Elijah Borodin

The University of Manchester · Department of Mechanical, Aerospace and Civil Engineering

The grain boundary character distribution strongly affects the properties of polycrystalline materials. Grain boundaries of similar characters form networks, whose topological invariants can be considered as distribution descriptors. Understanding the evolution of such descriptors during severe plastic deformations (SPD) can elucidate the evolution...

Nanomaterials are widely used in different fields, such as microelectronics, industry, and nanocomposites, and they can exhibit unstable deformation behaviour depending on the strain rates. Under strain rates of 10−4–10−1 s−1, the deformation of nanomaterials, unlike the quasi-static deformation of micromaterials, is characterized by the presence o...

The design of new ceramic materials with specific thermo-electrical and mechanical properties is important for a range of engineering applications. Recent research has demonstrated that inclusion of soft reduced graphene oxide (rGO) in hard ceramic matrix produces nano-structured ceramic composites with improved electrical conductivity and fracture...

The mechanical properties of Chelyabinsk LL5 chondrite (Chelyabinsk meteorite) were studied by uniaxial compression and diametral compression/indirect tension test. Twenty cylindrical samples, 10 for compression and 10 for tension, with the diameter 3.3 mm and 1.65 mm in height have been prepared for testing. It was shown that the strength of the t...

Describing dynamic recrystallisation is challenging with existing material characterisation tools, which are typically based on grain boundary character distribution. This is one barrier to further developments in grain boundary engineering. We consider the network of triple junctions in copper alloys as the sub-structure that governs continuous dy...

Based on a new model coupling both direct and inverse grain rotation processes, we discuss interrelations between the dislocation mechanism of plasticity and the grain boundary sliding in fine-grained solids. The high-strain-rate deformation conditions, corresponding to molecular dynamic simulations, and processes of severe plastic deformation are...

The finite element method is used for simulation of productivity in dynamic Taylor tests. Two different approaches for prediction of plastic deformation of finite element method is employed for numerical simulation of yielding under dynamic impact Taylor tests. Obtained results of modeling are compared with experimental ones. These are Johnson–Cook...

Proposed is a methodology for an accurate description of triple junctions’ network evolution in the course of severe plastic deformation (SPD). It is based on representations of polycrystalline solids with discrete combinatorial complexes, processes evolving different substructures (grains, grain boundaries, triple junctions) of these complexes, an...

The focus of researchers studying severe plastic deformation on the final grain size of material is often preventing them from observing a much wider spectrum of alterations to material defect structure. It can be asserted that the decrease in material grain size is, in fact, only the consequence of many different processes accompanying plastic def...

Theoretical model is suggested which describes the misfit stress relaxation near a misfitting nanowire (NW) having the shape of a long parallelepiped embedded in a nanolayer. The stress relaxation is assumed to occur through the emission of dipoles of edge partial (or perfect) dislocations gliding along the NW face normal to the free surfaces of th...

The evolution of a structural–temporal integral criterion of yielding is reported for the description of the dynamic deformation of metals. The values of characteristic relaxation times, considered as the constants of the material, are shown to be suitable for the description of dynamic effects upon the nanomaterial deformation in a wide range of l...

Available models of dynamic recrystallization have a number of disadvantages that in most cases make them inapplicable for practical predictions of material microstructure evolution. Both the microstructural and the empirically based approaches do not reflect physical processes leading to evolution of material defect structure in the process of pla...

The role of instabilities of plastic flow at plastic deformation of various materials is one of the important cross-disciplinary problems which is equally important in physics, mechanics and material science. The strain rate sensitivities under slow and high strain rate conditions of loading have different physical nature. In the case of low strain...

Theoretical models of viscoelastic behavior and plastic deformation mechanisms of human dentin are considered. Using the linear viscoelasticity theory in which creep and relaxation kernels have the form of fraction-exponential functions, numerical values of instantaneous and long-time Young’s moduli and other characteristics of dentin viscoelastici...

Theoretical models of viscoelastic behavior and plastic deformation mechanisms of human dentin are considered. Using the linear viscoelasticity theory in which creep and relaxation kernels have the form of fraction-exponential functions, numerical values of instantaneous and long-time Young's moduli and other characteristics of dentin viscoelastici...

The evolution of a structural–temporal integral criterion of yielding is reported for the description of the dynamic deformation of metals. The values of characteristic relaxation times, considered as the constants of the material, are shown to be suitable for the description of dynamic effects upon the nanomaterial deformation in a wide range of l...

This paper investigates the microstructural evolution and grain refinement kinetics of a solution-treated Cu-0.1Cr-0.06Zr alloy during equal channel angular pressing (ECAP) at a temperature of 673 K via route BC. The microstructural change during plastic deformation was accompanied by the formation of the microband and an increase in the misorienta...

The microstructure evolution and grain refinement kinetics of a solution treated Cu – 0.1Cr – 0.06Zr alloy during equal channel angular pressing (ECAP) at a temperature of 673 K via route BC were investigated. The microstructure change during plastic deformation was accompanied by the microband formation and an increase in the misorienations of str...

Dependences of the yield strength of metals on the grain size and the dispersion of the grain size are discussed for quasistatic and dynamic conditions of loading. In these two cases, the size distribution of grains influences differently on the slope of the Hall–Petch curve. The presence of wide size distribution of grains shifts the maximal yield...

Possible mechanisms of inelastic deformation at the I-mode crack tip in dentin are theoretically studied. We consider the relative shear of collagen fibers in their nodes without breaking intermolecular bonds, the detachment of collagen fibers from each other in the nodes, and tearing of the individual fibers. For each of these mechanisms, we estim...

Fracture mechanism of teenage crown dentin is discussed. It is shown that at microscopic and nano-scale dentin behaves like a viscoelastic solid, such as some polymer films and rubber. Considerable irreversible deformation, which is localized in the long narrow area, precedes an appearance of a crack in a thin sample of dentin. The brittle behavior...

Plastic deformation of samples undergoing Taylor anvil-on-rod impact test is simulated utilising finite element method (FEM). Classical (bilinear plasticity using von Mises stress, Johnson-Cook plasticity model) plasticity models and a new plasticity model based on notion of incubation time of plastic flow initiation are employed to model dynamic d...

Based on the concept of the incubation time of plastic deformation, an integral yield criterion is introduced and time effects of irreversible deformation are considered. The efficiency of the approach is demonstrated using micro and nanocrystalline nickel as an example. The parameters of the phenomenological model are treated physically from the v...

Human hard tissues dentin and enamel exhibit deformation behavior like biopolymer and biomineral, respectively. Cracks appear in dentin and enamel samples under loading, which however are stable. There is extensive plastic zone ahead every crack tip in the tooth hard tissues. The plastic zones are examined in the thin samples of dentin and enamel i...

Some recent experiments with ultrafine-grained metal samples reveal that it has an abnormal mechanical response on the intensive dynamical loading caused by its impact or electron beam irradiations. On the basis of the original plasticity model, which takes into account dislocation slip and grain boundary sliding, we show that this response is usua...

Results of microstructural investigation of the D16 aluminum spall surface are presented in comparison with the numerical simulation of the fracture process. A fracture model based on the plasticity driven growth of voids is used in simulation. Different scale levels of fracture are discussed, and the main level of fracture is attempted to be alloc...

It is shown that separation of scalar dislocation density into two parts, giving densities of mobile and immobile dislocations, is providing a possibility to predict continuous dynamic recrystallization (DRX) process caused by severe plastic deformation of metallic materials. The proposed approach is making it possible to predict a rather extent se...

On the basis of the Maxwell model for very viscous liquid we derive equations for definition of characteristic relaxation times that are used in the integral criterion of plasticity. Relaxation times are constants for the material with current microstructure and do not depend on the features of the deformation process, but they change at the change...

A computational plasticity model with accounting of coupled evolution of the dislocations and twins in metals under the dynamic loading is presented. The model is based on our previous results for the dislocation plasticity, but generalizes them and accounts mechanical twinning in addition. It includes equations of the mechanics of continua for ela...

In this report, we present our twinning model intended for simulation of the dynamic deformation of metals with low values of the stacking fault energy, as well as the results of application of the model to numerical simulation of intensive loading of metals. Generation of a twin is described as an appearance of a stacking fault with size more than...

The generality of the dynamic approach to a wide range of problems of the continuum mechanics, including deformation at the rates determining quasi-static deformation conditions has been demonstrated using the example of deformation of cadmium and copper whiskers. The sharp yield point phenomenon has been analyzed in terms of the theory of dislocat...

Mechanical model for plastic relaxation of stresses in metals has been proposed. Our approach based on a characteristic plastic relaxation time, which is assumed as a material parameter. In a number of tasks values of its parameter become similarly high and it leads to dynamic effect appearing even at low strain rates deformation condition. The phe...

The dependence of the yield strength of metals on the grain size and initial dislocation density in a wide range of strain rates has been analyzed within a unified approach. It has been shown that the barrier stress and characteristic time of plastic relaxation completely determine the shear strength of metals for all strain rates. The existence of...

CRS computer program is presented, which calculates the dynamical deformation of metals under irradiation by high-current electron and powerful ion beams. The incorporated mathematical models allow one to calculate stresses, deformations and structural changes induced by the irradiation. The CRS code numerically solves the equations system, which c...

A version of the metal plasticity relaxation model based on a plasticity integral criterion with the characteristic relaxation time parameter is suggested. The dislocation concepts of metal plasticity together with the Maxwell model for a strongly viscous fluid are used to show that this characteristic relaxation time parameter can be interpreted i...

We have performed numerical simulations for the early stages (till several tens of microseconds) of dynamical channel angular pressing (DCAP). New dislocation and twinning models have been used for description of the kinetics and dynamics of defect structures; these models are described in the paper. In DCAP of copper with the initial sample veloci...

The distribution of dislocations and twins over the cross section of shock-loaded copper and 18Cr-10Ni-Ti steel specimens is investigated experimentally and numerically. It is found that the volume fraction of twins near the loaded surface and a spall crack is an order of magnitude higher than their fraction at the center of the target. The feature...

The effect of plastic flow localization, which is significant for obtaining ultra-fine-grain metals by intense high-rate plastic straining, is studied numerically. Large-scale localization of plastic flow, which is determined by the geometry of the problem, as well as microscopic localization appearing due to instability of plastic strain during th...

Micro mechanisms of plastic deformation and the defect structure evolution are sufficiently changing with the strain rate increase. It leads to non-monotonic relations between the macroscopic characteristics of metal strength or ductility and the structure parameters such as a grain size. Our simulations predict an inverse Hall-Petch relation for u...

We have investigated numerically an evolution of initial perturbations of temperature or dislocation density in metals at high-rate deformation and its influence on the localization of plastic flow. A high-rate simple shear of micro-samples of pure metals and alloys, coarse-grained as well as nano-crystalline, has been simulated in two-dimensional...

High stain rate experiments demonstrate a deviation from the Hall-Petch relation even for ul-trafine grained metals. Our simulations predict an inverse Hall-Petch relation for ultrafine-grained metals at extremely high strain rates (above 10 6 s −1). Also we discuss the grain size dependence of the shock wave attenuation rate in aluminum and resist...

A high-rate plastic deformation of fine-grained materials has been considered as a result of competing processes of dislocation gliding in the grains and grain-boundary sliding. A structural model has been proposed for describing the grain-boundary sliding as a dominant mechanism of plasticity of nanocrystalline metals. The dependence of the yield...

The numerical study of high-rate plasticity of Cu target with different grain sizes under the action of nanosecond relativistic high-current electron beam has been carried out in the paper. The model of microcrystal material plasticity includes dislocation kinetics and dynamics as well as the stress relief in the grain boundaries of the polycrystal...

In this paper we consider grain boundary sliding as a dominant mechanism of plasticity in nanocrystalline metals. A mechanical model for barrier resistance to sliding has been proposed. Characteristic time of plastic relaxation due to grain boundary sliding has been estimated based on molecular dynamics simulation data. At quasi-static deformation...