Printable Version of Topic
Click here to view this topic in its original format
914World.com _ 914World Garage _ carbon fiber experts??
Posted by: r_towle Jan 26 2006, 05:00 PM
So,
Carbon fiber is 6 times stronger than steel.
here are my thoughts.
take off the outer rocker.
Fix the rust with new steel.
sandblast the area
Lay on a layer of CF directly to the inner long front to back, wrap in to the bottom and top horizontal layers.
when using CF and bonding it to steel, I have read that you would use an epoxy resin to bond it directly to the steel, so it would be the same as putting por 15 on steel (por 15 is an epoxy layer)
So, thoughts? plus, minus?
Rich
Posted by: alpha434 Jan 26 2006, 05:23 PM
Yeah. That's mostly true. Much more brittle. And don't forget that you can selectively heat treat and anneal portions of the bodywork- If you know what needs to be strong and what doesn't.
And then, you aren't getting the strength unless the cf is very tight against the metal. Very many bubbles would make it worthless.
Posted by: alpha434 Jan 26 2006, 05:24 PM
Of sourse, you could use por15 as the epoxy to hold it on.
Posted by: Jeroen Jan 26 2006, 05:32 PM
I don't think it'll give you the desired strenght unless you put it in an autoclave
then again, I'm no expert...
go ahead and let us know if it works 
Posted by: alpha434 Jan 26 2006, 05:37 PM
Wait. It's six times as strong as steel by weight!!!
Just joking.
Posted by: majkos Jan 26 2006, 05:43 PM
What you use for making a mold? 
Does the template has to be perfect?
Posted by: Brian Mifsud Jan 26 2006, 05:44 PM
If the bond isn't excellent, I suspect there is no benefit and its a waste of time. Epoxy will pop loose and the carbon fibers will never do any of the load sharing. The thermal expansion coefficents of each material are different enough that there will be relative movement between the two, even with the car sitting and no preload on the CF.
Of course.. carbon fiber and aluminum are commonly bonded together in racecars and mountain bikes.. so somebody out there has figured out how to bond them, I just don't think it's with the commonly available epoxies.
you could always make up a test specimen, bond it, then torture it. That would really be the only way you'd have any confidence in it.
If you have any aspirations to put it on the INSIDE of the car, better slap a layer of kevlar over the Carbon Fiber. When carbon fiber/epoxy break from impact, you have shrapnel. The kevlar keeps the shrapnel away from the human body.....I'm still picking pieces out of my forearms before we learned this trick back when.
Posted by: lapuwali Jan 26 2006, 05:44 PM
Lots of dangerous assumptions here.
The resin used is fairly important in any composite, and there's a huge difference between air-dry, room-temp curing epoxies and the exotic stuff the aerospace and F1 people use in their autoclaves.
Any figures you read in a book on relative strengths are theoretical, and stuff you can get off the shelf isn't necessarily up to top standards, unless that shelf happens to belong to Boeing, et al.
Strong in pure tensile strength does not mean strong in all dimensions under all uses. It's hard to align CF fibers so all of the forces are taken only in tension along the length of the fiber, and CF is actually quite weak under bending loads.
Posted by: alpha434 Jan 26 2006, 06:20 PM
Yeah Yeah. But if its already against a steele underlayer, then it wouldn't be in much of a bending situation. And the mold would be the part that you're layering.
I think you should use the por15 as the curing agent.
Por15 is very hard, so haveing a peice of CF soaked in the stuff would be like caking it on an eight of an inch thick.
And if anyone wants boeing style epoxies- boeing actually has to sell there excess stock after completing a contract. Me and all my buddies get stuff from northrup grumman.
Posted by: lapuwali Jan 26 2006, 07:05 PM
| QUOTE (alpha434 @ Jan 26 2006, 04:20 PM) |
| Yeah Yeah. But if its already against a steele underlayer, then it wouldn't be in much of a bending situation. And the mold would be the part that you're layering. I think you should use the por15 as the curing agent. Por15 is very hard, so haveing a peice of CF soaked in the stuff would be like caking it on an eight of an inch thick. And if anyone wants boeing style epoxies- boeing actually has to sell there excess stock after completing a contract. Me and all my buddies get stuff from northrup grumman. |
What, you don't think the longs bend?
POR-15 is almost certainly a crap "epoxy" compared to anything that will provide any actual strength.
Posted by: alpha434 Jan 26 2006, 07:10 PM
Yes. They bend. But they wouldn't bend so much as to crack the CF off.
And por-15 bonds to metal. That's going to be important.
And maybe once every couple of seasons, you'll have to change up the CF layer.
Posted by: jd74914 Jan 26 2006, 07:14 PM
| QUOTE (lapuwali @ Jan 26 2006, 08:05 PM) | ||
What, you don't think the longs bend? POR-15 is almost certainly a crap "epoxy" compared to anything that will provide any actual strength. |
100%, longs bend and POR though flexible and able to bond to metal is not a proper resin, or even a good bonding agent to the longs. If it was why would people use anything else? 
Posted by: bondo Jan 26 2006, 07:28 PM
What if you layed up all the carbon fiber and then lay a sheet of plastic on it... Then close the doors and fill the car with sand while it sets up. Instant even pressure to push out any bubbles! 
Posted by: TimT Jan 26 2006, 07:35 PM
I think its a bad idea to try and reinforce the long with CF.
First to get a get a proper bond between the CF and steel substrate you need to finish the substrate (steel) with an anchor profile which will provide enough "tooth" for a good mechanical bond between the resin and the steel.
Second the CF strands have to be oriented properly (as mentioned earlier in the thread). I have a feeling the longs on these cars move in three planes.
Third, even if you prepare the substrate with a proper anchor profile..You will have holidays in the resin.. ie corrosion paths right to the raw steel..
best bet to reinforce is thoughtful application of extra sheet metal rosette welded to the tub ..or a roll cage..
Posted by: anthony Jan 26 2006, 07:37 PM
Sounds like a big waste of time. Just fix the longs, por15 them, or paint them. Store the car in the garage whennot used and don't drive it when it rains. Once a year clean out the rockers. The longs should last another 40 or 50 years.
Posted by: alpha434 Jan 26 2006, 08:01 PM
| QUOTE (bondo @ Jan 26 2006, 05:28 PM) |
| What if you layed up all the carbon fiber and then lay a sheet of plastic on it... Then close the doors and fill the car with sand while it sets up. Instant even pressure to push out any bubbles! |
Thats an ok Idea. But if your already covering with plastic- then why use sand instead of a vacuum to suck the epoxy down.
Posted by: alpha434 Jan 26 2006, 08:04 PM
| QUOTE (TimT @ Jan 26 2006, 05:35 PM) |
| I think its a bad idea to try and reinforce the long with CB. First to get a get a proper bond between the CB and steel substrate you need to finish the substrate (steel) with an anchor profile which will provide enough "tooth" for a good mechanical bond between the resin and the steel. Second the CB strands have to be oriented properly (as mentioned earlier in the thread). I have a feeling the longs on these cars move in three planes. Third, even if you prepare the substrate with a proper anchor profile..You will have holidays in the resin.. ie corrosion paths right to the raw steel.. best bet to reinforce is thoughtful application of extra sheet metal rosette welded to the tub ..or a roll cage.. |
Wow. You guys have no interest in R&D data at all, do you.
If we find out that the CF bonds properly, then we can do reinforcement bars out of CF instead of steel.
And CB stands for cardboard. That definately has no application here.
Posted by: r_towle Jan 26 2006, 08:17 PM
lots of good thoughts...
I will tell you what I know...
Carbon fiber has been tested in a specific application...to reinforce aging bridges..it is applied cold to bare sand blasted steel to add structural integrity to these aging structures...
The epoxy is very specific, and por 15 is not it.
I would use the correct epoxy, it is available.
So, in the bridge application, it is applied in the field, in varying weather conditions, and has held up to being exposed to many different twisting and bending stresses.
I would use the same cloth and epoxy that is being used for the bridge application.
I still have my concerns...but I am gonna run this by a few composite engineers to get some real world feedback, I may even track down the company that is doing the bridge tests to get some feedback...
I was just thinking that it would be a great way to stiffen up the car with less weight.
And, if it does not work...I can always remove it and add more steel.
Rich
Posted by: TimT Jan 26 2006, 08:29 PM
thats cool manipulate my response when you quote me, make CF appear as CB "cardboard" 
I actually may have a clue about how some of these things work..Besides being a PE, I am very involved with AWS(CWI), and NACE. I have done structural analysis for years
CF reinforcement may be applicable, but many controls need to be in place.. first would be preparing the substrate with a proper anchor profile., which is probably beyond the capability of a home mechanic.
It would be much easier and cost effective to weld some reinforcments in the hot spots..
Por-15?...lets find out which composite mfg recommends that to be used with their fabric.
Posted by: TimT Jan 26 2006, 08:32 PM
| QUOTE |
| I would use the same cloth and epoxy that is being used for the bridge application. |
Id love to see the white papers on this..
Ive been working on the Suspension Bridges surrounding NYC for 25 years, and have yet to see a FRP applied...
Im very curious
Posted by: r_towle Jan 26 2006, 08:34 PM
Tim,
From what I read, the correct anchor profile that is being used on the bridges is sandblasting....
So far the testing is positive...but it is a limited test right now...
It just got me thinking when I read this in a different journal...that mmmm this might work on a car too...
Rich
Posted by: r_towle Jan 26 2006, 08:38 PM
http://www.new-technologies.org/ECT/Civil/cfrp.htm
http://www.pubs.asce.org/WWWsrchkwx.cgi?Fiber+reinforced+polymers
http://www.vzavenue.net/~chlorine/publications/str_trb_2005.pdf
Actually lots more if you google it correctly...
really cool emerging technology.
Rich
Posted by: r_towle Jan 26 2006, 08:47 PM
Sorry to drone on,,,but this stuff is facinating and its happening out there...
"Based on the worldwide research and development work, the use of CFRP strips to rehabilitate structures is already routine for many firms in Western Europe and Japan. In the U.S., Sika has introduced Sika CarboDur, which is a CFRP laminate used to strengthen concrete, steel, or wooden structures. CFRP materials will not replace traditional construction materials, but will be used increasingly to supplement them as needed."
Quoted from http://www.new-technologies.org/ECT/Civil/cfrp.htm
Cool stuff..
And lots of R&D has already been done...
All the different epoxies are being tested in labs and all I have to do is read to find what I am looking for...
God, I than Al Gore for inventing the Internet.
Rich
Posted by: TimT Jan 26 2006, 09:02 PM
ok this study impressed me
http://www.vzavenue.net/~chlorine/publications/str_trb_2005.pdf
still the weak link is the person at home doing it..Id be worried about porosity in the CF layer which will just be a homing beacon for corrosion.
And attaining a good anchor profile is not just by sandblasting.. you need to test your blast media and measure the profile, and adjust the mix of abrasives to suit
I think for the DIY guy its easier to reinforce the longs via extra sheet metal..
You can get it at Homey D, and make sparks and have it welded in..
Por-15?
Posted by: r_towle Jan 26 2006, 09:06 PM
Tim,
check out www.sika.com
look in the construction division papers.
search for carbon fiber and steel
Get the brochures...it might apply to your daily gig.
It seems to have been tested with in field applications for bridge repair pretty extensively in Europe, it has all the standards bodies approvals over there...
Apparently they have been playing with this since 1987..
It has not made it over here yet...that may be why you have not seen it...it is not being done in the US...but you could be the first..
Rich
Posted by: TimT Jan 26 2006, 09:19 PM
I know Sika reps
We use some of there other products often..
Unfortunatley there is mucho inertia that prevents some of the Bridge owners here from using these cutting edge enhancements. Some of the bridge and road owners arent willing to take a chance on new tech, though some are.
Posted by: SpecialK Jan 26 2006, 09:39 PM
Oooh Yeah! Right up my alley! 
I actually have a 1000' roll of unidirectional, aerospace grade, defunct NASA project CF, just for this purpose!
I did nearly all of the structural repairs on the AV-8B Harrier wing (entirely CF, with the exception of the titanium outrigger attach points), and most of the CF/Kevlar repair on the F/A-18E/F SuperHornet fuselage/wing/stabilator up until a few years ago. CF is a super stiff/super light material if applied "correctly". An autoclave would give optimum results, but vacuum bagging and heat curing (one hour 70F under vacuum, followed by one hour at 190F +/- 10F under vacuum [29 in. hg]) will give satisfactory results also. The correct epoxy for the strongest/stiffest material would be Hysol EA956 http://www.theengineerguy.peachhost.com/ct_PRhysolea956qtkit.htm.
I talked to a couple of strength engineer buddies of my at work on whether it would be stronger to bond the CF directly to the prepped metal, or use the longs as molds, and then bond them on with a high-strength adhesive like Hysol EA934. One issue of bonding directly to the metal is that CF will corrode damn near any metal it comes in direct contact with (dissimilar metal corrosion) with the exception of Titanium, so a barrier of FG would have to be laid down first, and then the CF over that. Since an autoclave is not an option, only about 4 layers of the uni-CF could be laid down at a time to ensure correct resin content, with a final layer of peel-ply to ensure that the following layers (also laid in no more than 4 layers at a time) adhere (the peel ply give the last layer "tooth" for the following layers to adhere to without damaging fibers of the previously laid CF as you would by sanding). The Uni-CF will be laid with 50% of the plies parallel to the longs, with 25%/25% on a 45 deg. bias.
I ultimately decided to go with the "mold" method, using high-strength adhesive, and CRES pull-type fasteners (corrosion resistant steel pop-rivets [counter-sunk] http://www.aircraftspruce.com/catalog/hapages/cherrymax.php ) for a little added strength, but mainly to get the proper squeeze out of the EA934 HSA. It'll be made in 4 separate parts, all on the interior of the car (I'll use whatever's left of the roll on the outer longs....someday). One piece for each inner long that overlaps a few inches onto the lower firewall, another piece that runs across the lower firewall (overlapping the long pieces), and up each side of the center tunnel, and one piece that runs across the lower front of the passenger compartment, and ties into the forward end of the long pieces and the center tunnel.
I'm going to have to do a little experimenting with the CF to see how many layers I'll need to lay down to get the desire thickness (shooting for .080").
PS- Unidirection is made specifically for strength/stiffeness in a given direction, most of the other weaves are for aesthetic purposes.
I guess I'll have to take some pics as I go along. I hope to get going on it in April when the weather starts cooperating....we'll see, lot of irons in the fire.
Posted by: alpha434 Jan 26 2006, 09:53 PM
see where that got us? some really great research. I'm very glad that that one didn't get stifled. 
Posted by: lapuwali Jan 26 2006, 10:04 PM
| QUOTE (alpha434 @ Jan 26 2006, 07:53 PM) |
| see where that got us? some really great research. I'm very glad that that one didn't get stifled. |
Cool your jets, guy. No one is trying to "stifle" anyone here. Us naysayers were simply pointing out that it's a lot more complicated than some might think. Certainly, it's a lot more complex than buying CF sheet and slapping it on with POR-15.
Buzzard, I'm guessing, works at what was recently McDonnell/Douglas, since it's located not far from Pacific, MO, and they were certainly part of the AV8 program a few years ago when I used to AX with the McDonnell Sports Car Club. So, he's far more qualified than most to discuss this topic, and he basically backed up exactly what was said by those you say are "stiflining": it needs special epoxies, and several plies of unidirectional material, and a heat cure. Not at all easy to do.
Posted by: SpecialK Jan 27 2006, 04:36 PM
| QUOTE (lapuwali @ Jan 26 2006, 10:04 PM) |
| Certainly, it's a lot more complex than buying CF sheet and slapping it on with POR-15. ... it needs special epoxies, and several plies of unidirectional material, and a heat cure. Not at all easy to do. |
Correct on the McDonnell Douglas/Boeing assumption James, and I hope to drag my car out to the Company Sports Car Club (drive what you bring, not too many rules
) when I finally get one of them done. 
As far as the actual laying down of the CF and bagging, the only "special" tools required would be a vacuum pump (I plan on using the vacuum pump I use for evacuating central A/C units....actually a better unit than we have at work), a couple/several IR heat lamps (I've got the big floodlight looking bulb types), and a fairly accurate pyrometer (thermometer with a sensing lead). The bagging materials can be purchased at any reputable composite material supplier, I've got US Composites, and Fiberglast bookmarked.
I can't, for obvious reasons, lay out the process spec. for you guys in writing (I could tell you....but then I'd have to kill you
), but http://www.fibreglast.com/contentpages-vacuum%2Bbagging%2Bequipment%2Band%2Btechniques%2Bfor%2Broom-temp%2Bapplications-230.html lays out the equipment and techniques pretty well, and a Google search would bring up tons of tips. Definitely do a couple of practice pieces (not on the car!) to get comfortable with the time-table you have to work with, make accurate templates of all of the pieces you're applying, and have everything organized and ready to go before you mix a drop of resin. It can get pretty messy, but I enjoy the hell out of the process and firmly believe that doing it this way will make an ultra stiff chassis with minimal weight........not to mention I'm a shitty welder, and would probably end up with a 2000lb lump of slag on my garage floor if I tried to install an Engman kit. 
Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)