On nonlinear strain vectors and tensors in continuum theories of mechanics
A non-linear mathematical model of hyperbolic thermoelastic continuum with ﬁne microstructure is proposed. The model is described in terms of 4-covariant ﬁeld theoretical formalism. Fine microstructure is represented by d-tensors, playing role of extra ﬁeld variables. A Lagrangian density for hyperbolic thermoelastic continuum with ﬁne microstructure is given and the corresponding least action principle is formulated. 4-covariant ﬁeld equations of hyperbolic thermoelasticity are obtained. Constitutive equations of microstructural hyperbolic thermoelasticity are discussed. Virtual microstructural inertia is added to the considered action density. It is also concerned to the thermal inertia. Variational symmetries of the thermoelastic action are used to formulate covariant conservation laws in a plane space-time. For micropolar type II thermoelastic Lagrangians following the usual procedure independent rotationally invariant functional arguments are obtained. Objective forms of the Lagrangians satisfying the frame indifference principle are given. Those are derived by using extra strain vectors and tensors.