SAN-PVC-PET foam core

Discussion in 'Multihulls' started by RampantMule, Nov 6, 2021.

  1. RampantMule
    Joined: Nov 2021
    Posts: 15
    Likes: 2, Points: 3
    Location: Castaway

    RampantMule Junior Member

    That looks pretty slick there Fallguy
    fallguy likes this.
  2. rxcomposite
    Joined: Jan 2005
    Posts: 2,752
    Likes: 608, Points: 113, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Might as well post the spreadsheet. Here is How To Do it:

    Using a reliable material property data of the material you plan to use,
    1. Plot the modulus of the carbon fiber Laminate. Multiply modulus of elongation by the strain. Strain is % Elongation/100. That value is the force required to break the laminate (ultimate strength). For our purpose, although irrelevant, the cross sectional area is 1 mm2 and the value is N/mm2.

    2. Stop when your value equals the ultimate strength.

    3. Draw a vertical line from the intersection of the modulus and the ultimate strength. That value is the max strain of the material.

    4. Divide that Ultimate stress value by 2, the maximum safety factor allowed in composites. You are allowed to use at most 50% of the value to keep within the yield point of the laminate. It is called design strength.

    5. Draw a vertical line on the intersection of the designed value. That is your allowable strain.

    6. Plot the modulus of the Eglass Laminate. Follow the same procedure as above.

    7. Plot the same for compression properties. You will need it because when the outside surface is at tension, the opposite surface is in compression.

    From the graph, you can see that the CF has a higher design value but low strain. If you apply a force (stress) on the CF, you will see that you have reached the maximum value allowed for the Eglass. Theoretically, you cannot use a value greater than the designed strength of the Eglass.

    All is not lost however. In design of laminate, the outermost fibers receive the highest stress and reduces to zero when it reaches the neutral axis then reverses. It is called Fiber Placement strategy. Place the laminate with the highest allowable value on the outside. The second laminate with the lower designed value goes inside. Just make sure the allowable stress is not exceeded. With laminates that are too far apart in values, you might be overbuilding on certain area to compensate for the weaker laminate. That is for single skin laminate.

    For cored laminate, which is basically your Q, you cannot place the Eglass immediately after the CF. The reason is obvious from all of the explanation given above.

    Attached Files:

    RampantMule likes this.
  3. RampantMule
    Joined: Nov 2021
    Posts: 15
    Likes: 2, Points: 3
    Location: Castaway

    RampantMule Junior Member

    That pretty much explains lots of problems home builders do. We tend to unnecessarily overbuild out project which adds costs and weight and sometimes worst than the original design.

    On the other hand that is kind of reasonable. In the solar panels, it is not wise to use epoxy to encapsulate the cells, due to the expansion when heated. When a diy epoxy build solar panel gets warmed up from the sun, it expands and the cells are destroyed/crasked. That is why the use of EVA film and glass that are more elastic and allow more room for the heat expansion. Sometimes the anwer is in from of your eyes but you havent connected the dots . :)

    Now I understand Louis build
  4. fallguy
    Joined: Dec 2016
    Posts: 7,557
    Likes: 1,659, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Carbon and wood more closely share elongation properties. Simple as that..

    But people are putting c/f on foam all the time.
  5. Moewaka
    Joined: Jun 2016
    Posts: 9
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Christchurch, NZ

    Moewaka Junior Member

    Hi all. Sorry a little off topic, but I hope someone can help.

    I'm struggling to find a supplier for any core materials in Christchurch, NZ. Some that look likely in Auckland, but not a lot of information on their websites.

  6. guzzis3
    Joined: Nov 2009
    Posts: 840
    Likes: 159, Points: 43, Legacy Rep: 42
    Location: Brisbane

    guzzis3 Senior Member

    UTEK in china are a wholesaler. If you know someone with a registered business, doesn't matter what sort, they will sell you PVC foam glass bagging supplies etc at great prices.

    Rob Denny is using the stuff to build his proas.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.