Imagine a firefighter trying to put out three house fires at once by spraying a hose back and forth over them all. There’s never enough water in one place to extinguish the blaze. Now try to imagine a stress analyst trying to measure strain with three discrete sensors in different directions.
In this podcast Tom and Darryl discuss about the benefit of using 3 element rosette strain gage.
A strain gage rosette is, by definition, an arrangement of two or more closely positioned gage grids, separately oriented to measure the normal strains along different directions in the underlying surface of the test part. It is not a sufficient condition for doing so accurately. Knowledge in the selection and application of rosettes is critical to their successful use in experimental stress analysis. Knowledge in the selection and application of rosettes is critical to their successful use in experimental stress analysis
The simple determination for when a three-element rosette should be used is the answer to the question, “Are the directions and magnitudes of the principal strains and stresses known?”. If the answer is no, then a three-element rosette most likely is needed.
Two parameters are important in rosette selection.
(1) the rosette type — tee, rectangular, or delta; and (2) the rosette construction — planar (single-plane) or stacked (layered)
Tech Note TN-515: Strain Gage Rosettes: Selection, Application and Data Reduction: http://www.vishaypg.com/docs/11065/tn-515.pdf