Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thickness of material to support a heavy load

  1. Jun 11, 2012 #1
    My situation is i have a 10kg battery that is mounted on top of a plastic material. How would i exactly calculate the right thickness for the plastic to support the 10kg battery?
  2. jcsd
  3. Jun 11, 2012 #2
    first you need to know what the other two dimensions are. the third dimension - it's thickness- will be dependent on them.

    second, you need to describe the exact type of plastic.
  4. Jun 11, 2012 #3
    Other two dimensions?
  5. Jun 11, 2012 #4
    The length and width of your peice of plastic (along with the locations of any supports) will dictate the thickness required to support the load.

    The type of plastic, as well, will be a required known.
  6. Jun 11, 2012 #5
    Personally I'd go for some glass fibre reinforced plastic or perhaps steel mesh reinforced.

    A sheet up to 400mm x 400mm x 5 mm thick would readily take a 10Kg point load if supported on two or four edges.

    Is this for a boat or car?
  7. Jun 11, 2012 #6
    What if i were to use syntactic foam for the base to support the load?...Give me your thoughts anyone..
  8. Jun 12, 2012 #7
    dude, it really depends. how accurate do you need to be? how important is that accuracy?

    you need an exact material spec to start. then you need to model the 3 dimensional structure.

    the basic strength analysis would be to determine thickness by strength necessary for a given cross section.

    i mean who knows about this foam? it could be super strong in tensile but super weak in yield or compression.

    you could always run tests of varying thickness foam. it would super awesome if you documented the process and and posted links or info here.
  9. Jun 12, 2012 #8
    What if you did?
    What would you then support that on?
  10. Jun 12, 2012 #9
    Or you could just by a piece of really thick plastic. It's not that expensive. There's no sense modelling it, jut build it bigger than it needs to be.
  11. Jun 12, 2012 #10
    Do u have any formula to calculate the thickness needed?
  12. Jun 12, 2012 #11
    google "strength of materials + bending stress" and youll see equations like:

    E = (P*L^3)/(4*w*y*t^3)

    For E you can use modulus of elasticity. P is the load, L is the length, w is the width, t is the thickness and y is the deflection or bending. Look up E, solve for t.
  13. Jun 12, 2012 #12
    By p/load, you meant the force or the weight of the load and the length and with is of what?
  14. Jun 12, 2012 #13
    For P use weight. I prefer SI units and in this case it would be 10kg * 9.8 m/S^2 or 98 N.

    The dimensions (L, w, t) are for the plastic or whatever supporting material you wish to use.
  15. Jun 12, 2012 #14
    Thank you very much!
  16. Jun 12, 2012 #15
    Hey bro, but by Y, what does it mean by deflection at load point?? Sorry, i need to know this
  17. Jun 12, 2012 #16
    While considering the center of mass of the battery to be the load point, and the battery would be on the center of the supporting material, y is the maximum amount of bending from a neutral flat position.

    These types of equations are great, but this is just about as simple as they get. The expression I gave is for a highly idealized and restricted situation.
  18. Jun 12, 2012 #17
    Bear in mind, zero delta, that the OP has already been asked about the available supports without response.
  19. Jun 12, 2012 #18
    So if i do not want it to bend, meaning i will calculate y as zero. I do not have the material with me and most importantly do not want it to bend while supporting the load.
  20. Jun 13, 2012 #19
    Everything bends, even if you can't see it with the naked eye.
  21. Jun 18, 2012 #20
    If you have a Mechanics of Solids/Mechanics of Materials book I would refer to them. The type of chapters in those books you are looking for is "Bending of Straight Beams" and "Bending of Flat Plates" or just general beam deflection/thickness theory. But from intuition alone, you are working with a 10 kg load = 22 lbs, considering a common plastic = PVC, I would say that a thickness of 5-8 mm thick depending on the other two dimensions because bending would have to be considered. Any more than 8mm would be excessive.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook