Strain analysis using Star rosette

[IanLoh]

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.

 

[timthereaper]

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.

 

[IanLoh]

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.

 

[IanLoh]

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?

 

[DeeNos]

Hello,

Thank you for sharing your question about strain analysis using Star rosette. I understand that you are having trouble identifying the points on the rosette that indicate the planes it acts on, as well as the meaning of a "strain rosette with gauge X acting along a principal direction."

Firstly, in order to identify the planes that the rosette acts on, it is important to understand the design of the Star rosette. The rosette is composed of three strain gauges, with each gauge aligned along a specific direction (typically at 0, 60, and 120 degrees). These gauges measure the strain along these three directions, and their readings can be used to construct a Mohr's circle.

To identify the planes, you can refer to the gauge orientations on the rosette. The 0-degree gauge measures the strain along the x-axis, the 60-degree gauge measures the strain along the y-axis, and the 120-degree gauge measures the strain along the z-axis. These directions correspond to the principal directions of the stress tensor, and the planes on which the rosette is acting are perpendicular to these directions.

Regarding the "strain rosette with gauge X acting along a principal direction," this means that one of the three gauges on the rosette is aligned with one of the principal directions of the stress tensor. This allows for a more accurate measurement of the strain along that specific direction.

I hope this helps to clarify your questions. If you need further assistance, please don't hesitate to reach out. Best of luck with your studies.