Strain Gauge

Strain and Its Measurement

Strain refers to the amount of deformation a material exhibits when subjected to external forces. This deformation may manifest as elongation or contraction and varies with the magnitude of the applied external force.

A strain gauge detects and measures this strain as a electricity signal. Numerous building exist, made from various materials and in different sizes and shapes. These include applications in automobiles, aircraft, railway vehicles and ships like transportation vehicles place.

To ensure the safety and durability of such structures under extreme work conditions, stress measurements are performed. Knowledge of stress is essential to evaluate structural strength and safety, determine design parameters, develop lighter structures, select appropriate materials, and implement innovative ideas. Today, computer-aided stress analysis techniques have been developed and are used efficiently in design processes. However, every theoretical and numerical calculation must be validated by experimental work using strain gauges.

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Working Principle of Strain Gauges

Metals exhibit changes in electrical resistance when subjected to mechanical deformation. Strain gauges operate on a measurement principle that exploits this physical property to detect strain.

Electrical resistance is inversely proportional to the cross-sectional area of the metal and directly proportional to its length. When a metal wire is subjected to an axial tensile force, its cross-sectional area decreases while its length increases, resulting in an increase in electrical resistance. Conversely, when the wire is subjected to axial compression, its cross-sectional area expands, its length shortens, and resistance decreases.

The change in the metal’s electrical resistance is proportional to the amount of deformation at a specific fixed ratio. If a metal wire is securely bonded to the structure being measured, elongation or contraction in the structure is directly mirrored in the wire.

According to this principle, measuring the change in electrical resistance of the metal wire enables precise detection of the strain experienced by the structure. Due to these properties, strain gauges are used in engineering and materials science for stress analysis, structural health monitoring, and mechanical system design processes common.

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Resistance Change and Measurement Process of Strain Gauges

The electrical resistance changes of strain gauges are determined based on the object being measured, converted into a tension signal, amplified, and made easier to analyze. Strain gauges must be securely attached to the surface using special adhesives to ensure accurate tracking of elongation and contraction movements of the structure.

To enable precise measurement of resistance changes, a bridge circuit is employed to convert these changes into voltage signals. However, since the resulting voltage levels are typically in the microvolt (μV) range, the signal is amplified by a factor of 5,000 to 10,000 to enhance measurement sensitivity.

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