Physical Meaning of Physical-mesomechanical Formulation of Deformation and Fracture

International audiencePhysical mesomechanics is a relatively recent theory of deformation and fracture. Based on the physical principle known as gauge invariance, it has derived field equations that describe the displacement behavior in plastically deforming materials. By the nature of the way the gauge invariance is applied, the theory is capable of describing all stages of deformation on the same theoretical basis. Previously, we analyzed this formalism from the mathematical point of view, and discussed the dynamics resulting from the field equations. In this paper, we focus on the physical meaning of the field equations and related dynamics. It is shown that plastic deformation is characterized as the dynamics where materials' longitudinal resistive force is proportional to the local velocity as opposed to the elastic regime where the longitudinal resistive force is proportional to the displacement. Consequently, in the plastic regime, part of the work done by external force is not stored in the material as potential energy but dissipated as heat. In this dynamics, a quantity called the deformation charge plays an important role. From the gauge theoretical viewpoint, the deformation charge is associated with the charge of symmetry. From the viewpoint of conventional mechanics, it is normal strain whose energy is unrecoverable to the mechanical field. Experimental results that support these arguments are present