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Resistance from a cable?

  1. Apr 16, 2009 #1
    Hello,
    I have a project for my diploma.And i have some questions. If someone can help me
    i would be very pleased.
    I have to know what the cables resistance ( σ ( N/mm2)) is,i mean, how big a force, do i need for cut the cable's plastic?I have a disc (it should be the knife), when it turns around it, it should cut the plastic-all the cover; and the copper should appear.

    I thought like this ; σ = F / A and if i know σ, i could find the force, and from force to momentum and then the engines HP ..

    Did i thing exact?

    Thanks..
     
  2. jcsd
  3. Apr 16, 2009 #2

    mgb_phys

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    Not sure what you are asking
    the ultimate tensile stresss = breaking strain of the cable is normally given in N/mm^2 (or GPa) - but this is the maximum force/area in tension when it breaks - not the resistance to cutting.
    The plastic sleeve doesn't really add any strength.
    It is also only true for hard materials, copper will stretch and change shape before it brakes so there isn;t a simple maximum N/mm^2
     
  4. Apr 17, 2009 #3
    First of all thanks for your response,

    you say that the plastic doesn't add any strenght, so for me is the cover important? The

    steel-fiber wire etc...Where can i find the propertys from a cable, because i need a force or

    a strength... Which way should i follow?
     
  5. Apr 17, 2009 #4

    mgb_phys

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    If you are just looking for breaking load (in tension) then you can look up the "ultimate tensile strength" or "yield strength" for the material. This will be given in GPa (N/m^2) which is 1000N/mm^2 see here for list http://en.wikipedia.org/wiki/Tensile_strength

    This also gives you an idea of how much force is needed to cut the wire.
    You need to calculate the area of the tip of the blade and the force to get the pressure
     
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