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Homework Help: Solid mechanics

  1. Nov 21, 2009 #1

    now i am looking for the stress [tex]\sigma[/tex] for the aluminium and for the steel
    i would want to say simply [tex]\sigma[/tex]=F/A but i need to somehow take into account the types of materials and their elasticity,
    i think that hookes law could help me here but i dont know the strains
    also how do i take the volume into account? the only equation i have for volume is [tex]\Delta[/tex]=[tex]\epsilon[/tex]x + [tex]\epsilon[/tex]y + [tex]\epsilon[/tex]z, but i doubt thats going to help
  2. jcsd
  3. Nov 21, 2009 #2


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    You know a little about the strains, since the rigid top plate supplies a constraint on the components' deformation. What can you say about the strain of the steel and aluminum?

    Each component will have its own stress, cross-sectional area, and force. Can you relate the forces to the applied load?
  4. Nov 21, 2009 #3
    i would think that the aluminium and steel have the same strains.
    i can find the ratio of forces on each material as their area of the rigid plate? is this correct?

    F(Al) = 4P/7
    F(Steel)= 3P/7


    can i say that since i only have forces on the y axis


    now since the strains are the same


    now i have t equations and 3 unknowns, but i know

    [tex]\sigma[/tex]Al*2*10-3 + [tex]\sigma[/tex]Steel*1.5*10-3=385*103

    thanks for the help
  5. Nov 21, 2009 #4
    does that mean that the stress has nothing to do with the height of the element
  6. Nov 21, 2009 #5


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    That's what it looks like.
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