Material properties for composite foam sandwitch simulation

Discussion in 'Software' started by Velas, Feb 29, 2016.

  1. Velas
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    Velas Junior Member

    Hi,

    As a preparation for a much bigger project, I'm trying to learn simulation and FEA using standard software (Solidworks, which I can use after hours at work).

    I have a problem with estimating the mechanical properties of the reinforcement+resin plies, without having to make and break samples. I understand that it all depends on fibre and resin types, and also on the resin proportion and type of layup (infusion, wet, vacuum etc) and post-curing.

    I hope that for starters, some generic information would be "enough" to get into the proper order of magnitude for a relatively plausible simulation.

    For example, it could be enough to have elastic modulus/tensile and compression strength and yield of a generic "e-glass" of specified weight with a layout of 0-90 and +/- 45 infused with "generic" epoxy.

    Any hints on where to find such data? All I can find is data for carbon prepregs.

    thank you.
     
  2. TANSL
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    TANSL Senior Member

    You're going pretty well on your investigations.
    You should be aware that, indeed, the mechanical properties of composites depend on all the things you have related and, above all, the % of fiber content of the components.
    The ISO 12215 standard clarifies these issues and also is mandatory for vessels wishing to obtain the "CE". The standard specifies how to calculate the design pressures in each area of the ship, the maximum allowable stresses and also explains how to study the stresses to which it is subject each layer and how to check whether or not exceed the maximum allowable values.
     
  3. Velas
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    Velas Junior Member

    I have not read the ISO 12215-5 (perhaps I shall buy a copy).

    There must be some formulas/methods for calculating the properties of the ply starting from the properties of the fibres and the matrix ?

    EDIT: I'm looking at rules of mixtures, Hart-Smith 10% Rule. A little over my head notation and concepts, but I'm slowly working it out.
     
  4. TANSL
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    TANSL Senior Member

    A sample of what you can find in ISO 12215-5.
    I highly recommend that you take a look at the standard .
     

    Attached Files:

  5. Velas
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    Velas Junior Member

    Thank you TANSL. I'm going to buy it. I'll need it for sure.
     
  6. TANSL
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    TANSL Senior Member

    I can not resist the temptation to tell you about my SCT software. It is an application that serves to calculate boats scantlings according to ISO 12215. The program can be downloaded from my website.
     
  7. Velas
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    Velas Junior Member

    Yes, I found your software before my first post. Also I'll give MyR a go ;)
     
  8. DriesLaas
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    DriesLaas Weekend Warrior

    You will have to start with classic laminate theory (CLT) if you want to estimate the mechanical properties from first principles, using the properties and orientation of each ply, together with the FVF (fiber volume fraction) and the mech properties of the resin (which can usually be disregarded because it makes so little contribution.) It does however have an influence on the thickness of each ply which is very important.
    There should be many references to CLT on the www.
     
  9. TANSL
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    TANSL Senior Member

    Working with heterogeneus materials, the thickness must have a minimum value, but you should always check the distribution of stresses in the various layers of different materials. Do not rely only on the thickness, that is dangerous.
     
  10. rxcomposite
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    rxcomposite Senior Member

    It is the resin that has the greatest influence on strength. Low strength, low stretch resin like ortho will crack first rendering the laminate useless. It dictates the yield point of the laminate as a cracked laminate is a failure.

    The strength of the fiber is way way up the slope but it is useless if the resin has cracked.

    The better rule of thumb is to have a resin that has the same or lower modulus than the fiber, thus when the fiber "stretch" the resin stretches also, increasing the yield strength.
     
  11. Velas
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    Velas Junior Member

    I made some spreadsheets for calculating the volume fraction and estimate the strengts in the "X" direction and then assuming hte strengts in the Y direction to be only due to the matrix.

    I'm a little stuck with estimating the ply ticknesses of the single layer of fiber+matrix versus the weight in gsm of the fibers.
     

  12. DriesLaas
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    DriesLaas Weekend Warrior

    I took this from Gurit guide, and also checked Hexcel's guide to prepregs:

    (The formula in the Gurit guide is messed up by the way, or maybe it is just the way the PDF rendered)
    Anyway, here goes:

    Cured Ply Thickness from Ply Weight:

    CPT (mm) = WF/(ρF x FVF x 1000)

    Where FVF = Fibre Volume Fraction
    ρF = Density of Fibres ( g/cm3)
    WF = Fibre Area Weight of each Ply (g/sqm)

    So to estimate, a ply of 450 gsm glass, at FVF of 40%, will give:

    CPT=450/(2.5*0.4*1000)=0.45mm

    I regularly build a laminate with 16 plies of 450 glass, and it measure about 7mm, ie 0.435mm per ply, but my FVF is quite good ;-)

    Which brings you to a rule of thumb for boatbuilding (if it is a well made glass laminate:) 0.1 mm per 100 gsm Wf, very easy and pretty good for mere mortals.

    Prepregs will have higher fiber fractions, and will often be made with carbon fibre, which obviously changes everything(or does it???) (ρF =1.8 g/cc)

    For a prepreg 200 gsm carbon ply:

    CPT=200/(1.8*0.55*1000)=0.202mm, so that same rule of thumb holds good for carbon prepregs!!

    The harder estimates are the bad quality laminates - I use the following for chopped strand mat laminates (pardon the poor format of the table, from Excel:)
    Chopped strand mat
    Glass (oz/sqft) glass (g/sqm) resin (g/sqm) thickness (mm)
    Thickness 1 300 700 0.762
    1.5 450 1050 1.143
    2 600 1400 1.524
    3 900 2100 2.286

    Glass/resin ratio 30/70 0.428571429
    You have to determine the FVF for this laminate from the FWF, the formula is once again available in the Gurit guide.
    FVF=1/(1+(ρF/ρM)*(1/FWF -1))
    ρM is the density of the matrix. or resin.
    The FVF for this poorly made laminate is 0.146

    Using the formula for 1.5 oz glass:

    CPT = 450/(2.5*0.146*1000)=1.23mm, which is close to the estimate table I gave above.

    Hope this helps.
     
    Last edited: May 27, 2016
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