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- resistance strain gauge
strain gauge
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What is a strain gauge?
A strain gauge is a device used to measure changes in distance between points in solid bodies when the body is deformed. Strain gauges can provide data to calculate stresses (internal forces) in bodies, or to act as indicators on devices measuring force, pressure, and acceleration.
Resistance strain gauges operate on the principle that the electrical resistance of a wire changes when stretched or compressed. The gauge consists of fine wire looped into a grid pattern and cemented between thin paper sheets. It is glued to the surface where strain is measured, energized by electric current; deformation changes its resistance, which is amplified and converted into strain after calibration.
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What does a strain gauge measure?
A strain gauge measures changes in distances between points in solid bodies when the body is deformed. It can provide data to calculate stresses (internal forces) or to act as indicators on devices measuring force, pressure, and acceleration.
The resistance strain gauge operates on the principle that the electrical resistance of a wire changes when stretched or compressed. The gauge is glued to the surface where strain is measured, and when the part deforms, the gauge stretches or contracts, changing its resistance. This change is amplified and converted into strain after calibration.
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How does a strain gauge work?
A strain gauge measures changes in distances between points in solid bodies when the body is deformed. The resistance strain gauge operates on the principle that the electrical resistance of a wire changes when stretched or compressed.
The gauge is firmly glued to the surface on which the strain is measured and is energized by an electric current. When the part is deformed, the gauge follows any stretching or contracting of the surface, and its resistance changes accordingly. This change is amplified and converted into strain after proper calibration.
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Where are strain gauges commonly used?
Strain gauges are instruments used to measure changes in distances between points in solid bodies when the body is deformed. They can provide data to calculate stresses (internal forces) or act as indicators on devices measuring force, pressure, and acceleration.
Resistance strain gauges are valuable for experimental stress analysis. They work on the principle that the electrical resistance of a wire changes when stretched or compressed. These gauges are made in various shapes, sizes, and types and can be used on almost any solid material or embedded in concrete. Because they are light, they are suitable for measuring rapidly varying strains and strains in rotating shafts.
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How do you attach a strain gauge to a surface?
A strain gauge measures changes in distances between points in solid bodies when the body is deformed. The resistance strain gauge operates on the principle that the electrical resistance of a wire changes when stretched or compressed.
To attach a strain gauge, firmly glue it to the surface where strain is measured. The gauge follows any stretching or contracting of the surface, changing its resistance. This change is amplified and converted into strain after calibration.
These gauges come in different shapes, sizes, and types and can be used on almost any solid material or imbedded in concrete.
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How do engineers use strain gauge data to test materials?
Engineers use strain gauges to measure changes in distances between points in solid bodies when the body is deformed. These devices help determine stresses (internal forces) or act as indicators for measuring force, pressure, and acceleration.
A strain gauge is glued to the material's surface and energized by an electric current. As the material deforms under stress, the gauge stretches or contracts, changing its resistance. This change is amplified, calibrated, and converted into a strain measurement. The data gathered from these tests helps engineers estimate anticipated stress and specify appropriate materials.
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strain gauge, device for measuring the changes in distances between points in solid bodies that occur when the body is deformed. Strain gauges are used either to obtain information from which stresses (internal forces) in bodies can be calculated or to act as indicating elements on devices for measuring such quantities as force, pressure, and acceleration.
Until the 1930s most strain gauges used either compound mechanical lever systems or mirrors and optical levers. Magnifications as high as 1,200 to 1 were common, and deformations as small as about 1 micron (0.00005 inch) were measured. The gauge lengths on these instruments were from 1/2 to 1 in. (1 1/4 to 2 1/2 cm), and their comparatively large size and weight made them incapable of responding faithfully to the fluctuating strains resulting from dynamic loading.
The resistance strain gauge is a valuable tool in the field of experimental stress analysis. It operates on the principle, discovered by the British physicist William Thompson (later Lord Kelvin) in 1856, that the electrical resistance of a copper or iron wire changes when the wire is either stretched or compressed.
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The gauge shown in the consists of a length of very fine wire looped into a grid pattern and cemented between two sheets of very thin paper. It is firmly glued (bonded) to the surface on which the strain is to be measured and is energized by an electric current. When the part is deformed, the gauge follows any stretching or contracting of the surface, and its resistance changes accordingly. This resistance change is amplified and converted into strain, after proper calibration.
The wire-type grids were the first commercial form of the resistance gauge; they are now produced as flat foils by printed-circuit techniques, in the form of a grid on a plastic backing.
Resistance gauges are made in a variety of shapes, sizes, and types, mostly about the size of a postage stamp; gauge lengths as short as 0.015 in. (0.038 cm) are available, and strains as small as 0.000001 inch per inch can be detected. These gauges can be used on the surface of almost any solid material or imbedded in the interior of concrete; being light, they are particularly suitable for measuring rapidly varying strains and the strains in rotating shafts.
Resistance gauges can be classified as transducers, i.e., devices for converting a mechanical displacement into an electrical signal.
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Two other methods of measuring the strain on an object are photoelasticity and stress-analysis holography. Photoelasticity provides a visual method of observing the strain on an object by viewing the effects of polarized light on a bi-refringent (double-refracting) material bonded to the object. As the test object is stressed, fringe patterns in the bi-refringent material represent the regions of strain within the object. Stress holography also allows direct visual observation of the strain on an object. The hologram of an object is superimposed over the object. As long as the original object and the hologram match, nothing is observed. If the object is stressed, however, fringe patterns form from which the strain on the object can be determined.