# Measuring Strain on a circular tube.

1. Oct 21, 2009

### JD88

If I wanted to determine the principle stresses on the surface of a circular tube could I use a 45deg planar rectangular rosette to measure the strains $$\epsilon$$x, $$\epsilon$$y and $$\gamma$$xy? I only ask because on a flat surface the gauges could be oriented along the x-axis, the y-axis and 45 deg between them, but is this still true on a curved surface?

Lets say the y-axis is parallel to the axis of the tube. The x-axis is obviously perpendicular to the y-axis but this means the x-axis is tangent to the surface of the tube. So is it still valid to say I am measuring $$\epsilon$$x ? Should I be using cylindrical coordinates in stead of x and y?

Is there some other way to determine the principle stresses on the surface of a circular tube?