Carbon Composite Shear Modulus (G) for torsion bar

[6543w2qddsf]

Hi all,

I am trying to calculate the spring rate of a torsion bar, and analyse the feasibility of a cmposite design to substitute the steel one.

Now in order to calculate the spring rate i need to know the Shear Modulus of elasticity. How does CF comapre to steel in that regard?

I am aware that it (G) depends on the layout of the composite and the type of manufacturing.. etc

Here is where i need your advice, if you wanted to replicate the same spring rate of a torsion bar with a composite design how would you go about it?

 

[patprimmer]

The matrix resin will also have a significant effect as will resin to fibre ratio in addition the the fibre orientation you have mentioned. You need data on your exact composite.

You will get a weight advantage, but at a considerable development time and materials cost.

Regards

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[Compositepro]

As patprimmer says shear properties of fibrous composites are highly dependent on the matrix resin and fiber volume. Shear is also one of the weakest properties. You can reduce shear loads by optimizing the fiber orientation. I believe that for a torsion bar it would probably be best to orient the fiber in a helix in the bar. Also since composites are often relatively expensive, a tube rather than bar should be considered (or a plastic core). Coil sprngs have been made with braided carbon fiber.

 

[6543w2qddsf]

Compositepro,

I was thinking of using a filament winding technique around a core (what material are typically used for cores?).

I am intrigues by the application of composites in compression springs, but i could not find much information on the web or through SAE.

Can you tell me where to find more information on the topic?

 

[TVP]

http://www.sardou.net/springs.htm

 

[patprimmer]

Styrene foam should suffice as the core simply is a mould to form the tube on. Once cured it would make little difference if the styrene is left in place or dissolved out.

Polyurethane or PVC foam will also work.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[6543w2qddsf]

So in effect you would achieve a hollow bar, since the core would provide little stiffness.

Do you think through filamnet winding you could achieve a comparable shear modulus to that of steel?

 

[Rink]

Fegizii,

What you need is a _pultruded_ CF tube.

And, possibly, move this to the Engineering tips - Composite engineering Forum.

Reinking

 

[6543w2qddsf]

Reinking

i will investigate the pultruded technique and move the topic on the proper forum.

Thank You
Fegizii

 

[patprimmer]

If a suitable pultruded tube is available, that is a good suggestion, but to custom make a pultrusion for a very small production run might be very costly vs a hand wound article.

Regards

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