Strain Gage
A strain gage is a simple measuring system that determines the amount of strain, which is the displacement and deformation that results from an object under stress. It measures mechanical quantities by converting tension, force and pressure into an electrical signal. Strain gage types vary in construction and measurement method. The most popular type is foil that is adhered to the object. Other kinds include piezorsistive, semi-conductor, bonded metallic wire and carbon resistive. When measuring the strain of an object, the temperature, material properties, adhesive that bonds the gage to the object's surface, and the stability of the metal all effect the resistance. Strain gages are used to detect cracking in machinery parts, as crack propagation, an extensometer, to measure temperature, residual stress, to gage shear modulus and transducer.
There are three main types of strains that are measured by strain gages. Poisson strain is the thinning and elongation that occurs when a bar is strained. Bending strain is determined by measuring the relationship between the force and the amount of bending that results from a twisting action. Shearing strain occurs when stress causes angular distortion of the object being measured. The most common type of strain gage, made of foil and adhesive, has an insulating and flexible backing which supports the metallic foil pattern. It is attached to an object by adhesives. As the object deforms, so does the flexible foil. The electrical resistance thus changes, and is measured.