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Mohr's circle

  1. Dec 14, 2016 #1
    1. The problem statement, all variables and given/known data
    DSC_0038.JPG Why cant i use the equation to determine the normal stress and shear stress ? Is my concept wrong ? I use the method in the link to do this question. The question said the
    stress on a plane making angle 30 degree anticlockwise from plane AD .
    2. Relevant equations


    3. The attempt at a solution

    When it's anticlockwise , the angle is positive
    http://www.dummies.com/education/science/using-mohrs-circle-to-find-principal-stresses-and-angles/
    Mod note: Image of work has been deleted. OP will be including work in a subsequent post.
     
    Last edited by a moderator: Dec 15, 2016
  2. jcsd
  3. Dec 15, 2016 #2
    $$\sigma _(max) $$ = ((25-15 )/2 ) + 20cos60 + 20sin60 = 32.3MPa


    $$\sigma x_(min) $$ = ((25-15 )/2 ) - 20cos60 - 20sin60 = -22.3MPa

    But the ans is 12.5 and -2.3MPa
     
  4. Dec 15, 2016 #3
    ##r = sqrt ( ((\sigma _x -s \sigma_y) /2 )^2)+ (\tau_xy)^2) = 28##

    ##tan2\theta_p = 2\tau_xy / (\sigma _x -s \sigma_y)
    = 2(20) / 40## , ##\theta_p = 22.5## degree ,
    This is different from the ##\theta_p ## = -68 degree given
     
    Last edited by a moderator: Dec 15, 2016
  5. Dec 15, 2016 #4
  6. Dec 15, 2016 #5
    Is the ans provided wrong ? Or is my concept wrong ?
     
  7. Dec 16, 2016 #6
    bump
     
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