Rosette Principle

The normal strains are measured along any three directions   and then strain transformation equations are used to determine global strains .

(8.7)

When the normal strains  are known then, Eq. (8.7) is a system of three equations with three global strains  as the unknowns. It should be noted that when the rosettes are placed on both sides of flat specimen it provides the most complete information as to axial, transverse and shear strains. Further, it provides the information on the development of specimen curvature. The Figure 8.2 shows the arrangement of strain gages in a rosette.

One should pay attention while using the rosettes that the measurements are sensitive to temperature. Hence, appropriate gage should be used for the test. Further, the measurements are sensitive to fiber orientation of the composite and gage alignment. Therefore, it is very important to measure the fibre orientation and gage alignment accurately and must be used appropriately in the analysis of experimental results.