A strain gauge measures the amount of deformation in a material under stress. Elastic deformation disappears after stress is removed, while plastic strain results in permanent deformation. Metal foil strain gauges measure changes in electrical resistance when a conductive material strains, and require calibration through a Wheatstone bridge. They can be used for various measurement applications and can be permanently mounted for continuous measurements.
All materials will deform when a stress or load is applied. Strain is a measure of the amount of deformation that occurs when an object is under stress. A strain gauge is an instrument that is used to accurately measure this change in a material under load. Understanding the dimensional changes that occur when an object undergoes deformation is important in many mechanical design applications.
Elastic deformation occurs when a material is subjected to a low level of stress. It will disappear after the stress is removed and the material will return to its original state. At high levels of stress, a substance will deform to the point where it will not recover and return to its original size. This is called plastic strain. A strain gauge can be used to determine when a material has undergone plastic deformation and permanent deformation has occurred.
The metal foil strain gauge is commonly used when a very small amount of strain and dimensional change occurs. This type works by measuring the change in electrical resistance that occurs when an electrically conductive material strains. The metal foil strain gauge typically consists of a series of very thin parallel lines of conductive metal applied to a thin foil. The film is attached to a backing material which is electrically insulating and does not conduct voltage or current.
The metal foil strain gauge is glued to an object to be measured. When a stress is applied and the object deforms, the metal foil will also deform and its electrical resistance will change. The change in electrical resistance is measured and can be related to the strain of the material. The numerical relationship between the change in electrical resistance and the corresponding mechanical strain is known as the measurement factor.
Foil strain gauges require careful calibration to ensure that the strain measurement is accurate. Calibration is completed through the use of an electrical circuit known as a Wheatstone bridge. This is used to determine the measurement factor and also compensates for temperature changes that cause the metal foil material to expand and contract, which could lead to erroneous measurement results.
Strain gauges are available for a variety of measurement applications. These are used to measure strain due to elongation caused by a tensile force, compression caused by a pushing force, or even pressure applied to a surface by a weight or other load. Strain gauges are often used for experimental tests in the laboratory and can be permanently mounted to an object to allow for continuous measurements.
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