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Homework Help: Experimentally Determined Young's Modulus

  1. Feb 10, 2017 #1
    1. The problem statement, all variables and given/known data

    So in my mechanics of materials lab, we calculated Young's modulus after measuring the strain and applying force to a beam. What I'm trying to figure out is, why are you able to use both a bending force and an axial force when calculating Young's modulus?

    2. Relevant equations

    Young's modulus = stress/strain
    3. The attempt at a solution

    Is it because they both induce a normal force on the beam?

    Thanks for any help!
  2. jcsd
  3. Feb 11, 2017 #2
    Is this a beam bending situation, or is it a situation where you are applying a tensile force along the beam axis?
  4. Feb 15, 2017 #3
    Sorry I forgot to include that, its a bending situation. We had a beam placed into a cantilever flexure frame and loaded weights on one end of the beam.
  5. Feb 15, 2017 #4
    Please describe your understanding of the axial stress distribution and the axial strain distribution on an arbitrary cross section of the beam, say half way along the length of the beam. What is your understanding of the kinematics of the deformation?
  6. Feb 15, 2017 #5
    The stress and strain distribution for the cross section was assumed to be uniaxial, so does that mean in the lateral direction the stress and strain is zero?
  7. Feb 15, 2017 #6
    Are these stress and strain distributions uniform over the cross section of the beam, or do they vary with position over the cross section?
  8. Feb 15, 2017 #7
    We assumed them to be uniform.
  9. Feb 15, 2017 #8
    You need to go back and review beam bending. They are definitely not uniform. The variation of stress over the cross section is what causes the bending moment. Where over the cross section of the beam would your intuition tell you that the tensile stress (and strain) are highest? Lowest? Zero?
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