Strain analysis using Star rosette

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Discussion Overview

The discussion revolves around the use of a star rosette in strain analysis, particularly in relation to Mohr's circle. Participants explore the identification of planes for the rosette, the orientation of the rosette for analysis, and the implications of gauge readings in determining principal strains.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in identifying the planes on which the star rosette acts and seeks clarification on the concept of a strain rosette acting along a principal direction.
  • Another participant explains that the rosette is bonded to a plane and consists of three strain gauges at specific angles, which helps in determining principal stresses in complex scenarios.
  • There is a suggestion that the orientation of the strain gauges is crucial for accurate analysis, particularly in relation to Mohr's circle.
  • A participant asks how to orient a star rosette for use with Mohr's circle, noting a contrast with the orientation of a delta rosette.
  • One participant mentions that the center of the strain circle and principal strain lie on the same horizontal line, which may aid in understanding the relationship between the rosette and Mohr's circle.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the orientation and application of strain rosettes, with some clarity on the use of delta rosettes but ongoing uncertainty about star rosettes. No consensus is reached on the best approach for using star rosettes in conjunction with Mohr's circle.

Contextual Notes

Limitations include the lack of detailed equations and specific examples for constructing Mohr's circle with a star rosette, as well as the need for further information to fully address the questions posed.

Who May Find This Useful

This discussion may be useful for students and professionals involved in strain analysis, particularly those interested in the practical application of strain rosettes and Mohr's circle in engineering contexts.

IanLoh
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Hi I'm studying strain analysis using Mohr's circle. I have some problem using a star rosette to construct the circle. My problem lies with trying to identify the points which indicate the planes the rosette act on.

Besides that, what is meant by "strain rosette with gauge X (gauge X being one of the gauges of the delta rosette) acting along a principal direction"?

Sorry, no equations to show as Mohr's circle is really based on graphs.

Any help is appreciated.
 
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The rosette acts on the plane it's bonded to. Since a rosette is basically 3 strain gages at certain angles to each other, it's useful to find the directions of principal stress if you don't know already or are analyzing elements that are hard to calculate analytically. If you're familiar with Mohr's circle, you'll remember that it's only good for elements that are in bi-axial stress states and the rosette should be oriented in that plane. As for the "strain rosette with gauge X acting along a principal direction", I would assume that one of the strain gages was applied in the direction of principal stress. I would have to know more about the problem in order to be able to tell you more.

As for Mohr's circle having no equations, that's not entirely true. You can get the max and min stresses and max shear stress without ever having to construct Mohr's circle. Drawing Mohr's circle just allows you to get the direction of the principal stresses.
 
Thanks I seem to understand strain analysis better.

But if I may ask, how do I orientate a star rosette to be used on the Mohr's circle? While I understand how a delta rosette is re-orientated to be used in the circle, I can't seem to do the same with a star rosette.

And here is the question I have. Perhaps it is better if I post the entire thing on.

Figure shows a delta strain rosette with gauge 1 along a principal direction. If gauges 1 and 2 have readings of 100 and 10 microstrains respectively, find E3 and \Phi3.

And my bad for omitting the basic equations of constructing the Mohr's circle.
 
Regarding the question concerning principal direction, it was also pointed out that the center of the strain circle and principal strain both lie on the same horizontal line.

Perhaps that would be helpful?
 

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