Volume 20, Nº 1 (2017)

The fundamental supra-atomic scale of nanometer attosecond processes in condensed matter creates a multiscale hierarchy of electromechanical interfaces through two-electron dissipation of energy of quantum nanoelectromechanical systems. The space-time scales of electromechanical interfaces are specified, beginning with the subatomic scale of electron Compton length λ_e, by a sequence of degrees n = 1, 2, 3,... of the fine structure constant α ^-n. The third scale, with n = 3, corresponds to quantum mesoelectromechanical 2D interfaces which form functional matrices of electromechanical energy stores and converters as active nucleation centers of fractal topological defects in adjacent crystal structure regions. The hierarchy of electromechanical interfaces creates a hierarchy of dissipative structures in mesomechanics of solids and biomimetics of soft materials.

The theory of structural transformations in the planar sybsystem (surface layers and internal interfaces) of solids under plastic deformation is developed. The theory is based on a consideration for local curvature of the crystal lattice, with new structural states arising in its interstices, responsible for plastic distortion. To satisfy the superplastic condition, such high-rate mechanisms should develop in both planar and 3D crystal subsystems. In a translation-invariant crystal, this condition is met by concentration fluctuations. The multiscale criterion of superplasticity is formulated based on the scale invariance of plastic deformation of the planar and crystal subsystems in a deformable solid. Beyond the criterion, superplasticity passes to the creep mode with restricted plasticity of the material.

Stages of plastic shear instability and adiabatic shear failure are associated with the initiation of collective modes of defect ensembles that have a self-similar nature of autosoliton and "blow-up" structures. Experimental and structural studies have confirmed simulation results for the stages of plastic strain localization and adiabatic shear failure based on the constitutive equations that relate structural relaxation and failure mechanisms to the formation of multiscale collective modes in defect ensembles.

The scale-invariant mechanical behavior of a nanostructured solid is associated with plastic distortion as a major mechanism of nano- and microscale structural transformations. Active grain boundary sliding in a deformed material (microscale) within its highly developed planar subsystem (nanograin boundaries) causes a progressive increase in lattice curvature and plastic distortion of atoms which produces nonequilibrium vacant sites in the nanostructure. The motion of nonequilibrium point defects in nanostructure curvature zones provides conditions for noncrystallographic plastic flow, dissolution or dispersion of initial phases, and formation of nonequilibrium phases in a deformed material. The possibility of reversible structural phase transformations in the presence of high lattice curvature opens the way to greatly increase the fatigue life of surface nanostructured polycrystalline materials.

Multiscale mechanisms of failure of metals (Armco iron, titanium, aluminum) are studied for high cycle and very high cycle fatigue. By correlating with the results of structural studies, a theoretical approach is developed to describe fatigue crack kinetics in damaged material under high cycle and very high cycle fatigue loading conditions. Stages of crack nucleation and propagation are analyzed using the profilometry data from the fracture surface. The scale invariance of fracture surface roughness is established, which allows an explanation of the self-similar nature of fatigue crack kinetics under high cycle and very high cycle fatigue. Variation of elastic-plastic properties of Armco iron under very high cycle fatigue is studied using an acoustic resonance method. It is found that the material density decreases during fatigue damage accumulation, with the minimum of the material density in the bulk of the specimen.