stickability !! and peelability !! whats the differance ??

Discussion in 'Fiberglass and Composite Boat Building' started by tunnels, Mar 11, 2012.

  1. tunnels

    tunnels Previous Member

    Hi
    Please note i am only refering to Polyester and vinylester resins !! "NOT EPOXYS"
    Over the years i never seen these two thing mentioned as a subject ! Ok maybe i missed it them !!
    Stick is just that ! How well will resin stick to other resins ??
    This can be a problem when doing repairs and going over old surfaces ! If a new part has come from some where and the type of resin used to make that part is unknown this can be a problem .
    On one big boat we were fitting out polyester resin was used over the Vinylester laminate and the bonding was not stuck very well at all !!

    Has anyone seen how easy A layer of glass laminate will peel off foam core ??
    WOW This is really scary !!
    First time i saw it i wondered why the hell do we even bothed using foam as a core at all !!
    Then the differant densitys of the core made me wonder if it improved as the core got harder so did a little exsperimenting of my own .
    The lower density foams peel off really easy and that gave me a whole new prospective about using foams !!,as the density went up then it get harder to peel , even Balsa will peel but its hard work !! .
    Now what makes it peel ??
    The resin holing the glass to the foam is not letting go !, the stickablity of the resin /glass to the surface of the foam was always 100% !!
    Everytime Its the foam its self thats letting go !!!
    My own testing convincingly made up my mind there and then i would never ever use the low density foams for anything ever again !! .
    Foam has its place like all things used to make boats but the way its used needs to be very carefully looked at. The size of panels is another consideration no one ever really thinks to much about !! and all the internal structure and frame work is sat on and glassed to the glass skin over the foam on the whole of the inside of the boat normally reguardless of the size of the boat !!
    Hulls Foamed from Gunwhale to gunwhale are scary !! Oh yes they been done for long long time !! and sure theres a mixture of densities and the bottom foam is harder than the top sides but the peelability still scares the hell out of me !! :eek::confused::confused:
    Have a nice day !!
    Get a off cut some time and see for yourself what i am talking about !!:p
     
  2. benglish300
    Joined: Jan 2012
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    benglish300 Junior Member

    I dont think i follow...of course said laminate will peel away from a foam core, you can scrape foam away with your finger nail. But this is not what foam core is meant for. It is a lightweight stiffening substrate, meant to limber up a otherwise heavy, flexible structure. I dont know what your experiments lamination schedule was or how it was laminated (i.e. core sandwich, just covering the top) but, When it is sandwiched between multiple laminates and consolidated properly, I deify you to attempt to peel the glass off the foam. The foam should never be exposed to carryout this experiment if its installed properly.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Peel strength strictly speaking, is the adhesive bond or more simply put a material's ability to resist being pulled apart. In your context, it's the adhesive qualities, plus the physical attributes of the substrate. If stickability was a word (it might be), it suggests the same thing, though we could get into tack and adhesion attributes.

    Yep, some cores have much better peel strength then others and possably why plain old wood, still has considerable use, as it's stickability with most adhesives (even polyester) is better then most other core materials.

    The point I think you're missing is the modulus of elongation factor. Tensile properties are understood in different ways, for several things such as elongation, tensile strength, yield point, yield strength, size and area reductions, elastic limit, etc.

    In cored structures, skin delamination is a concern, but under loads that threaten this, you'll (should) have enough damage, where it's a moot point. If the core, resin system and fabrics are well matched for the anticipated loads, then catastrophic failure when over loaded is the result, which is good.

    In other words, it makes no sense to have a high elongation core with a particularly rigid skin. Under a simple bending load, it'll delaminate. On the other hand if the fabrics and resin have a similar elongation and the core sufficient compressive and peel strength, about the time you begin to see fiber failures in the fabric, you'll also see cracks and deformation in the resin and core. The result of this engineering means lighter and yep, stronger structures, but the structures have to be well thought out or most times you can live with another build method, probably less costly and lighter.
     
  4. tunnels

    tunnels Previous Member

    It dosent matter if you have 4 mm thick glass each side of foam it still peels off real easy . Which then takes you to Core shear!!!!! and core shear is really frightening !!!
    Dont you guys do any exsperimenting of the products you use ?? :D
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    If you run into a situation, where a big pair of pliers is peeling off your skins, then worrying about core sheer is the least of your concerns.

    The point here is you have to look at the whole, not just elements of it. If you have a properly made and designed sandwich panel, under a bending load the skin will do what I know you already know they do, ditto the core. If this bending load exceeds the ability of the panel, what difference is the damage type? It's a bit like looking at two cars after an accident; one with a sheet steel body, the other with a 'glass body. The steel got bent, wrinkled, torn and crumpled. The 'glass body fractured, cracked, splintered and broke up. Both, if engineered to the same loading situations have similar damage, though the type of damage does look different. In the big picture it's irrelevant, they're both in need of repair.

    Yep, taken alone, you sure can peel skins off of cores, but if the panel is intact and asked to work within it's designed loading envelop, just as strong, possably stronger pound for pound, than other build methods.
     
  6. tunnels

    tunnels Previous Member

    Scary to say the least . I am always concerned when i see low density cores specified on drawings and question repeatedly the reasoning in there choice !! and make sure the plans are signed by the designer or the boss !!!
    Please note thickness of the core is not the issue here its how easy glass peels off foam core !!:confused:
    Try it some time !! makes you wonder and even think a little !!
    .
     
  7. benglish300
    Joined: Jan 2012
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    benglish300 Junior Member

    Par explained this conundrum very well, so im a bit confused why this is still your point? De lamination would be your biggest worry, and to be honest its a very small worry.
     
  8. tunnels

    tunnels Previous Member

    So you are saying delamination is only a small worry !!! :confused:
    Wow its the major worry if the skins of any panel become unattached you have a major problem and once it starts from hitting an object without actully putting a hole on the skin it just grows with every wave you hit !!. if it does get holed with water pressure it simply blows the skins apart like paper in the wind .
    Need to get to see and do boat repairs and how things break and fall apart ! Its scary !!!!:eek:
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Tunnels, you are focusing on just an element, within an engineered panel. This is like saying the glass on a car is weak, you can break it with a ball point pen, so the whole car must be questioned. In fact, the glass on a car is structural and part of an engineered whole. Taken separately and out of context, yep it's weak, but it's a moot point to ponder, as within the structure it's intended to reside, it's considerably stronger. Ditto a 5 pound foam core, with appropriately scaled sheathings, surrounding it.
     
  10. tunnels

    tunnels Previous Member

    Yes i understand what you are saying but i am pointing out the fact that foam really is weak when it comes to peel and its has very little to do with stickability of the resin or core bond or what ever else has been used !!It is the foam core its self that is letting go !,the cell structure of the foam really is quite weak .so be very careful when you are specifying density!!! always use highter density rather than lower density !! mater of fact dont even think about low density foam for anything !!
    Have you ever seen how easy layers of glass seperate when using polyester resin ? its possible to peel whole layers apart . But if you change to Vinylester resin ,things change , all of a sudden the resin is much stronger and peel ability of the glass layers is much harder and almost impossible to peel layers . Its a good way to also understand the differance between stitched glass matts and woven glass as well and should you use chopped strand matt between the layers ?? and if so how much and to gain a better understanding of what to use and why and where to use !,all depending on what you are making of course .
    I spent hours doing repairs and looking closely at damaged panels and laminates and how they distruct . Some come apart with very little effort, while others will peel only a little amount and tear and are impossible to rip or tear more than a couple of inchs if you are lucky . I then made a point of asking why did this happen and why does this stay together when that came apart but the same glass was used on each !!, , the resin that was used was the biggest surprise and how much stronger it was ! the differance between Vinylester and polyester can be great !!. I am always using either polyester or vinylester and have nothing to do with epoxys !!!!:D
     
  11. Herman
    Joined: Oct 2004
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    Herman Senior Member

    Composites in general, and due to their laminair structure, are more vulnerable to peeling forces than for instance aluminium and steel.

    It is bad practice to design a structure which is loaded in peel.

    Core shear strength and peel have little in common. Peel can be translated into tensile, and as a foam mostly consists of air, tensile strength is low.

    As for you comment "The size of panels is another consideration no one ever really thinks to much about " I can say that designer continuously think about that. About all scantlings are based on panel size. Interior, bulkheads and stringers are there to divide the largest panel (the hull) into smaller panels.
     

  12. tunnels

    tunnels Previous Member

    Ok lots good stuff coming to light here iF anyone is taking note ! Lets get to panel size ! how do you interprate panel size ?the size of the foam panel or the size of a panel as a whole from side to side top to bottom ? My interpritation is the size of the foam that can be panels within a panel where glass touchs glass and so divides the bigger panel into a series of smaller panels that will have sringers of bulk head attached etc etc !
    When i mount a sail-drive unit its on a solid glass laminate not ontop of the foam and the foam dug out and filled with bogg or what ever , same with the floor grid around the keel its fixed to a solid glass layer and the foam is stepped back a minimum of 80mm around all parts of the frame its not on top of the foam !!. More work but Much more robust and solid !!
    so stringers are ontop of the foam ? or the foam is stepped back 80mm bothsides ??
    Funny peel seems to be the high point everyone is concentrating on and stickability hasnt had hardly a mention . Putting Foam on wet glass is a bit of a worry even when Vac bagged !, a instant bleed of resin to the bleed holes when the vac is applied is a good sign !!,if its slow some where means theres not enough resin in the glass.same with Core bond ! always look for the consistancy of bleed over the whole panel !!! it is possible to suck the side of the sheet hard down and force the core bond back under the sheet !!,if there a excess thickness so when fitting the bag dont let it clamp the side of the foam sheet hard to the surface , Have seen this happen on sheets 20mm thick and sheets up to 40mm thick and thicknesses in between . I have a habit of disecting all and any off cuts no matter what size off all panels and parts reguardless where they come from !! its where i check peelability of glass layers and peelability of foam off the glass !! Its a good way to check the stickability consistancy as the peel always is able to be seen through to the stick surface and check for bubbles and there size if there are any !! Heres another topic i will post yet again How much vac do you actually need to hold the foam onto the adhesive ? and what are some of the problems accosiated with to much vac being used ?? Yes to much vac can be applied !! Its not limitless and fool proof !!
     
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