Single Skin Monocoque

[Will M]

I was reading this article on RCE and it mentioned that the "tub used a innovative single skin with no honeycomb construction technique first used in aviation"
This was for the Japanese F4 cars.
While I suppose it such a construction is doable I have never seen one.
It sounds like it might be a slightly easier construction method; AKA good for FSAE.

I couldn't find much of anything on these chassis; have any of you seen one?
Or better yet know about their construction method?


Article: http://www.racecar-engineering...orsport-engineering/ (http://www.racecar-engineering.com/articles/features/formula-4-the-future-of-motorsport-engineering/)
Also this talks a bit about how they are made about half way down: http://www.jmia.jp/img/kit_racer_100908e.pdf



-William

[Markus]

Well, it looks like a solid carbon fibre monocoque. There are plenty of usable manufacturing methods, mainly all the different ways of producing CFRP composites.

Have to say I really enjoyed all the marketing talk in the kit racer brochure. You rarely see 2 contradictive sentences in 1 chapter. This brochure had that at least twice. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Will M]

Markus,

Yeah I also thought it was just a solid CFRP monocoque.
But I figured that would be giving up a lot of the benefits of a monocoque.
I mean for a given weight it can't be as stiff...
However if it did work then the CFRP might could be replaced with Tegris.

I haven't seen any Tegris applications in FSAE yet but it has ~similar properties to CFRP but is cheaper and much tougher.
I'm not sure what equipment is needed to work with it.
Could be interesting...

---
Links to the Milliken website for Tegris and an article describing it's use in the Delta Wing.

Tegris: http://www.milliken2.com/MFT/M...ml.nsf/page/home.htm (http://www.milliken2.com/MFT/MFThtml.nsf/page/home.htm)

Delta Wing: http://openpaddock.net/2010/04...th-milliken-company/ (http://openpaddock.net/2010/04/26/indycar-deltawing-announces-partnership-with-milliken-company/)
---

-William

[Z]

Will,

Here is a slightly different way of looking at it.

Just say you decide that your weight budget allows 30kgs for the chassis (maybe because you found this to be a typical number for many spaceframes). Also you figure that an FSAE monocoque would need about 4 m^2 of surface area, assuming (very roughly) a 2m long square tube of 0.5m sides. The thickness of a solid skin for this monocoque now depends on the material's density. So, since you are allowed about 7kg per square metre of skin;

1. Steel skin would be (roughly) 0.6mm to 1mm thick. This is quite thick compared with modern cars, which are often half that. Note, of course, that on cars any loads that are initially perpendicular to the skin have supporting ribs, bulkheads, etc., to spread the load.

2. Aluminium skin would be 2mm to 3mm thick. This is getting industrial tough. You might just be able to dent this with a well swung baseball bat.

3. Glassfibre or CF, depending on detail of layup, would be around 4+mm thick. Again, very resistant to incidental damage. (Edit: Just read the Jap F4 link and its side skins are 5mm to 7mm thick for ~45kg total chassis weight (longer than FSAE).)

4. Aircraft grade plywood, which I mentioned on another thread recently, would be 8+mm thick. I reckon a baseball bat would mostly bounce of this...

Bottom line is, as long as you feed the loads in correctly (ie. at the main roll hoops, at bulkheads, at the floor/wall corner, etc., so that the forces are directed into the plane of the skin) a single skin monocoque should work just fine. A lot easier too. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

[Will M]

Z,

So based on your estimates:

7kg per square meter of skin --> 7 (kg / m2) ---> 0.7 g / cm2

Density of Tegris = 0.78 g/cm3

0.7 (g/cm2) / 0.78 (g/cm3) = 0.897 cm

Right?

Meaning that a Tergis Monocoque would be about 9mm thick for the same weight.
Based on this hand-dany chart it would be not quite as stiff as carbon or wood but would be better than GFRP, aluminum, or steel.

http://www.milliken2.com/MFT/MFThtml.nsf/page/tech6/ (http://www.milliken2.com/MFT/MFThtml.nsf/page/tech6.htm)

-William

[RStory]

Lamborghini has been doing some chassis with no core, I don't remember which cars it is, but if you look up Lamborghini 'Forged Composites' you can find some info on it.

Those cars are built more like a regular road car chassis, just replacing stamped steel with carbon, like Z mentioned with supporting ribs and such.

I think you'd need some kind of ribs or other geometry in there. If you wanted to pass the side impact test with just a flat carbon panel I'm pretty sure you'd be looking at a minimum of 10mm thick, probably more to get enough stiffness.

[Will M]

RStory,

Yeah I saw something about that Lambo process as well.
It sounded like they were cutting the CF into small 1" sq pieces and then epoxying them all together.
So it might would be less labor intensive than a regular lay up.

I'm not a mechanical engineer or a materials guy.
My studies were in industrial engineering, same with my current work.
One of the things I liked about the Tegris material was it is cheaper and its forming process (just thermo-forming) would likely scale better than anything I've seen for CFRP.

-William

[Edward M. Kasprzak]

Originally posted by Will M:
Links to the Milliken website for Tegris and an article describing it's use in the Delta Wing.

Tegris: http://www.milliken2.com/MFT/M...ml.nsf/page/home.htm (http://www.milliken2.com/MFT/MFThtml.nsf/page/home.htm)

Delta Wing: http://openpaddock.net/2010/04...th-milliken-company/ (http://openpaddock.net/2010/04/26/indycar-deltawing-announces-partnership-with-milliken-company/)


To avoid any confusion, note that there are two "Milliken" companies mentioned on these forums.

The one quoted above is Milliken & Company, a maker of textiles, chemicals, floor coverings and composites. www.milliken.com (http://www.milliken.com)

I'm at Milliken Research Associates, Inc., a company specializing in vehicle dynamics engineering. www.millikenresearch.com (http://www.millikenresearch.com)

We occasionally get an e-mail requesting some kind of industrial strength spot remover....

[Z]

Originally posted by Will M:
... Meaning that a Tergis Monocoque would be about 9mm thick for the same weight.
Will,

Yes, Tegris appears to be similar to wood, but not quite as good. http://fsae.com/groupee_common/emoticons/icon_smile.gif

I only had a quick look through the links, but the "thermoforming" strikes me as a potential problem. I am picturing a large, heavy, and relatively expensive heated steel mould/press (ie. requiring significant heat and pressure) that sucks in flat sheets of Tegris and pops out hundreds of thousands of whatever. Not sure if that method suits a one-off FSAE tub.

On the other hand, a pot of glue and lots of thin sheets of plywood...

Z

[Will M]

Z,

I’m not sure if you’re familiar with it but there was one car built at my uni call the “Splinter Car”.
It used a wooden monocoque chassis by weaving thin strips of wood together to make a sheet and then epoxy just like carbon fiber.
This is the build blog. June 2008 has most of the good stuff.
http://joeharmon.blogspot.com/2008_06_01_archive.html
Real interesting but I don’t think it ever ran.

As far as the thermoforming the fabric type nature of the material would likely rule our vacuum thermoforming and require a press mold.
For full production aluminum would be ok according to Milliken, but if you were only doing one a wooden mold might would work.
I’m not familiar enough with the process or material to say for sure.
Though there is a company in my state that builds kayaks out of the stuff, who should know more.
http://nativewatercraft.com/boat.cfm?id=4

-William

[Will M]

While doing some research for work I came across a metal shaping process called ‘super forming’.
It is similar to thermoforming plastic sheets but with aluminum, magnesium or titanium.
I feel that this process would be a top candidate for making a single skin monocoque, especially for a ‘regular production’ car.

This website describes the process: http://www.superform-aluminium.com/
And here is a pretty good PDF about it : http://www.nichevehiclenetwork.co.uk/LinkClick.aspx?fileticket=54Q-gFsAHHQ%3D&tabid=920
Overall I am very impressed with it and it would be worthwhile for a team to contact them (they are located in the UK but have a California facility).

If tooling can be made without huge cost (hours of cnc time) this could be a very economical option.
-William