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Old 07-09-2017, 10:50 AM   #1
Zebra

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Default Carbon fiber strength vs steel

If you love carbon fiber as much as I do, then you'll enjoy this video which demos how much stronger a carbon fiber drive shaft is than a steel one:

https://m.youtube.com/watch?v=hjErH4_1fks


I like this practical experiment because it doesn't talk about that strength to weight ratio stuff which isn't terribly useful in most real world applications. It's simply: here's a steel part and here's the same part made of carbon fiber. Look how much lighter and stronger it is.
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Old 07-09-2017, 11:14 AM   #2
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Pretty interesting. They didn't discuss the production method of the carbon drive shaft, looks like 100% carbon toe.
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Old 07-09-2017, 03:07 PM   #3
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Pretty interesting. They didn't discuss the production method of the carbon drive shaft, looks like 100% carbon toe.
I agree. It looks to be some type of filament winding process. It seems like the most efficient method of creating cylinder-like shapes.

The guy in the clip is from the British TV show Top gear. It used to be a great show (if you like cars) but not the sort of show that would go into any more than superficial detail on the cf production process. They were just explaining why cf is such a big deal in the performance car market.

I am interested in learning more about filament winding. I like the idea of being able to make parts without molds and being able to specify custom weave directions based on where you need the strength to be. It just seems a little too complex and expensive to set up if you aren't with a large company.

Judging from the appearance of parts from other auto manufacturers, it looks like sheet molding compound is the preferred method for non-round parts outside of the hyper-car makers.

The interesting thing to me about the test results is that they don't marry up to a lot of the data online about the strength and stiffness of CF compared to other materials.

The charts on Wikipedia show that steel has slightly greater stiffness than CF pound for pound. That test didn't just show cf to be stronger than steel. It seemed to show far greater stiffness too. The steel bent with 1/3 of the pressure even though the cf part weighed less. This means that either the online data is wrong, or I don't understand the online data properly...
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Old 07-12-2017, 01:01 PM   #4
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You have to use a mold with filament winding. Though it's called a mandrel. There are various types, some are removed others washed out.

As for material properties... there are various types of carbon which greatly effect things like tensile strength or modulus. And then the ply schedule, geometry, and resin type also make massive differences. This is why composites are more black magic than metals. You cant just compare a piece of steel to a similar piece of carbon and expect that to be the final results.

Filament winding is a good process for particular types of shapes and loads. It's fairly time consuming and requires specialized machinery to be done properly. If you have money or access to a machine it is probably a useful process.

I have a tube that I made using wet layup and silicone pressure molding for the sampe bridge contest some years ago.... i don't remember the exact figures but it weighed in at like 3 lbs or something silly and held 15000lbs of force on a 3 point bending machine with like less than .1" deflection before it failed on the edge but was otherwise completely un damaged. I could post a pic if you were interested. I used unidirectional sleeve and braided tube. Some great materials and exceedingly strong with super long fiber lengths.
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Old 07-13-2017, 08:26 AM   #5
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I work in the firearms industry, the new craze is carbon wrapped rifle barrels. With the barrels, they turn down or re-profile the steel barrel blank followed by wrapping with 6K carbon tow and high temp epoxy resins. Using a lathe similar to an old threading lathe, you can control the RPM of the lathe and the feed rate and angle of the tow as it is applied. After post cure, they do mill the profile a bit, not sure how that is done and a quality finish is obtained.

Pretty neat process and I can see a lot of benefits.
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Old 07-15-2017, 05:26 PM   #6
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Quote:
Originally Posted by sammymatik View Post
You have to use a mold with filament winding. Though it's called a mandrel. There are various types, some are removed others washed out.

As for material properties... there are various types of carbon which greatly effect things like tensile strength or modulus. And then the ply schedule, geometry, and resin type also make massive differences. This is why composites are more black magic than metals. You cant just compare a piece of steel to a similar piece of carbon and expect that to be the final results.

Filament winding is a good process for particular types of shapes and loads. It's fairly time consuming and requires specialized machinery to be done properly. If you have money or access to a machine it is probably a useful process.

I have a tube that I made using wet layup and silicone pressure molding for the sampe bridge contest some years ago.... i don't remember the exact figures but it weighed in at like 3 lbs or something silly and held 15000lbs of force on a 3 point bending machine with like less than .1" deflection before it failed on the edge but was otherwise completely un damaged. I could post a pic if you were interested. I used unidirectional sleeve and braided tube. Some great materials and exceedingly strong with super long fiber lengths.

Very cool and good information. Did you do regular infusion and some off the shelf epoxy or did you use something special?
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Old 07-17-2017, 07:31 AM   #7
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For the tube, it was actually wet layup. I used a toughened epoxy from PTM&W that had a very long cure time, I think it was something like 8 or 10 hours with a required post cure. But we actually finished up closed the molds and then heated it to like 150 or 180, so that the silicone would expand and compress the laminate. THing came out amazing. Looks like it was autoclaved. That process is amazing for making very strong parts. A little bit of a pain to make the mandrels and all the molds as they have to be pretty strong to resist the expansion of the silicone. A bladder is probably easier in some ways. Both of those methods work great though.
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Old 07-17-2017, 08:55 AM   #8
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Quote:
Originally Posted by sammymatik View Post
You have to use a mold with filament winding. Though it's called a mandrel. There are various types, some are removed others washed out.

As for material properties... there are various types of carbon which greatly effect things like tensile strength or modulus. And then the ply schedule, geometry, and resin type also make massive differences. This is why composites are more black magic than metals. You cant just compare a piece of steel to a similar piece of carbon and expect that to be the final results.

Filament winding is a good process for particular types of shapes and loads. It's fairly time consuming and requires specialized machinery to be done properly. If you have money or access to a machine it is probably a useful process.

I have a tube that I made using wet layup and silicone pressure molding for the sampe bridge contest some years ago.... i don't remember the exact figures but it weighed in at like 3 lbs or something silly and held 15000lbs of force on a 3 point bending machine with like less than .1" deflection before it failed on the edge but was otherwise completely un damaged. I could post a pic if you were interested. I used unidirectional sleeve and braided tube. Some great materials and exceedingly strong with super long fiber lengths.
It's so true about the "black magic" element of carbon fiber strength and stiffness. It's a hard one to explain to people who are more used to working with metals that have finite specs.

People like to compare the strength of materials using neat little charts with a simple numerical value for each one but it doesn't work like that.

A part is not automatically stronger and lighter just because it's made from carbon fiber. A poorly designed cf part can be heavy and weak. A well designed one can be light and 3 times stronger than steel like in that video.
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Old 07-17-2017, 09:29 AM   #9
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I agree. Just using black aluminum is a waste of the material. Metal is much easier to predict and machine. The process to get an equivalent or stronger composite part takes a bit more finesse and lots more details. The advantages are worth it if the costs justify. For transportation, it's a no brainer.

I'd be interested in seeing what your up to? I'm pretty into the 3d printing and composites. THere are tons of possibilities there. I wish I could get my hands on one of the LSAM large 3d printers, and then just print high temp molds... would make things much faster and more interesting.
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Old 07-17-2017, 05:36 PM   #10
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Quote:
Originally Posted by sammymatik View Post
I agree. Just using black aluminum is a waste of the material. Metal is much easier to predict and machine. The process to get an equivalent or stronger composite part takes a bit more finesse and lots more details. The advantages are worth it if the costs justify. For transportation, it's a no brainer.

I'd be interested in seeing what your up to? I'm pretty into the 3d printing and composites. THere are tons of possibilities there. I wish I could get my hands on one of the LSAM large 3d printers, and then just print high temp molds... would make things much faster and more interesting.
I went to Thermwood last November and got to see LSAM in action, along with some moulds they made to demo their machine. It was amazing. In discussion with them and Ingersol a bit for their machines. A lot of potential, and a lot of advancements still to be had. SAMPE had a great convention in Seattle a couple months ago, completely on additive manufacturing, small and large.
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