Strain gauge
To understand the concept of strain gauge we need to understand the concept of stress and strain. When external forces are applied to a stationary object, stress and strain is caused. Stress is described as the material’s internal resisting forces, where as strain is described as the displacement and deformation that take place. Strain is described as the quantity of deformation per unit length of a material when a load is put on. Usual values for strain are not more than 0.005 inch/inch and are frequently explained in micro-strain units.
Strain possibly be compressive or tensile and is usually calculated by strain gauges. Essentially, every strain gauge is made to translate mechanical motion into an electronic signal. A change in capacitance, inductance, or resistance is proportional to the strain experienced by the sensor. Let’s take an example, when a wire is held under tension, it becomes somewhat longer and its cross-sectional area is reduced. This alters its resistance in proportion to the strain sensitivity of the wire's resistance. The strain sensitivity is also sometime referred as the gauge factor.
The perfect strain gauge would change resistance only due to the deformations of the surface to which the sensor is attached. On the other hand, there are other things that affect the detected resistance such as heat, objects characteristics, the bonding agent that attaches the gauge to the surface, and the strength of the metal. For the reason that nearly all objects do not have the identical properties in all directions, understanding of the axial strain only is inadequate for a comprehensive study. Poisson, bending, and torsional strains also require to be calculated. Each needs a different strain gauge arrangement.
Shearing strain takes into account the angular distortion of a material under stress. It can be described as the angular change in radians between the vertical y-axis and the new position. Poisson strain described as both the thinning and elongation that occurs in a strained bar. It is defined as the negative ratio of the strain in the traverse direction to the strain in the longitudinal direction. Bending strain is measured by determining the relationship among the force and the amount of bending which results from it.
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