V. A. Romanova

Simulation of elastic–plastic deformation and fracture of materials at micro-, meso- and macrolevels

Abstract Physical Mesomechanics of materials is a new branch of mechanics that focuses attention on a mesovolume of loaded material. It is a macro particle in classical continuum mechanics and its behavior under load is equivalent to the bulk. The structural elements for a particular application requires specific models while the computational techniques have to be developed. These research groups have been studying heterogeneous materials behavior at the mesolevel under different types of loading. Hierarchical models are developed to study deformation and fracture of solids at the micro- meso- and macrolevels. Taken into account are the influence of micro- and mesostructure of loaded material in relation to its macro behavior. This work focuses on unifying the method of approach to be supported by tests and calculations. In particular, deformation and fracture mechanisms at the micro-, meso- and macrolevels are examined for metals and composites.

Mesoscale plastic flow generation and development for polycrystals

Abstract The traditional yield criteria of plasticity such as Mises, Tresca, etc. make use of averaged macroparameters while mesomechanics consideration is based on the physical notion of plastic deformation mechanisms. They may involve the development of plastic shears on the surfaces and interfaces of internal structure elements involving stress concentration and relaxation. A criterion of plastic flow is proposed; it is based on the stress–strain state in a cell of computational grid as well as in the neighboring cells. An algorithm of plastic shear generation is developed for the progressive propagation of the plastic shears over the crystal. Test calculations of the crystal behavior under tension are made and the results are presented.

Plastic deformation behavior of mild steel subjected to ultrasonic treatment

Investigated in this work is the plastic deformation of mild steel subjected to ultrasonic treatment. Such behavior could arise in machining where ultrasonic vibrations are introduced directly by ultrasonic concentrator and/or magnetic-strictive converter. An ultrasonic shock wave could also result. Calculated are the stress-time history and the tool displacement in addition to the accumulation of plastic deformation that reflects the material damage evolution process at tbe different scale levels. 6 1997 Published by Elsevier Science Ltd.

Simulation of crystal plasticity under dynamic loading

Phenomenological constitutive equations of relaxation type have been constructed and applied to simulate plastic deformation of heterogeneous media. Both the dislocation kinetics and the viscous model with function of relaxation times were used to calculate the plastic strain rate. The deformation at the meso scale level of polycrystals subjected to dynamic loading (including shock waves) has been numerically investigated. The results obtained are reported and discussed.

Simulation of deformation and fracture of coated material with account for propagation of a Lüders-Chernov band in the steel substrate

The paper studies deformation and fracture of boride-coated steel. The dynamic boundary-value problem is solved in the plane strain statement by the finite difference method. The geometry of the coating-substrate interface corresponds to those experimentally observed and is explicitly specified in the calculations. The mechanical response of the steel substrate is described by an elastoplastic model of isotropically hardening material with relations for slow flows. The peculiarities of plastic strain localization and fracture during the propagation of a Lüders-Chernov band in the steel substrate are investigated under tension.

MESOMECHANICS OF INTERFACE IN SURFACE-HARDENED AND COATED MATERIALS

Results of comprehensive experimental studies and numerical simulations of the plastic deformation processes involved in coated and surface-hardened materials on the mesoscopic and microscopic scale levels are presented. The effects of the processes evolving at the coating/substrate interface on the development of plastic deformation of the entire composition are shown. The data reported provide the basis for the optimization of surface-hardening and coating deposition regimes and the development of advanced materials with outstanding service properties.

Strategy of computational predictions for mechanical behaviour of additively manufactured materials

ABSTRACT This paper presents a new computational framework to describe the evolution of grain structure during metal additive manufacturing and to simulate an inelastic deformation of the additively manufactured material, taking into account the grain structure explicitly. A combined effect of grain structure and loading conditions on the evolution of the stress–strain state in additively manufactured specimens is investigated. The results of the research highlight the need to account for the realistic microstructure, to properly describe the mechanical behaviour of additively manufactured specimens and parts. This is part of a thematic issue on Small Scale Mechanics - EUROMAT.

Numerical simulation of deformation and fracture of a material with a polysilazane-based coating

The paper studies the localization of plastic deformation and fracture in a material with a porous coating. A dynamic boundary value problem in the plane strain formulation is solved. The numerical simulation is performed by the finite difference method. The composite structure corresponds to the experimentally observed one and is specified explicitly in the calculation. A generation procedure of the initial finite-difference grid is developed to describe the coating structure with adjustable porosity and geometry of the substrate-coating interface. Constitutive equations for the steel substrate include an elastic-plastic model of an isotropically hardening material. The ceramic coating is described by a brittle fracture model on the basis of the Huber criterion which accounts for crack nucleation in triaxial tension zones. It is shown that the specific character of deformation and fracture of the studied composite results from the presence of local tensile regions in the vicinity of pores and along the coating-substrate interface, in both tension and compression of the coated material. The interrelation between inhomogeneous plastic flow in the steel substrate and crack propagation in the coating is studied.

NUMERICAL STUDY OF STRESS-STRAIN LOCALIZATION IN THE TITANIUM SURFACE MODIFIED BY AN ELECTRON BEAM TREATMENT

Numerical simulation is performed to investigate the mesoscale stress-strain localization in a surface-modified commercial titanium alloy. The calculated crystalline microstructure corresponds to that observed in experiments and is accounted for in an explicit way as initial conditions of a dynamic boundary-value problem. The latter is stated in terms of plane strain developing in microstructure subjected to tension and is solved numerically by the finite-difference method. Elastic-plastic constitutive models were built to describe the experimental mechanical response both of the substrate and of the modified layer. Plastic strain localization is found to depend on the grain yield strength.

Numerical study of the surface-hardening effect on surface phenomena in 3D polycrystalline specimens

Surface hardening effect on the mesoscale surface deformation in polycrystalline specimens subjected to uniaxial tension is numerically studied. Basing on the experimental findings, three-dimensional microstructure-based constitutive models of the unhardened and surface-hardened polycrystalline specimens are constructed. The mechanical behavior of the polycrystalline models is analysed numerically by the finite-difference method. The grain structure is shown to be responsible for the free surface roughening under uniaxial loading. Microscale stresses acting in the bulk of the material across the free surface give rise to the formation of surface ridges and valleys. The hardened layer in a surface-hardened specimen moves the grain structure away from the free surface, thus smoothing out the microscale folds caused by displacements of individual grains. The thicker is the modified layer, the smoother is the surface relief.