thoughts on carbon dropouts on carbon forks

I have C/F drop-outs and steerer Tube, so far no problems...I have taken the front wheel off many times and haven't noticed any deformation...

I can't imagine any reputable Manufacturer (Cannondale in my case) using dangerous Forks...

thomaslee said:

Hi All,

I am noticing that some road carbon forks are now being made with carbon dropouts instead of aluminum dropouts. Is this safe? If I remember right, carbon fiber does not do well when it is deformed. My concern is that someone can tighten their quick release to tight and deform the dropout. At this moment, I feel safer with aluminum dropouts. What is everybody's thought?

Thomas

thomaslee said:

Hi All,

I am noticing that some road carbon forks are now being made with carbon dropouts instead of aluminum dropouts. Is this safe? If I remember right, carbon fiber does not do well when it is deformed. My concern is that someone can tighten their quick release to tight and deform the dropout. At this moment, I feel safer with aluminum dropouts. What is everybody's thought?

Thomas

Whether a CF fork uses aluminum dropouts and steer tube, or is all CF, isn't really the issue. More important is the basic level of design, testing and manufacturing quality control that went into the product.

I'd select a high-quality brand fork, and not worry a minute about it's strength. On the other hand, the $69 no-name superlight special isn't something I'd want to ride.

thomaslee said:

If I remember right, carbon fiber does not do well when it is deformed. My concern is that someone can tighten their quick release to tight and deform the dropout.

The compression from the quick release isn't a problem. The high stress point is the transition from the leg to the dropout. If it's properly designed, there's no reason why making this all out of carbon will be any weaker than carbon glued to aluminum.

I agree, in fact, it could be even stronger!

artmichalek said:

The compression from the quick release isn't a problem. The high stress point is the transition from the leg to the dropout. If it's properly designed, there's no reason why making this all out of carbon will be any weaker than carbon glued to aluminum.

artmichalek said:

The compression from the quick release isn't a problem. The high stress point is the transition from the leg to the dropout. If it's properly designed, there's no reason why making this all out of carbon will be any weaker than carbon glued to aluminum.

Campy record BB shells and other CF parts like bars,seatposts, and seattubes and steerer tubes fail from compression.

boudreaux said:

Campy record BB shells and other CF parts like bars,seatposts, and seattubes and steerer tubes fail from compression.

Not really. There's a big difference between crushing a hollow tube and squeezing solid piece of the material. While those cases you site may have some somewhat compressive loads involved, none of them are actually compressive failures.

thomaslee said:

Hi All,

I am noticing that some road carbon forks are now being made with carbon dropouts instead of aluminum dropouts. Is this safe? If I remember right, carbon fiber does not do well when it is deformed. My concern is that someone can tighten their quick release to tight and deform the dropout. At this moment, I feel safer with aluminum dropouts. What is everybody's thought?

Thomas

Since you are compressing the material in a direction perpendicular to the fiber layers, you are basically just compressing the epoxy matrix material. It's going to be like compressing a piece of plastic. But since you have a relatively large amount of surface area on the dropout its not a big deal.

On the other hand there is such a thing as stupid light. The trend towards making things out of carbon fiber is more of a marketing tool than anything else. For most people, even amateur racers, the difference between a 200 lbs bike+rider is going to be unnoticeable compared to a 199 lbs bike+rider.

Durability>light weight unless your sponsored and can get replacement stuff for free.

Mr_Potatohead said:

Since you are compressing the material in a direction perpendicular to the fiber layers, you are basically just compressing the epoxy matrix material. It's going to be like compressing a piece of plastic. But since you have a relatively large amount of surface area on the dropout its not a big deal.

It's considerably more complicated than that. Fork dropouts have fiber volume ratios well over 70%. When you compress the composite in an orientation perpendicular to the fiber orientation, most of the deformation (which won't be much) comes from the fibers being compressed. The failure mechanism is tensile fracture in the matrix.

artmichalek said:

Not really. There's a big difference between crushing a hollow tube and squeezing solid piece of the material. While those cases you site may have some somewhat compressive loads involved, none of them are actually compressive failures.

BS...............

boudreaux said:

BS...............

Insightful as always. Got anything to back that up with?

artmichalek said:

It's considerably more complicated than that. Fork dropouts have fiber volume ratios well over 70%. When you compress the composite in an orientation perpendicular to the fiber orientation, most of the deformation (which won't be much) comes from the fibers being compressed. The failure mechanism is tensile fracture in the matrix.

Your smoking crack. First you say the deformation is from the fibers being compressed then you say failure is from the tensile fracture of the matrix.

First off, things loaded in compression don't fail in tension.

Second,stress is proportional to strain. So if you are saying the strain is in the fibers, then the load is in the fibers and the matrix cant fail.

But that BS anyway. The modulus of the matrix is easily ten to one hundred times less than the fibers. It's going to account for most of the deformation even if it were 10% by volume.

In a direction perpendicular to the layers the stiffnesses are in series not in parallel.

Mr_Potatohead said:

Your smoking crack. First you say the deformation is from the fibers being compressed then you say failure is from the tensile fracture of the matrix.

First off, things loaded in compression don't fail in tension.

It's called the Poisson Effect genius. Look it up.

Quoted post said:

But that BS anyway. The modulus of the matrix is easily ten to one hundred times less than the fibers. It's going to account for most of the deformation even if it were 10% by volume.

More like ten thousand, but you're close.

Quoted post said:

In a direction perpendicular to the layers the stiffnesses are in series not in parallel.

That's a contiuum assumption that doesn't apply to high fiber volume ratios.

artmichalek said:

It's called the Poisson Effect genius. Look it up.

Well the poisson effect relates strains not stresses. In the case of the poisson effect you can have positive lateral strain without lateral stress under axial compression.

But go to your local ME and tell him your analyzing a composite loaded by a preloaded bolt perpendicular to its surface and you want to know what the tensile ultimate strength of the matrix is in order to predict failure and see what he says.

A typical epoxy modulus is 500000 psi versus fiber modulus of 30E6-50E6 psi

thus the 100 ratio.

Mr_Potatohead said:

Well the poisson effect relates strains not stresses. In the case of the poisson effect you can have positive lateral strain without lateral stress under axial compression.

So you know the words, but what do they mean? Or is that something you look forward to learning in your second mechanics of materials course?

Quoted post said:

But go to your local ME and tell him your analyzing a composite loaded by a preloaded bolt perpendicular to its surface and you want to know what the tensile ultimate strength of the matrix is in order to predict failure and see what he says.

I am my local ME. And I've done more than enough material tests to know how brittle materials fail under compressive loading. In fact most non-metalic materials are tested in compression to find their ultimate tensile strengths.

artmichalek said:

So you know the words, but what do they mean? Or is that something you look forward to learning in your second mechanics of materials course?

I am my local ME. And I've done more than enough material tests to know how brittle materials fail under compressive loading. In fact most non-metalic materials are tested in compression to find their ultimate tensile strengths.

Put down the crack pipe noob!

Any thoughts on filing the lawyer nubs off a carbon dropout? Would it weaken the dropout more than doing the same on an Al dropout? Should you seal the filed down area?

steve_wmn said:

Any thoughts on filing the lawyer nubs off a carbon dropout? Would it weaken the dropout more than doing the same on an Al dropout? Should you seal the filed down area?

file away its probably just a little nub of epoxy, non structural just a retention mechainsim.

Mr_Potatohead said:

Put down the crack pipe noob!

Clearly you are known by Mr Potatohead outside the cycling forum as well... There is nothing inaccurate or BS about anything Art posted (at least on this thread 😉 ).

wilmar13 said:

Clearly you are known by Mr Potatohead outside the cycling forum as well... There is nothing inaccurate or BS about anything Art posted (at least on this thread 😉 ).

Like the part where he said the fiber modulus is 10,000 times that of the epoxy matrix modulus? Which would put the eposy at about 5,000 psi. hmmmm...I don't think so.

You're bogarting the crack pipe aren't you?

You're both such funny little engineers.