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Homework Help: Stress, strain and deflections due to temperature change

  1. Nov 24, 2009 #1
    in the following problem

    i know that ΔT=120

    now the maximum deflection is 0.5mm so i looked for the total deflection had there been no restrictions

    ΔL(aluminium)=300*(23e-6*120)= 0.8280
    ΔL(st steel)=250*(18e-6*120)= 0.5400

    this is clearly more than the maximum deflection of 0.5- there are 0.868 "extra" which cause the stress.

    now putting this all together is where i get stumped.

    and ΔL=ε*L


    now the force in the aluminium and in the steel must be equal so i have 3 equation system to solve, after solving i get

    F= 1.3201e+011
    ε(al)= 0.942928e-3

    now simply using

    σ=ε*E or σ=F/A


    but the correct answer is -114.6MPa

    i can see where this might be wrong, nowhere in my stress calculations do i take into account the amount that each material expands. but i have no idea how to fix it
  2. jcsd
  3. Nov 25, 2009 #2
    think i got it,

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