Composite Axles

[PBR-keith]

Does anyone have some information on calculations of composites in torsion? Any info would be a great help. Thanks

Keith

[PBR-keith]

Does anyone have some information on calculations of composites in torsion? Any info would be a great help. Thanks

Keith

[TorqueWrench]

I know we gave up on calculations when designing our torsion tube this year. You need to remember with composites that a change in the angle of your layup, how many layers you use, and how much/what type of resin you use is going to have an impact on strength.

My suggestion, build one and test it. Only way to know for sure if it is going to work or not.

[Grant Mahler]

Delft is the only team that I know of that has successfully used full composite halfshalfts. They used (I believe) machined alu for the splined ends, and layered carbon for the shaft itself. They were beautiful. I have seen more than one other team wrap alu or steel half shafts in carbon. Don't really understand that one.

Please forgive me if I am unaware of another team that is doing so.

[DG]

We (Bath) had carbon half shafts until the Friday of Silverstone this year (when I had a blonde moment and stalled the car at high revs, breaking both http://fsae.com/groupee_common/emoticons/icon_cool.gif). They ran fine in normal running conditions
We used full carbon tube with steel inserts at either end, designed by someone as a Final Year Research project/Dissertation. As far as I know, setting correct boundary conditions etc was a bit of a pain in the ass

[DanVaan]

We used Kevlar axles with aluminum ends this year and they have worked great.
I agree with Chris though, build one and test it. We tested nearly a dozen test shafts to verify our design assumptions, and we have the broken specimens to prove it.

Daniel Vaandrager
University of Alberta
Team Leader

[Vittorio]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DG:
We (Bath) had carbon half shafts until the Friday of Silverstone this year (when I had a blonde moment and stalled the car at high revs, breaking both http://fsae.com/groupee_common/emoticons/icon_cool.gif). They ran fine in normal running conditions
We used full carbon tube with steel inserts at either end, designed by someone as a Final Year Research project/Dissertation. As far as I know, setting correct boundary conditions etc was a bit of a pain in the ass </div></BLOCKQUOTE>

What do you mean with "stalled the car at high revs"? (I'm italian)

[Thrainer]

Hi Keith,

my advice for the most basic calculations would be to look at the properties of a plate of your lay-up and then apply the shear stress that is caused by the torsional moment.

However, you'll find that the bonding is the weak link in most cases, not the tube. That's why most composite driveshafts have a large diameter.


Grant, as far a I know, DUT does not use splined inserts, but bonds the tripod housings into the driveshafts.
Some other teams that attended FS UK which have composite driveshafts: Stuttgart, Munich, Zurich, Zwickau.

Daniel, why are you using Aramid? What advantage does it have compared to carbon in the application of driveshafts?


We were planning to use Taylor driveshafts. But two weeks before our rollout, I found out they were not in stock. So I made some composite driveshafts with CFRP tubes and splined steel inserts, which have been holding up fine.

Regards,
Thomas
www.amz.ethz.ch (http://www.amz.ethz.ch)

[DG]

As in: Gave it loads of revs and went to bang it into gear without having the clutch in.
Didn't go down too well...

[Tim.Wright]

From my short stint in composites;

Kevlar would be a good material for this type of loading (fatigue and impact loading). It might be a bit heavier, but you woudn't have to be so precious with it. Its a much more forgiving material. Unfortunately its a pain to process without the right cutting gear.

I've always thought that a low to intermediate modulus CF tube would do the trick. This will give the tube a bit of 'give' before it snaps. Also look for pre-pregs with 'toughened' epoxies.

A driveshaft has a pretty brutal life in terms of loadings and quite often needs a absorb a lot of energy (rough clutch work?!). Composites are usually brittle in nature, so a lower modulus material will give you a bit more area under the stress-strain curve before it fails.

More area means more joules which means you will ultimately have a higher BOTF count(burn-outs till failure). No-body likes a driveshaft that can't support burnouts.

Tim

[TimR]

There is a company in Sydney that makes composite tubing. I was looking into making some but was pointed in their direction.

[Adambomb]

I like the idea of using a lower modulus material. Would be nice to have some energy absorption capability somewhere in the drivetrain. Anyone who has driven these cars at light throttle knows how jerky they can be with the chain slop. Had sort of a cool idea (to copy) when I had the rear wheel of my ancient '88 Ninja 600 off. They used a rubber puck flex coupler between the rear wheel and the sprocket. Thought it might be a cool thing to add at some point (once you get completely bored with getting everything else 100% dialed in...as if that would ever happen http://fsae.com/groupee_common/emoticons/icon_biggrin.gif).

I have asked around some on making CF halfshafts, and there is quite a bit of trickery involved in the bonding...there's more to it than you might think. Could easily make a senior design project out of that alone.

As for some analysis, Solidworks Simulation 2009 (formerly COSMOS) can now do composites analysis, you specify weave type and direction, no. of layers, etc. Looks pretty cool.

[TorqueWrench]

I'll have to look into Simulation 09 tomorrow as we got our new licenses in the other day. That should come in handy a good amount, but I still wont trust it as well as some weights on the end of a bar and a dial indicator. I think this should be especially true for teams like us that use wet lay over pre-preg as we don't always have the "ideal" amount of resin in our parts.

Side note on the jerkiness at partial throttle, its part of the reason why I like CVT cars so much. The majority of the jerks/shocks are taken up by the belt and clutches, so on and off the throttle is really smooth.