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Brittle Fracture Self Study Question

  1. Feb 26, 2015 #1
    1. The problem statement, all variables and given/known data

    A tensile load F is to be applied to a tie bar. The tie bar is 50 mm diameter. The surface of the bar has defects resulting from the manufacturing process, these have a maximum depth of 1.5 mm and have a shape factor of 1.4.

    If the fracture toughness of the material used is 120 MPa m–0.5, determine the maximum load which can be applied if brittle fracture is not to occur. Use a factor of safety of 3.


    2. Relevant equations


    Fracture toughness, Kic = σf√Mc = 120 MPa m-0.5

    shape factor, Q = 1.4

    surface flaw shape, M = 1.21π / Q = 2.715


    3. Attempt at an Answer

    not really sure where to start here. can anyone advise?
     
  2. jcsd
  3. Feb 27, 2015 #2
    KIc=120 MPa m-0.5
    Q = 1.4
    M = 1.21π/1.4



    120 MPa m-0.5 = σf √ ((1.21*π*1.5*10-3) / 1.4)

    120 MPa m-0.5 = σf * 0.06382


    σf = 120 MPa m-0.5 / 0.06382

    σf = 1880.29 MPa


    safety factor = 3

    σf = 1880.29 / 3 = 626.76 MPa


    cross sectional area = π*r2 = 3.14 * 252 = 1963.5 mm2

    Force = Stress * Area

    1963.5 * 626.76 = 1230643.26 pascals = 1.23Mpa


    1.23Mpa = 1200 Newtons


    would this be correct?
     
  4. Mar 9, 2015 #3
    can anyone help with this please?
     
  5. Jul 2, 2015 #4
    anyone?
     
  6. Feb 24, 2016 #5


    how did you get 1200 newtons from 1.23 Mpa?
     
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