# What is a Strain Gauge Rosette?

A strain gauge rosette is the name given to a configuration of multiple strain gauges positioned in such a way that they can measure strains from one component in different directions.

Image credit: Hottinger Baldwin Messtechnik GmbH

Single strain gauges, due to their directional constitution, can only measure a strain in one direction. Using multiple gauges in unison allows for different directional strain measurements to be taken which gives a more accurate evaluation of the surface strain to be measured.

## The Biaxial Stress State

Historically, stress has always been considered as one single unidirectional force, which made stress measurement simple. However, it has since been found that some forces apply stresses that act in planes at a right angle to one another, meaning measurement of biaxial stresses is important.

Biaxial stress refers to an analysis of the stress in two dimensions (the X, Y planes) with the stress normal to this plane assumed as zero. The biaxial stress is given by the sum of the two ‘normal’ stresses. Biaxial stress occurs in most structures meaning strain gauge rosettes are commonly used for stress analysis.

Strain gauge rosettes are frequently found in one of two configurations – delta and rectangular:

• Delta strain gauges use three strain gauges in the configuration of an equilateral triangle (at 60° to one another)
• Rectangular strain gauge rosettes have three different strain gauges (A, B and C). A and C are on the X, Y axis, at 90° to one another, and B sits in the middle at a 45° angle to both

There are various other configurations of strain gauge rosettes in addition to the above.

## HBM’s Strain Gauge Rosettes

Along with their standard offering of strain gauges, HBM also provides a range of strain gauge rosettes.

XY strain gauge rosettes from HBM use two different measuring grids to determine biaxial stress states of known principle directions with measurements on compression and tension bars. These strain gauges are at 90° to one another.

RY strain gauge rosettes from HBM use three measurement grids to determine biaxial stress states of unknown principal directions. The three different grids are arranged at angles of 0°/45°/90° for types RY1, RY3, RY8, RY9, and RY10, or 0°/60°/120° for types RY4 and RY7.

These different varieties of strain gauge rosettes can be provided in different shapes and sizes. All are available with temperature responses for the following materials:

• 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
• Ferritic steel (10.8 ppm/K; 6.0 ppm/°F); temperature matching codes: 1
• Molybdenum (5.4 ppm/K; 3.0 ppm/°F); temperature matching codes: 9
• Plastic (65 ppm/K; 36.1 ppm/°F); temperature matching codes: 8
• 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

This information has been sourced, reviewed and adapted from materials provided by Hottinger Baldwin Messtechnik GmbH (HBM).

For more information on this source, please visit Hottinger Baldwin Messtechnik GmbH (HBM).

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