# Strain Measurement Glossary

This section explains terms used in strain measurement.

## Bridge circuit

A circuit in which current is divided between two parallel circuits, which are connected with a circuit that works as a “bridge,” to measure the resistance accurately under the condition where each circuit has the same potential. Bridge circuits are also called Wheatstone bridges.

## Dynamic strain

Strain whose deformation is repeated in a short time cycle due to vibration.

## Linear expansion coefficient

The ratio of the increase in the length of a substance to its original length for a 1°C (1.8°F) increase in temperature. It is approximately one third the coefficient of volume expansion, which expresses the change in volume.

## Low-pass filter

A filter that only attenuates the components above a specific frequency, while hardly attenuating the components at or below the frequency, to cut high-frequency noise in dynamic strain measurement.

## Poisson’s ratio

The ratio of the strain that occurs, when stress is applied to an object within its elastic limit, in the direction perpendicular to the stress (longitudinal strain) to the strain that occurs along the direction of the stress (lateral strain).

## Static strain

Strain whose deformation remains fixed and changes little over time.

## Strain

A scale that expresses the deformation state of an object as a ratio of expansion/contraction from the original length.

## Strain gauge

A mechanical sensor designed to measure the strain of an object. This gauge is structured with a metal resistor (metallic foil) laid in a zig-zag pattern on a thin insulator. A strain gauge measures the change in electric resistance due to deformation and converts this change to the strain amount.

## Stress

The value obtained by dividing the resistance force that arises inside an object, after it has received an external force, by its cross-sectional area (the value converted to per unit area).

## Young's modulus

The constant of proportionality between stress and strain in the state where both are in a linear relationship (the range of the strain amount in which the object can return to the original state, or the elastic region).