Dmitry Moiseenko

Effect of notch shape on strain localization in steel under shock loading: Hybrid CA simulation

A hybrid discrete-continuum Excitable Cellular Automata (ECA) approach is proposed to study the vector character of the mass and energy transfer flows in a solid under high-rate loading. Based on the torsion energy calculations, the model of generation and accumulation of defect structures is proposed. Numerical simulations of uniaxial shock loading of specimens with three typical notch shapes are performed to validate the proposed approach. It is shown that stress relaxation occurs most effectively when the modulation of various components of the force moment takes place at various scales. This offers the possibility to reduce the stress concentration substantially by tailoring the materials microstructure.

Influence of notch shape on deformation mechanisms and energy parameters of fracture of 12Cr1MoV steel under impact loading

Impact loading curves and fracture energy of the notched 12Cr1MoV ductile steel specimens are analyzed. The qualitative description and quantitative parameters are obtained for major stages of ductile and brittle fracture depending on the shape of the notch and the stress stiffness ahead. It is shown that a zone with enhanced plasticity is formed in the vicinity of V-, U-, and I-shaped notches at 20°C testing temperature, giving rise to ductile fracture. The stress stiffness at the notch tip increased with testing temperature reduced to –40°C. Using the quantitative description of fracture surfaces, a physical-mechanical scheme of the specimen fracture was suggested for the case of enhanced and localized (constrained) plasticity near the stress concentrator tip.

DEFECT ACCUMULATION IN NANOPOROUS WEAR-RESISTANT COATINGS UNDER COLLECTIVE RECRYSTALLIZATION. SIMULATION BY HYBRID CELLULAR AUTOMATON METHOD

Abstract. A modification of a multiscale hybrid discrete-continual approach of excitable cellular automata is developed. The new version of the method is completed by taking into account porosity and nanocrystalline structure of a material and the algorithms of calculation of local force moments and angular velocities of microrotations. The excitable cellular automata method was used to carry out numerical experiment (NE) for heating of continuous and nanoporous specimens consisting of nanocrystalline TiAlC coatings. The numerical experiments have shown that nanoporosity allows to substantially reducing the rate of collective crystallization. Nanoporosity slowed down propagation of the heat front in specimens. This fact can play both positive and negative roles in deposition of coating and its further use. On the one hand, by slowing the heat front propagation one can significantly reduce the level of thermal stresses in deeper layers of the material. On the other hand, such deceleration in case of the high value of the coefficient of thermal expansion can give rise to the formation of large gradients of thermal stress, which initiate nucleation and rapid growth of the main crack.