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Homework Help: Thermal Expansion, Young's Modulus

  1. May 24, 2010 #1
    1. The problem statement, all variables and given/known data
    6. A steel beam is used in the road bed of a bridge. The beam is mounted between two concrete supports when the temperature is 23⁰C, with no room for thermal expansion. What compressional stress must the concrete supports apply to each end of the beam, if they are to keep the beam from expanding when the temperature rises to 42⁰C?
    Co-efficient of linear expansion for steel = 11 x 10-6K-1
    Young’s modulus for steel = 210GN.m-2



    2. Relevant equations

    deltaL/L=alpha deltaT
    F/A*=delta L/L*Y

    3. The attempt at a solution

    Ive found delta L/L to be 2.09*10^-4 ive also done about a thousand other things but everything i try needs an original length, i feel like ive overlooked a simple step or something.... can someone please give me a hand.
     
  2. jcsd
  3. May 24, 2010 #2
    You don't need the original length if you have ΔL/L
    Young's modulus= stress / (ΔL/L)
    You are given the modulus and need to calculate stress.
     
  4. May 24, 2010 #3
    ok i have never seen this formula is stress defined as force of force/unit area??
     
  5. May 24, 2010 #4
    Yes, stress is force per unit cross section area = F/A
    strain is extension per unit length = ΔL/L
    Young's modulus is stress/strain
     
  6. May 24, 2010 #5
    ok i remember that from an early lecture thanks
     
  7. Jun 1, 2011 #6
    How/where can I find Young's Modulus for paper?
     
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