Design with carbon fibre 1

[shorion]

Hi all,

I'm looking into upgrading a design to carbon fibre or fibre glass from the ones we have that are currently made from steel. Its a simple inspection hatch and associated access parts. a couple of rungs. some tread plates.

Where would I be able to find information on how to design with carbon fibre, connections, design practice, limits, guides etc. Just anything to get me started really. Structural connections. Calculations and examples.


Regards

 

[adfergusson]

Hi,

Perhaps you should have a look at the current EdX course on Composite Materials:

https://www.edx.org/course/composite-materials-overview-engineers-uwashingtonx-aa432x

It looks like it goes through the basics of composites, including the very basics of CLA (although not in much depth by the look of it) and signing up will give you free access to MatLab and MatLab scripts for doing laminate analysis. Would have thought that would be enough to get you started.

If you want a more 'conventional' source of info then I'd recommend Barbero's Introduction to Composite Materials Design. Barbero's book is the only composite intro text that goes into damage based modelling. Alternatively, Kaw's book is a very good intro text and is particularly good on treating residual stresses. Third on my list would probably be Rawlings and Matthew (its well written, it just doesn't go through as much material as the previous two) and then Chowla.

Another big thing to look into is the effect of manufacturing process and other parameters on material performance (which you won't find much about in the above). I'd guess that if you were to replace steel with composite you'd use a woven or non-crimp fabric with a liquid resin based manufacturing process so the properties you might get from these could be very different to the values you mostly see in the above books (which are mostly from autoclaved prepreg materials).

 

[RPstress]

While I agree with adfergusson's recommendations (I particularly like Barbero and Kaw is also quite practical) you can find a bit of advice online at John Pilling's site at

http://www.mse.mtu.edu/~drjohn/my4150/

(you can also try his stuff at

https://sites.google.com/site/compositematerialsdesign/).

And you can also try

http://www.matter.org.uk/matscicdrom/manual/co.html.

That EdX course also looks quite interesting (I've signed up to check it out—thanks adfergusson).

You can design in composite as you can in any material but to get good results you should account for manufacturing methods early. You must also try to account for weaknesses of composite laminates (if you use a laminate) compared with isotropic materials you may have used before. This is similar to designing a structure in wood rather than metal. The analogy of wood is apt as wood has grain and it is similar in some ways to the fibers in continuous fiber composites. (Short fiber reinforced plastics such as glass/Nylon or carbon/PEEK can approximate isotropic materials but you must be quite careful to account for their idiosyncrasies such as how different manufacturing methods may align the fibers to a greater or lesser extent. Sheet molding compound or bulk molding compound are very common for simple parts such as hatches. They are often press-formed and given an elevated-temperature cure at the same time.) Some specialised manufacturers use continuous-fiber/thermoplastic matrix material to hot-form shapes from sheets, which with careful allowance for fiber deformation can be very effective.

Polymer matrix composites can be quite compact but they often end up taking up more volume than either steel or aluminum. See manhole covers at

http://www.structuralscience.net/wp.../09/SSC-B125-BM-Range-8pg-Data-Sheet-Awk.pdf.

Glass manhole covers have been one of the great successes, being much more handleable (injuries are much reduced) and durable than even steel covers.

Because a composite laminate may be a bit thicker than a metal one it is often a lot less likely to buckle for a given strength. (For a simple plate buckling goes with thickness cubed and strength with either thickness (in-plane) or thickness squared (bending).)

As well as the general references above you could try more specialised marine ones such as Professor Vasconcellos at

http://www.oceanica.ufrj.br/ocean/cursosead/materiaiscompositos/compositematerials/

or Eric Greene at

http://www.marinecomposites.com/.

These have a lot of general engineering information which may be more applicable to the sorts of hatches and the like you seem interested in.

From your description you will almost certainly want to use a glass or carbon fiber reinforced polymer. While many options are available those are good starting points (if you want to be a bit green you might consider a natural fiber rather than glass but bear in mind that they are very vulnerable to moisture, a bit flexible even compared with glass (which is pretty flexible) and are mostly very weak fibers without much consistency of their mechanical properties). Also bear in mind that regulations about fire may well affect the choice of a polymer matrix a lot.

Any further information about your intended products (or the existing ones you make in metal) will get you much more relevant information.

 

[RPstress]

Oops, Eric Greene's info has been moved and is now at

http://www.ericgreeneassociates.com/images/MARINE_COMPOSITES.pdf.