More on deep aero carbon tubeless rims.



If you look at the link I posted above, you'll see what I believe is the answer to your question. Carbon fiber fabrics that contain other fiber types are readily available, with carbon/Kevlar being widely used in some products. I don't see it in the bike biz, however.

I think you misunderstood my post. I'm not talking about different fiber types.

CF fiber strands in a CF fabric are almost exclusively arranged in 'x' and 'y' orientations (in a flat, 2D layer) like the fabric in your clothing. Even if they are molded in tubes and other 3D shapes shapes, CF fabrics are still generally made in a flat plane. When multiple fabric layers are present, each fabric layer is fully separated by a resin layer and this causes delamination near the point of failure.

What I meant are long fibers arranged in all x, y, and also z orientations (3D). This means some of the fibers will be laid across multiple fabric layers. The present manufacturing processes prohibits such fiber orientations. Such fabric layup in theory would prevent delamination of the material all the way to failure leading to CF products with far greater durability and better able to withstand extreme application of forces.
 
I see what you're saying, but there are issues with it when you're dealing with fibers, especially with high modulus (stiff) fibers like carbon. You can only bend them so much in a layup before you start damaging the fibers. Crossing the fibers in a woven pattern has limitations, as it creates pockets within the fabric and between layers that must be filled with resin, which adds weight and reduces the overall strength. That's why bike frames are made largely with unidirectional carbon fiber layers, with woven fabric used mainly on the more "cosmetic" outer layers and in parts that see considerable torsional stress. Probably the two closest things to what you're envisioning are the woven tubes that Time and BMC use, and the use of carbon nanotubes in resins, which adds considerable strength, but also cost.

All that said, we're dealing with a proven, mature technology that continues to evolve. It's one thing to imagine improvements - which is good - but another to over-think and over-inflate the limitations of a technology. Whether you choose to trust composite technology or not, the bottom line is that it currently works extremely well and keeps getting better.
 
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I see what you're saying, but there are issues with it when you're dealing with fibers, especially with high modulus (stiff) fibers like carbon. You can only bend them so much in a layup before you start damaging the fibers. Crossing the fibers in a woven pattern has limitations, as it creates pockets within the fabric and between layers that must be filled with resin, which adds weight and reduces the overall strength. That's why bike frames are made largely with unidirectional carbon fiber layers, with woven fabric used mainly on the more "cosmetic" outer layers and in parts that see considerable torsional stress. Probably the two closest things to what you're envisioning are the woven tubes that Time and BMC use, and the use of carbon nanotubes in resins, which adds considerable strength, but also cost.

All that said, we're dealing with a proven, mature technology that continues to evolve. It's one thing to imagine improvements - which is good - but another to over-think and over-inflate the limitations of a technology. Whether you choose to trust composite technology or not, the bottom line is that it currently works extremely well and keeps getting better.

We're not sure it's going to be weaker (overall) or even get heavier. When I was doing destructive testing of CF parts, the first sign of failure is delamination at the fabric-resin interface in areas seeing compression forces.

In a CF part, the CF fabric provides most of the tensile strength while the resin provides compressive strength. The resin is much weaker in tension compared to the CF fabric and the forces acting to cause delamination between layers is under tension and since there are no fibers across the fabric layers, there's nothing reinforcing the resin against tensile failure between layers.

You are correct to point out putting some of the fibers across would create pockets within the fabric, etc. However, this only reduces the tensile strength of a CF part. A CF part is much weaker in compression where delamination first occurs when stressed to failure. That's why I'm thinking if we reinforce the weakest areas of a carbon fiber part (against delamination in areas under compression using 3D lay ups) would improve overall strength and durability of the part. This may even lead to weight savings as you don't need to reinforce areas under compression with more material as much as before.
 
Carbon nanotubes can dramatically increase the compressive strength of a layup (~30%), as they do exactly what you're suggesting. However, given the increased cost and complexity of using them, it's probably not feasible to do so in consumer products, though perhaps that will change at some point. For now, it's easier and cheaper to add just more carbon layers and make the layup stronger and stiffer that way, but it adds weight, too.
 
Carbon nanotubes can dramatically increase the compressive strength of a layup (~30%), as they do exactly what you're suggesting. However, given the increased cost and complexity of using them, it's probably not feasible to do so in consumer products, though perhaps that will change at some point. For now, it's easier and cheaper to add just more carbon layers and make the layup stronger and stiffer that way, but it adds weight, too.

The first mode of failure of a CF part during compression tests is the layers delaminate. We simply need to orient some of the fibers across the layers to delay the onset of delamination.

That way, a CF part can withstand higher compression forces / weight without damage. No need to use carbon nanotubes and make things a lot more expensive.

Why should we care more about compressive forces is because carbon parts are already very strong against tensile forces. Way way stronger against safety margins and much higher against compression strength. That means we can still allocate that excess strength under tension into compression strength and make the produce overall stronger against real world conditions.
 
The first mode of failure of a CF part during compression tests is the layers delaminate. We simply need to orient some of the fibers across the layers to delay the onset of delamination.
It's easy to say that we "simply" need to do something, but if it was simple, manufacturers would already be doing it. It's not as if nobody else has recognized this limitation and I'm sure there are plenty of brilliant engineers working on solutions. Apparently, a cost-effective and easy to manufacture solution doesn't exist...yet.
 
Hey, totally agree. The complexity lies in finding that cost-effective and manufacturable solution. Patience is key! ;)
 

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