Appendix: Rosettes

Cartesian Strain Components from Rosette Measurements

It is sometimes desired to obtain the Cartesian components of strain (

, and

) relative to a specified set of X-Y coordinate axes. This need can arise, for example, when making strain measurements on orthotropic composite materials. The Cartesian strain components are also useful when calculating principal strains from rosette data using matrix transformation methods.

When the X axis of the coordinate system coincides with the axis of the reference grid (Grid 1) of the rosette, the Cartesian components of strain are as follows:

Rectangular Rosettes

Delta Rosettes

The foregoing assumes in each case that the gage elements in the rosette are numbered counterclockwise as indicated. When the calculated

is positive in sign, the initial right angle at the origin of the X-Y coordinate system is decreased by the amount of the shear strain.

Appendix