Measuring Strain with a Strain Gage

Strain is the amount of deformation of a body due to an applied force. Specifically, strain is defined as the fractional change in length.

Strain can be positive (tensile) or negative (compressive). In practice, the magnitude of measured strain is very small. Therefore, strain is often expressed as microstrain (µε).

When a bar is strained with a uniaxial force, Poisson Strain causes the girth of the bar to contract in the transverse, or perpendicular, direction. The magnitude of this transverse contraction is a material property indicated by its Poisson's Ratio.

To measure strain, you typically use one or more strain gages in a Wheatstone bridge in one of several bridge configurations.