Carbon fibre monocoque joints

[speed_demon44]

I am trying to find the best way to join two parts of a carbon fibre monocoque chassis after manufacture in an autoclave in a female mould. I have been told a 'tongue and groove' joint would be best but how is this arranged with the outer skins and honeycomb core?

[speed_demon44]

I am trying to find the best way to join two parts of a carbon fibre monocoque chassis after manufacture in an autoclave in a female mould. I have been told a 'tongue and groove' joint would be best but how is this arranged with the outer skins and honeycomb core?

[Mike Sadie]

Are you planning on laying the inner skin after the two halves are joined or finishing both pieces and then bonding them after?

[James Waltman]

You've asked a question with a lot of right and wrong answers. This is a big subject.
First up, a "tongue and groove"� joint is a terrible idea. Stop listening to whoever told you that.

Take a look at this handbook from Ellsworth:
http://www.ellsworth.com/display/displayFile.aspx?docid...PDFs/JointDesign.pdf (http://www.ellsworth.com/display/displayFile.aspx?docid=226&filename=/Vendor%20PDFs/JointDesign.pdf)

Something like a joggle lap joint (with a doubler) would work pretty well.

Who are you and where are you from? Are there any companies near your school that do composites manufacturing?

Ask some more specific questions and you'll get good answers.

[RiNaZ]

and maybe pictures would be nice too. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[A Richards]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> I have been told a 'tongue and groove' joint would be best but how is this arranged with the outer skins and honeycomb core? </div></BLOCKQUOTE>

That would surely never work.


Probably the easiest way to join two sandwhich panels is to cut the ends square so that they butt up against each other neatly, remove a certain amount of the inner laminate and core, leaving just the other layers touching. Re-laminate in the gap you just created, over the outter layers that is, put in new sections of core material and cure. then finally laminate over your two panels inner layers and your new core.

If you design your molds correctly this can all be done very easily. if i wasnt at work i would draw a diagram because im sure that this makes no sense at all.

ash

[murpia]

I have heard the term 'tongue and groove' applied to the type of joint used to join e.g. F3 monocoques together.

I doubt the details have much to do with woodworking (http://en.wikipedia.org/wiki/Tongue_and_groove)... I have never seen a picture of how this is done.

Regards, Ian

[Brian Evans]

Remember the Ferrari monocoque that broke in half at a vintage race? I think that had a tongue and groove type joint and you could see a lot of detail in the pictures as it sat there in the middle of the track with the poor (but wealthy) driver's feet hanging out. He was on the phone ordering a new car before the old one was unloaded off the wrecker...

Brian

[Mike Sadie]

I could see a "tongue in groove" working if you were bonding finished parts similar to this example:

On one side, have a mold support the inner skin 1 inch in from the bonded edge and butt the honeycomb up to this mold. Pull the mold out after curing.

On the other side, use slightly thinner honeycomb and an extra mold feature to joggle in both the inner and outer skins a small amount. This would then be bonded inside the other piece, both skins bonded appropriately (inner to inner, etc).

It would be a pain. I think you would be better off doing an inward joggle on your outer skin, join and bond the parts, then lay all of the inner skin in 1 shot if you can accurately fasten the molds together.

[Mike Sadie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Brian Evans:
Remember the Ferrari monocoque that broke in half at a vintage race?

Brian </div></BLOCKQUOTE>

Do you have any links?

[James Waltman]

I'm pretty sure that's a joggle on the Ferrari and not tongue and groove.
Anyone have bigger pics?

http://www.alfabb.com/bb/forums/anything-about-alfa-rom...historics-print.html (http://www.alfabb.com/bb/forums/anything-about-alfa-romeos-alfabb-com/6155-big-accident-monterey-historics-print.html)

http://www.motorsport.com/photos/select.asp?S=VINTAGE&E...&N=Bob_Heathcote&O=0 (http://www.motorsport.com/photos/select.asp?S=VINTAGE&E=Monterey_Historics&Y=2004&N=Bob_Heathcote&O=0)

From Here (http://www.autoracing1.com/Archives/Photos/2004/PhotoOfWeek.asp):
http://www.autoracing1.com/Images/PhotoOfWeek/2004/0815Ferrari1.jpg
http://www.autoracing1.com/Images/PhotoOfWeek/2004/0815halfedferrari2.jpg
http://www.autoracing1.com/Images/PhotoOfWeek/2004/0815halfedferrari1.jpg

[Mike Sadie]

After enlarging those pictures it seems like there is a very short joggle on the outer skin (~1/4 inch). I'm amazed at how thin the honeycomb is in that section of the car (also around 1/4 inch).

[LU-Bolton]

Speed Demon,
You need way more detail if you want a definitive answer, but in general...

Either do a butt joint or a lap joint(with joggles as James suggested)

Use a bond adhesive designed for composite materials to join carbon-to-carbon faces. After bonding, wet lay glass plies over each side of the joint.

You could use carbon, but then you would have to bag it. And that may require bagging your entire chassis again with a post-cure.

A contact layup with glass is easier and faster with minimal performance loss. Glass is used because you can see the bubbles easier. Use a room temp cure epoxy because its cheap, easy, and will work.

By the way, I did this identical thing before to my '07 FSAE chassis. After it was done, no one could even tell the chassis had seams in it. Mine was a butt joint: potted the core pieces together, 3-ply glass layups on either side of the joint.

This explanation is very basic. You may not understand what I'm saying. My best advice is to talk to someone in person who has done this many times before. This way you won't screw it up. Joints are the hardest thing to do right in composites.

Aaron Cassebeer

[Mully]

Just throwing another suggestion on the table.
You can do a chassis as a one piece cure so that there is no need to post bond halves together. There are still issues with this process as far as getting a good technique down is a must, and is a bit dependant from case to case, but it can be done.

[A Richards]

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

You can do a chassis as a one piece cure so that there is no need to post bond halves together. </div></BLOCKQUOTE>

Its possible because we manufactured our chassis this way in 2006. Never again!!!! We did our 07 chassis in two halves, much more simple, and a much better result.

Ash Richards
Deakin Race Technologies
Team Manager

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by A Richards:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mully:

You can do a chassis as a one piece cure so that there is no need to post bond halves together. </div></BLOCKQUOTE>

Its possible because we manufactured our chassis this way in 2006. Never again!!!! We did our 07 chassis in two halves, much more simple, and a much better result.

Ash Richards
Deakin Race Technologies
Team Manager </div></BLOCKQUOTE>

You just need to work on your composites game Ash http://fsae.com/groupee_common/emoticons/icon_wink.gif

[A Richards]

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

You just need to work on your composites game Ash http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

Its not my composites game that is the problem, more so someone having to climb inside a tiny car to perform a wet layup with resin that does your head in and can kills you if you get enough on yourself. After watching your driveline go through your chassis in our car park last year it would seem that you guys need to sort out your hard point location game http://fsae.com/groupee_common/emoticons/icon_wink.gif. I did enjoy watching the euro vans conversion into a composites oven. http://fsae.com/groupee_common/emoticons/icon_smile.gif


When picking a place to make a join i think that it is important to make it as easy as possible. You can see from the photo below where we joined our car last year. I'm interested to know why most teams that i have seen join upper and lower halves??? To me it would seem that this would make the process much more difficult and the bond much longer, heavier etc.


http://i197.photobucket.com/albums/aa249/deakinracetechnologies/IMGP0549.jpg

Ash Richards

[Bertie]

joggle FTMFW!!!

if ur smart you can have ur chassis as a 2 piece to simplify layup then cure as one piece.

have ur 2 part mould, then layup the outer skin. you then have options of:
1. join the 2 mould haves together and complte layep.
2. lay in the core and inner skin except for 50mm of core either side of the part line. then join the 2 halves together, run in strips of core to fill the join then cover the split with carbon.
3. a conbination or variaton of the above with differing overlaps etc.

[Composites Guy]

Here is the butt-joint of which LU-Bolton speaks above. Hand laying the glass is a bit of an art form, and I'd get a book on it or ask someone who's done it before to give you a demonstration. I suggest using Hexcel 7715 semi-unidirectional glass from Wicks or Aircraft Spruce, and getting West-Systems hand laminating epoxy from them also.

You may be hesitant to use glass with carbon. After all, glass is inferior, right??? If you think about it... glass and carbon have somewhat the same strength (different density, modulus and strain to failure, but similar strength)... so from a structural standpoint each would give a similar joint when used as a doubler (the hand laminated part). The key is getting all the bubbles out to get a strong bond. The reason that you use glass is so that you can see the bubbles and try to remove them.

Also, prior to hand-laminating, you should sand the carbon down to the first layer of fibers and thorougly remove all traces of oil with a good degreaser. Fill in any low spots with a mixture of microbubbles and hand-laminating epoxy and then laminate over with glass while still wet.

http://i110.photobucket.com/albums/n114/lehigh_jack/jointdiagram.gif

[murpia]

Here (http://www.flickr.com/photos/7480659@N06/sets/72157603388084446/) is a photoset showing the production of the Elan Superleague chassis. Clearly 'tongue and groove'.

Regards, Ian

[James Waltman]

Edit: I don't know what I was looking at last night. I see it now.
My apologies.
That would be hard to pull off but they've done a nice job of it.


<STRIKE>That's funny. I look at those pictures and I see that it's clearly a joggle lap joint.</STRIKE>

The hosting for this picture was down when I posted earlier in this topic. Take a look at the joggle lap joint.
http://dot.etec.wwu.edu/fsae/HostedPics/Adhesives_and_Bonding/Loctite_Joint_Guide.JPG

Here is a tongue and groove joint:
http://images.encarta.msn.com/xrefmedia/aencmed/targets/illus/ill/000f0ef3.gif

<STRIKE>Those are quite different.</STRIKE>
<STRIKE>Maybe we're getting hung up on definitions.</STRIKE>

The big images from the gallery:
http://farm3.static.flickr.com/2343/2090647129_c77aa4f62c_o.jpg
http://farm3.static.flickr.com/2096/2174414899_daf433129a_o.jpg

[ben]

I'm with Ian - it's a tongue and groove joint.

Digressing slightly, I spotted this pic in that set:

http://www.flickr.com/photos/7480659@N06/2175205982/in/set-72157603388084446/

Anyone know what the rosette welds are down the wishbone leg. Is there an internal rib, and if so is this common practice?

Ben

[James Waltman]

Edit to my post between Ian and Ben.

[exFSAE]

Might be ben. I have a Lola champcar a-arm (unfortuantely not with me atm) and while it didn't quite have that style welding.. there were some spots where it looked like there was an internal rib welded in.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ben:
Digressing slightly, I spotted this pic in that set:

http://www.flickr.com/photos/7480659@N06/2175205982/in/set-72157603388084446/

Anyone know what the rosette welds are down the wishbone leg. Is there an internal rib, and if so is this common practice? </div></BLOCKQUOTE>
I suspect there is an internal rib as that looks like a true aero section tube rather than oval. Probably the rib is there to stabilise the tube in compression, wishbones tend to be the right sort of length to have 'intermediate' slenderness ratios so can fail by inelastic buckling (see here (http://www.efunda.com/formulae/solid_mechanics/columns/intro.cfm)). I assume a rib can help this significantly, it looks a lot of extra work.

I'm quite impressed by what I see of that Superleague car, it looks very well engineered. As to the racing concept, I'm not so sure...

Regards, Ian

[Aaron@Kaist]

Dear members, I was wondering if I could get a hold of James Waltman at WWU, hoping to get some info on the cut and fold carbon fiber handling technique. "http://dot.etec.wwu.edu/fsae/ " this site doesnt work!! AHHH!

[James Waltman]

Try the email listed in my profile:
http://fsae.com/eve/personal?x_myspace_page=profile&u=5806054511