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Re: [Michalak] Re: OSB

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  • Thomas Hamernik
    A little bit of googling turned up this reference...
    Message 1 of 32 , Apr 30 8:18 AM
    • 0 Attachment
      A little bit of googling turned up this reference...

      http://books.google.com/books?id=NJE3wTL6IDYC&pg=PA318&lpg=PA318&dq=modulus+of+elasticity+of+fiberglass+epoxy&source=bl&ots=QZls4DWkGh&sig=Sn0k1gmkXZPGODegATVG0VmHJFY&hl=en&ei=bb_5SbuSAqa2tAODwdXzAQ&sa=X&oi=book_result&ct=result&resnum=10

      Note that fiberglass and epoxy (exact type not indicated, though the table does suggest unidirectional layup - likely with higher resulting stiffness) is approximately 4 times stiffer than aircraft-grade spruce.  Graphite/epoxy is approximately 17 x as stiff!

      TJH




      ________________________________
      From: Thomas Hamernik <onevenkeel@...>
      To: Michalak@yahoogroups.com
      Sent: Wednesday, April 29, 2009 9:57:13 PM
      Subject: Re: [Michalak] Re: OSB





      I've had the same experience.  My S&G kayak has 4 mm decks.  Even thoughe arched, I thought the deck had too much give.  So, I upturned the kayak and placed some fiberglass set in epoxy on the underside of the deck - immensely stiffer.  I understand that carbon fiber is often similarly used by the strip kayak builders to beef up the decks - carbon fiber set in epoxy will be much stiffer than wood or fiberglass.

      Stiffness is a function not only of geometry (thickness), but of the mechanical properties of the materials, as well.  I can't recall, off hand, the modulus of fiberglass, though I suspect it is significantly higher than that of wood.  A higher modulus means that a given thickness of fiberglass would contribute more stiffness than an equal addition of wood.  When placed on the tension side of the member, the neutral axis (the dividing point between where the section is in tension and where it is in compression) shifts toward the fiberglass, thereby putting more of the wood in compression while the fiberglass takes a share (or perhaps all) of the tension - this could be very beneficial is the tensile wood is cracked as Chris describes since its compression strenght is likely to remain.

      TJH

      ____________ _________ _________ __
      From: Chris Feller <chrisbfeller@ yahoo.com>
      To: Michalak@yahoogroup s.com
      Sent: Wednesday, April 29, 2009 9:46:46 PM
      Subject: [Michalak] Re: OSB

      I have had a similar experience to Robb. On my Junebug I used a poor quality 1/4 inch BC Pine plywood board for the aft deck. This board had a lot of cracks along the grain which under a load flexed a great deal and started to crack open. Once I added one layer of 6oz glass the board stiffened up quite a bit. Most of the strength came from the glass on the bottom side of the deck. I would assume this is due to the increased tensile strength.

      I don't think that adding glass is as simple as just adding thickness to the board. If that was the case then there would be a very small increase in strength. I think it has more to do with the increase in strength across the grain. The glass holds the grain together and prevents failures along the grain of the plywood. This is especially helpful on a piece of plywood with a lot of cracks along the grain like my Junebug deck.

      Perhaps one of our engineer members might chime in to explain.

      Chris Feller
      --- In Michalak@yahoogroup s.com, "Robb" <robb@...> wrote:
      >
      > well....in my experience it does add alot of stiffness. I am able to use 1/4 ply on decks of some of the boats I build. with a layer of glass/epoxy on the top side the deck becomes much stiffer. I don't even know why this is even an arguement. If Chris or whoever doesn't think it adds any strength then don't use it. I know from experience what it does. Robb
      >
      >
      >
      >
      > ----- Original Message -----
      > From: Rob Rohde-Szudy
      > To: Michalak@yahoogroup s.com
      > Sent: Wednesday, April 29, 2009 12:35 PM
      > Subject: [Michalak] Re: OSB
      >
      >
      >
      >
      >
      > Well, first of all what do you mean by "structural" strength? Tensile I'll buy. Cross-grain tensile I'll definitely buy. Compressive not so much. And you don't add much section depth, so I also don't buy the increase in stiffness being very large.
      >
      > My main point, however, was that if you take the wood out from in between, all bets are off because the two sheets of glass are no longer part of the *same* system. E.g. tensile forces in one do not necessarily equate to compressive forces in the other because buckling is not inhibited.
      >
      > --Rob
      >
      >
      >
      > Re: OSB
      > Posted by: "Robb" robb@... rube2112us
      > Date: Tue Apr 28, 2009 4:21 pm ((PDT))
      >
      > One layer of fiberglass and epoxy on a plywood hull GREATLY enhances the structural strength of a boat. If your adding a layer just for abrasion resistance your getting alot more strength and stiffness at the same time........ Robb
      >
      > [Non-text portions of this message have been removed]
      >
      >
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >

      [Non-text portions of this message have been removed]



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    • Thomas Hamernik
      A little bit of googling turned up this reference...
      Message 32 of 32 , Apr 30 8:18 AM
      • 0 Attachment
        A little bit of googling turned up this reference...

        http://books.google.com/books?id=NJE3wTL6IDYC&pg=PA318&lpg=PA318&dq=modulus+of+elasticity+of+fiberglass+epoxy&source=bl&ots=QZls4DWkGh&sig=Sn0k1gmkXZPGODegATVG0VmHJFY&hl=en&ei=bb_5SbuSAqa2tAODwdXzAQ&sa=X&oi=book_result&ct=result&resnum=10

        Note that fiberglass and epoxy (exact type not indicated, though the table does suggest unidirectional layup - likely with higher resulting stiffness) is approximately 4 times stiffer than aircraft-grade spruce.  Graphite/epoxy is approximately 17 x as stiff!

        TJH




        ________________________________
        From: Thomas Hamernik <onevenkeel@...>
        To: Michalak@yahoogroups.com
        Sent: Wednesday, April 29, 2009 9:57:13 PM
        Subject: Re: [Michalak] Re: OSB





        I've had the same experience.  My S&G kayak has 4 mm decks.  Even thoughe arched, I thought the deck had too much give.  So, I upturned the kayak and placed some fiberglass set in epoxy on the underside of the deck - immensely stiffer.  I understand that carbon fiber is often similarly used by the strip kayak builders to beef up the decks - carbon fiber set in epoxy will be much stiffer than wood or fiberglass.

        Stiffness is a function not only of geometry (thickness), but of the mechanical properties of the materials, as well.  I can't recall, off hand, the modulus of fiberglass, though I suspect it is significantly higher than that of wood.  A higher modulus means that a given thickness of fiberglass would contribute more stiffness than an equal addition of wood.  When placed on the tension side of the member, the neutral axis (the dividing point between where the section is in tension and where it is in compression) shifts toward the fiberglass, thereby putting more of the wood in compression while the fiberglass takes a share (or perhaps all) of the tension - this could be very beneficial is the tensile wood is cracked as Chris describes since its compression strenght is likely to remain.

        TJH

        ____________ _________ _________ __
        From: Chris Feller <chrisbfeller@ yahoo.com>
        To: Michalak@yahoogroup s.com
        Sent: Wednesday, April 29, 2009 9:46:46 PM
        Subject: [Michalak] Re: OSB

        I have had a similar experience to Robb. On my Junebug I used a poor quality 1/4 inch BC Pine plywood board for the aft deck. This board had a lot of cracks along the grain which under a load flexed a great deal and started to crack open. Once I added one layer of 6oz glass the board stiffened up quite a bit. Most of the strength came from the glass on the bottom side of the deck. I would assume this is due to the increased tensile strength.

        I don't think that adding glass is as simple as just adding thickness to the board. If that was the case then there would be a very small increase in strength. I think it has more to do with the increase in strength across the grain. The glass holds the grain together and prevents failures along the grain of the plywood. This is especially helpful on a piece of plywood with a lot of cracks along the grain like my Junebug deck.

        Perhaps one of our engineer members might chime in to explain.

        Chris Feller
        --- In Michalak@yahoogroup s.com, "Robb" <robb@...> wrote:
        >
        > well....in my experience it does add alot of stiffness. I am able to use 1/4 ply on decks of some of the boats I build. with a layer of glass/epoxy on the top side the deck becomes much stiffer. I don't even know why this is even an arguement. If Chris or whoever doesn't think it adds any strength then don't use it. I know from experience what it does. Robb
        >
        >
        >
        >
        > ----- Original Message -----
        > From: Rob Rohde-Szudy
        > To: Michalak@yahoogroup s.com
        > Sent: Wednesday, April 29, 2009 12:35 PM
        > Subject: [Michalak] Re: OSB
        >
        >
        >
        >
        >
        > Well, first of all what do you mean by "structural" strength? Tensile I'll buy. Cross-grain tensile I'll definitely buy. Compressive not so much. And you don't add much section depth, so I also don't buy the increase in stiffness being very large.
        >
        > My main point, however, was that if you take the wood out from in between, all bets are off because the two sheets of glass are no longer part of the *same* system. E.g. tensile forces in one do not necessarily equate to compressive forces in the other because buckling is not inhibited.
        >
        > --Rob
        >
        >
        >
        > Re: OSB
        > Posted by: "Robb" robb@... rube2112us
        > Date: Tue Apr 28, 2009 4:21 pm ((PDT))
        >
        > One layer of fiberglass and epoxy on a plywood hull GREATLY enhances the structural strength of a boat. If your adding a layer just for abrasion resistance your getting alot more strength and stiffness at the same time........ Robb
        >
        > [Non-text portions of this message have been removed]
        >
        >
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >

        [Non-text portions of this message have been removed]



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        Get inspired
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        Start a group
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