# Strain analysis using Star rosette

1. Jun 23, 2011

### 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.

2. Jun 23, 2011

### 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.

3. Jun 23, 2011

### 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.

4. Jun 23, 2011

### 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.