Thermoelasticity and entropy flow; pp. 142–144Full article in PDF format | doi: 10.3176/proc.2008.3.04
The well-known theories of thermoelasticity are based on thermal expansion, and recently the theory of heat conduction has been looked into for improvements. The reason is that heat conduction is described with scalar and vector variables but elasticity with second order tensors, and in linear order there is no direct coupling between second order tensors and vectors or scalars if the material is isotropic. The observed deviations from the present theories urge that new tracks for research be sought. Such a new track can be opened by Onsager’s thermodynamics supplemented with dynamic degrees of freedom. This theory is usually referred to as extended thermodynamics. The key moment is in the general form of the entropy current out of local equilibrium, which leads to the formal introduction of the transport of the dynamic degrees of freedom. The skeleton of the possible theories is based on the introduction of one or more vectorial dynamic variables. They can be coupled to the current density of the heat flow, while their ‘diffusion’ intensities are second order tensors coupled directly in linear order to the stress tensor even if the material is isotropic. The possibilities are demonstrated on an example with one dynamic degree of freedom.
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