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Elongate but dont bend

  1. Jul 29, 2012 #1
    hello!

    is there a material that doesnt bend, but can elongate? in the form of a very thin fiber

    thanks!
     
  2. jcsd
  3. Jul 30, 2012 #2

    Mech_Engineer

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    No, because bending is simply non-uniform elongation accross a material's cross-section.
     
  4. Jul 30, 2012 #3
    In response to what loading?

    For a single load, bending is a response to a transverse load whereas elongation is a response to an axial load. These loads are obviously at right angles.

    So there is no bending with an axial load.

    For a triaxial stress loading it is perfectly possible for the response to be elongation along one axis with no bending.
     
  5. Jul 30, 2012 #4

    AlephZero

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    An anisotropic material can bend (or at least, have a transverse deflection) under an axial load. The princpal directiosn of the material don't have to be aligned with the axis of the rod. and in general you have 21 indepedendent elastic constants to play around with, compared iwth 2 for an isotripoc material.

    But I agree with the earlier posts. Pure bending (into a circular shape) is a strain field with all the components zero except the axial direct strain, so I can't see how you can have a material than can elongate and contract, but can't bend.
     
  6. Jul 30, 2012 #5
    I was thinking about a materialwith its molecules placed in such way that would let it elongate, but not bend
     
  7. Jul 31, 2012 #6
  8. Jul 31, 2012 #7
    I like your confidence :D
     
  9. Jul 31, 2012 #8
    I mean, maybe somewhere down the line with something like piezoelectrics or something similar you might be able to achieve something like this. But a "very thin fiber" that can elongate, but doesn't bend? I may be wrong, but I am pretty confident that "Nope" is a pretty sufficient answer for this one lol
     
  10. Jul 31, 2012 #9

    Mech_Engineer

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    You'll have much better luck finding a material that can bend but not elongate (or at least is very stiff axially).
     
  11. Jul 31, 2012 #10
    Mather, I have said this before.

    You will get much better replies if you supply full information.
    What you have said is not enough.

    Bending is a function of the load system, not the material.

    Since you are talking about elongation I assume you mean under tension?

    Of course any ideal string has no flexural rigidity or strength so undergoes elongation but not "bending".
    Of course this is strange because the string is floppy transversally.
    The greater the tension the greater the transverse load that can be supported.

    Many materials approach the ideal strin behaviour or can be considered to be close enough to make no difference to stress/strain calculations.

    So over to you to fully describe what you are looking for.
     
    Last edited: Jul 31, 2012
  12. Jul 31, 2012 #11
    I wish I could describe it more precisely, believe me
    maybe it's that i am not native english speaker and/or i cannot form it precisely in my imagination

    i was thinking of a direct fiber of .00 mm that will not bend (in any non-direct angle) under any circumstance (force of any direction)

    however if we attach the one edge of that fiber to a stable point and extend the other edge to the opposite direction, the fiber will elongate axially

    at the same time, if eg. i press that fiber under an angle to the ground, it will condense, but only axially (ie. it wont bend)
     
  13. Jul 31, 2012 #12
    This does not exist. Is this spam?
     
  14. Jul 31, 2012 #13
    This is fine, any elastic material will do, if the pull causing the extension is the only force acting on the fibre.

    This is not fine have you heard of buckling?
     
  15. Jul 31, 2012 #14
    the point is what molecular properties give materials their mechanical properties?
    and in which extend, we can, by manipulating molecular properties, adjust or design mechanical properties of materials?
     
  16. Jul 31, 2012 #15
    I keep saying this,

    The stress regime imposed upon a body is due to the magnitude, direction and geometric distribution of the loads.

    It is not due to the material properties of the body.

    The response of the body to that stress is due to its material properties, not the loads above.

    The actual material properties form the link between the two systems (load and response)
     
  17. Jul 31, 2012 #16
    can we adjust this at molecular level?
    not as we adjust it in a building construction for example, where we use various techniques (however similar technics in molecular level would be interesting)
     
  18. Jul 31, 2012 #17
    How do you mean?

    Force is still force and moment force times perpendicuar distance.

    These properties still work at the distances between the component atoms of a molecule and allow the calculation of vibrational energies and spectra.

    If you get any smaller than that you are into particle and quantum physics.
     
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