Carbon Fiber Construction: 3

[EngineerJoe]

Hi,

I am looking at constructing a carbon fiber part that is essentially a 9"x12" sheet bent into a U shap. It need to have a strength comparable to a part made form 16 gauge sheet steel. I would most appreciate if some one could kindly point me to

- a description of process and technique for constructing carbon fiber composites, and
- a shop / contractor who can make small quanties of such things.

Thanks in advance.

 

[griffengm]

If you can get hold of a copy of the magazine "Aero Sports Connection", about April, 2003, I think, there is an article by Dave Ahlberg on making a part much as you describe.
The process can be done by most anyone but making the mold is the hardest part.

 

[MintJulep]

Carbon fiber is not magic. Simply copying an existing shape does not ensure that you will have a stronger part because it is carbon fiber. You need to design the part in such a way that it takes advange of carbon fiber's properties.

The basic process for producing carbon fiber composite parts is the same as for glass fiber composites. Any of the same processes can be used.

To griff's point, yes, most anyone can make a part of composite fiber. They may not make the part you need.

Of course, if you are just using carbon for sex appeal...

Take a look at the Composite Fabricator's Association web site.

http://www.cfa-hq.org/

 

[EngineerJoe]

Griffengm,

Thanks for the lead. I have not been able to track down how do get a back issue of the "Aero Sport Connection" mag yet, but it sounds just like what I need.

 

[EngineerJoe]

MintJulep,

Thanks for the cfa link, very helpful information for me who has no experience in this area.

I am not sure about sex appeal. Haven't seen any woman impressed by carbon fiber parts on motor cycles or in cars. But it does provide a cool factor for guys.

The reason I am looking at Carbon Fiber is to make this part very stiff for part of it (more layers), and some what flexible else where (few layers). I assume that is possible. Please correct if this is not the case.

 

[MintJulep]

Joe,

Ok, it is possible to make a thing from carbon fiber composite that has different stiffness in different locations. Fishing poles come to mind.

However, the difference in stiffness really has more to do with the geometry of the part. You can accomplish the same thing with glass fiber composite, metal, plastic, wood, etc.

So, if a difference in stiffness is the only reason you are thinking about carbon fiber composite, there are likely less expensive options avaiable.

 

[EngineerJoe]

MintJulep,

The reasons for carbon fiber are that the part must be as thin and light as possible and looks cool.

Since the part has a fixed shape, I am hoping to control its stiffness at different loction by using different number layer of fabric...

 

[CMcF]

Carbon Fibre is .... fiberous. To achieve stiffnes in a component, the fibres must be laid in a way that they will be in direct tension. To achieve flexibility lay them so that they will twist or bend. For serious stiffnes and strength, the fibres should be pre-loaded, before setting in resin. Think of reinforced concrete, not fibre-glass mat. I have used a company called TURBOFLEX for CF shafts, but I am not sure if they do anything else. Was it Lotus that made that CF bycycle?

 

[MintJulep]

So sex appeal is a factor.

CMcF is right on. The direction of the fibers in addition to the basic part geometry is what controls the stiffness. If the layup is such that the fibers are bending, then they provide very little strength to the part, and the properties of the cured resin are really what control the strength of the part.

 

[EngineerJoe]

CMcF/MintJulep,

Thanks for the tips.

I am planning on getting some fabric and resin to make a few flat pieces just get a feel of it. Any idea where I may find a step by step instruction on how to layup and vacum bagging?

 

[griffengm]

Joe,
The part described in Aero Connections was a nose panel for an ultralight airplane and from your description sounds like the cool factor is met.
If you want some additional insight into DYI vacuum baging, I suggest you contact System West who manufactures supplies you may need, review some back issues of Wooden Boat magazine, and check out Aircraft Spruce & Specialty book section for some of the publications on use of composites in homebuilt aircraft.

Griffy

 

[EngineerJoe]

Griffy,
Thanks for the info. I will check those out.

 

[dwegan]

Yea it was lotus who made the carbon bike. I guy that was involved in it used to have it on a web page but I cant find it anymore-

 

[snubengr]

Try this site. He built a bike from CF in his garage.

http://www.sheldonbrown.com/rinard/howibuil.htm

BTW, many high end bikes are made from CF these days and have been for many years. I ride one from the late '80s.

Cheers,

DA