Hi everybody, I have a few concerns about how my professor performed this experiment where we were using a strain gage rosette to measure strain in an aluminum tube we were applying torque to.
First of all, everywhere I look at the use of these rosettes, one gauge is set on along the length of the tube, one at 45°, and one perpendicular to the length, however ours was placed at 0°, 45°, and -45°, which seems to make no sense to me when looking at the calculations to find shear strain based on the normal strain measurements taken from the strain gage.
This leads to my second concern that the equation we are using, supposedly based on a text called "Transformation of Plane Strain" by Beer, Johnston, and DeEwolf, is stated as (gamma)xy = (epsilon)45° - (epsilon)-45° - (epsilon)0° (angles should be a sub script.
But the only published calculation I can find is for the rosette placed as previously stated and the equation is stated as (gamma)xy = 2*(epsilon)45° - (epsilon)0° -(epsilon)90°
The reason the concern popped up for me is because the percent error between the experimental shear strain and the calculated shear strain is around 100%
Thanks for any help.
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