Is the orientation of a rosette strain gauge important?
It depends on the type of rosette, and the state of strain you expect. If you use a two-element 90 degree rosette and you want to measure shear strain, the orientation does matter. For example if you put the gauges along the axis and round the circumference of a shaft with a torsional stress, both gauges will read a direct stress of zero. If you align them at + and – 45 degreess, one gauge will be in tension and the other in compression, and you can find the shear strain using Mohr’s circle. For rosettes with more than 2 elements, the orientation is not critical, since you can find the complete state of strain from 3 measurements of direct strain in different directions. However aligning some of the gauges along the expected principal strain directions (if you know them in advance) can make it easier to do a “quick check” that the results are sensible while you are taking the measurements.
