S Glass

Discussion in 'Boat Design' started by Sail Nut, Jul 31, 2013.

  1. TeddyDiver
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    TeddyDiver Gollywobbler

    Concur with Sailnut... Speaking of myself I've used basalt instead of S-glass. Allmost the same characteristics..
     
  2. Mike Graham
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    Mike Graham Junior Member

    I'm not talking about make-it-and-break-it for all the components like the aircraft industry--I'm sorry if I wasn't clear about that. I'm talking about things like coupon testing, of small samples for representative layups. Being able to use whatever material you have selected to more of its full potential can be extremely beneficial and is often very cost-effective.
     
  3. rxcomposite
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    rxcomposite Senior Member

    You almost got it right.

    1. The less resin, the higher the modulus. This is especially true with high modulus fibers.
    2.Mixing resin and fiber is very relevant to obtain the maximum "efficiency" of the fiber, Both must "stretch" at the same time otherwise you don't get the maximum performance of the fiber. That is, Carbon + High Modulus resin.
    http://www.boatdesign.net/forums/design-software/free-iso-12215-5-scantling-45435-2.html#post627651
    3. When mixing different laminates, the highest modulus fiber is placed at the surface, as far as possible away from the neutral axis. Works with thick laminates and sandwich structure but not so effective in thin laminates. You must watch out for the strain characteristics too because if the outer laminate is stressed too much, it will fail. Any early failure whether it is resin or fiber is a failure of the laminate.

    So why is S glass not popular? Its elongation characteristics is about 3.2%. Hard to match a resin. ISO is 1.8-2.1%, VE is 4.8-5.2%. EP is less than 5% but some are higher up to 8%.
     
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  4. jonr
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    jonr Senior Member

    > So why is S glass not popular? Its elongation characteristics is about 3.2%

    Do you have a reference for this?
     
  5. Sail Nut
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    Sail Nut Junior Member

    On 1. you are correct in the limited context of "what is the modulus of X composite". I tend to think of this in a different way: given fibers arranged in some manner, does the choice of resin have any effect on the choice of material for those fibers? If we've placed the fibers in a particular arrangement, we can pile all sorts of resin of various kinds and, as long as there is a sufficient bond to hold the fibers together in their designed position, there is very little affect on the tensile stiffness of the resulting structure. The resin does have a critical function to carry out, but the effect on modulus that you point out is simply dilution of the fiber's modulus.

    On 2., I think you're referring to making sure that the Elongation at Break on the resin is no less than that of the fiber. I'm with you so far, but I don't see any disadvantage to having a resin that can strain further than the fiber without breaking (no particular advantage, either).

    http://www.matweb.com/search/datasheet.aspx?matguid=ccd3fcc24efb46a88a091f560487cee5 gives 5.7% for S, a bit higher than the 4.8% http://www.hexcel.com/Products/Aerospace/AGlass-Fiber gives for E . (You seem to be using numbers from a different source.) I don't see a huge difference, so I don't see why the range of resins used for E wouldn't be satisfactory for S. In any case, this is only relevant to the extent that strength to failure or strength to yield are the primary consideration. In sailboat performance (where my thinking is directed) the primary characteristic is stiffness. I've never seen a boat hull fail structurally, outside a collision; those failures that don't involve a collision generally boil down to failure at some critical point or defective bonding, rather than too-thin a laminate throughout the hull. The factor determining how thick most hull laminate need to be is stiffness. Good design spreads the point loads out into the broader hull, so the strength-dominated portion of the hull is in a narrow region, near the mast, shrouds, and stays. This small region has a fairly small effect on the overall weight, which is mostly controlled by the weight of the rest of the hull (plus various things not directly relevant to this discussion).

    On 3., that would make sense for structures where the full thickness is laminate. I was thinking primarily about cored construction. The "thick laminate" case is a lot like cored construction, with E glass playing the role of core. I would have thought balsa would make a more weight-efficient core than E glass composite.

    It seems as though the mixed-modulus (not cored) case depends on matching the ratio of distance from the neutral axis to the ratio of modulus to be completely efficient. Now that I think about it, any non-cored design is going to be inefficient, in that sense.

    I'm not recognizing the abbreviations you're using for resins; you got any references that would shed more light on the selection of resins for use with S glass?
     
  6. rxcomposite
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    rxcomposite Senior Member

    Based on the data I have gathered. Note that some published material property data maybe out of range. I did not include them.
     

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  7. rxcomposite
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    rxcomposite Senior Member

    SL,
    Deep topic. 1 & 2. You have to match the resin elongation property to the fiber elongation property to get the most efficiency. Elongation is defined in %, Strain in decimal. It is the same thing. A 0.01 strain is equivalent to a 1% elongation.

    Modulus is a straight line, the rate of change of stress to a corresponding strain (or elongation).

    If the resin has a much higher elongation than the fiber, the fiber breaks first before the resin but here is the caveat. Brittle resins are known to crack at about 50-60% of the load before the ultimate tensile strength is reached. Cracking is a failure. That is why modulus properties are used. It is a straight line riding on the back of the most linear properties of the resin before it droops down. Same is true with fiber. That means only the usable or most lineal portion of the fiber or resin is used. See attached. I match the cracking of the resin with the fiber break and not look only at the elongation properties.

    On some resin, cracking occurs much higher, say more than 60%. Typical of EPoxy and VinylEster.

    Further, "tough" resins are formulated so it does not crack. It just stretch and stretch until it breaks. No cracking. These are low modulus resins in the order of 8-32% elongation.

    After the matching of the resin and fiber properties, the fiber orientation is checked. All this modulus calculations are based only if the fibers are aligned to the direction of the load. Off axis loads changes dramatically the modulus of the LAMINATE. See http://www.boatdesign.net/forums/sailboats/elastic-modulous-fo-frp-47579.html#post639358

    3. Fiber placement is critical. The outermost fibers (or skin) received the most stress, the inner (or core) receive the most shear. Typical layup would be WR/UD outermost-CSM on the inner. On thick laminates, the inner is replaced with core as long as the core meets the shear criteria. High modulus skins makes it efficient as it receives the most stress away from the N.A.
     

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  8. Sail Nut
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    Sail Nut Junior Member

    I'll confess that I'm still confused about how to "match elongation" between the fiber and the resin.

    Your definition of elongation seems to be the percentage change in linear dimension, which seems equivalent to strain, in different units.

    In a composite that hasn't failed, the strain of the fiber is very close to that in the resin, regardless of the particular materials. If they weren't very close to each other, one would have changed shape significantly differently from the other, which indicates the bond has failed, which I would call "cracking".

    Since you're presenting an elongation number for each material independently, I assume you're referring to something more specific than "elongation"; this would mean something along the . I had assumed you meant "Elongation at Break", since that's the property that I see commonly specified. You didn't agree with that, so I take that to mean that you meant something else, so I'll take another guess: It sounds like you're talking about the maximum elongation at first crack. I'm familiar with polymers that have extensive microcracking before ultimate failure; it's common, perhaps even universal.

    I'd probably call that property "Maximum Elongation before Yield", but I haven't found any references that present that for the relevant materials; perhaps there's a more standard name for that property. I would think for hard materials, like glass fiber, that the value for "Maximum Elongation before Yield" would be 99% of Elongation at Break, since any yield is going to produce a crack, leading to a stress concentration that propagated the crack at the speed of sound. For most resins, if your claim is that "Maximum Elongation before Yield" is about 60% of Elongation at Break, I have no data to argue the point and my gut feel is that it's in the ballpark.

    I guess I don't understand what you mean by "modulus properties are used"; the part about linear makes it sound like Young's Modulus. That makes no sense, because the Young's Modulus of any sane fiber is hugely larger than that of any resin I've heard of, so to match Young's modulus between the fiber and the resin would be impossible.

    In your attachment, I see a graph with 2 straight lines, clearly showing different moduli: the strain in the matrix and fiber are the same, the stress (force per unit area) is different. In any case, both lines are completely straight, so the attachment doesn't explain what you mean by the " linear properties of the resin before it droops down". The diagram is clear, but it only shows the linear portion of the stress/strain relationship. In this range, I don't see anything to "match", other than Young's Modulus, which is clearly not being matched in this diagram.

    Your other attachments (replying to jonr), show various numbers for various fibers and resins, but without the legends, I'd have to guess as to what they mean. I'm guessing, in the first one, the percentage row is what you're calling "elongation characteristics". I'm unclear as to why you think the Standard Epoxy is unsuitable for S glass, since they nearly match in elongation characteristics. Your second attachment appears to refer to the characteristics of a series of composites: various fibers in an epoxy matrix. While interesting and possibly useful, it doesn't purport to report the elongation characteristics of S glass, as such. It does report something labelled epsilon-super s-sub L (if I'm reading it correctly) for the composite. I'm guessing that is a strain under some condition, but without the legend, I can only suppose that this is max elongation before failure. This attachment seems to support my contention: a composite of S glass is stronger and stiffer than E glass in the same resin by 20% or more. If the max elongation is higher, as well, then the energy to failure is higher by 40% or more.

    On "3. Fiber placement is critical.": true. Equally true of designs using a single modulus fiber and designs using just S glass, therefore irrelevant to the decision as to which fiber to use, except in the limited sense that mixed-modulus seems to be a bit trickier to figure out what the optimum design would be, leading to some combination of higher design expense, using suboptimum design, or the occasional failure of an inadequate design. Given the design challenges, it seems easier and cheaper to make a 20% weight saving by substituting S glass for E than by substituting some exotic fiber for 25% and keeping E glass for the rest.
     
  9. jonr
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    jonr Senior Member

    > Its elongation characteristics is about 3.2%

    Your second reference appears to be for the combined result of S-glass and epoxy, not S-glass itself. Around 5% is the correct value for S-glass alone.

    "Fiberglass and Glass Technology: Energy-Friendly Compositions and Applications" has some discussion of the ideal situation being where the resin matches the fiber and that the resin should never be less than the fiber.

    https://dspace.ist.utl.pt/bitstream/2295/1005412/1/Guide to composites.pdf talks about a resin exceeding 5.3% is a match for s-glass.
     
  10. rxcomposite
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    rxcomposite Senior Member

    Don't assume 5% is the only value and the correct value for S glass. You could be looking at only one type of weave. My research was limited to unidirectional fibers to keep things in the proper perspective. Very close to a "melted" glass.

    Weave type will produce varying elongation characteristics. If you find 5% suits you, then go ahead and use the methodology to find the correct resin type which in this case will be the standard epoxy or vinyl ester. Note also that epoxy resin has a wide range of formulations. We are talking of standard epoxy within the range.

    As for your comment on the "typical" material properties of resin and fiber, I included the LAMINATE properties. Keeping the resin modulus constant (epoxy in this case), and the Volume Fraction constant. The resulting samples shows how the relative properties of the laminates fare with each other.
     
  11. rxcomposite
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    rxcomposite Senior Member

    Sail Nut,

    Let us use the proper terminology instead of using assume or try to place another engineering description to the properties. I tried to described the behaviour in laymans terms but I guess we have to talk in technical terms. Avoid the use of "impossible" until you gain a full understanding of the mechanics involved.
     

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  12. michael pierzga
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    michael pierzga Senior Member

    And you can see that eglass matches the resin properties and that as a result correct eglass density, fiber orientation and resin ratio give that best bang for the buck.

    If you have a lot of bucks then exotics are the best way to use them.

    I remember reading an interview with the X Yacht builder Jesperson . When asked why X Yachts, a popular and well built racer cruiser , doesnt use carbon or exotics in hull construction his reply was similar to Rxcomposite. The materials dont match his construction method
     
  13. TeddyDiver
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    TeddyDiver Gollywobbler

    Have you better scan of the left side 'picture' ? Now it's unreadable.. The other one is useless without any values..
     

  14. rxcomposite
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    rxcomposite Senior Member

    Sorry for the bad image. Not much success with Paint.

    Here is the original Excel while I was developing it. Not scaled. Just trying out the sin curve. Takes too long to upload also because of the illustrations.
     

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