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Homework Help: Elasticity and Young's Modulus

  1. Apr 22, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider a metal bar of length L, cross-sectional area A, equilibrium atomic separation x, and Young's modulus E. When a tension force F is applied to the bar, it causes an extension ΔL. Calculate the atomic force constant k by deriving expressions for (a) the number of chains of atoms in any cross section, (b) the number of atoms in a single chain of length L, (c) the microscopic extension Δx between atoms, and (d) the tensile force f between atoms. (e) Write f= kΔx and show that k=Ex. (f) Calculate the value of k for a typical metal for which E = 1.2 GN/m[itex]^{2}[/itex] and x=0.16 nm.

    2. Relevant equations



    stress = modulus x strain

    F/A = E ΔL/L

    ΔL= FL/(EA)

    3. The attempt at a solution

    Part f is probably the only part of the problem I feel confident about doing. As far parts a through e, I can't make heads or tails of how to derive the expressions involving atomic separation x. This problem seems to somewhat relate Hooke's law with elastic materials and a picture on my book describes the interatomic forces in the material as spring-like.
  2. jcsd
  3. Sep 19, 2012 #2
    What is the difference between the modulus of elasticity in compresão and modulus of elasticity in tension?
    Which Modulus of elasticity should employ a finite element model?
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