Thermodynamic Variables
Thermodynamic local state of a system at any given time and space in a point can be
completely defined by the thermodynamic variables using the fundamental
relations. Evolution of thermodynamic state under external loading is defined by a
succession of equilibrium states.
Each microstate in energy landscape is an equilibrium point. However, that does
not mean that it is at a maximum entropy point. As Lemaitre and Chaboche (1990)
suggest, the ultrarapid phenomenon for which the time scale of the evolution is in the
same order as the atomic relaxation time for a return to thermodynamic equilibrium
(atomic vibrations) is excluded from this theory’s field of applications, because in
continuum mechanics, the time scale to reach equilibrium is much longer.
Any physical phenomena can be defined with appropriate choice of thermodynamic variables. Any physical process defined by thermodynamic variables is
admissible if it satisfies all laws of thermodynamics.
It is essential to point out that when degradation is introduced into Newton’s laws
of motion, Lemaitre and Chaboche (1990) opine that there is no objective way of
choosing the internal variables best suited to study a phenomena. This is an opinion
that the choice is dictated by empirical experience, “physical feeling,” and very often
by the type of application. We believe researchers’ latter opinion is based on their
phenomenological curve fitting approach for Kachanov-type damage mechanics
models. However, in unified mechanics theory, all thermodynamic variables must
be chosen objectively to be able to assemble the fundamental equation. They must
represent the active micro mechanisms responsible for entropy production. In
Lemaitre and Chaboche (1990) approach, which is based on Newtonian mechanics,
thermodynamic variables are up to the scientist/engineer to decide so that model and
experimental data can be fit to the same curve. In unified mechanics theory, the
actual micro mechanisms that are responsible for entropy generation must be
identified objectively, and they must be physically formulated in the fundamental
equations without curve fitting.
Observable Thermodynamic Variables
1. Temperature.
2. Space coordinates.
While some authors define total strain and stress as observable variables, we do not
subscribe to this school of thought, because strain and stress are human, construct
definitions, not physical quantities. We can only measure displacement and then
calculate strain and stress.
100
3 Thermodynamics
Thermodynamic local state of a system at any given time and space in a point can be
completely defined by the thermodynamic variables using the fundamental
relations. Evolution of thermodynamic state under external loading is defined by a
succession of equilibrium states.
Each microstate in energy landscape is an equilibrium point. However, that does
not mean that it is at a maximum entropy point. As Lemaitre and Chaboche (1990)
suggest, the ultrarapid phenomenon for which the time scale of the evolution is in the
same order as the atomic relaxation time for a return to thermodynamic equilibrium
(atomic vibrations) is excluded from this theory’s field of applications, because in
continuum mechanics, the time scale to reach equilibrium is much longer.
Any physical phenomena can be defined with appropriate choice of thermodynamic variables. Any physical process defined by thermodynamic variables is
admissible if it satisfies all laws of thermodynamics.
It is essential to point out that when degradation is introduced into Newton’s laws
of motion, Lemaitre and Chaboche (1990) opine that there is no objective way of
choosing the internal variables best suited to study a phenomena. This is an opinion
that the choice is dictated by empirical experience, “physical feeling,” and very often
by the type of application. We believe researchers’ latter opinion is based on their
phenomenological curve fitting approach for Kachanov-type damage mechanics
models. However, in unified mechanics theory, all thermodynamic variables must
be chosen objectively to be able to assemble the fundamental equation. They must
represent the active micro mechanisms responsible for entropy production. In
Lemaitre and Chaboche (1990) approach, which is based on Newtonian mechanics,
thermodynamic variables are up to the scientist/engineer to decide so that model and
experimental data can be fit to the same curve. In unified mechanics theory, the
actual micro mechanisms that are responsible for entropy generation must be
identified objectively, and they must be physically formulated in the fundamental
equations without curve fitting.
Observable Thermodynamic Variables
1. Temperature.
2. Space coordinates.
While some authors define total strain and stress as observable variables, we do not
subscribe to this school of thought, because strain and stress are human, construct
definitions, not physical quantities. We can only measure displacement and then
calculate strain and stress.
100
3 Thermodynamics