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Free online Strain Rosette calculator for calculating direct strains in X and Y direction and shear strain in XY direction. Strain gauge working principle.



Strain Gauge

What is a strain gauge

Strain gauge is a device which measures strains induced in an object by measuring the electrical resistance across a thin conductive foil.

Strain Gauge
Strain Gauge (https://commons.wikimedia.org/wiki/File:Strain_gauge_-.jpg)
Strain gauge application
Strain gauge application

A typical strain gauge consists of gauge backing on which the resistive foil is placed.

The gauge backing is placed on the material whose strain under a loading has to be tested.

When load is applied the cross section of the conducting wire changes and thus the resistance changes.

This change in resistance is correlated to strain using the gauge factor of the strain gauge.

Working Principle

Wheatstone bridge strain gauge
Wheatstone bridge strain gauge

The resistance in a strain gauge is measured using a Wheatstone bridge.

A Wheatstone bridge is used to for measurement of unknown resistance.

The Wheatstone bridge setup is very simple with Rx being the unknown resistance, two known resistance values (R1 and R2) and a variable resistance (R3).

The output voltage is given by the following equation:

Wheatstone bridge equation

For a balanced Wheatstone bridge the output voltage is 0. This is achieved by varying the variable resistance R3, till the output voltage is achieved as 0. 

Further the unknown resistance is given by the ratio:

R1/R2 = Rx/R3

Types of strain rosettes

Delta Rosette

Delta Rosette strain gauge

Delta rosette is a configuration of 3 strain gauges where each strain gauge is at 60 degrees apart from each other.

The configuration can be either in equilateral triangle format or in open configuration.

First strain gauge is at an angle of 60 degree, second strain gauge at 120 degree and third strain gauge at angle 180 degree.

Rectangular Rosette

Rectangular Rosette

Rectangular rosette is a configuration of strain gauge in which each stain gauge is separated by an angle of 45 degree.

Hence the angle of first strain gauge is 0 degree, 2nd strain gauge is at angle of 45 degree and third strain gauge is at an angle of 90 degree.

How to use calculator

  1. Choose the type of strain gauge from dropdown. This step is not compulsory however if type of strain gauge is selected it automatically defined the angles for the strain gauges.
  2. Input the strains measured by strain gauges. The calculator only allows 3 strain gauge rosette configuration and hence only 3 strain measurements can be input.
  3. If type of strain gauge is not defined in first step, then the angles have to be input manually by the user.
  4. In result section the strain in X direction, Y direction and shear strain is calculated.
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