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Discussion Starter #1
So i was going to start a thread about the strength (or what I felt was a lack there of) on the CF tubes floating around lately. Although I have not done the strength test myself, I have had a conversation with a sales rep at the following company and was surprised as to the strength characteristics offered in the thicker options.
Carbon Fiber Small Tube

Chris explained that although they have completed no test themselves on the Round Pultruded Tubes offered, they did have a large section dedicated to describing the general strength of the products on a single layer basis. When asked, "what would happen if the structural integrity of the unit where to fail under extreme load?" said that the products general shape would hold but the product would split.

The prices on the site are very cheap and I think If I ever do mount a set of CF tubes, i may go for something a bit thicker in light of the potential for CF to damage my hand in a crash as some have eluded to.

This type of tube steps up the rigidity to yet another level.
Carbon Fiber Small Tube > Round Wound Tubes

I do want to continue my with my promise in a video to illustrate the strength of the tubes I have in possession. I will be taking an unbiased position on this topic and merely want to show the facts.

Take a look at their technical data found here.
What is Carbon Fiber? Carbon Fiber Technology
 

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Because im on here all the time?:woot:

Yes, I ride as much as I can but I "work" much more than I ride to be able to pay for all the sheet I buy and look at late at night while drinking and not riding. :D
Amen! Painful to see all kinds of people nickel and diming each other for 2nd hand garbage parts because they don't work hard.:eek:
 

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tensile modulus:

carbon 33
6063 aluminum 10
titanium 15

tensile strength:

carbon 580
6063 aluminum 36
titanium 170

Tensile Modulus:
Tensile modulus can be used as an indicator of the stiffness of a part. It is basically the applied tensile stress, based on the force and cross-sectional area, divided by the observed strain at that stress level. It is generally constant before the material approaches the point at which permanent deformation will begin to occur. It is most easily observed as the slope of the stress-strain curve prior to the yield point. In our chart the tensile modulus is shown as (MSI), or million pounds per square inch. Tensile modulus can also be shown as (10^6 PSI).
Tensile Strength:
The ultimate tensile strength is defined as the maximum stress that a material can withstand before failure in tension. Values are determined by an extension test. A simple example of tension would be the rope used in tension during a tug-of-war. Tensile strength tests are a common way to compare the strength of two materials. In the chart above tensile strength is displayed as (KSI), or thousand pounds per square inch. Carbon fiber is used most efficiently when loaded in tension. When a tube is loaded in bending some of the fibers experience tension while others experience compression.

while i look forward to the testing the numbers have been figured out long ago.

while tubing might not be best suited for frames(unless made correctly) the thought they are somoehow going to snap when most aftermarket companies use thinwall aluminum not known for its KSI or MSI.

I have mentioned b4 to several people take a woodcraft tube and a carbon one and do two or three tests and side by each the carbons are going to win every time like clockwork. Some will say the aluminums crash better and then just buy another set and anybody buying carbons is not looking for a crashproof set anyhoo i hope. they are lightweight,3 times stronger then aluminum and IMO vibes less and look cool too
 

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Some will say the aluminums crash better and then just buy another set and anybody buying carbons is not looking for a crashproof set anyhoo i hope.
Why not? If the aluminum bends, you may actually have a chance to ride back after a street crash. The carbon would snap and leave you waiting for ride home.
 

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Dr. Carbon
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tensile modulus:

carbon 33
6063 aluminum 10
titanium 15

tensile strength:

carbon 580
6063 aluminum 36
titanium 170

Tensile Modulus:
Tensile modulus can be used as an indicator of the stiffness of a part. It is basically the applied tensile stress, based on the force and cross-sectional area, divided by the observed strain at that stress level. It is generally constant before the material approaches the point at which permanent deformation will begin to occur. It is most easily observed as the slope of the stress-strain curve prior to the yield point. In our chart the tensile modulus is shown as (MSI), or million pounds per square inch. Tensile modulus can also be shown as (10^6 PSI).
Tensile Strength:
The ultimate tensile strength is defined as the maximum stress that a material can withstand before failure in tension. Values are determined by an extension test. A simple example of tension would be the rope used in tension during a tug-of-war. Tensile strength tests are a common way to compare the strength of two materials. In the chart above tensile strength is displayed as (KSI), or thousand pounds per square inch. Carbon fiber is used most efficiently when loaded in tension. When a tube is loaded in bending some of the fibers experience tension while others experience compression.

while i look forward to the testing the numbers have been figured out long ago.

while tubing might not be best suited for frames(unless made correctly) the thought they are somoehow going to snap when most aftermarket companies use thinwall aluminum not known for its KSI or MSI.

I have mentioned b4 to several people take a woodcraft tube and a carbon one and do two or three tests and side by each the carbons are going to win every time like clockwork. Some will say the aluminums crash better and then just buy another set and anybody buying carbons is not looking for a crashproof set anyhoo i hope. they are lightweight,3 times stronger then aluminum and IMO vibes less and look cool too
and whitw wings

the problem imo is that if the part is not overbuilt to compensate for the part of the tube experiencing the compression then the part is at risk for failure well before the tensile limits are reached because the compressive strength of a carbon part is essentially the compressive strength of the resin, which usually is nothing to write home about. By over building, or better yet structurally building the part to distribute forces in tension one can capitalize more on it's desired properties. obviously this is not achievable with a tube so one needs to overbuild it enough that the forces that it will see are distributed thru the part such that the tension side of the load is burdened in excess so that there is next to no flexion and minimal compressive forces are transmitted to the opposite side.

imo the most meaningful test would be to place the tube held up by both ends horizontally and determine how much force/mass it takes to destroy the part when this force is exerted midway between 2 ends. please post any results, this will be interesting.
 

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I'm not sure that tensile strength is the spec that should be looked at. Tensile strength is tested by pulling along the tubes longitudinal axis until the tube fails. I haven't witnessed any accidents where that type of failure would occur.

Shear strength is the spec I would be paying attention to; the amount of force that it would actually take to fail the tube in the lateral axis. That's similar to hanging the tube off the edge of a bench and hitting it with a known mass until it fails.

The carbon fiber tube with the honeycomb internals would probably be the strongest.

I think Jami has it right; although a carbon fiber tube could have a higher failure point, it would fail catastrophically whereas a metal tube would deform before total failure.
 

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Usual Suspect
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I think Jami has it right; although a carbon fiber tube could have a higher failure point, it would fail catastrophically whereas a metal tube would deform before total failure.
+1

If you've ever ridden/raced MTN bikes and have seen a carbon bar break, you'd know exactly what to expect if you crashed with a carbon tube on a motorcycle and why most that have crashed or have seen a crashed carbon bar would never ride one. The OPs concern about possible sharp edges from the carbon tube failing are well based.

FWIW the same could be said of Ti vs other metals in some applications. For example I won't run a Ti spindle in my BMX crank because I've seen a Ti spindle snap whereas a 4130 spindle will just twist. I'd rather have a slow and noticeable failure than a sudden, catastrophic failure any day.
 

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Discussion Starter #14
I'm not sure that tensile strength is the spec that should be looked at. Tensile strength is tested by pulling along the tubes longitudinal axis until the tube fails. I haven't witnessed any accidents where that type of failure would occur.

Shear strength is the spec I would be paying attention to; the amount of force that it would actually take to fail the tube in the lateral axis. That's similar to hanging the tube off the edge of a bench and hitting it with a known mass until it fails.

The carbon fiber tube with the honeycomb internals would probably be the strongest.

I think Jami has it right; although a carbon fiber tube could have a higher failure point, it would fail catastrophically whereas a metal tube would deform before total failure.
This I agree with. I'm making a jig (other than the obvious mount to one of the bikes) to test a load increased on a bar sitting in a clip on. I wish I had a heat camera to get NUTS on this to show where the most force/pressure is being focused.:rockon

I say the local RC riders and members come over for a Sunday Fun day to help me with this experiment.

I have two tubes buring a hole in my pocket...who's coming with me?

 

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+1

If you've ever ridden/raced MTN bikes and have seen a carbon bar break, you'd know exactly what to expect if you crashed with a carbon tube on a motorcycle and why most that have crashed or have seen a crashed carbon bar would never ride one. The OPs concern about possible sharp edges from the carbon tube failing are well based.

FWIW the same could be said of Ti vs other metals in some applications. For example I won't run a Ti spindle in my BMX crank because I've seen a Ti spindle snap whereas a 4130 spindle will just twist. I'd rather have a slow and noticeable failure than a sudden, catastrophic failure any day.

Having raced expert class MTB and CAT2 USCF, Ive destroyed many high end carbon parts. Ive seen many high end carbon parts explode on impact. While its can be made very light, and also made to be stiff, carbon has limited re-world uses. If you really thing carbon slip-on tubes will save you lap time, you need to actually go ride. Stop posing and go ride.
 

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I'm not sure that tensile strength is the spec that should be looked at. Tensile strength is tested by pulling along the tubes longitudinal axis until the tube fails. I haven't witnessed any accidents where that type of failure would occur.

Shear strength is the spec I would be paying attention to; the amount of force that it would actually take to fail the tube in the lateral axis. That's similar to hanging the tube off the edge of a bench and hitting it with a known mass until it fails.

The carbon fiber tube with the honeycomb internals would probably be the strongest.

I think Jami has it right; although a carbon fiber tube could have a higher failure point, it would fail catastrophically whereas a metal tube would deform before total failure.
Shear Strength: 12,500 psi


It will fail catastrophically possibly but people buy $3500 BST's.

Thet are not bought for longevity or crashes, they get tossed away each time to ruin them which is about the same for most aftermarket parts that ger ruined or even OEM's

I have run carbons now for 9 years without issue and factually they are stonger then aluminum in every count including shear strength. Aluminum is one of the weakest, softest, and cheapest metals and it is widely accepted as the norm for clip tubes i am not sure why a superior, stronger, lighter product is so far a reach for some to understand?

it is many times stronger then steel of the same weight

withstands more laod cycles then metals

lighter then titanium

many times stiffer then metals

while i understand the initial concern from a i never heard of that b4, i do not understand the when it breaks it is broken worry.

has anybody crashed ohlins forks and OEm back to back and performed testing to show which ones are most likey to make it home or be less repairable? how about wheels, do mags crash better then OEM cast?

Just using these as examples i really don't want people tossing their bikes down the road and i know such tests do no exsist:D
 

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carbon fiber tube could have a higher failure point, it would fail catastrophically whereas a metal tube would deform before total failure.

we are not referencing any metal tube. i would assume we are referencing very thin wall 6061 hollow aluminum tubing. while it will deform the the aluminum the force needed to make that failure on the carbon the aluminum will be laying on the floor Lou.

really, 30% of the force needed to make the carbons fail will have completely ruined and made the aluminum worthless except for the rubber grips may be holding the halves together J/K:D

metal can bend and it weakens the parts where the carbon does not.

while the test will be interesting for sure the main question i have is will it show them to be safe or not. The test will be done in one or two direct manners that may or may not reflect on the direct application they are being used for and what the main goal of them is. I am sure testing the ti tubes i have against the aluminums will yield the same results as the carbon aluminums and yet they are not readily for sale either due to cost not safety:twocents

The strength and stiffness of composite tubing is very difficult to compare to metal tubing because of the possible variation in fiber orientation during layup. The strength, stiffness, and weight of composite tube is dictated by fiber modulus, fiber direction/placement, and resin system used. With metal tubing the properties are only dictated by the material type and dimension of the tubing itself. There is no directional element involved. This is actually one very large advantage composite tubing has over metal tubing.
 

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+1

If you've ever ridden/raced MTN bikes and have seen a carbon bar break, you'd know exactly what to expect if you crashed with a carbon tube on a motorcycle and why most that have crashed or have seen a crashed carbon bar would never ride one. The OPs concern about possible sharp edges from the carbon tube failing are well based.

FWIW the same could be said of Ti vs other metals in some applications. For example I won't run a Ti spindle in my BMX crank because I've seen a Ti spindle snap whereas a 4130 spindle will just twist. I'd rather have a slow and noticeable failure than a sudden, catastrophic failure any day.

how are you crashing the bike then holding onto sharp edges that cut you?

I am all for opinions but how is crashing aluminum bars on your bike a slow and noticeable failure? the bars do not fail on by themselves either slow or fast. they either fail or weaken do to human error/crashing. I am not sure the need for bars that won't beak or if they do break why you don't just replace them? If one is looking for $140 aftermarket clip-ons with unbreakable tubes using 6061 $10 a pair tubes might not have been the best choice.

It is pretty much accepted crashing ruins parts and you buy new ones
 

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From a Physics standpoint, the highest stress on a clip-on is just outboard of the mount. It would have tensile stress on the weighted side and compression stress on the underside. In a crash, it would absorb tensile stress on the impact side and compression stress on the opposite side. Shear stress is found in an ovoid transition zone, as a round object tends to distribute stresses as opposing tensile and compression forces.

From a Materials standpoint, none of that really matters. The clip-on is only as good as its flaws. For example, Aluminum can be cast or forged and made in varying thicknesses to increase its rigidity and crashworthiness. Likewise, CF can be made thicker or with a tighter weave to increase rigidity.

The only question is one of malleability. Metal is malleable and can bend. CF is not malleable. If metal clip-ons are stressed beyond their limit by a crash or even a pothole, they will bend. If CF is stressed beyond its limit it will simply break.

Another interesting issue is repeated cycle stress. This would be the constant loading and unloading of the clip-on as you ride. Metal tends to lose strength gradually through crack propagation when undergoing repeated cyclical stress, and tests such as dye penetrant, magnafluxing and eddy current can determine cracks and the part can be replaced before failure. However, CF maintains full strength with no crack propagation right up to the moment of complete failure, so there is no advanced warning. That is precisely the reason why we had issues with the CF wing spars on the F-117 stealth fighter.

And that is the longest post I have EVER made.

Eric
 

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Kurt, text me when you want us to show up and I will be there. Not sure Tom will show up as he will probably be drunk...
 
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