1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is it well analyzed? Doubt about a bar: tension/compresion

  1. Apr 23, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-4-23_0-6-37.png

    Calcular the force P when a bar starts yield, when 2 bars start yield, and when the 3 bars start yield
    Diameter = 25 mm (for every bar), Yield Stress of Steel = 250 MPa.

    2. Relevant equations


    3. The attempt at a solution

    [F][/AD] + [F][/BE] + [F][/CF] = P

    2[Δ[/AD] - 3[Δ][/BE] + [Δ][/AC]= 0

    I calculate first what happend when the 3 bars were in elastic zone, with the Hooke law I obtain:

    [F][/AD]= 0.14P
    [F][/BE]= 0.29 P
    [F][/CF] = 0.57P

    So the firs bar in reach yield stress is CF.

    0.57P = [σ][/y] * A => P=215, 295.54 N


    When the 2 bars (BE and CF) are with the yield stress, [F][/BE]=[F][/CF]

    From equations of equilibrium, sumatory of moments in C:

    0.4P = 1.2 [F][/AD] + 0.8 [F][/BE]

    and I know from the eq (1) [F][/AB] + [F][/BE] + [F][/CF] = P, so 2[F][/BE] + [F][/AD]= P. Solving this 2 eq. I obtain P=243, 605.30 N and [F][/AD]= -1831.62 N ....So I dont know if this answer is correct, because it says that the bar AD now is in compresion, when before it was in tension
     
    Last edited by a moderator: Apr 23, 2015
  2. jcsd
  3. Apr 23, 2015 #2
    Can you explain how you got this equation?
    2[Δ[/AD] - 3[Δ][/BE] + [Δ][/AC]= 0
     
  4. Apr 23, 2015 #3
    From semejant triangles, ( delta AD - delta BE) / 0.4 = (delta AD- delta CF) /1.2. Is the C.G.D compatibility geometry of deformation
     
  5. Apr 23, 2015 #4
    What is Δ? Maybe a picture would help.
     
    Last edited by a moderator: Apr 23, 2015
  6. Apr 23, 2015 #5
    upload_2015-4-23_7-37-51.png
     
  7. Apr 23, 2015 #6
    OK, I see now. The ΔAC was a typo then.

    Can you show how you used Hooke's Law to get the forces?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Is it well analyzed? Doubt about a bar: tension/compresion
Loading...