Experiences on Carbon Fibre Monocoque

[Jerry Lin (R&D)]

Hi everyone, I have seen everywhere in the discussion that people are taking interests in a full carbon fibre monocoque chassis. I'd like to ask you CF unis such as Monash, RMIT about your experiences on CF Monocoque, like what's the easiest part, difficulties you guys encountered. Few things I am most interested at:

1.) How to bond the carbon body to the steal subframes. How to go around the fact that they have differnt heat expension factors

2.) How do you go about analysing using ANSYS or any other program because I know since they are fibreous materials they are not the same as usual space frame tubes.

Thanx guys~

[Jerry Lin (R&D)]

Hi everyone, I have seen everywhere in the discussion that people are taking interests in a full carbon fibre monocoque chassis. I'd like to ask you CF unis such as Monash, RMIT about your experiences on CF Monocoque, like what's the easiest part, difficulties you guys encountered. Few things I am most interested at:

1.) How to bond the carbon body to the steal subframes. How to go around the fact that they have differnt heat expension factors

2.) How do you go about analysing using ANSYS or any other program because I know since they are fibreous materials they are not the same as usual space frame tubes.

Thanx guys~

[Ashley Denmead]

Hi Jerry,

Firstly, as im sure many of the other guys will tell you going down this path is very rewarding and also fraught with danger!

Building a tub is fairly straight forward however the tooling required can be a pain in the butt.

decide early if you want to play with prepreg, do a wet layup or try to infuse as this also has a bearing on how your tooling should be constructed.
good design pays off, a full cad model is a must before you do anything as you must know where the inserts should be placed during layup.

we've just finished our second tub at deakin and it seems there is no substitute for experience as it seems to be 100% better than the last!

in response to your first question....no experience with bonding to steel spaceframe and dont intend to ever go down that path so i'll leave it for someone else to answer, however note that carbon and steel dont like each other so be sure they dont come in direct contact as corrosion sets in quickly.

As far as modelling goes we have used a number of packages including hypermesh/optistuct, lsdyna etc. have also heard good reports about fibresim. can be a pain to model properly thats for sure.

thats all i have time for now....


Ash

Team Leader

Deakin Race Technologies

[Boston]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ashley Denmead:



however note that carbon and steel dont like each other so be sure they dont come in direct contact as corrosion sets in quickly.
</div></BLOCKQUOTE>

Are you sure about that? I'm almost positive that carbon fibre gets along well with steel (usualy even aluminum isnt a problem due to the epoxy insulation). I'd like to know more since our team is planning on using carbon fibre more this year.

[Boston]

nevermind, it looks like 4130 is close to aluminum

[Travis Garrison]

1) I beleive most teams bolt the subframe somehow...typically to inserts that were layed up or bonded in after the fact. As for CTE issues, don't worry about it, the differences are NOT that bad (carbon and al gets worse) and I doubt you'll be making either section so stiff it can't flex a little to accomadate expansion differences.

2) Ansys is a pain the @SS...try shell 91 (at least I believe thats the correct one) be sure your elements are all pointed the right way if you're using them to call out fiber direction, and do some test laminates early on. You might look into other systems, I'll be doing just that myself this year as I'm just not happy with how much work it takes to analyze something in ansys. One of the local companies here recomended Patran, and there are several userfriendly systems that claim to work well such as sim designer (composites plugin).

I would recomend playing around with your basic shapes using an isotropic approximation until you're sure you have the CFRP working well in your FEA program of choice...

[Jerry Lin (R&D)]

Wow, thanks guys for your opinions, you guys made me feel really welcome in this community.

Yeh I know that a CF monocoque is not going to be easy to do the first time since it relys much on experiences and the fact that toolings are so expensive that makes us really wonder if it's worth all that money or not, but a CF monocoque is definiately something worth pursuing, it's just a matter of money, time and experiences.

I agree that ANSYS classic is a pain, I almost wet my pant when I've been told by my lecturer that I should do the analysis in ANSYS, so I'll be looking at the programs that you guys recommanded me.

Again thanx guys, and more opinions are very welcomed, since this is our first time on trying this thing, we need as much info and experiences. Thanx guys

[Jersey Tom]

Talk to the guys at Colorado State University...they're pro with that stuff I must admit. Hopefully one of them will jump in here.

[JPS]

Bonding steel and carbon will be not problem interms of expansion. At work we build cars with structural panels bonded+riveted to tubes that form the firewall (less than 2" from exhaust) with no problems.

For those that have experience, how do you locate in (layup and final assembly) the inserts? ive seen picutres of some teams using 3D mapping arms, is this necessary? Thanks

[Travis Garrison]

You can put witness lines into your molds, you can machine locating features into your core or probably your best bet you can integrate locating features into your molds.

On the WWU cars we used cnc'd bulkheads for pickup points and then it was simply a matter of spacing out the bulkheads evenly. (steel rule + bigg @ss calipers http://fsae.com/groupee_common/emoticons/icon_smile.gif )

If it were me, I'd put locating features into the molds and then fit machined parts into the locating features.

I'd say a 3d mapping arm is a touch of overkill but if thats what you've got might as well use it.

[Ashley Denmead]

hahaha sounds like to much stuffing around to me, all we've done in the past is use an accurate measuring device (ruler), mark out the insert area (size depends on what attaches there) cut away core and fill with microspheres/epoxy mixture before the inner skin is layed.

[El Joe]

hey guys,
I am looking for values for the torsional rigidity values of other teams monocoque chassis

[Erich Ohlde]

KU torsional rigidity. ~6500ft*lbs/degree Wheel-to-Wheel

[Travis Garrison]

El Joe,

Don't worry about what other teams get...just figure out what you need and go from there...There's a pretty good thread on chassis stiffness elsewhere, do a search.

Erich, how did you measure that? At what loading did you get 6500? seems high..

[Erich Ohlde]

We constrained front and RR uprights, we then hung weights from the LR hub. Chassis had a pivot along its centerline. Measured 4-5 times for accuracy.

[Travis Garrison]

At what loading did you get 6500?

[Denny Trimble]

How did you constrain the uprights, and if 3 uprights are constrained, why did you add another constraint (the pivot along the centerline)?

Can you post a picture?

[Travis Garrison]

Good point Denny, I missed the constrained rear upright, that might do it.

[Erich Ohlde]

oops. looks like i mixed up our test methods. one method we used was constrained the front uprights and pivoted on the rear. the second was constrain 3.

http://eohlde.portstorm.com/2wheel.JPG
this is the 2 upright constraint

http://eohlde.portstorm.com/3wheel.JPG

and the 3 upright constraint

[Erich Ohlde]

bump

[Matt Gignac]

Seems like a pretty simple way of doing things. What is it holding the front right upright from the top though? I imagine to get any kind of accurate value, you'd have to ensure extremely little movement of this support (like an order of magnitude below the chassis movement, which I imagine is tough when you have 6000lb-ft/degree)

Matt Gignac
McGill Racing Team

[Erich Ohlde]

we have a chassis lift that held it in place
http://eohlde.portstorm.com/frontwheel.JPG