge without any apparant damage- till months later. Then I also saw boats that apparantly has only just touched another obstacle and sprung a leak almost immediately.

Carbon fibre is the new Fibre glass and is stronger than GRP (Glass Reinforced Plastic) But it still has that fragility. It has a quality that has a lot of riders raving about it but I am afraid that it does not have the Durability of Steel- Aluminium or Unobtanium.

And going onto weight for a Bike frame. Taking it as about the lightest that can be made for durable use- and not the full out and out race frames that are lighter but made for a limited life. A CF frame can easily be as low in weight as 1 Kg. My Boreas frame is 1.2 Kg and the lightest steel frame I ever had was 1.6 Kg. Relative strength would be about the same on each but now drop a 5 lb weight on the frame from 10 ft. The CF would shatter- Alumiium would bend and the steel one would probably get a dent in it.
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Old 01-15-08, 02:11 PM   #15
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I worked as a fibre glass Laminator back in the 70's and at that time- Fibre glass only had an expected life of 10 years before it started to degrade. Some of those boats made then are still going today.
I've read that the expected life of a carbon fiber product, using current manufacturing techniques, is greater than 100 years. Thus its use in aircraft applications where a lifespan of 30+ years is normal.

Also that in tests which simulated the stresses on a bike frame from all angles normally experienced in a ride, that the typical CF frame lasted 3X-4X that of a steel frame. To the point of where they essentially never wear out in a practical sense.

Of course there is the impact damage issue that changes all of the above.
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Old 01-15-08, 04:10 PM   #16
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What does "strong" mean?
+1. These kinds of comparisons just drive me mad.

The other is saying things like "it's 3 times lighter than steel". What the h3ll does that mean? Does it mean it weighs one third as much for a volume of material, e.g. one cubic inch, or does it mean that given greater strength, less volume can be used resulting in a weight reduction of two thirds?

I have weighed specific stainless steel parts compared with Ti twins (both parts machined to identical internal/external dimensions) and the "volume displacement" math doesn't work out.

I hear the same kind of comparison tripe almost daily for all manner of topics. So many of us are so dumbed down we don't know how to compare things and the announcers don't want to sound stupid by repeatedly saying "X is better by a really, really whole lot".
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Old 01-15-08, 04:19 PM   #17
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Spider webs are said to be 5 times stronger than steel
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Old 01-15-08, 04:54 PM   #18
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Here's an interesting article of carbonizing warboats:
< http://www.cnn.com/2008/TECH/01/13/seals.new.boat.ap/ >

Don't know of strength, but the new warboat is supposed to add more cush for the crewmen's keisters. In this case, carbon wins over steel.

All good for the squids, but I doubt Army tanks get made of carbon any time soon.
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Old 01-15-08, 06:17 PM   #19
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We read the numbers, consider the claims.....and then live by our own "seat of the pants", personal empirical evidence. My 21 year old SL frame continues to ride true and straight, shows no cracks or ripples, and has a lovely "twang" on pavement. The Ultimate Ride is whatever pleases my senses and imagination. Scientific studies and laboratory are merely interesting-- sometimes.

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Old 01-15-08, 06:18 PM   #20
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Maddmax how dare you

Maddmaxx how could you. This is the over 50 forum and you have the nerve to mention young molecules. You know that this forum is limited to old molecules and some very old molecules. Once again you have to remind me that I will never have young molecules again

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Old 01-15-08, 06:28 PM   #21
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It looks like DG's avatar.
And that's another thing. I can't tell for sure but that photograph sure looks like me. Assuming that it is my photograph, shouldn't Digital be sending me a royalty for using it that way?

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Old 01-15-08, 06:52 PM   #22
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Maddmaxx how could you. This is the over 50 forum and you have the nerve to mention young molecules. You know that this forum is limited to old molecules and some very old molecules. Once again you have to remind me that I will never have young molecules again
Thus demonstrating shear strength of will!
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Old 01-15-08, 07:11 PM   #23
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I've worked with carbon fiber for 30 years... The problem in making comparisons is that metals have isotropic properties, meaning they have the same properties in all directions. Composites are anisotropic and only have mechanical properties in the directions fibers are placed, like the grain in wood. There are also many different carbon fibers, with different properties.

For example, and these numbers are rough but close, steel is typically somewhere around 100,000 psi in tensile strength and there is a carbon fiber that is almost 1,000,000 psi in tensile strength, ten times as strong. If this fiber were used to make tubing and all the fibers were oriented lengthwise, the tube would normally be around 60% fiber and 40% resin, so the tensile strength would be about 600,000 psi, six times as strong as the steel. The problem now is that this tubing could easily be crushed and wouldn't handle any torque, so fibers also have to go in those directions, further reducing the multiplier for tensile strength. Next problem is this particular fiber, 1,000,000 psi tensile strength, is hundreds of dollars per pound and used mostly in aerospace applications and not in bicycles. The fiber usually used in bicycles is around 600,000 psi in tensile strength to begin with, but then fibers need to go in several directions, so you can see that to get sensation on TV, it might be a truth to say there is carbon fiber that is 10 times as strong as steel, but it won't be realized by the time it is in a useable product.

In terms of stiffness, there is carbon fiber from 33 million psi modulus to 135 million psi modulus (this one is $1500 per pound, raw on the spool) and steel is about 30 million psi. All the same rules apply as far as fiber % vs. resin % and mixing different fiber orientations to make a complete product, so again the multiple depends on the fiber used and the use the tubing has been designed for.

The density of carbon fiber composites are actually 1/5 that of steel, but by the time you have fibers in all the needed directions, the wall is usually thicker than a steel tube designed to do the same job, so you don't usually get a product that is only 1/5 the weight of steel.

The fatigue life of carbon fiber composites is much longer than any metal and is actually ignored in many designs, and there is no corrosion, but carbon fiber composites can not take near the impact that metals can, so again - which one lasts longer? Depends on use and care.

I don't mean to write a textbook here, just hopefully clear some confusion. My point is that you can't really make a simple comparison that defines a multiplier for carbon fiber in general being "stronger" than steel. There ar elots of good frames out there in all materials. What we ride is really just a matter of personal choice unless we are so elite we should be thinking about the Tour de France, etc...
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Old 01-15-08, 07:19 PM   #24
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We read the numbers, consider the claims.....and then live by our own "seat of the pants", personal empirical evidence.
True that. I've actually got a bike with an aluminum fork, a couple with steel forks, and a one with a CF fork. I actually never give their "strength" much thought. I just get on my bike and ride. My own seat-of-the-pants thinking believes that bikes of all materials are modern-day marvels and (dare I say it) better than ever in most ways.
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Old 01-15-08, 07:20 PM   #25
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How hard is CF to work with relative to other materials in order to get good "strong" reliable, long lasting results?
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