Flat plate bending in two planes

Discussion in 'Boat Design' started by Annode, Apr 26, 2020.

  1. Annode
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    Annode Senior Member

    WITHOUT FORMING

    From this thread:
    Max steel plate curve without forming ? https://www.boatdesign.net/threads/max-steel-plate-curve-without-forming.13766/
    There was a very useful estimate for bending steel plate in one plane of roughly 700x th plate thickness. Very useful number for first apporixmation work.

    Also considering:
    ease of fairing of larger boats https://www.boatdesign.net/threads/ease-of-fairing-of-larger-boats.14666/

    Given comments in other threads that hull plating can be forced into almost any shape with enough force, I began to wonder what curvature in longitudinal AND vertical planes might be possible with moderate forces to enduce slight curvature in both directions into flat plate to avoid welding sections together and the associated uglyness.

    Assuming an elastic modulous of 210GPa,
    Flat Plate Deflection Calculator | Flat Plate Stress Calculator - Engineers Edge https://www.engineersedge.com/calculators/flat-plate-deflection.htm
    Using this calculator to apply a point load over 1mm sq (.56mm radius yeilds 1 mm area) of 1.5N - about the eqivalent of 2 Nautical Engineers applying their bodyweight with two fingers )
    The deflection is calculated at about 2 inches which equates to a radius of about 38m. This is adequate for the longitudinal plane.

    Since the plate will be significantly longer in the longitudinal direction along the hull, adjusting the length to say 5 or 6 m with the same two NAs hard at work applying a point load, the deflection is now 3in which equates to a radius of about 25m. My desired radius in the vertial plane is about half that which will take about 9N/mmSq or 1300 psi. Thats going to take some mechanical advantage like a come along.

    If the plate were rolled it would have to be cut into much smaller sections requiring welding and resulting uglyness, hence the exploration of using force to form the hull plating over the framework.

    Does anyone with HANDS ON experience of forming plate in this way have a comment abou these numbers?
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Try it with thin sheet in a greatly scaled down version, and get a feel for the possibilities, why can't you just use developable shapes, the degree you will be able to deviate from that will be pretty limited with manual means.
     
  3. Annode
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    Annode Senior Member

    Hi. Thanks for that sugestion. I was going to try that, but I am not sure how I would scale appropriately. If I scale 24m to 24inches, a factor of 40x, then the thickness would be scaled to .15mm, thats less than 1/64 in. Is the same elastic modulous mild steel available that thin?

    the surface is developable, but the above waterline side plating will require fairing after all the welding. Welding is time consuming and expensive. This thread is a consideration of a technique to avoid that, and the forming. Boat builders report they are able to form curves. This is an exploration of that.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Well, I don't know, mild steel is mild steel, isn't it ? You might get some offcuts from a sheet metal workshop.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm no expert in metal fabrication, but I'm pretty sure Ad Hoc mentioned the undesirability of alloy welded whilst under the stress of being bent to shape, not rolled into shape, steel of course is not the same.
     
  6. Annode
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    Annode Senior Member

    Perhaps this material..

     
  7. Annode
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    Annode Senior Member

    I think you are referring to this thread
    Origami steel yacht construction https://www.boatdesign.net/threads/origami-steel-yacht-construction.248/
    in which the residual strength without framing was discussed. This design will have suitable framing.

    Another calculator
    eFunda: Plate Calculator -- Simply supported rectangular plate with point load eFunda: Plate Calculator -- Simply supported rectangular plate with point load https://www.efunda.com/formulae/solid_mechanics/plates/calculators/SSSS_PPoint.cfm

    4000N point load is equivalent to hanging 100kg on each corner of a plate supported in the middle. Thats not excessive.[/QUOTE]
     

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  8. Barry
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    Barry Senior Member

    Line Heating is a Flourishing Metal Fabrication Technology at Machinists Inc. | Machinists Inc https://www.machinistsinc.com/blog/line-heating-is-a-flourishing-metal-fabrication-technology-at-machinists-inc/

    refers to a site that uses line heating to form non developable curves in steel plate

    Go the search tab above and insert " Big Ship Steel Plate Curving Process" which was a thread a couple of years ago that has a very long video about plating large ships and curving plates using the application of line heating.
    The video in one of the posts shows how they do it, about the 39 minute mark

    You can also google "line heating" of steel plates

    You did not mention the thickness that you are trying to work with but in your one example in your first post, you or your example showed 6mm plate, is this the thickness that you are considering forming?
     
  9. bajansailor
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    bajansailor Marine Surveyor

  10. Annode
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    Annode Senior Member

    This only has S235 which is a structural steel that is a little stiffer but still yields 84mm of delfection
     

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  11. Annode
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    Annode Senior Member

    Yes thank you for mentioning that. I studied that very carefully. As you will note, the guys doing that do ONLY that and have been doing that for 18yrs. I suspect it takes a while to get right.
    Regardless, this thread is not about forming.
     
  12. Annode
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    Annode Senior Member

    Well that is a very good question. The answer is simple. F:LAT PLATES ARE UGLY.
    The Greeks understood this a long time ago. Pillars in their architecture ALL HAVE CURVES.
    let me see if i can find a video...
    The bilge will be a round design pre rolled by the supplier
     
    Last edited: Apr 27, 2020
  13. Annode
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    Annode Senior Member


    8:24
    20:40
    34:50
    41:10 a radius of a mile
    44:20 ENTASIS curve on long spans
     
    Last edited: Apr 27, 2020
  14. Dejay
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    Dejay Senior Newbie

    Not sure if this is applicable, but the physical analogy behind thin plate splines actually refers to how thin metal sheet bend into compound shapes. So maybe there are relatively easy analytic models to precisely calculate the shape a sheet will take and calculate how much stress it will have and if it would yield. Maybe this gives you the right keyword to search for papers or software to do this.
     

  15. bajansailor
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    bajansailor Marine Surveyor

    I think I would be very happy to own a boat with a radiused chine hull form, as I think they do look rather attractive. And it should be possible to get away with using no filler if one is careful.
    I know you like Jongerts Annode - in contrast, some friends of my parents had a 46' steel centre cockpit Jongert ketch built in the mid 70's - they were called Trewes then.
    The hull had complex curves everywhere and was very fair - but they later found that filler had been literally plastered on very thickly everywhere in order to achieve this. And it was millimetres (often many mm) rather than microns thick.
     
    Last edited: Apr 27, 2020
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