Calculating Principal Strains using a Rectangular Strain Gage Rosette

Strain gage rosettes are used often in engineering practice to determine strain states at specific points on a structure. Figure 1 illustrates three commonly used strain gage rosette configurations. Each of these configurations is designed with a specific task in mind. The far right rosette in Figure 1 is referred to as a tee rosette. Tee rosettes are two element rosettes and should only be used when the principal strain directions are known in advance from other considerations. The middle rosette in Figure 1 is referred to as a rectangular rosette and the far left as a delta rosette. These three element rosettes are used in applications where the principal strains are unknown. There are many other parameters that need to be taken into consideration when choosing a strain gage. Literature from manufacturers of strain gages provides some guidance in choosing the proper strain gage for a given application.