# What is a Strain Gauge Rosette?

A strain gauge rosette is a term for an arrangement of two or more strain gauges that are positioned closely to measure strains along different directions of the component under evaluation. Single strain gauges can only measure strain effectively in one direction, so the use of multiple strain gauges enables more measurements to be taken, providing a more precise evaluation of strain on the surface being measured.

## The Biaxial Stress State

Previously stress was considered a single force action, which made the measurement of stress relatively easy. The discovery that certain combinations of forces produce stresses that act in planes at right angles, resulted in a requirement to measure the biaxial stress state.

The term biaxial suggests a 2D analysis of stresses in the XY-plane, and the stress normal to this plane is assumed to be zero. The biaxial stress state is the sum of two normal or shear stresses.

Biaxial stress is a common occurrence for most structural parts, so strain gauge rosettes are routinely used for experimental stress analysis.

There are two common configurations of strain gauge rosettes; rectangular and delta. A rectangular strain gauge rosette consists of three strain gauges; A, B, and C. Strain gauges A and C are placed at a 90o angle on an XY-axis, and strain gauge B is placed in between the two at a 45o angle.

A delta strain gauge also consists of three strain gauges, which are in an equilateral triangle orientation, which features 60o angles. There are many other types of strain gauge rosette configurations in addition to rectangular and delta.

## Strain Gauge Rosettes from HBM

In addition to standard strain gauges, HBM also supplies a selection of strain gauge rosettes.

The RY strain gauge rosettes have three measuring grids for analyzing biaxial stress states with unknown principle directions. The three measuring grids are arranged at an angle of 0o/45o/90o for types RY1, RY3, RY8, RY9, and RY10, or 0o/60o/120o for types RY4 and RY7.

The XY strain gauge rosettes have two measuring grids for analyzing biaxial stress states with known principle directions and measurements on tension and compression bars. All of these strain gauge rosettes are arranged at a 90o offset from each other.

These types of strain gauge rosettes are supplied by HBM in different geometries and sizes, and they are all available with temperature responses adapted to the following materials;

• Ferritic steel (10.8 ppm/K; 6.0 ppm/°F); temperature matching codes: 1
• Aluminum (23 ppm/K; 12.8 ppm/°F); temperature matching codes: 3
• Austenitic steel (16 ppm/K, 8.9 ppm/°F); temperature matching codes: 5
• Silica/composite (0,5 ppm/K; 0.3 ppm/°F); temperature matching codes: 6
• Titanium and gray cast iron (9 ppm/K; 5.0 ppm/°F); temperature matching codes: 7
• Plastic (65 ppm/K; 36.1 ppm/°F); temperature matching codes: 8
• Molybdenum (5.4 ppm/K; 3.0 ppm/°F); temperature matching codes: 9

If you would like any more information about the strain gauge rosettes offered by HBM, please contact us.