14 replies to this topic

[NeilR]

I was reading Staniforth again and in particular the wet layup carbon tub car there in. I also noticed that a european FSAE team had completed a similar project - a tub in two parts then bonded together. clearly this is not going to be in the same league in performance terms as say a Dallara tub...but what sort of weight penality would there be if it were properly done? I assume for the amateurs they simply added X more material and core material.

I will note that the FSAE car was vacuum bagged and resin infused, but not post cured in an autoclave.

Edited by NeilR, 25 December 2013 - 11:38.

[Pat Clarke]

Which team was that Neil?

I may well have their Design Report.

 

Pat

[NeilR]

Hi Pat, I found their website and was too busy reading the captions to the images to note the uni, so I'll look it up again today.

[NeilR]

Delft Uni

[bigleagueslider]

The biggest weight penalty with wet layup vs. prepreg materials is from lower fiber fraction in the cured laminate. A higher resin content basically means reduced mechanical properties for a given volume/mass of cured laminate. It is also easier to maintain accurate fiber alignment with prepreg material vs. wet layup. Misaligned or wavy fibers can significantly reduce stiffness of the cured laminate.  Oven cured resins usually have better properties than RT cured resins, and autoclave cured laminates are best of all. However, RT and out-of-autoclave resin formulations are rapidly getting better. The weight penalty of a wet layup vs prepreg could vary quite a bit depending on the skill level of the people doing the wet layup.  The weight difference could vary from 10% to 30% or more.

 

As for a two-piece chassis construction with a beltline(?) adhesive joint vs a single piece chassis construction, there is a definitely a weight and/or strength penalty from the adhesive bond joint.  The adhesive bond joint interrupts the fiber load paths, and the strength in the adhesive bond joint is only as good as the adhesive properties allow.  If equivalent strength and stiffness properties are required from both chassis designs then the two-piece FSAE chassis will be a couple pounds heavier.

 

The FSAE car designs are tightly regulated for things like material cost, but not for labor. Two-piece construction and wet layup were probably chosen to minimize the cost of materials and machining of the tooling done by vendors.

[NeilR]

Thanks for your thoughts BLS and good point on the wet layup cost.

[kikiturbo2]

when you are talking about wet layoup vs. prepreg... where does vacuum infusion stand?

[bigleagueslider]

when you are talking about wet layoup vs. prepreg... where does vacuum infusion stand?

The fabric is layed up dry with VARTM.  The laminate fiber fraction with VARTM is probably somewhere between wet layup and prepreg. The benefit of VARTM is lower production costs than prepreg.

[Pat Clarke]

Neil,

 

I just read their 2013 Design Report, the compulsory eight page submission, and there is absolutely no mention of their chassis construction!

They focus mainly on their electric powertrain, torque vectoring etc and their aero package.

 

Just as an aside, When Claude Rouelle and I were inspecting this car during the Design event, we saw evidence of delamination of the structure at the lower front wishbone pickup point. This was serious enough that I had to report it to the Scrutineers, who promptly removed the scrutineering sticker.

 

The ream were forced to fabricate an aluminium brace that went inside the chassis to support the wishbone pickup points.

 

Pat

[Canuck]

There is, or was a member here that was heavily involved in CF fabrication for Honda aircraft. He and I corresponded briefly several years ago, but I'm afraid his PMs have been lost. Fairly certain I've seen his name on LinkedIn as someone I might know. Perhaps Desmo has the contact.

[carlt]

I believe this is a wet carbon car -  very competitive against comparable 'high tec' carbon tubs 

http://www.lee-adams...gwr_raptor.html

built by this chap

http://en.wikipedia....raeme_Wight,_Jr.

 

interesting things to note-

his first carbon tub 

I believe zero droop/roll front suspension on the mono shock ?

 

Josh Goodyear has the mk2 1600cc megabusa , beating 3.5l Goulds and setting outright records on some of the British Championship hills in 2013

http://www.google.co...iw=1560&bih=773

 

 

Merry New Year

Edited by carlt, 01 January 2014 - 17:44.

[MclarenF1]

The weight penalty will depend on what the critical margins of safety (or RTR, FoS) and failure modes are.  The difference between the two manufacturing processes may effect certain properties differently.  For example, in-plane shear stiffness critical applications may have a smaller "knockdown" then inter-laminate shear strength critical applications.  As BLS  pointed out the low FV of wet layup means fiber dominated properties will have a different knockdown then matrix dominated  properties.  There are typically no designs where optimization on one requirement results in the overall ideal product, as with everything, compromises must be made.  Consideration needs to be made on what the stiffness, strength, envionronment, crashworthiness (damage tolerance), repairability, manufacturability or some combination of all of these (amongst many, many others).  Which makes estimating the weight penalty for switching materials difficult to do without detailed knowledge of the design in question.  

 

I would recommend looking at some NCAMP material properties.  Remember that some of the materials are OOO and some are full 350 F cure autoclave materials.  You can also check out CMH-17 and ASM Vol 21 (Composites), all good references to get you started.  

 

http://www.niar.wich...u/coe/ncamp.asp

 

http://www.cmh17.org

 

http://www.asmintern...000701e010aRCRD

[bigleagueslider]

MclarenF1-

 

Excellent points about design FoS, margins, etc.  The biggest diference I've seen between wet layups and prepreg is reduced buckling margins due to fiber misalignment. It is very difficult to get accurate fiber alignment/straightness (especially with uni plies) with wet layup or infusion.

[Greg Locock]

The chassis and front forks for our 96 solar car were built from a mixture of prepreg and vac bagged wet layup (the geometry was not really suitable for a pure prepreg approach). The guy who fabricated it and pretty much designed the layup as he went is Jim Cook, who also used to build composite motorbike frames. He was based in Melbourne at the time.

 

It gave absolutely no trouble and so far as I know is still racing. So if you can find him he may be a helpful source (he taught me a lot). He is a bit of a personality.

 

i'd add that in Oz a post cure at 80 deg C at least is pretty much essential with epoxy, because your car will easily hit 60 in the sun. Or I suppose you could use the ever reliable polyester.

[NeilR]

Thanks McLaren and Greg. Good reading and I'll try to find Jim Cook.

Just as an aside, some in australia are using Dallara F3 tubs for hillclimb cars.

Edited by NeilR, 08 January 2014 - 11:35.