Drawing Uniaxial Compression and Completing Mohr's Circle

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Discussion Overview

The discussion revolves around the sketching of stress elements under uniaxial compression and the drawing of Mohr's circle. Participants explore the implications of uniaxial stress, the determination of shear and normal stresses, and the geometric representation of these stresses on Mohr's circle.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents a sketch and a partially complete Mohr's circle for uniaxial compression, seeking feedback on their approach.
  • Several participants discuss the values of \sigma_y and \tau_{xy}, with some suggesting that \tau_{xy} should be zero due to the nature of uniaxial stress.
  • There is a debate about whether the shear stress should be included in the Mohr's circle representation, with some arguing it should be labeled as zero.
  • Participants calculate the center and radius of Mohr's circle, with one confirming the values as correct.
  • Questions arise regarding the orientation of the element and the angles involved in determining maximum shear stresses.
  • One participant notes that the problem requires determining maximum shear stresses and the orientation of the element, leading to discussions about the relationship between angles and points on Mohr's circle.
  • Another participant raises a question about the implications of a radius of zero in the case of biaxial compressive stress.
  • There is a suggestion that the angle of rotation in Mohr's circle corresponds to the rotation of the element itself, with participants discussing how to derive stress values from the circle.
  • Some participants emphasize the importance of understanding Mohr's circle and its geometric representation to solve the problem effectively.

Areas of Agreement / Disagreement

Participants express differing views on the treatment of shear stress in the context of uniaxial compression and the interpretation of angles in Mohr's circle. There is no clear consensus on the correct approach to sketching the stress element and completing Mohr's circle, indicating multiple competing views remain.

Contextual Notes

Participants note that the problem does not provide certain values, such as \sigma_y and \tau_{xy}, leading to confusion. The discussion also highlights the dependence on the definitions of uniaxial stress and the assumptions made about shear stress.

  • #31
No, that's not right. First, what are \sigma'_x, \sigma'_y, and \tau'_{xy} equal to? Second, since you have to rotate by 90 degrees on Mohr's circle, that means 2\theta=90^\circ, so \theta=45^\circ. What do you suppose this 45 degrees corresponds to?
 
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  • #32
I believe there are formulas to solve for \sigma_x', \sigma_y', and \tau_{xy}'.

Would the 45 degress correspond to the rotation of the element?
 
  • #33
Yes, it's the angle through which the element is rotated. The stresses you should be able to read off of Mohr's circle. There's no need to resort to formulas for this problem.
 
  • #34
So I use trigonometry to find those values?
 
  • #35
So if I rotate on the Mohr's circle by 90 degrees I will reach the max and min shear stresses?
 
  • #36
I think it would help you immensely to go back and read up on Mohr's circle to understand what it represents.
 
  • #37
Your Mohr's circle is almost complete. Try not to forget to draw the sigma-tau reference before you draw a circle. Then you will see that the circle is on the left side of the reference (Uniaxial compression). Note that the right part of the circle touches the origin. I think now the problem solved. If you want stresses at X’Y’, just rotates the horizontal line through the angle you want (it doesn’t matter whether the angle is given since, generally, we often need the principle stresses and maximum shear stress which are on the horizontal and vertical lines)
 

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