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Homework Help: Composite beams and young's modulus

  1. Apr 1, 2009 #1
    1. The problem statement, all variables and given/known data

    "A polymer, with Young’s modulus 2GPa and yield stress 50MPa, is reinforced by
    uniaxially aligned glass fibres which have Young’s modulus 70GPa and fracture at
    1400MPa. The volume fraction of fibres is 40%.

    (a) Calculate Young’s modulus for the composite in the direction of the fibres.
    (b) The composite is loaded parallel to the fibres. What would be the stress on the
    matrix when the composite yields ?"

    2. Relevant equations

    3. The attempt at a solution

    (a) E = xE_f + (1-x)E_m
    E = 0.4(70e9) + 0.6(2e9) = 29.2 GPa

    firstly, i don't know if the above is right. also, i have o clue how to do part (b).
  2. jcsd
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