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Dr. Rob
05-12-2003, 04:35 AM
Recently reading up on laminates and composites. New to that game; don't really know much about it. Some of you guys do, however.

So, it seems that thin laminated sheets are often comprised of a fiberglass fabric of greater or lesser density, which is thoroughly embedded (wetted) in an epoxy matrix. Layer upon layer is added, until a generally homogenous structure is achieved. Sometimes the fabric is of carbon fibre, or aramid, or flakes of all three...

So, how come I have never seen such a structure like this, where a metallic mesh is used instead of fabric?

Would this not possibly offer advantages in terms of strength, rigidity, thermal conductivity or heat resistance? Or would it just be a POS; doesn't work? Am I missing something?

PS: What would happen if the epoxy were replaced by silicone?

[This message has been edited by Dr. Rob (edited 05-12-2003).]

Doc Nickel
05-12-2003, 05:58 AM
From what I recall when I asked someone a similar question, the expansion ratio is somewhat greater between metal and epoxy than the glass/carbon and the epoxy. Eventually the mechanical bond between the larger and less-numerous wires and the epoxy breaks down, and you're back to having just the mesh providing the mechanical strength.

The size of the fibers is another thing. It's like filling a gap with glue- a hair-thin glued gap is stronger than a wide seam filled with glue. The more numerous glass fibers allow for tighter spaces between filaments, and thus better mechancial bonds. If that makes sense.

Overall weight is involved there too.

Doc.

eXoticforms
05-12-2003, 09:29 AM
I am just startng a book about composites that is pretty good.

http://www.industrialpress.com/item.asp?BookID=36

I am totaly new to composites, but maybe the book may help.

Cass
05-12-2003, 12:10 PM
The elastic modulus of the glass and carbon fibers is much higher than metals. For example, common carbon fiber has a tensile modulus of 300 million psi vs 30 million psi for steel. That feature and the need to have the matrix material have a good bond to the fiber are the main reasons metal fibers are not used with organic matrix materials. There are metal matrix composites where carbon fibers are used in copper and aluminum and silicon carbide fibers are used in aluminum. In both cases the fiber modulus and strength is much greater than metals such as steel. The so called "bulk" properties of the composite are about ten times less than the fiber properties because it is a "composite" of the properties of the matrix and the fiber with all the complexities of how the fiber is bonded to the matrix, the direction of the fiber layers etc. Some fiber has a negative thermal expansion so you can make a composite with near zero thermal expansion by using the right fiber in the right orientation. It will be zero in only one direction most of the time so you have to allow for that complication. Generally not a home project to make high tech composites but fiberglass is relatively easy, strong, light and real handy.

CompositeEngr
05-12-2003, 01:35 PM
Epoxy doesn't wet as well to metal as to some other fibers. Glass fibers generally have a sizing applied, which is basically like a primer. The size can be tailored to bond better to the resin you are using. Carbon fibers also have good thermal conductivity. Not as good as metal, but not something you'd want to hold up in the air during a thunderstorm, either.
Epoxy is also quite brittle compared to the mesh. The mesh will deform and crack the resin off, leaving you with just a mesh.
(Hypothetically) If the epoxy were replaced by silicone you would have a very heavy and flexible laminate. I suppose the properties of the silicone could be tailored to work, but the "store bought" stuff wouldn't be suitable. The function of the resin is mostly to transfer load between the individual strands in the fiber composite (tension loading). In the case of compression loading, the resin will take most of the load (can't push a rope).
As far as the laminates being "generally homogeneous": that's possible, but then you are better off using metal (or solid plastic). The key benefit of composite laminate is that they are directional. Say you need a plate to support an axial load of 150 lbs, but only 100 lbs across the width; a metal part will withstand 150 lbs in all dir, while a composite plate can have most of the fibers oriented to support the larger axial load, and only enough to support the transverse load. Theoretically (!) at least, the composite part is more efficient.

Whew.. long post.

dvideo
05-12-2003, 01:52 PM
CF will be a home project material from here on out... It is what cars and small transport vehicles (Bicycles - and motor bikes) will be heavily made of. It already is important in Aircraft, is moving to RC and ROV arenas, and is a real possibility for homes constuction.

CF is going to so many places. A derivative is used for glass windows... Ultralight, and an awesome insulator. So you can see how it is commecially feasible for buildings in colder climates - a well as for tall buildings. Stronger than glass, or at least can be, as well.

CF is headed to Aerogel derivitives - capacitiors that are HUGE in value. Where to use these? Almost all yard work equipment could have the motors replaced with the right Aerogel caps. Such caps are also critical to commercial success of Fuel Cell Vehicles. Fuel Cells provides steady current - are not good in pulse applications... you can see how auto applications need the function - and batteries are not the solution. Already, a simple aerogel cap can extend the life of an alkaline battery - by providing the surge - so all alkaline battery products can substantially increase the operating life... With LED lights, you won't even need Alkaline batteries anymore. Same is true for Walkmen & small radios. How big? Coke can size is 2400F now......

They are also critical to solar power, but that explanation is involved.

I can rattle some more - but won't (I know, you are thankful).... but CF is mondo useful stuff - especially in the home arena. Machining and forming are different arts. So we have to learn as we go here. Don't just abandon the technology to offshore visionaries who see the successor to plastics and steel.

-- jerry

Thrud
05-12-2003, 04:59 PM
Jerry

A company in Ontario has patented a flexible solar cell - you can roll it up and it does not break. Once full automated production gets up they will be dirt cheap. It uses spheres of silicon instead of plates - mondo cool.

Carbon fibre technology is just taking off. It is expected that the nanotube carbon fibre cloth wil prove much stronger than current products.

About the aerogel batteries - are they using the same Rare-Earth metal powders used in the current "Gold Caps" dispersed in the aerogel?

Did you know that several companies are working on flexible printed circuits made with ink jet printers - the traces and organo-semiconductors, resistors, caps! Sharp is saying they will have flexible Organic LED displays on our desks by 2006! We live in interesting times, indeed.

[This message has been edited by Thrud (edited 05-12-2003).]

dvideo
05-12-2003, 05:40 PM
Flexible is one really important thing. For a lot of reasons. To be wide spread, it cannot break with a small impact. So now, if you live in Texas, one small hail stone *could* shut down your whole power array. That is unacceptable... The other thing is continous prodution. Can't be like IC type semiconductors, with slices, cleanrooms, diamond saws... etc.. It has to be continous ribbon, shop floor machines to be cost effective. There is a company doing that... They just need some support and they will expand radically.... I hope...

Carbon Fibre working has a lot in common with machining, or it will.. that is the long term prognosis. Feynman saw it all coming early on.. "there's lots of room at the bottom" to paraphrase him.... Bucky tubes build structures. Sructures you can machine and form. Given controls and communications, I can do things. If the machine tool guys had either brains or balls, they would JUMP on this bandwagon.. But they, with only a couple of small exceptions, don't. Drag $$ out of the Gov't and start to making things... I don't think the Chinese gov't or machine tool makers will make this mistake. Perhaps it means that there is room do do gararge shop R&D and pound a few patents out, eh? So Thrud, you got the know how... Done any patents? Who else better to pound on worthless policians for cash (Canadian, of course) to do development?

The Aerogel cells should not - do not - need the rare earth material. Everyone is so closed mouth about it though.... You are talking revolutionary stuff in multiple areas, so everyone is "hush-hush". Just one app is replacing all *home* yard equipment with efficient electrics. Europeans and Asians would go nuts over it... I am playing with some of this stuff, there is a lot more out there..... there is more out there than I have access too, as well. there are people working on this, expecially in the car business. So I can hack some kind of Capacitor driven Weed Wacker together and write it up - this summer....

I seemed to have been hanging on to this technology wave for dear life since I got on board.... It is interesting.. but It seems a lot of people on this board are also doing the tech things, too... Pretty amazing sometimes..

I will likely get deeply involved with cells and power stuff this summer.... It is a wide open field..

BTW.. there are actually Employment positions proposed for Warp Drive Engineering out there... may be it is PR - but there is that kernal of reality behind it.... truly interesting times....

jerry

Dave Opincarne
05-12-2003, 07:42 PM
Sorry to disagree Jerry, but I think carbon fibre in the home/small shop is a lot further out. Not unforseable, but not around the corner. Simple wet layups are doable now, but to take full advantage of the materials qualities takes more money and equipment.

Wet layups are easy to do, but getting the right ratio of resin to cloth is not. Too much resin and the structure is weekend (see the glue bond analagy), too little and you've got resin starvation and no streangth. Pre-preg (pre impregnated cloth) solves this problem, but a roll will set you back more than most machine tools and even some German cars. Carbon fiber is a lot more expensive than fiberglass or even aramid fibre. The pre-preg resin cures at a high tempature (around 350*) and the cure cycle is supposed to be ramped up under very controled conditions. Both wet layup and pre-preg need to be vacum baged during cure for maximum density. Because of the higher modulus of elasticity CF does not like to conform to curves, espesialy compond ones so the vacum is esential. If repairs or secondary layups are needed, CF does not recieve resin well once cured so non mechanical bonds tend to fail. Finaly, CF is very unpleasent to work with after words. Glass and aramid never botherd me the way CF did. Like a really bad case of hives.

Given these difficulties and the advancments and low cost of glass, I think for guys in the home shop CF is not an ideal material. But that doesn't mean I don't find it a great material for many things though, it just demands a lot more experience and resources than glass.

Aramid fiber is also problimatic. Aramid fiber is much larger than CF or glass and aramid strands will not saturate. The fibres remain esentialy dry and are encapsulated with resin. This makes it very difficult to cut cleanly without fraying. Many cutting geomitries have been developed but I haven't seen any that work well. Also because of this quality aramid parts tend to absorb water in wet conditions by wicking moisture into the fibres through exposed edges. Many exterior parts on the Harrier made of aramid were replaced with CF for this reason. The planes were getting heavier.

-Dave

gunsmith
05-12-2003, 07:56 PM
On a forgotten note here might be that composits with steel as the fabric go back in a form that we all pass under almost every day in the structure of bridges and general construction. Also if you want flex just take a look at "fero cement" (wire mesh and a concrete mix). This is a process that everything from structural columns, pools and even boats have been built from for over a hundred years that I am aware of. New fibers are finding there way into construction such as "fiber mesh " a plastic material, but it will be a long time before any of the fellows will have to give up there concrete trowels for resin rollers.

Dave Opincarne
05-12-2003, 08:27 PM
Fero-cement hulls- Oooo, ICK, Get it away from me, I'm going to get a disese!!!

Sorry, couldn't resist.

Speaking of more basic composites: Most of our tools started out as PFPs off the master model. PFP's are Plastic Faced Plaster molds. A face coat is applied to the master. When it has kicked but is still tacky hemp fiber is lightly and sparsley pressed in and followed by large quantities of hemp soaked in plaster. After it sets and a back structure is built in it is pulled off. Very cheap and accurite until it gets dinged up or someone forgets to put release on for subsequent operations.

-Dave

Edit: This was for the composite shop not the pattern shop although it's done a lot there too.

[This message has been edited by Dave Opincarne (edited 05-12-2003).]

dvideo
05-12-2003, 08:33 PM
I think CF is early in the cycle, cost wise. I know there will be better pre-packs of stuff avaiable for use. Now, it is mostly aimed at big outfits with very little flexibilty... That changes!

But...

Motor Bike parts in CF are really nice. Rims, especially.... at $3K+, they are not for everyone or even likely to stay at that price.

Carparts will be in CF - so repair kits will have to aimed at garage shop applications to make it marketable..

Windows in CF derivatives will catch on... Where most economical first - you might even find a few warm Canadians in winter with it... CF derivative windows should be incredibly thermally effective. Sister processes to Solar Cells, at some point....

It does not mean I want to make Harrier parts in my garage, actually I would choose a propeller based system.....

Lots of folks would like to dump the gas burning weedwacker and mower. Just stick the beastie in the sun till it's happy. Then wack. Or recharge in a terrific hurry... It might have an Aerogel cap, and not a Ni-Cad battery. CF gets back to manufacturing here, if you think about it.... Weight is light and continous process... Think of beer making... 2V, 2400F, coke can size Cap.

So I see it in the garage, yard, windows, roof, and on the bike. That sounds like home applications to me. It is still early on in the game.. very early....

-- jerry robinson

Dave Opincarne
05-12-2003, 08:47 PM
Oh, I see what your saying. Sorry. Yes, it's definitly spreading out into the consumer level.

"Carbon Fiber- It's not just for jump jets anymore"

Many useful applications. Also a lot of hype. I've seen a lot of poorly made products out of CF which sold well because of the aura of high tech material. Also a lot of parts that had only one ply for appearence sake or worse yet CF DECALS.

But yes, a lot of good legitimate consumer uses. I made my then wife a realy nice CF and aramid ankle brace she could wear inside a shoe. Friend of mine borrowed it to show to his orthapedic surgon. Doc went nuts over it but the idea of medical libability scares the bejezus out of me. If I could find a doctor or operation to sheild me from that and take responsability for the fit I'd be willing to start making a new and improved version.

-Dave

CCWKen
05-12-2003, 10:43 PM
I don't think you'll ever see CF in general automotive production. Specialty uses yes, but not in general. You may see it in chassis componets or support members for weight savings but it's too production intensive for body or panel use.
Plastics are far less expensive and more production friendly. One company, I think Dupont, has been advertising pre-colored panels for cars in the near future. (I hope this doesn't put me out of business) Saturn Motors (GM) has a good handle on plastic panels and others are starting to follow.
Also, new advances in sheet metal forming (electro-magnetic) have and will lower the cost of steel forming. Competition between the technologies is what will lower costs and advance the net benifit to the consumers.
You're already starting to see previously exotic metals spreading into production use. Once the government releases it's top-secret hold on other materials, you'll see many more useful compounds hit the market. Don't hold your breath for CF. It will die of non-use unless the Mfg. lowers their Bazilion percent mark-up.

Dave Opincarne
05-12-2003, 10:55 PM
That may be true of price point cars, but moderate to high end cars are already using it for door skins and the like.

dvideo
05-13-2003, 12:57 AM
The extreme markup of many manufacturers is what creates a great opportunity for Asian companies to clean their clocks. Boeing sees it, I think... Small boats and small commercial aircraft are headed that way, too.

If you were in China now, would you go back and stamp fenders or leap forward and lead technology? No one knows the answer, but precision ceramics have had a home in China for 400+ years. They could well become the masters of the technogy... Largest TV and bicycle companies in the world are there... both are prime CF opportunities.

-- jr

CCWKen
05-13-2003, 02:11 AM
Dave;
If you're talking about moderate price cars like Fararri or high end cars like Lamborgini, IRL or Formula One, then yes it is used in front and side panels. But I would not call that general automotive use and hardly volume production. What auto maker do you know that's using it in production door skins? I don't know of any.
It's used in some helmets, aftermarket motorcycle parts and auto accessories but these are more show than go. $1200 fairings, $800 dash panels and $500 steering wheels are a nitche market. I've even seen bracelets made out of the stuff. It's more of a fad than a functional use.
Edit:
I forgot to mention, those mid and high-end cars (except IRL & F1) still use aluminum skins over CF. The CF that is used can't be seen. It's more of a support panel or inner panel. Even so, it's still not on the "for sale" cars. These are pre-production test cars. I still think the move will be to plastics and lighter metals. This alone will drive the insurance companies mad. It's been going on for some time. Check insurance rates on the low-end cars. (Called one-time use or throw-aways) Collision rates are higher than any mid-sized car because of the cost to repair. (Or cost not to repair--Totaled) The same will occur with cars using CF. Once it's cracked, it's hard to repair and costly to replace.

[This message has been edited by CCWKen (edited 05-13-2003).]

CompositeEngr
05-13-2003, 03:07 AM
Carbon fiber isn't going to make too many inroads into automobiles for the road. Watch F1 or CART. They hit wall and **KABOOM!** Nothing left. The elongation at break is 0.8 to 1.2%, compared to steel at 7% or so.

Glass is slightly better, but a lot heavier. Aramid is light and impact resistant, but expensive.

Ford and others have already used composite parts to replace metal assemblies. The last generation Ford Escort is one I know of in particular. A composite (chopped glass with a plasticizer) panel replaced the front crossmember, reducing parts count and assembly time drastically. Also tripled replacement cost and labor. By now, the value of the car is probably low enough that a front end collision is not economically repairable.

Thrud
05-13-2003, 03:55 AM
Jerry
First off, I dont't want the government having any say in what direction my endevours take - goverment grants mean they are on your ass all the time. Now, if that interference was because they are concerned that you are not ripping off taxpayer money I would not mind it.

The best idea I have had lately is old fashioned chocolate milk - that and nap time! Stuff that really matters. http://bbs.homeshopmachinist.net//biggrin.gif

dvideo
05-13-2003, 04:42 AM
What you say about the current situation is dead on....

But I think future things have changed. When we discuss CF hybrid vehicles, I think light weight (<1200#), Fuel Cell Power and Aerogel backup, electric motors, and modern electronics. Things targeted for Malaysia, China, and Europe. Markets that are far larger than Canada or Australia.

Think cell phone manufacturing - not engine plants. For such vehicles, features are the race - not the track. The track is just a proving ground, as we know.

In a world of expensive fuel and tight space, the competition is on a different playing field.

My 914 is 2139# and will go faster than I want with 95 HP. With 50 HP, I can likely hit 100. With 25hp and 1200#, bikers can tell you a lot about performance in that range. I can put a solar cell array on it, some batteries, an electic motor and stop buying fuel altogether. I will have to buy (Amsoil - Thrud) transmission fluid so it can leak on the ground though. :> This key point is, I can almost get there today. Still have to buy a few big batteries, but I will figure out how to solve that one as well. A tweaked 914 almost hits the ticket. What would a modern design vehicle be able to do? with some real R&D and not me hacking on things... ? From objective designers and not corporate protection hacks?

So be thinking of Cars with CF/Plastics aspects, sold at Walmart, and targeted to countries other than the US.

Yeah... I see CF mattering a lot in the near future - GW and his "proton fuel" aside. The goal is to dump fuel altogether for small transport things.... Failing that, minimize it.

-- jr

crossthreaded
05-14-2003, 02:25 AM
Thrud,
The Av Week article on Burt Rutan's commercial space plane states he not only didn't ask for assistance from Uncle Sam, he didn't tell them untill he was mostly Finished. Otherwise the Gov't folks would throwing his money at problems that don't exist yet.
I saw a metal foam product used in lightweight structures for telescopes. Bizare stuff, but sure saves weight.

Dr. Rob
05-14-2003, 02:46 AM
Yes, aluminum foam is pretty neat stuff. It comes from, um...what was their name? An aerospace company in California. I'll get back with that. In any case, they don't sell slabs or chunks of it; (bummer) they manufacture to spec at their plant.

This is proving to be a most educational thread. About the Asian thing though, why should it come as any surprise? A vast majority of carbon fibers originate in SEA. In fact, it's completely accurate to say that very few originate anywhere else. The applications thereof, however, seem to develop in our part of the world.

Aerogel has me a little confused, though. I have read up on it, but have not been able to get a grip on what it is, exactly. Frozen smoke, yeah. Open cell foam, yeah. Gel? Don't know. How does it store energy? (Not that I would understand the explanation).

CompositeEngnr, are you familiar with G-11?


Edit: ERG Aerospace, Inc. That's www.ergaerospace.com (http://www.ergaerospace.com)

[This message has been edited by Dr. Rob (edited 05-14-2003).]

dvideo
05-14-2003, 05:35 AM
Aerogel is magic smoke. First time I saw it, I thought it was a solid jellyfish. Had to put on gloves to feel it.

Now, there are lots of different forms. It has apps in lots of places...

Extreme Insulator, Power storage, Structural, etc.

You can get 2400F at 2V in a coke can size object. Low ESR, so it surges well. Fuel cells do not surge well. Transportation needs low surge power... See? Make an LED Flashight, PWM the power to the LED, and you get long life. Put an Aerogel Cap on it, stretch out the life a lot... it supplies the surge... Just so motors love it....

It might work like this. Replace the weed wacker engine with a DC or AC electric motor. Source power from an Aerogel pack. It does not run that long, but... It can charge VERY fast. and if you need more juice, wear a Power Backpack... It is light, remember...

I could hack something together this summer and see how it works, if there is interest. As a novelty, and as a demo, there would be a lot of show and tell value.

jerry

Dave Opincarne
05-14-2003, 10:07 PM
Re autos: The ferrari and Lambrogini would be clasified under the high end cars part of my statment. Audi and Porsche would be closer to the moderate end. Although I have to admit that after checking with my Porsche expert the CF while available for the consumer is not at the low end of their product line. Not Ferrari, but not moderate either. Sorry.

Audi has been using CF for door components mixed with aramid. They also produced a CF quatro but that was only enough to have the car count as a "production" vehicle so I wouldn't count that. Mazda put a lot of CF into some versions of the last version of the RX-7 but only for aesthetic purposes. Talk about beuty only being skin deep.

The aerospace company I used to work for did make a CF cell for a new class of formula racer (don't know what you'd call it, all built around the same engine so it's more about the tuning and driver) I don't think it caught on but it was solid CF.

-Dave

[This message has been edited by Dave Opincarne (edited 05-14-2003).]

CompositeEngr
05-15-2003, 01:42 PM
We use something like G-11 for tooling at work. Wave solder pallets mostly. If designed correctly, it doesn't warp as bad as metal when exposed to 480F on one side only. Not sure what our material's exact designation is.

Dr. Rob
05-15-2003, 01:52 PM
Really...480 is a lot. What kind of heat is this, convection, radiation or conduction?

CompositeEngr
05-15-2003, 02:07 PM
480F is the processing temp of solder. If you go too much hotter there is a lot of dross created, too much colder and the solder doesn't wet as well.
Solder melts at 361F (183C). There are other alloys we use, but this is the main one. We also use a 1-2% silver alloy solder paste that melts a bit hotter.
The boards are preheated using convection because it is quite a bit more even than the old radiant heaters.
For surface mount work, we use a usually use a paste that reflows at 183C. The PCB usually sees around 190 or so for 45-90 seconds. Much easier on the newer IC's. Starting to see a lot more devices that are sensitive. A lot of our parts now are getting so that they won't resist the heat cycle involved in wave soldering.

Here's a vendor of the wave solder machines and reflow ovens. Slow site today.
http://www.cooksonee.com/about/about_electrovert.html
[This message has been edited by CompositeEngr (edited 05-15-2003).]

[This message has been edited by CompositeEngr (edited 05-15-2003).]