Plastic Deformation Of Metals Research Articles

A REVIEW OF THEORECTICAL CONCEPTS OF HYDROGEN CRACKING IN METALS AND ALLOYS

Today the demand for high-strength metal materials to be used in critical structural elements and facilities that operate under variable temperature and stress conditions is steadily growing economic and engineering tendency. However increased strength features of a metal are opposed by its reduced plasticity so the metal often becomes unfit for large plastic straining. In this case solid body brittle failure starts and this process is quite often of random character, which may result in big financial loss and human injuries. Available literature contains little information on delayed failure issues in principle, however, many research findings demonstrate that the decisive role in this process belongs to hydrogen that interacts with different types of micro-defects in the matrice. In order to understand why a more easy propagation of dislocations from the crack tip down results in embrittlement it is necessary to study the crack growth pattern in inert media for plastic materials. Common features of different hydrogen embrittlement processes make it possible to conclude that a solid theory should be based on consolidated concepts of hydrogen-induced failures with taking into account the synergism of metal-hydrogen systems, i.e. the change in embrittlement mechanism in the process of the material structural self-organization at different structure-scale levels. Here a very important issue is to investigate the response of the material fine structure (structural relaxation) to the influence of a hydrogen medium under various straining temperature and speed conditions. Such investigation should be conducted with the help of electronic microscopes by applying acoustical emission and inner friction methods. Thanks to them it is possible to study the auto-wave nature of metal plastic deformation and to identify the most typical sustainable dissipative structures that emerge during the material self-organizing under combined impact of tensile stress and corrosive media.

Micromechanics of plastic deformation through paired twinning in nanomaterials and polycrystals

A theoretical description of the plastic deformation of nanostructured and polycrystalline metals through paired nanotwinning on grain boundaries has been proposed. Within the micromechanical approach developed, deformation nanotwins are formed as a result of successive plastic shears. The energy characteristics and critical stresses of paired twin nucleation in titanium are calculated.

Conchoidal Fracture of Zr- and Mg-Based Amorphous Glass

In metallic glasses plastic deformation occurs via the creation and the propagation of a softened region in the shear bands. Some of the high strength metallic glasses (as Zr-based metallic alloys) exhibit complex shear band topography and the final failure respects the allocation of the shear bands. We studied the differences in the fracture surfaces of Zr-and Mg-based amorphous alloys. Ductile behaviour of the shear bands in Zr-based amorphous alloy tends to the dimple creation during the failure. On the fracture surfaces the vein pattern morphology manifestations were present. Conchoidal fracture was typical for Mg-based amorphous glass. Two different surface morphologies, plumes and rib marks ornament the fracture surfaces.

Micromechanics of plastic deformation through grain-boundary migration in metal–graphene nanocomposites

A theoretical description of the plastic deformation of metal–graphene nanocomposites through stress-induced migration of grain boundaries is proposed. Within the micromechanical approach developed, the plastic deformation induced by this migration leads to the formation of disclination quadrupoles (intense elastic stress sources). The energy characteristics and critical stress are calculated for the plastic deformation mode under consideration. The influence of graphene nanoinclusions is shown to cause significant hardening of metal–graphene nanocomposites. This conclusion is consistent with the corresponding experimental data.

Electrostimulated machining of metals

New mechanical equipment requires structural materials whose high performance cannot be ensured by traditional methods. A promising approach to the shaping of steel is the use of powerful unipolar current pulses with the following characteristics: amplitude 10–15 kA; pulse frequency up to 400 Hz; pulse length up to 100 μs. The widespread industrial use of this technique is hindered by the low efficiency of the corresponding pulse generators, which also draw considerable power from the ac grid and are not sufficiently controllable. In the present work, a generator of powerful unipolar current pulses that is free of those defects is described. It includes a charging system connected to power capacitors; and a thyristor switch that discharges the capacitors to a low-resistance load. To reduce the power drawn from the grid, the generator includes a recharging device based on a thyristor, which is connected to a reverse-parallel thyristor switch. To permit regulation of the pulse amplitude and increase its power, the uncontrollable dc source in the charging system is replaced by two irreversible thyristor converters in series. That permits control of the voltage at the power capacitors. To optimize capacitor charging, a two-loop subordinate control system regulates the parameters of the pulse generator: the external control loop governs the voltage charging the capacitors, while the internal control loop governs the charging current. MATLAB Simulink software is used to create a model of the proposed generator. The model corresponds to the actual pulse generator used at Siberian State Industrial University to investigate the electrostimulated plastic deformation of metals and alloys. The model permits improvement in the characteristics of the pulse generator and its operating conditions. A benefit of the proposed generator over its counterparts is that the power drawn from the grid is considerably reduced, while the voltage charging the capacitor may be regulated in the range up to 600 V, with pulse frequencies up to 400 Hz. The generator may be used industrially—in particular, in rolling mills when drawing steel wire that is hard to deform.

МОДЕЛЮВАННЯ ПРОЦЕСУ РІЗАННЯ ОДИНИЧНИМ АБРАЗИВНИМ ЗЕРНОМ ПРИ КРУГЛОМУ ГЛИБИННОМУ ШЛІФУВАННІ

Urgency of the research. The quality and accuracy layers surface of the part, in the first place, is determined by the parameters of the grinding operation. The cutting process, at grinding, is not performed by all the cutting grains of the working surface of the abrasive wheel, but only by those that are above the bunch. The effectiveness of the grinding process influences not only the cutting edge of abrasive grains, as well as wrought.Target setting. Finishing operations including grindings, are rather difficult non-stationary, thermal stress process. 3D modeling of cutting process of single abrasive grain allows investigating in detail the process and increase efficiency finishing details.Actual scientific researches and issues analysis. In the last researches was considered the method of determining the components of the cutting forces during grinding with crossed axes tool and details, method of deep single-pass grinding with the crossed axes tool and detail. Considered a methodological aspects of modeling cutting processes by method of final elements.Uninvestigated parts of general matters defining. Absence of design and research of cutting process by single abrasive grain at round deep grinding.The research objective. The purpose of this work is modeling of cutting process by single abrasive grain at round deep grinding.The statement of basic materials. Before beginning cutting process of abrasive grains a fairly long slip sliding of the cutting edge in the place of contact. This sliding is followed by plastic deformation of metal which occurs without shaving removal. Using appropriate software equipment may create a 3D model of cutting process single abrasive grain and determine the cutting force on this grain of abrasive tools.Conclusions. The first was created 3D model of cutting process a single abrasive grain during at round deep grinding and considered cutting force in the relevant points of abrasive grain. This model can be used for a research of cutting process by an end face, a transitional edge and the periphery of a grinding circle.

ДЕФОРМАЦИОННЫЙ РЕЛЬЕФ – ОТРАЖЕНИЕ ВНУТРЕННИХ ПРОЦЕССОВ ПРИ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ МОНОКРИСТАЛЛОВ НИКЕЛЯ

In spite of the fact that the deformation relief is the case study of the scientists of physics of metals for several decades, there are a large number of issues associated with the mechanisms and the objective of its formation. Moreover, the development of the instrumental base allows carrying out the detailed experimental studies at the better than ever level. One of the most relevant issues during plastic deformation of metals is the destruction of a crystal that is caused by the formation of areas with the high allocation of deformation. Basing on the deformation relief, many researchers analyze the state of a material from the point of view of preserving the crystal integrity. This study is aimed to determine the methods of formation of structural elements of deformation relief of various types (slip traces, meso- and macrobands, and corrugated surface) and to identify the role of each type of relief in the increase and decrease of local deformation. The authors carried out the experimental study on the compressive deformation of FCC nickel single crystals of different crystallographic orientation and the further study of the deformation relief. To analyze the relief, the authors used optical microscopy, confocal laser scanning microscopy, and the reflection electron diffraction method; to process the results, the statistical and fractal analysis was used. The study determined the methods of formation of structural elements of the deformational relief (slip traces, meso- and macrobands, and corrugated surface), specified their common and distinctive features. The paper sets the objective of self-organization of traces of slip into the relief elements of a larger scale level (band of slip tracks, meso- and macrobands) and identifies the methods of self-organization of slip traces at the micro- and mesolevel.

Evaluation of metal plastic deformation using radio‐frequency reflection features

Plastic deformation may occur in metal structure during the manufacturing and service process which will affect the service life of equipment. This study proposes a radio-frequency method resulting from electromagnetic properties variation for metal plastic deformation monitoring. There is a clearly correlation between the macroscopic electromagnetic properties and the plastic deformation of materials. The energy distribution of radio-frequency varies obviously due to electromagnetic properties variation according to the simulation results. Meanwhile, the reflection features are mainly affected by permeability and electric conductivity of the material. Experiments have been conducted to verify simulation results. The results of the experiments indicate that the reflected radio-frequency signal strength decreases with progressive plastic deformation in metal, which has been in conformity with simulations.

Existence of Localizing Solutions in Plasticity via Geometric Singular Perturbation Theory

Shear bands are narrow zones of intense shear observed during plastic deformations of metals at high strain rates. Because they often precede rupture, their study attracted attention as a mechanism of material failure. Here, we aim to reveal the onset of localization into shear bands using a simple model from viscoplasticity. We exploit the properties of scale invariance of the model to construct a family of self-similar focusing solutions that capture the nonlinear mechanism of shear band formation. The key step is to desingularize a reduced system of singular ordinary differential equations and reduce the problem into the construction of a heteroclinic orbit for an autonomous system of three first-order equations. The associated dynamical system has fast and slow time scales, forming a singularly perturbed problem. Geometric singular perturbation theory is applied to this problem to achieve an invariant surface. The flow on the invariant surface is analyzed via the Poincaré--Bendixson theorem to construct a heteroclinic orbit.

Theoretical FLD Prediction Based on M-K Model using Gurson's Plastic Potential Function for Steel Sheets

The aim of this study is to develop a new analytical method for predicting localized necking in the plastic deformation of sheet metals with internal cavitation. This method is based on the model of Marciniak and Kuczynski (M-K) as well as Gurson's plastic potential function. Stowell's model was used to illustrate void growth behavior during plastic deformation. In order to examine the effect of the voids on localized necking, the void volume fraction was considered in the imperfection factor and the plastic volume constancy principle. The nonlinear system of equations was solved with the modified Newton-Raphson method with globally convergence procedure, using MATLAB software. This new analytical method (M-K-Gurson) was used to predict the forming limit diagram (FLD) of different steel alloy sheets and the results were compared with those of other researchers. The results showed that the M-KGurson method predicted the FLD with good agreement.

MODELING THE DEVELOPMENT OF LARGE PLASTIC DEFORMATIONS IN A ROTATING DISK IN THE FIDESYS PROGRAM

The paper presents a finite element analysis of the localization of plastic deformations in the region of fracture of the model disk during rotation. At a certain angular velocity of rotation of the disk, an ejectionis observed experimentally. This effect occurs when the material stability is lost, is analogous to the known neckingin the specimen tension. In view of the finiteness of the observed experimental displacements and for the detection of the tighteningeffect in a numerical experiment, the equilibrium equations are integrated taking into account the finite deformations. The model calculation was carried out in a quasi-static setting with a step-by-step increase in the rotational speed. The plastic behavior of the metal alloy of the disk material is described according to the Huber-Mises limit surface. The material parameters used in the calculation are determined from the experimental tension curve of the sample. Elasto-plastic governing relations are used in finite deformations with a multiplicative decomposition of the deformation gradient into the elastic and plastic components. In fully plastic deformation of metals, due to the constancy of the first invariant of plastic deformations, the process of deformation is close to isochoric. In such cases, linear isoparametric finite elements show the effect of “volumetric locking which distorts the numerical result. Therefore, in calculations we use twenty-node volume finite elements of the second order, which have no specific feature. The calculations were carried out on the IMERS-Fidesis hardware-software complex. The energy and noise efficiency of a cluster in distributed computations is studied. The article concludes by comparing the numerical results with the experimental data and the energy efficiency level of the cluster.

Development of Finite-Element Modeling of Processing Metals Under Pressure Using Variational Principles of Mechanics Proposed by V. L. Kolmogorov

On the basis of the variational principle of metal virtual stresses and flow rates in high plastic metal deformation with complex processes of hardening and softening, we propose an iterative procedure using finite-element simulation of processing metals under pressure, taking into account the heterogeneity of mechanical properties in the volume of the deformation zone. The proposed method of solving the boundary value problem increases the computational precision for the workpiece shape deformation, satisfying the condition of ideal plasticity for the material particles at any arbitrary point in time, as well as improving the accuracy of determining the field of the average normal stress in the deformation zone.

Experimental study on transverse displacement of the metal during cold thin strip rolling

Abstract The theory of metal plastic deformation is an important part of the strip shape control theories. In order to control the shape and gauge accurately during cold thin strip rolling, the mechanism of the lateral flow of the metal must be revealed clearly. In this research, the transverse displacement of thin strip was studied by the grid method. Grids with line thickness of 10 μm and clear boundary were successfully manufactured on the surface of 304-stainless steels using lithography technology. Then, the effects of reduction, front and back tension, and taper angle of the first intermediate roll on the lateral flow of the metal were studied. The calculations of strip shape were compared with the measured results. It is shown that the effect of the transverse displacement on the strip shape can’t be neglected.

Study on Magnetic Memory Signal Character of Metal Plastic Deformation Based on OLCAO Algorithm

Study on Magnetic Memory Signal Character of Metal Plastic Deformation Based on OLCAO Algorithm

Effect of RE2O3 (RE = La, Ce) fluxes on A-TIG welding of Ti6Al4V

The effect of RE2O3 (RE = La, Ce) fluxes on penetration and microstructure in 3-mm-thick Ti6Al4V weld joints made by activated flux tungsten inert gas (A-TIG) welding process was investigated. The mechanism of penetration increase was discussed. Microstructure characterization in the fusion zone region was also observed under optical microscope. It is shown that RE2O3 fluxes can effectively increase weld penetration of Ti6Al4V for applying a thin layer paste when welding. The mechanism would comply with changing the Marangoni convection in the weld pool, rather than the arc. A-TIG welding with RE2O3 fluxes can slightly refine the width of β-Ti grains. Phase constitution shows single α′-Ti in solidification structure in both two welding process. There are no significant changes in weld metal microstructure with and without Re2O3 fluxes. Microhardness distribution of weld seam indicates that the appearance of RE2O3 has not affected the metal plastic deformation capacity.

Investigation of the effect of tooling parameters on weld formation in resistance flash welding

Special features of the process of resistance flash welding of ring-shaped components made of large-section pressed aluminium profiles are investigated. The effect of different parameters on the process of plastic deformation of metal during upsetting is studied. Recommendations are given for decreasing the number of defects in welded joints and increasing the wear resistance of the tooling.

On the Taylor principles for plastic deformation of polycrystalline metals

Grain orientation evolutions and texture formation based on the Taylor principles offer important references to reveal crystallographic mechanisms of deformation behaviors. Strain equilibrium between grains is achieved in Taylor theory, however, stress equilibrium has not yet been reached perfectly even in many modifications of the theory though the textures predicted become very close to those of experimental observations. A reaction stress model is proposed, in which mechanical interactions between grains are considered in details and grain deformation is conducted by penetrating and non-penetrating slips. The new model offers both of the stress and strain equilibria and predicts the same textures indicated by Taylor theory. The rolling texture simulated comes very close to the experimental observations if the relaxation effect of the non-penetrating slips on the up-limits of reaction stresses is included. The reaction stress principles open theoretically a new field of vision to consider deformation behaviors of polycrystalline materials, whereas the Taylor principles become unnecessary both theoretically and practically. Detailed engineering conditions have to be included in simulations if the deformation textures of industrial products should be predicted.

Nanovoid growth in BCC α-Fe: influences of initial void geometry

The growth of voids has a great impact on the mechanical properties of ductile materials by altering their microstructures. Exploring the process of void growth at the nanoscale helps in understanding the dynamic fracture of metals. While some very recent studies looked into the effects of the initial geometry of an elliptic void on the plastic deformation of face-centered cubic metals, a systematic study of the initial void ellipticity and orientation angle in body-centered cubic (BCC) metals is still lacking. In this paper, large scale molecular dynamics simulations with millions of atoms are conducted, investigating the void growth process during tensile loading of metallic thin films in BCC α-Fe. Our simulations elucidate the intertwined influences on void growth of the initial ellipticity and initial orientation angle of the void. It is shown that these two geometric parameters play an important role in the stress–strain response, the nucleation and evolution of defects, as well as the void size/outline evolution in α-Fe thin films. Results suggest that, together with void size, different initial void geometries should be taken into account if a continuum model is to be applied to nanoscale damage progression.

Measurement Methods of Friction Coefficient for Plastic Deformation of Metals under High Strain Rate

This paper introduces some representative measurement methods of friction coefficient for plastic deformation of metals under high strain rate both in our country and abroad in recent years, and mainly includes several measurement methods of friction coefficient based on the upsetting, forging, extrusion and tube hydroforming. Furthermore, the working principles, applicable occasions and technical characteristics of these methods are explained, and the development of these methods in the future are presented.

Investigation on Strength Model of Metal Plastic Deformation under High Strain Rate

In the fields of explosive forming, aerospace industry, military industry etc. metallic materials will withstand a high strain rate in the process of deformation. It is very instructive to put forward an accurate strength model which can be used to describe the process of deformation reasonably. In this paper, several strength models are introduced which are mainly based on the macroscopic mechanical behavior of materials and the mechanisms of deformation of material, and their sphere of application, shortcomings and advantages were introduced and reviewed.