Calculating Stresses at an Angle: Why Does it Matter?

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    Angle Matter
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Discussion Overview

The discussion revolves around the calculation of normal and shear stresses on a plane at an angle, specifically addressing a homework problem involving Mohr's Circle and the interpretation of angles in stress analysis. Participants are exploring the application of equations and concepts related to stress transformation.

Discussion Character

  • Homework-related, Mathematical reasoning, Debate/contested

Main Points Raised

  • The original poster questions the validity of their approach to calculating normal and shear stresses, suggesting a potential misunderstanding of the concepts involved.
  • One participant presents calculations for maximum and minimum normal stresses, but notes a discrepancy between their results and the expected answers.
  • Another participant provides a formula for calculating the radius in Mohr's Circle and derives an angle for principal stresses, which differs from the angle given in the problem statement.
  • There is a request for clarification on whether the provided answers are incorrect or if the original poster's understanding is flawed.
  • A later post simply bumps the thread, indicating a desire for further engagement or responses.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the correctness of the answers provided in the problem versus the calculations performed. There is no consensus on whether the issue lies with the answers or the understanding of the concepts.

Contextual Notes

Participants have not fully resolved the assumptions regarding angle definitions and the application of Mohr's Circle in this context. The discussion reflects varying interpretations of the problem and its requirements.

fonseh
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Homework Statement


DSC_0038.JPG
Why can't 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 .

Homework Equations

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.[/B]
 
Last edited by a moderator:
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$$\sigma _(max) $$ = ((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
 
##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:
Image for mohr's circle
https://www.physicsforums.com/attachments/dsc_0038-jpg.110448/
 
Is the ans provided wrong ? Or is my concept wrong ?
 
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