Rubber elasticity

With rubber elasticity ( entropy ) is called a material resistance to stretch, which is based on a reversible entropy change in the macromolecules of the matrix material in rubber -like materials. The macromolecules are composed of long chains of identical blocks. The angle between the two blocks is smoothly at a stretching of the molecule, ie subject to change without expenditure of energy; at the same time while the entropy is reduced (reduction of disorder ). However, it may also stored energy.

If the leading for drawing external force is removed, leads an absorption of energy from the environment ( heat ) cause the molecules to twist again, the entropy is increased and the molecule is contracted (see also: Elastomer ).

Which occurs with an increase in length ε ( Relativmaß! ) restoring force K (per cross-sectional area ) is defined as usual, ie a so-called modulus of elasticity E - this is, however, comparatively small - or non-linear generalizations.

So Thermodynamically, however, rests the elasticity of hard materials (eg metals ) mainly due to the increase in internal energy U, the rubber elasticity to a decrease in the entropy S in the formula for the change in free energy at a given elongation.

The affected group of materials (elastomers, rubbers, rubber, silicone rubber ) is characterized by a non-linear stress-strain curve, damping and deformation history effects as well as a pronounced incompressibility.

For a description of these materials, a green netic material model should be used. Wherein the Green's materials are the voltages calculated .. For elastomeric materials, this approach has been derived by the thermodynamics of the entropy of the strain energy density as a function of strain.

Known approaches for the energy density are the Mooney -Rivlin, neo- Hookean, Yeoh and Ogden models.