Deformation Processes In Materials Research Articles

МОДЕЛЬ КРИВОЙ НЕЛИНЕЙНОГО ДЕФОРМИРОВАНИЯ СТАЛИ 20ХГР И СТАЛИ 35

In most cases the deformation curves that determine the properties of elastoplastic materials are empirical dependencies that interpolate a certain sample of experimental points. At the same time, empirical curves do not provide an idea of the physics of deformation processes in such materials. As an alternative, the article proposes to construct deformation curves as a solution to a differential equation, each term of which has a physical meaning and determines a certain deformation mechanism specific to each material. The offered differential equation is a fourth-order equation with variable coefficients, whose eigenfunctions are polynomials and power functions, which ensures the continuity of this model with the empirical Ramberg-Osgood model. It is shown that the operator of this equation is the Euler operator and is the product of two second-order operators. The first operator defines the mechanism of linear deformation, and the second - the mechanism of nonlinear deformation of the material. The parameters of the material for processing experimental data are determined by the methods of applied mathematics. To reduce the amount of calculations, a method of compressing a two-dimensional (in the coordinates of deformation-stress) region is proposed to find the characteristic point of the deformation curve, which is the proportionality limit. The proposed method for determining the proportionality limit is formal, mathematical and devoid of subjectivity, in contrast to the method prescribed by the current GOST. A consistent physically substantiated system of four boundary conditions on the interval of nonlinear elasticity of the deformation curve is formulated. The mathematical model of building of deformation curves of various physically nonlinear materials allows to create mathematical models of the resource of such materials.

Prediction of injury to passengers of railway rolling stock based on modern physical simulation methods

A technique for assessing the levels of injury to passengers and train crew members in emergency collisions is proposed. It is based on the use of physical methods for simulating fast-flowing non-linear processes of material deformation in emergency situations and anthropometric dummies. Based on the analysis of world and domestic experience in the study of injuring people in emergency situations in transport, an anthropometric 50 percentile male Dummy Hybrid III was adopted as a research tool. Its mathematical model is developed. It was verified by data from field experiments. The developed dummies are integrated into mathematical models for the development of emergency scenarios. As objects of study, the most promising types of rail car layout and two locomotive options were considered for the domestic rolling stock. Based on the simulation results, the values of the criteria for injuring passengers and members of locomotive crews in emergency situations are obtained. The most dangerous positions of passengers in the car during longitudinal collision of trains for the considered layout options are determined. It has been established that the most serious injuries are suffered by passengers and members of locomotive crews as a result of their interaction with car interior items and controls of the driver’s cab.

Under-microscope Mechanical Pulse System for Studying Deformation Processes at High Strain Rates

We present a miniature experimental system that allows real time optical observation of deformation processes in materials. The system can apply controllable force pulses with strain rates of up to 2000 s−1. The force pulse is generated by electrical activation of two antagonistic NiTi actuating wires that load and unload the sample. The magnitude and duration of the applied force pulse are adjusted by controlling the energy transferred to the loading wire and setting the time delay between the activation of the two wires. The actual force profile acting on the sample is measured directly using a dedicated force sensor. The entire setup is placed under an optical microscope equipped with a high-speed camera that enables monitoring the macroscopic displacement as well as the evolution of the microstructure during the mechanical loading. The capabilities of the method for studying deformation mechanisms are demonstrated by visualization of stress-induced twinning reorientation in Ni-Mn-Ga under different strain rates. High speed imaging allows measuring dynamic stress-strain curves that reveal the strain-rate sensitivity of the twinning reorientation stress. In addition, the proposed method allows obtaining velocity-stress relations for individual twin boundaries, which suggest that twin boundary velocity is determined not only by a kinetic relation but also by local interactions with other defects.

The Meso-inhomogeneous Deformation of Pure Copper under Tension–Compression Cyclic Strain Loading

The investigation based on experiments and crystal plasticity simulation is carried out to undertake research on meso-deformation inhomogeneity of metals under cyclic loading at grain level. Symmetrical tension–compression cycle tests are performed on pure copper specimens to observe the inhomogeneous distribution of slip deformation and its evolution with cycle number. Cyclic hardening process and stable hysteretic behavior of pure copper under cyclic loading are simulated by applying a crystal plasticity constitutive model including nonlinear kinematic hardening associated with the polycrystalline representative volume element (RVE) constructed by Voronoi tessellation. Inhomogeneous deformation processes of materials under six different strain amplitudes are simulated by 1600 cycles, respectively. We discuss the variation law of the inhomogeneous meso-deformation distribution of material with the increase in cycle number, and research the rationality of characterizing the inhomogeneous deformation distribution and variation with the statistical standard deviation of the micro-longitudinal strain or the statistical average of the first principal strain based on the statistical analysis of the inhomogeneous deformation of the polycrystalline RVE model during the cycling process. It is found that these two parameters are related to and approximately inversely proportional to the length of measuring gauge.

Analysis of the effect of the cutting speed on specific cutting energy in turning process

In machining process, the cutting temperature and cutting force produced is an important parameter need to be control or reduce. The cutting temperature and cutting force will effected the tool life thus effected the tool cost. Metalworking fluids are essential coolants and lubricants used in material removal and deformation processes to improve manufacturing productivity.This Research will look the effect of cutting speed to specific cutting energy in workpiece on Turning Process using SCCO2 as the coolant. The results of the analysis on this study will compare the results from simulations using Autodesk Software Simulation of Mechanical 2016 with the results of the journal as a reference. From theoretical calculations, the cutting forces decrease while the cutting speeds increase. Then the specific cutting energy will decrease with the increase of cutting speed. The specific cutting energy is. 1,805 J/mm3 to cutting speed 50 m/min, 1,765 J/mm3 to cutting speed 65 m/min and 1,733 J/mm3 to cutting speed 80 m/min [8].

A new approach to evaluating the moisture damage of semi-rigid base materials based on the eroding test by the hydrodynamic pressure generator

The present study developed a new erosion test device, termed hydrodynamic pressure generator, for evaluating the moisture susceptibility of semi-rigid base materials. The hydrodynamic pressure generator was used to generate hydrodynamic loads at variable frequencies and pressures to erode the semi-rigid base materials, and a triaxial apparatus was used to provide confining and axial pressures to the specimens during erosion. After the erosion test, the uniaxial compression strength test was performed on the specimens. The results showed that the deformation process of the semi-rigid base materials under the long-term hydrodynamic erosion can be approximately divided into five stages. In addition, strong correlations were found between the air void and the compressive strength in the erosion test, suggesting that the air void could be used as a reliable indicator for evaluating the moisture susceptibility of the semi-rigid base materials. The results also revealed that the decrease of moisture resistance of semi-rigid base materials could be caused by the erosion of high hydrodynamic pressures, which largely depended on the confining pressure and the axial pressure conditions of the specimens. Because the newly proposed hydrodynamic erosion test allows the quantitative determination of the loss of the strength of specimen subjected to the hydrodynamic erosion and gives an insight into the design of improving moisture resistance for the semi-rigid base materials, it provides a promising approach to evaluating the moisture damage performance for semi-rigid base materials.

Insights into fundamental deformation processes from advanced in situ transmission electron microscopy

Abstract

Concept of Plastic Gas and Model Medium for Dilatable Isotropic Materials

The approach to the study of plastic deformation processes of dilatable isotropic materials from the viewpoint of the concept of plastic gas is considered. A definition of the dilatation medium, which is called a plastic gas, is presented. The loading function and its possible types are given. The dependences of the porosity coefficient on pressure are established and the areas of its variation are determined. Relationships between mean stress, density, and compaction coefficient are ascertained. Using the hypothesis of coaxiality of stress deviators and strain rates, the relationships between stresses and strain rates are determined. For the case of a plane deformation of a dilatable medium that obeys the Coulomb plasticity condition, formulas are obtained for calculating the components of the stress tensor, allowing analysis of the stress-strain state, i.e., performing a full study of the process.

A three‐dimensional coupled Euler‐PIC method for penetration problems

SummaryIn this paper, a three‐dimensional coupled Euler‐PIC (particle in cell) method is proposed to solve the numerical analysis in which the Eulerian method cannot track the deformation process of material during the penetration problems. In the proposed method, the particles with a certain volume and influence domain are adopted to simulate real material flow, and the bidirectional mapping is achieved to physical quantities by the influence domain‐weighted average based on the topological relationship between grids and particles. For the complexity of parallel algorithm of hydrocode, the solution of data dependence and the realization of the parallel algorithm are presented. The numerical simulations of the typical penetration problems are compared with the corresponding experimental data to verify the effectiveness of the proposed method. Moreover, the numerical simulations of shaped charge and projectile penetration of reinforced concrete targets are carried out. The deformation process of reinforcing bars on the penetration process is obtained. Numerical results show that the coupled method has the advantages of both Lagrangian and Eulerian method and efficiently calculates the process of large deformation of the material.

On the question of the applicability of G.V. Samsonov’s activated sintering concept in studying the processes of powder material deformation

Some Yu.G. Dorofeev’s memoirs about joint work and meetings with outstanding materials science expert G.V. Samsonov are given. Meetings in Yugoslavia were of particular importance where G.V. Samsonov and M.M. Ristićtogether with other worldfamous scientists created the International Institute for the Science of Sintering. In the last years of his life, G.V. Samsonov proposed the concept of sintering activation by additives that act as electron acceptors and additionally contribute to the ionic bond in the matrix material. The paper considers the possibility of using this concept in the development of activating additives that reduce the activation energy of the plastic deformation of iron-based powder materials. Sintering activation when forming stable electronic configurations can be accomplished by: 1) accelerating the grain-boundary heterodiffusion of the matrix material in the presence of phase segregations containing an activating microadditive (W–Ni system); 2) intensifying shrinkage durng the plastic flow of matrix material particles facilitated by diffusion porosity formed in the additive particles as a result of predominant additive atom diffusion into base metal particles (Fe–Ni, Fe–Co, Fe–Mn systems); 3) increasing the self-diffusion coefficient of base metal atoms due to the expanded area of a less close-packed crystal lattice (αphase) upon activating additive dissolution (Fe–Mo system). The article reviews the information available on the prospects for using manganese and chromium as compaction activating additives. The compaction activation energy of iron-based powder materials can be reduced by introducing manganese additives. At the same time, the use of diffusion saturation technology is promising. The question of using chromium as an activator does not have an unambiguous answer and suggests the need for further study.

Machine Learning\u2013Based Reduce Order Crystal Plasticity Modeling for ICME Applications

Crystal plasticity simulation is a widely used technique for studying the deformation processing of polycrystalline materials. However, inclusion of crystal plasticity simulation into design paradigms such as integrated computational materials engineering (ICME) is hindered by the computational cost of large-scale simulations. In this work, we present a machine learning (ML) framework using the material information platform, Open Citrination, to develop and calibrate a reduced order crystal plasticity model for face-centered cubic (FCC) polycrystalline materials, which can be both rapidly exercised and easily inverted. The reduced order model takes crystallographic texture, constitutive model parameters, and loading condition as inputs and returns the stress-strain curve and final texture. The model can also be inverted and take a stress-strain curve, loading condition, and final texture as inputs and return the initial texture and constitutive model parameters as outputs. Principal component analysis (PCA) is used to develop an efficient description of the crystallographic texture. A viscoplastic self-consistent (VPSC) crystal plasticity solver is used to create the training data by modeling the stress-strain behavior and evolution of texture during deformation processing.

Corotational derivatives in the numerical simulation of shock loading of deformable solid on the example of aluminum alloy 2024

The peculiarities of the use of the Jaumann and Green-Naghdi corotational derivatives were investigated for modeling deformation processes in isotropic and anisotropic materials under shock loading. Using the aluminum alloy 2024 as an example, it has been shown that taking into account the anisotropy of mechanical properties affects the values of the Jaumann and Green-Naghdi corotational derivatives upon returning the alloy to an unstressed state. It was proposed to use the combination of the Jaumann and Green-Naghdi corotational derivatives to increase the accuracy in numerical calculations of the stress tensor components.

Meshfree analysis on dynamic behavior of hard brittle material in abrasive flow machining

Erosion mechanism of hard brittle target subjected to abrasive particles has been investigated numerically in the present study. A coupled model based on smoothed particle hydrodynamics and finite elements was established. The large deformation and high strain rate of eroded material were concerned by using a strain rate-dependent constitutive model. Dynamic processes of material deformation and fracture growth were analyzed. The results indicated that the radial and lateral cracks were the main fracture modes of aluminum nitride target material. Moreover, the effects of different incident parameters such as impact angle and velocity on erosion mechanism were also investigated.

The Nature of Acoustic Emission during Deformation Processes in Metallic Materials

The theoretical foundation of the method of acoustic emission (AE) was established in the pioneering studies by V. Natsik and his colleagues, which were published in the 1960s–1980s. The source functions corresponding to elementary dislocation mechanisms of plastic deformation and fracture were calculated based on continuum dislocation dynamics. The results remain up to date. Despite the existing experimental difficulties in verifying some of the basic formulations, these works clearly demonstrated the differences between potential sources of acoustic emission in materials. Based on these fundamental premises, statistical methods for recognizing the AE mechanisms, utilizing spectral and cluster analysis of AE time series, were recently proposed. This brief communication reviews theoretical models of AE sources, as well as some key experimental findings, to provide insights into the nature of the acoustic emission peak in the early stages of plastic deformation of metals. The methods for analyzing the AE signal and recognizing the AE sources are also discussed.

A new visco-plastic self-consistent formulation implicit in dislocation-based hardening within implicit finite elements: Application to high strain rate and impact deformation of tantalum

Modeling deformation processes of materials under high strain rate and impact conditions in which the strain rates vary spatiotemporally over several orders of magnitude is challenging, especially in terms of constitutive description. Visco-plastic power-law flow rule, commonly used within crystal plasticity constitutive models, usually introduces superfluous strain rate effects, entering numerically via the slip activation criterion, which result in artificially high flow stress predictions under high strain rate deformation conditions. This paper presents a novel, implicit finite element implementation of a visco-plastic self-consistent polycrystal model that is implicit in dislocation-based hardening with removed strain rate sensitivity introduced by the power-law flow rule. In the model, the strain rate dependence of the flow stress is defined solely by the rate sensitivity of Peierls stress and the evolution of dislocation density within the hardening law, enabling the prediction of high strain rate and impact deformation. As a result, the predicted flow stress is accurate in its magnitude. The physically based strain rate and temperature sensitive model also features, in addition to Schmid, the non-Schmid activation contribution for slip, which is necessary for understanding and modeling the plastic deformation of body-centered cubic metals. The model is calibrated to simulate the strain rate- and temperature-sensitive monotonic deformation of tantalum and is subsequently applied to a Taylor impact test of the same material. Since the impact simulation required remeshing and interpolation of state variables, the spherical linear interpolation algorithm in the space of quaternions is implemented to facilitate the interpolation of texture. Predictions of the simulation were found to compare favorably with experimental measurements of post-test geometrical changes and texture evolution. The implementation and insights from these predictions are presented and discussed in the paper.

Enriched Galerkin finite elements for coupled poromechanics with local mass conservation

Robust and efficient discretization methods for coupled poromechanical problems are critical to address a wide range of problems related to civil infrastructure, energy resources, and environmental sustainability. In this work, we propose a new finite element formulation for coupled poromechanical problems that ensures local (element-wise) mass conservation. The proposed formulation draws on the so-called enriched Galerkin method, which augments piecewise constant functions to the classical continuous Galerkin finite element method. These additional degrees of freedom allow us to obtain a locally conservative and nonconforming solution for the pore pressure field. The enriched and continuous Galerkin formulations are compared in several numerical examples ranging from a benchmark consolidation problem to a complex problem that involves plastic deformation due to unsaturated flow in a heterogeneous porous medium. The results of these examples show not only that the proposed method provides local mass conservation, but also that local mass conservation can be crucial to accurate simulation of deformation processes in fluid-infiltrated porous materials.

Development of a three-dimensional tomography holder for in situ tensile deformation for soft materials.

An in situ straining holder capable of tensile deformation and high-angle tilt for electron tomography was developed for polymeric materials. The holder has a dedicated sample cartridge, on which a variety of polymeric materials, such as microtomed thin sections of bulk specimens and solvent-cast thin films, can be mounted. Fine, stable control of the deformation process with nanoscale magnification was achieved. The holder allows large tensile deformation (≃800 μm) with a large field of view (800 × 200 μm before the deformation), and a high tilt angle (±75°) during in situ observations. With the large tensile deformation, the strain on the specimen can be as large as 26, at least one order of magnitude larger than the holder's predecessor. We expect that meso- and microscopic insights into the dynamic mechanical deformation and fracture processes of polymeric materials can be obtained by combining the holder with a transmission electron microscope equipped with an energy filter. The filter allows zero-loss imaging to improve the resolution and image contrast for thick specimens. We used this technique to study the deformation process in a silica nanoparticle-filled isoprene rubber.

High‐temperature short‐range compressive responses and contact effect of ultrahigh porosity 3D random fibrous materials

AbstractThrough experiments and finite element modeling (FEM) of contacting fibers, we study the compressive responses of a 3‐dimensional (3D) random fibrous (RF) material of ultrahigh porosity (89%) in the through‐the‐thickness (TTT) and in‐plane (IP) directions from 299 (room temperature) to 1273 K. The experimental results indicate that localized failure and overall compressive deformation dominate the deformation process of RF materials loaded in the TTT direction at low and high temperatures, respectively. On the other hand, only localized failure is observed in the IP direction upon loading. Based on its morphological characteristics, a FE model that considers contact between the fibers is developed to simulate the compressive responses of the tested 3D RF material. In this model, the contact mechanism between the fibers is simulated based on a user‐defined nonlinear spring element. The simulated strength and elastic modulus agree well with the observations from the compressive experiments.

Molecular Dynamics Study of the Deformation Processes of Metallic Materials in Structural and Phase (Martensitic) Transformations

The application of the method of molecular dynamics based on the use of pair interatomic potentials has been discussed to study various deformation processes during structural and phase (martensitic) transformations in metallic single and polycrystals. It has been shown that the method of molecular dynamics in a two-dimensional model makes it possible to qualitatively analyze the processes of grain-boundary sliding and other mechanisms of plastic deformation in polycrystals. It is also an efficient tool for describing diffusionless martensitic transformations in metallic materials. As an example, the use of the method for simulating grain-boundary sliding in a polycrystal with nonequilibrium grain boundaries is presented and the mechanisms of overcoming an obstruction in the form of a protruding segment of a grain have been demonstrated at the atomic level. The application of this method for describing the dynamics and morphology of the thermoelastic martensitic transformation has been illustrated by the example of the titanium nickelide and manganese alloys.

Correction to: Development of Criteria for Reliability of the Prediction of the Deformation and Relaxation Processes of Polymeric Materials

The acknowledgement on page 139 should read The work was financed within the framework of the base part of the state task of the Ministry of Education and Science of the Russian Federation, Project No. 11.4696.2017/8.9.