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  • Metal Mesh Matrix Composite Laminate Stuff

    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).]

  • #2
    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.
    Doc's Machine. (Probably not what you expect.)

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    • #3
      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.
      www.exoticforms.com

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      • #4
        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.

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        • #5
          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.

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          • #6
            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
            dvideo

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            • #7
              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).]

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              • #8
                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
                dvideo

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                • #9
                  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

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                  • #10
                    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.

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                    • #11
                      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).]

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                      • #12
                        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
                        dvideo

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                        • #13
                          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

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                          • #14
                            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.

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                            • #15
                              That may be true of price point cars, but moderate to high end cars are already using it for door skins and the like.

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