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!

Problem: Determine the maximum value of the average normal stress

  1. Nov 20, 2012 #1
    Hi guys.

    Please look at the uploaded picture.
    Normal stress is difined as: σ= P/A. And the Maximum normal stress σ = P/ (b*h/cos(θ)) ??

    The right answers should be σAB= 97,7 MPa and σBC = -66,5 MPa. But how do I calculate it?

    What I have tried:
    Force AB: 40* sin(60deg) = 34,641 kN = 34,641 * 10^3 N

    σAB= 34,641 * 10^3 N/((45-20)*12)/sin(60deg)) = 100 MPa
     

    Attached Files:

  2. jcsd
  3. Nov 21, 2012 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I think you are misreading the figure regarding the cross sectional area of the link.....its just b*h, where b is (45-20) = 25 mm, and h is 12 mm. Thus, A = 300 mm^2.
    But beyond that, you are not calculating the force correctly. You might want to draw a free body diagram of the joint at B and use Newton's 1st law in the x direction (sum of forces in x direction = 0) and y directions (sum of forces in y direction = 0), to solve for the force components in each link. Then the member force can be found from the sq rt of the sum of the squares.
     
  4. Nov 22, 2012 #3
    Thank you very much, that explanation helped me to could compute it :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook