Length of glass strands !

Discussion in 'Fiberglass and Composite Boat Building' started by tunnels, Mar 23, 2011.

  1. AndrewK
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    AndrewK Senior Member

    Peter, sorry another question, how does the cast resin shear strength correlate with ILSS. The reason why I ask is that SP & Hexion data for their laminating resins shows ILSS for a glass laminate at ~45MPa.
     
  2. petereng
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    petereng Senior Member

    Good point - Shear strength is usually calculated and tested by bonding two overlapping steel plates together then pulling them apart. This ensures that the resin fails. The test is severe as the steel is very very much stiffer than the resin. This means the resin bondline thickness is critical for good results. The companies that have spent time on this for their bonding resins will specify the ideal bondline thickness for that resin. ILSS depends on how the resin bonds to the fibres and how thick the bondline is between plies and how much eccentric load there is on the local laminate. The ILSS is tested by putting a short test coupon in the flexure test fixture so its like snapping a paddle pop stick between your fingers. The ILSS is usually higher than the SS figure as the loads can be better distributed within the flexing laminate as the area is less stiff then a steel fixture. ILSS can be up to 100MPa+ for laminates. Also the interface of the bondline in a ILSS test is the "rough and intermingled" fibres so there is a mechanical stickture to the bondline vs the smooth bondline in steel. Plus the ILSS is actually the "Apparent ILSS" test. The SS is implied by calculation from the flexure test. To determine the actual ILSS the test would need to be like the steel plate test but use actual laminates machined to an interply area then pulled apart in a true uni-stress situation. Quite difficult. The other shear strength is in-plane SS and for glass laminates can range from 40-110MPa. Over the years I have found this to be quite variabe with some hand laminates being better than some infused laminates & vise versa. Epoxy infused laminates are around 100MPa. So to cap this off - most projects will save quite a bit of money in materials if they spend $2000 on a set of mechanical tests so the Engineer or NA can do accurate calculations. If the analysist has to use estimated low figures for the design work then all the structures will be heavy. eg if you pick say 50Mpa for the in-plane SS but you actually have 100MPa then all of the beam webs in the boat could have been half the thickness. Quite a bit of weight and labour saved. In short I don't think that In-plane SS, bondline SS or ILSS correlate. If the resin suppliers can't provide the figures then use a supplier that can, if then your stuck do some tests. Resins for secondary bonding have tougheners and wetting agents that laminating resins do not have. Bonding resins need to be tough and elastic whereas laminating resins can be more brittle but work. The lower the cost of the resin the more brittle it is in general. Acrylic resin (PMMA) and toughened bonding resins can have high elongations (PMMA can be 50% eleongation) this allows the resin to distribute the load over the joint. The stiffer and more brittle the resin (PE e=2%) the more the load gets concentrated at the load entrance and leads to early failure and un-zippering of the joint. A good strategy for secondary bonded edges is to use a reverse chamfer so the resin is thick at the part edges. The thick resin can streth more than a thin resin giving the connection a better chance of transfering the load without zippering. This doen't help lainate to laminate connections though. Hope this helps. Cheers Peter S
     
    Last edited: Mar 29, 2011
  3. petereng
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    petereng Senior Member

    I have had clients do mechanical tests for projects that require certification that have not acheived manufacturers data. So be careful!! Cheers Peter S
     
  4. AndrewK
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    AndrewK Senior Member

    Yes it all helps and thanks for explaining the differences in the tests.
    What I have been considering here is mostly the laminate to laminate secondary bonding. I have always chosen epoxy resins with elongation >5% and if infusing on to a laminate I have used DB with stitched on CS on the base, so to have that slightly higher resin content at the bond line. Likewise for all PE tabbing I use the combination cloth.

    I haven't gone down the path of bonding components together with specialty adhesives. Well nothing other than an odd non structural join using sikaflex. The thinking has been that it is difficult to control the film thickness and not to trap air in the join.
    Cheers
    Andrew
     
  5. tunnels

    tunnels Previous Member

    Time you got out of your comfort zone and into the real world . They still make new chopper guns did you know !!
    On this planet chopper guns are still used and a good operator can do amazing amounts of work and keep two crews on the run all day long . Yes they can be dirty but thats completely up to the operator .
    I grew up and graduated from a venus saturator gun through various brands of chopper guns . Say what you like unless you have stood hanging onto one for many hours you have no idea what you are talking about .
    I have just reco_ed a 1980? something venus gun and it is a beaautiful gun to use and the place it came from must have used ton's of glass and who knows how much resin through it .
    Like all mechanical things it only as good as the person driving it !!
    :D:p;):p
     
  6. ondarvr
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    ondarvr Senior Member

    Closed molding isn't always the best way to build every product, there are many items when the cost is too high or the production rate is too slow for closed molding.
     
  7. War Whoop
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    War Whoop Senior Member

    Tunnels, same here,I used Venus most of my career and never had a problem,The 80 Guns were a pleasure to use fit the hand perfect and the manually charged Accumulators were no problem and enhanced the system greatly,Later we used the Proguns then they merged with Magnum,even on my ultra light Cats, I used a chopper on fairing the bottom with carbon fiber tow in the step areas instead of a putty,freaked the "Experts" Out when they saw that!
     
  8. petereng
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    petereng Senior Member

    They still make manual vs CNC laths but the CNC is more efficient/productive. Same as MiG welding vs stick welding. I understand what you are saying from a machinery and skill perspective but we don't make valve radios anymore, we don't have dials on our dashboards to control our spark advance and our mixture. We move on to better processes and technology. We still have blacksmiths doing things and yes chopper guns still exist. But if the composite industry is to exist rather then go the way the Smith has we need to move forward and this is happening. I have worked with gun crews on 45ft catamaran hulls and then I've trained them to dry stack and infuse them and after all of that they didn't want to go back to the gun and we built hulls faster. Just because crews are busy doesn't mean they are productive or fast just means they are doing their hours. I mean no disrespect to laminators or equipment out there, just times are changing. Cheers Peter S
     
  9. petereng
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    petereng Senior Member

    Ondarvr - You need to do your homework. If you are building a composite product then closed moulding is quicker for nearly every product. Cost is deceptive and if its too costly for closed moulding then its probably too costly for open moulding you just havn't done the costing right or you are accepting lower margins. Costing is badly done in the composites industry. I've worked in the automotive industry and they cost the product down to cents including the set up, shut down, end of life, contract costs, etc. Was an eye opener when I came back to the composties industry where it was pretty much a wet finger held up in the breeze. Cheers Peter S
     
  10. War Whoop
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    War Whoop Senior Member

    Right and Gelcoat is still the standard finish on production boats,So spray Equipment is involved and that requires mat backup , Skinout ,Check mat or whatever you want to call it,if the job calls for Chop so be it! We all infuse and use high end Epoxies or Prepregs (I have a job on the floor now),WHEN THAT job comes in!! meanwhile it is necessary to stay in business,that may involve nasty things like Contract open faced molding and Repair work.
     
  11. ondarvr
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    ondarvr Senior Member

    petereng

    I'm involved in far more types of production and products than you may think, the marine industry is only a portion of what I'm involved in. Building large hulls and similar parts are a no brainer for closed molding. There are many parts of the composites industry where closed molding can easily be incorporated, and others where the current costs don't allow it to be profitable. I actually take your position frequently when discussing methods of production with customers though.

    I work with very advanced companies where the rule is "if we can't make it by closed molding we won't bring it in the shop", they have a small corner in the back of the plant with a chopper gun because there are parts where its more profitable to do it that way. They don't like to talk about this corner of the shop though because they don't believe in open molding.

    By the way, I will be doing a closed molding demo in San Diego tomorrow, I'll be discussing resins.
     
  12. War Whoop
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    War Whoop Senior Member

    I Always had huge Industrial vacuum systems in my shops and was bagging in the early 80's anyway,started Infusing @ 1990 using it to fix glitches in the wet bagging and do some areas on my award winning first 11 Meter racing cat (One Off),from there we worked on a system to build small parts,which I used in the Middleeast that became my KRYPTON system and Quick Bag ,we also Know to do coupon and dynamic testing with samples from the laminating area ( I have testing up on you tube)not bad for a what was that ?? a Blacksmith!!
     
  13. idkfa
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    idkfa Senior Member

    ?Maybe a chopper could be used for core-material in tight curves, like a cat hull bottom, where heat bending of foams is required-problematic and the small radius gives some stiffness-so not thick.
     
  14. tunnels

    tunnels Previous Member

    nother interesting thing i found with the longer strands is it drapes over things better and you dont get it streaching apart as is so common with using the gun over hatch surrounds etc etc where the glass need to be rolled down and streached into place its much more uniform and easyer to use!!
    All plus'es from where i am standing so far the strength thing i cant see why it shouldnt be better !
    Going to persist with it a while longer till we find a problem where it doesnt do what i hope it will do :D:p .
    Next flat panel going to try just one blade and see what happens . all the strands should be close to 100 mm long ! nothing ventured nothing gained ! At the present they are 35 mm and 70 mm some long and some short combination
     

  15. War Whoop
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    War Whoop Senior Member

    Give it a go,your resin is not contaminated with binder so it is half way in place before rolling and the laminates are crystal clear,speaking of binder I have seen some real nasty loading of it in the mat and wondered if that did not have a partial hand in the old blistering problem some guys had.
     
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