Sergey Astafurov

Effect of dynamic stress state perturbation on irreversible strain accumulation at interfaces in block-structured media

The paper studies how the stress state of the interface between structural elements in a block-structured medium affects its deformation response to dynamic loading. It is shown that the normalized shear stress and mean stress are the major factors that determine the deformation response of the interface. We propose to describe the dependence of the value of induced irreversible displacement at the interface on the normalized shear stress using a logistic function. The central point of this function is the point of transition from the quasi-elastic to quasi-plastic stage of the interface shear deformation. The obtained empirical dependences are important for understanding the mechanism of irreversible strain accumulation in fault zone fragments and, particularly, for the development of an earlier proposed approach to estimate the characteristic level of active shear stresses in separate tectonic fault regions.

Influence of phase interface properties on mechanical characteristics of metal ceramic composites

The paper reports on theoretical study to elucidate the influence of geometric (width) and mechanical characteristics of phase interfaces on strength, ultimate strain, and fracture energy of metal ceramic composites. The study was performed by computer simulation with the movable cellular automaton method and a well-developed mesoscale structural composite model that takes explicit account of wide transition zones between reinforcing inclusions and the matrix. It is shown that the formation of relatively wide “ceramic inclusions-binder” interfaces with gradual variation in mechanical properties allows a considerable increase in the mechanical properties of the composite. Of great significance is not only the interface width but also the gradient of mechanical properties in the transition zone. The presence of defects and inclusions of nano- and atomic scales in interface regions can increase internal stresses in these regions, induce a steep gradient of mechanical properties in them, and hence decrease strain characteristics and fracture energy of the composite.

Peculiarities of the mechanical response of heterogeneous materials with highly deformable interfaces

Peculiarities of the deformation and fracture of heterogeneous materials with a large fraction of interfacial regions (interfacial materials) under the action of complex alternating loads have been studied by computer-aided simulation. The dependence of the character of fracture, deformability, dissipation of the applied energy, and strain distribution in the material bulk on the frequency of cyclic loading was determined. High-frequency vibrations at a frequency much greater than that of the natural oscillations may significantly increase the deformability of interfacial materials.

Influence of thermomechanical treatments on mechanical properties and fracture mechanism of high-nitrogen austenitic steel

In this paper, the mechanical properties and fracture mechanisms of the high-nitrogen austenitic steel Fe– 17Cr–10Mn–7Ni–0.95V–0.8N–0.1C (in wt %) processed by different thermomechanical treatments are investigated. Cold rolling and short-time solid solution hardening contribute to the formation of a rather homogeneous fine-grained structures in the steel, which possess high strength, sufficient plasticity and exhibit excellent product of strength and elongation (σYS = 540–570 MPa, σUTS = 900–950 MPa, EL = 36–37%, PSE=33–35 GPa %) in comparison with cold-rolled specimens possessing high strength properties, but extremely low elongation (σYS = 1200 MPa, σUTS = 1650 MPa, EL=1%, PSE=1.7 GPa %).