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Calculate the angle of the neutral axis from the x-axis

  1. Mar 16, 2013 #1
    1. The problem statement, all variables and given/known data
    Calculate the angle of the neutral axis from the x-axis when the beam is loaded with a positive couple of 6kNm acting around the X-axis



    2. Relevant equations
    i have calculated:
    Ixx: 2854758.6 mm^4
    Iyy: 1429034.6 mm^4
    Ixy: -1143476 mm^4


    3. The attempt at a solution

    i know that to calculate the angle:

    tanθ= - (IxxMy -IxyMx)/(IyyMx-IxyMy)

    since i am confused with the statement "positive couple of 6kNm acting around the X-axis"

    does that mean that Mx= 6KNm?

    thank you
     
  2. jcsd
  3. Mar 16, 2013 #2

    SteamKing

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    Ya got any pictures of this problem?
     
  4. Mar 16, 2013 #3
    ImageUploadedByPhysics Forums1363452818.241318.jpg

    This is the the question
     
  5. Mar 16, 2013 #4

    SteamKing

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    Mx is a couple which is acting as a bending moment on the cross section.
     
  6. Mar 16, 2013 #5

    nvn

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    That is correct.

    (1) By the way, always leave a space between a numeric value and its following unit symbol. E.g., 6 kN, not 6kN. See the international standard for writing units (ISO 31-0).

    (2) The unit symbol for kilonewton is spelled kN, not KN. Capital K means kelvin.

    (3) Two unit symbols multiplied together cannot be written together, and must be separated by, e.g., an asterisk or a space. E.g., kN*m or kN m, not kNm.
     
    Last edited: Mar 16, 2013
  7. Mar 16, 2013 #6
    Thank u! I will have it in mind! In addition my ixy when i calculate it is positive and when i got the answer from solidworks i get a negative value! Which one is the correct?
     
  8. Mar 16, 2013 #7

    nvn

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    vtaela: Although I have not tried it, it looks like Ixy perhaps should be positive. I do not know what SolidWorks is doing. Ensure your positive axes are pointing in the correct direction in SolidWorks.
     
  9. Mar 16, 2013 #8
    Thank you very much
     
  10. Mar 30, 2013 #9
    I got this except the Ixy was plus 1143476. Is this what you got when you did it again?
     
  11. Mar 30, 2013 #10
    Yes i calculates a positive ixy and a positive 38.66 degree
     
  12. Mar 30, 2013 #11
    When calculating the maximum stress did you use the unsymmetric bending equation? If you did what did you use as your x and y co-ordinates to input in that equation?
     
  13. Mar 30, 2013 #12
    X = -13.78 and y+= 38.11 getting a maximum stress of 136.7119
     
  14. Mar 30, 2013 #13
    How did you get them? Did you draw it out or is there a way to calculate them?
     
  15. Mar 30, 2013 #14
    Actually think i understand it.

    X = Xc - bredth of rectangle 1
    Y = height of rectangle 1 - Yc

    That how you got them?
     
  16. Mar 30, 2013 #15
    Yes thats right
     
  17. Mar 30, 2013 #16
    Are you sure about your final stress value? I get 151.9855 N/mm^2 every time.

    I've tried using hand calculations as well as using excel to double check the values and get that everytime.
     
  18. Mar 30, 2013 #17
    Take a picture of what you have done to compare the solution! I will reply tmr since i am not home now
     
  19. Mar 31, 2013 #18
    Heres my solution.
     

    Attached Files:

  20. Mar 31, 2013 #19
    Same procedure except i used a positive Mx
     
  21. Mar 31, 2013 #20
    Any idea how to do question 1 of the coursework?:p
     
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