What carbon do you use?

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#1

Hey everyone,

What kind of carbon fiber fabric is does everyone use for smaller motorcycle/car parts?

Can anyone give me a quick lesson on what the 3K or 6K and weight means when looking into buying fabrics?

Do some fabrics work better than others? I am having trouble with getting a perfect part when infusing, I assume its not the fabric but am ready to buy some more to continue testing.

I have only bought a couple yards from EasyComposites and am ready to buy some more. This is what I have bought so far. I don’t know if this is any good or not.

http://www.easycomposites.co.uk/products/carbon-fibre-cloth-fabric/22-twill-195gsm-3k-1m.aspx

#2

3K is the most common fabric when it comes to cosmetic parts. However, if you want faster buildup, and stronger parts. You’ll want to use a 6K or 12K fabric. Your first layer of carbon can be your 3K and then you can reinforce the part with a higher K fabric. You’ll save time, money, and have stronger parts :).

#3

So does a higher K fabric mean thicker? Meaning I would not need to use so many reinforcement layers? I have been using 3 layers of 3K 2x2 twill and even though I have not gotten a perfect finished part, the parts seem to be extremely strong.

What does the weight mean? When I am looking at fabric, I see 3K 5.7oz.

#4

The “k” of the fabric means how many individuals strands of carbon are in a single tow. So a 3k fabric has 3000 individual strands of carbon in one of the tows. A 6k fabric as 6000, and so on. The weight its exactly that, the weight of the fabric, usually in a per square yard unit.

#5

From what I have gathered the higher the number of threads per inch the less the fibre moves out of plane (also affected by weave type,) theoretically giving you better fibre orientation. That said as you increase the ‘K’ value the fabric generally becomes more difficult to manipulate, making applications to sharp bends an issue.

In terms of ideal mechanical properties you may want to use uni-directional cloth (can also increase the resulting fibre volume fraction) but due to cost/time vs. real world gains, actual gains may be considered negligible relative to cost…

#6

Also depending on the fabric the higher the K the harder it is to get nice join and cut lines for face work.

#7

Thanks everyone!

#8

Fabrics that have yarns with more filaments (6K, 12K) typically have a higher magnitude of crimp in the yarn. This moves the fibers further out of plane with the loading axis. As tension is applied the fibers try to straighten from their crimped state and stress the resin. Under compression the the out of plane fibers are prone do micro-buckling. The crimp can also reduce the tensile modulus of the laminate depending on the resin.

In general the flatter the yarn the better the yarn performs. For this reason crimp free UD materials perform best. HS8 typically perform the best out of the woven materials. I often have to resort to woven materials to meet the weight restrictions of the structure. If I need material going in 0,90, +45, -45 then 4 layers of UD exceed the weight requirements of the structure. Low crimp spread tow carbons are becoming more popular for this reason. Hopefully we will see a price drop soon for spread tow carbons.

If you’re just building bling at one atmosphere then is doesn’t matter. You can use whatever looks best or is the easiest to infuse/layup.

#9

ok so i was doing some reading (for my splitter) so my question is for a flat surface which one of these fabrics performs better?
1- 12K spread tow 5oz
2- 12K 2X2 twill 20 oz?
I am confused between K and weight! I know the K stands for number of strands in each tow but how do each of these properties change the performance of the finished laminate? I would appreciate if someone can explain it to me. or even direct me to where I can read and learn more about it. articles, books, anything :slight_smile:
and is spread tow easy to infuse?

#10

The “K” as you already represents the # of filaments in the yarn. The weight represents the areal weight of one square yard of fabric. So, the 12K spread tow only weight 5 ounce per square yard while the 12 twill weighs 20 ounces per square yard. The 12 spread tow in thin while the 12K twill is much thicker.

The major advantage to spread tow fabric is a reduction in crimp. Crimp is the waviness of the yarn as it goes up and over the crossing yarns. Crimp has two negatives: 1) It causes the fibers to be out of plane with loading axis. Think of it like a spring. When the fibers are put under tension the crimp tries to straighten which stresses the resin and reduces tensile stiffness of the laminate. Under compression the crimp promote micro-buckling. 2) The crimp creates more space between the fibers at the crossing yarn junctions that needs to be filled with resin. This increases the amount of resin need for a given amount of fiber.

Unidirectional fabrics and bi-directional mats have very little crimp. For this reason they are typically used in in the most demanding applications where higher fiber volume fractions and performance are needed. 1 atmosphere bagging/infusion can get a Vf 60% with UD materials. The only time woven materials are used is when “bling” is desired, speed of processing is required, or the available UD materials in multiple layers can’t meet the weight requirements.

Spread tow is very handy in very light structures where multiple layers of UD material can’t meet the weight requirements. It comes is very light arrangements and has fiber in two directions. It’s the next best thing after UD materials. It has low crimp but is usually psychotically expensive. You can get Vf of 55% or better with one atmosphere. It will infuse very nicely. Personally, I wouldn’t consider using the stuff unless the structure requires very thin and very light skins/walls.

The 12K 20 ounce twill has a very high degree of crimp. The yarns have go up and over rather large bundles. It’s typically used to speed up manufacturing and reduce cost. In general, multiple layers of lighter woven fabric is stronger, more durable, and yields a more favorable fiber volume fraction (Vf) than heavy woven fabrics. 4 layers of 3K will cost you $100 or more per yard while 1 layer of 12K twill is only $80 (often less), and less labor to handle. The advantage is with multiple layers you can very the orientations to maximize its properties while the one heavy layer to 12K will only allow fiber is two directions. It’s all compromises.

So, to answer your question :): Multiple layers of the 5 ounce 12K spread tow will perform better than the 12K twill 20 ounce fabric…but it will cost you a lot more money.

#11

Thank you for clearing that up, so one layer of 12k 5oz spread tow is weaker than 1 layer of 12k 20oz. however if I use multiple layers of 5oz to reach the same thickness of a 1 layer 20oz, it will be stronger but much much more costly :slight_smile:

#12

You got it.

Also do not forget multiaxials (often referred to as “non crimp fabrics” which are bundles of fibers stitched together. Can be cheaper and easier to layup than UD. Beware, though. There are different machines making multiaxials, and not all perform well. In theory, you would like the stitching not to go through a bundle, but just in between of 2 bundles. Some manufacturers can do that, some dont.

#13

So I get that the 4 layers of a 12K 5oz spread tow would be stronger/lighter than on layer of 20oz 12K twill. The question I have is, what if the weave pattern is similar?
So would laying up 4 layers of a 3K 5oz 2x2 Twill, or 2 layers of a 10oz 6K twill be much different then laying up one layer of a 12K twill 20oz? Would the three? layups have an equivalent amount of crimp in and the characteristics would be about the same?

#14

May guess is that 4 layers of 3k would have the edge in strengthen, weight, and durability over one layer of 20 ounce 12K. I never used 12K carbon so I’ve never done a batch test. I have tested glass samples and multiple lighter layers is usually stronger, more durable, and lighter.

#15

generally 3k weighs around 200gsm, 6k 370gsm and 12k 670gsm. This can vary on fiber type though, for example a 6k IM7 twill weighs around 200gsm and look the same as a standard 3k twill, this is because the fiber size for a IM7 fiber is much smaller than your standard HS carbon such as an AS4.

#16

Quite true. I would be interesting to test the difference between 3 layers of 3K and 1 layer of 12K.

#17

Make sure to use the right size fabric per piece. If you plan to make a tiny tiny part using 12K carbon fiber then you won’t get a good part. It also depends on how much detail your mold has.

#18

3K 2x2 twill is by far the most drapeable carbon fabric in my experience for making race car parts. My company have been making a number of parts from spread tow fabrics recently and these are definatly more tricky to work with than a twill fabric. Spread tow fabrics are good for making very light weight parts however that do not have any structural function. Such as an engine cover on a formula race car as we have found that you can oftern use just two plys of spread tow fabric where you may have previously used 3 or 4 plys of 2x2 twill.
However durability is greatly reduced compared to parts made from twill fabrics. This is simply because there is less materials used (hence is is lighter)

#19

You can use spread tow in structural applications. It’s very commonly used in wings, tail planes, and fuselages for UAV and competition RC gliders. It’s also being used for structural components in satellites. Spread Tow performs better than 2x2 twill in any structural application. It’s just very expensive to do so since it requires more layers and is very expensive to start with.