The Spring It is a single element or an association of elements (system) capable of assuming remarkable elastic deformations under the action of forces or moments, e, therefore, able to store a large amount of elastic potential energy. The characteristic elements of springs are the arrow, a rigidity it's at flexibility.
Arrow is the deformation suffered by the spring under the action of a given force, measured in the direction of the force itself. Such a concept can also be extended to an elastic element subjected to a torque, in this case the force is replaced by an applied moment and the straight deformation by the angular displacement.
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Coil Springs - Calculation Workbook