Elasticity (physics)

Elasticity is the property of a body or a material to change its shape under force and return on discontinuation of the force acting in the original form (for example, spring ). One case is different:

• The linear-elastic behavior is described by the Hooke's law,
• The non- linear elastic behavior (rubber elasticity), in which the voltage non-linear function of the deformation,
• Elastic hysteresis, wherein after removal of the force is a displacement.

For all materials, there is a limit of the elasticity area, the other side of an anelastic behavior is observed.

Mechanisms

Acts on a body, a force, a, the equilibrium position of its elementary building blocks (atoms or molecules) is disturbed. The distance between them is increased or decreased by a small amount, to the expended mechanical energy is stored and the workpiece changes its external form. After discharge, the atoms or molecules are returning to their original places and the body returns to its original external form again. The energy for the deformation is only stored and released again upon release.

If a certain value is exceeded in the force, so in addition to the elastic plastic deformation occurs. This value in each case depending on the material and is referred to as an elastic limit. In the stress-strain diagram, it is the point from which on unloading hysteresis occurs. Often here differs from the voltage curve and the linear gradient. This point, however, is not clearly defined, but depends on the measurement method. Therefore, can be inter alia a mandatory unambiguous assignment of bodies and materials on the properties of elasticity and plasticity not often perform, but there is on the extent, nature and duration of the force is a combination of two properties or a change from elastic to plastic behavior.

A special form of elasticity is the viscoelasticity. It occurs mainly in polymers and is characterized by a partially elastic, partially viscous behavior. The polymer only partially relaxed after removal of the external force, the remaining energy is dissipated in the form of flow processes. Here, an increase in elasticity, a reduction in the viscous behavior.

Applications

The linear elastic behavior of some materials at small deformation is exploited for the construction and use of springs, see also spring constant.

In the engineering strength of materials, special in the building construction and equipment-related construction, the elastic properties of materials are used to ensure the dimensional stability of structures and devices of force. By calculating the elasticity, even a high load -bearing structures and at the same time avoiding breaking risks is achieved.

In order to handle this calculation targeted, the elasticity of materials with the modulus of elasticity, the compression modulus and the shear modulus is described in detail. These three modules are the Poisson's ratio are linked.

• The modulus of elasticity describes the relationship between stress and strain in the deformation of a solid body with linear elastic behavior.
• The compression modulus is calculated, which on all sides of pressure change necessary to induce a particular reversible change in volume.
• The shear modulus gives information about the linear elastic deformation of a component due to a shear force or shear stress.

In the rheology of the linear elasticity is one of the three basic features in addition to the viscosity and plasticity and is illustrated in the rheological model by a spring, the Hooke - element.