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Factor of safety please help

  1. Aug 10, 2012 #1
    1. The problem statement, all variables and given/known data

    What is the factor of safety of a steel hanger having an ultimate strength of 550.00 MPa and supporting a load of 64000.000N. The steel hanger in question has a cross sectional area of 7.400cm squared

    2. Relevant equations



    3. The attempt at a solution
    i understand the equation is ulitamate stress divided by allowable stress but the cross sectional area gives me problems. please show me a the steps i should take to find the factor of safety




    well i went load/ area > 64000N/7.4cm squared = 8648.65 Pa


    550 MPa = 550000kPa/8.648kPa (ultimate stress/allowable stress) =63594.11
    63.59 as my answer is that correct ? if not please show me where i went wrong
     
    Last edited: Aug 11, 2012
  2. jcsd
  3. Aug 10, 2012 #2

    rock.freak667

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    Given the load and the area, how do you find the working stress i.e. stress due to the load?
     
  4. Aug 10, 2012 #3
    Load divided by area ...right ? , when it gives me cross sectional area do I need to do anything mathematically with it or do I plug that number in ?
     
  5. Aug 11, 2012 #4

    rock.freak667

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    Well you have the formula

    stress = load/area

    And you are given both. You want to get the value of stress.
     
  6. Aug 11, 2012 #5
    well i went load/ area > 64000N/7.4cm squared = 8648.65 Pa


    550 MPa = 550000kPa/8.648kPa (ultimate stress/allowable stress) =63594.11
    63.59 as my answer is that correct ? if not please show me where i went wrong
     
  7. Aug 11, 2012 #6

    CWatters

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    Check the units. cm2 ?
     
  8. Aug 11, 2012 #7
    oh , i need metres squared
     
  9. Aug 11, 2012 #8
    Load/Area= 64000N/0.074m= 864864.8649 Pa > 864.864 kPa
    F/S = Ultimate stress/ Allowable Stress = 550 MPa/ 864.864 kPa > 550000 kPa/ 864.864kPa = 635.938


    is (635.938 ) my answer ? (factor of safety) ??
     
  10. Aug 11, 2012 #9

    rock.freak667

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    1 cm2 = 0.0001 m2
     
  11. Aug 11, 2012 #10
    1.0 cm2= ?? m2
     
  12. Aug 11, 2012 #11
    1 cm = 0.01 m ....
     
  13. Aug 11, 2012 #12
    okay thank you... i see my mistake
     
  14. Aug 11, 2012 #13
    64000 N/ 0.00074m2 = 86486486.49 Pa > 86486.48649 kPa
    F/S Ultimate stress/Allowable Stress = 550 MPa/86486.48649 > 550000kPa /86486.48649= 6.359
     
  15. Aug 12, 2012 #14

    CWatters

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    Allowable / Actual
     
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