Papers by Keyword: Plasticity

Abstract: A mathematical model of the shaping processes of structurally inhomogeneous porous materials has been developed. Generalized relations of the theory of elastic-visco-plasticity for dispersed materials are used for rigid-plastic and elastic-plastic of the material solid phase models. The procedures of projection-grid methods for solving boundary value problems were used. It has been performed in form of step by step calculation. The special algorithm is used to consider some types of plastic deformation, including rigid plastic behaviour, elastic – plastic case and some other rheological behaviour of matrix materials. The algorithm procedures were realized in a form of numerical model. Some elements of this model were implemented in modern finite element software versions. The results of calculations, aimed at manufacturing of main and responsible parts are presented in article.

Abstract: At temperatures of 290 K and 77 K, the phase composition and mechanical properties ofnonequiatomic medium-entropy (MEA) alloys Fe40Mn40Co10Cr10 and Fe50Mn30Co10Cr10 werecompared in the coarse-grained (CG) and nanostructured (NS) states, in which additionaldeformation mechanisms are activated under load: phase transformations in the MEAFe50Mn30Co10Cr10 (MEA TRIP) and twinning in the MEA Fe40Mn40Co10Cr10 alloy (MEA TWIP). Itis shown that in the NS state in both alloys, in contrast to the CG state, a complete phase transitionfrom the fcc to the hcp phase is observed, the content of which weakly depends on the temperatureand the number of torsion revolutions during high-pressure torsion (HPT). The transition from theCG to the NS state leads to an increase in the microhardness (in the NS MEA TWIP by 3.7 and inthe NS MEA TRIP by 2.25). In the CG state, a thermally activated character of plastic deformationis observed for both alloys in the temperature range of 290 – 77 K. In the NS state, MEA TWIPremains plastic under active compression deformation at 290 K and 77 K, whereas in NS MEATRIP under similar conditions, macroscopic plasticity is absent. Tensile deformation up to 50 % at30 K in the CG state for both alloys leads to a significant decrease in the absolute values of Young'smodulus over the entire temperature range.

Abstract: Different fines of rice husk ash (RHA) are typically used as a binder for soil stabilization. This study aims to assess the performance of RHA fines as a binder with lime in the improvement of plasticity and compaction characteristics of stabilized soil. Consistency limits, particle sieve analysis, and compaction tests were conducted on the natural lateritic soil, while consistency limits and compaction tests were conducted on the stabilized lateritic soil. The tests conformed to BS 1377 (1990). The chemical compositions of the RHA were assessed. Lateritic soil samples were mixed with lime in the proportions of 2, 4, 6, 8, and 10% by weight of dry soil. Plasticity Index (PI) was used as the determinant of optimum performance of lime-stabilized lateritic soil and this was obtained at 8% of lime addition. Thereafter, binder ratios (Lime: RHA) of 0:8, 2:6, 4:4, 6:2, and 8:0 were employed in the blending of the lateritic soil. The Plasticity Index (PI) of the stabilized soil were generally lowered to 7.82%, 21.36%, 18.97%, 19.71%, 15.03% when stabilized with BR2:6₇₅μm, BR4:4₇₅μm, BR6:2₇₅μm, BR2:6₃₀₀μm and BR6:2₃₀₀μm respectively. All binder ratios containing both lime and RHA size of 75 μm reduced the PI. Also, the effect of all binder ratios containing both lime and all RHA sizes showed increment in the Maximum Dry Density (MDD). Similarly, soil stabilized with BR2:6₁₅₀μm, BR4:4₇₅μm, BR4:4₁₅₀μm, BR4:4₃₀₀μm, BR6:2₁₅₀μm and BR6:2₃₀₀μm offered a lowered OMC. 75μm RHA and BR4:4₇₅μm had the potential to improve Lime-RHA stabilized lateritic soil mixture especially for road application.

Abstract: In this paper, the possibility of characterizing the thermomechanical behavior of metals using the virtual fields method (VFM) and suitable specimens with heterogeneous strain and temperature fields was demonstrated using simulated experiments. The used geometry is a double-notched tensile test with a Gaussian distribution of temperature over the surface. The chosen constitutive model is the Johnson-Cook hardening law coupled with the Hill48 anisotropic yield criterion. First the VFM strategy and the simulated experiments are described. Then the results are presented showing three case studies, (i) only the effect of the temperature is identified, (ii) the whole set of constitutive parameters is identified at the same time, (iii) a two-step identification is performed. The potentiality of the method as well as the main problems are discussed extensively.

Abstract: In physics and mechanics, plasticity is defined as the ability of a material to undergo irreversible (plastic) deformation. Conventionally, the plastic strain at fracture in tensile tests, δ, has been used as a quantitative measure of plasticity. However, δ does not follow the scientific definition of plasticity. The influence of structural factors, temperature and strain rate on the value of δ were not elaborated over many decades. This lack of well-founded quantitative characteristic hindered efforts to control and to increase plasticity of materials. The plasticity characteristic that corresponds to the scientific definition of this quantity, δ* = plastic strain ε_р/ total strain ε_t, has been successfully used by many scientists to determine plasticity δ* by indentation. In the present work, the technique for the determination of the plasticity characteristic δ* during mechanical compression and tensile tests of metallic alloys has been introduced for the first time. In this case, δ* is determined more precisely than by indentation, and the second deformation curve δ*=f*(ε_t) is constructed. A theory of the influence of structural factors (grain size, dislocation density, disperse particles of the second phase) on the plasticity characteristic δ* has now been developed, making it possible to estimate the influence of the indicated factors on δ* and to design alloys with an optimal combination of strength and plasticity. The discovered correlation of the values of δ* and δ for steels and for aluminum alloys allows us to use the developed theory to calculate the influence of the structural factors on d for these materials as well.

Abstract: The evolution of the steel structure under thermocyclic action is considered. The possibility of increasing the complex of mechanical properties of steels after thermocyclic treatment is shown.

Abstract: The scheme of non-equal channel angular pressing (non-ECAP) of a magnesium billet has been analyzed. The modeling was performed by DEFORM-2D software. A high level of strain is shown to be achieved during non-ECAP. It leads to more homogenous structure refinement of magnesium and plasticity improvement that could favorably affect the subsequent deformation of a Mg-strip by cold rolling. At non-ECAP-process, the upper part of the strip is noted to be hardened more than the lower one. The lower part is supposed to be formed by extensional strain mainly, meanwhile for the upper one, the prime mechanism is likely to be shear strain. Based on hardness measurement of the samples cut from the obtained Mg-strip, conclusions have been made about the influence of the accumulated strain during non-ECAP on the strength properties of the strip.

Abstract: The authors present the results of evaluating the distribution of plastic properties on the height of a log ingot with the diameter of 145 mm, obtained by means of semi-continuous casting, from the aluminum alloy AD31. The authors study semi-continuous alloys of three manufacturers. One part of ingots was obtained with the use of only primary aluminum, secondary raw materials and secondary raw materials with the addition of primary aluminum. With the purpose of stabilizing the process of presswork the authors define the values of yield stress in the ingot lower and upper parts and study its microstructure. The research was conducted for the ingots without thermal treatment after accelerated homogenization. It is shown that the ingots, produced with the use of primary aluminum only, have less scattered plastic properties in terms of the height. That is why, for the case of press-working the items with thin components, it is reasonable to use the ingots from primary aluminum.

Abstract: One of the problems of studying the rheological properties and plasticity of metals and alloys from the results of tensile tests of cylindrical specimens is the need to determine the stress triaxiality value, which depends on the shape and size of the neck formed. An analytical description of the neck profile makes it possible to increase the accuracy of experimental measurements of its dimensions, in particular, the radius of curvature in the smallest cross-section of specimen. This paper is devoted to searching a universal neck profile equation that allows calculating the radius of neck curvature regardless of the nature of the material hardening curve and the stage of strain localization. The exact surface equation is established and its accuracy is estimated for hardening and softening material.

Abstract: Soft marine clay soil is characterized with highly compressible behavior, in which associated with poor bearing capacity and low in shear resistance. Soil improvement works are carried out to reduce the soil failure and destruction to the superstructure. Various techniques available for soil stabilization including the use of admixture to improve the engineering properties of the problematic soil. This paper aims to report on the use of waste steel dust retrieved from the medication supply industry as soil stabilization agent. Several series of Atterberg limit test and Unconfined Compressive Test were carried out to foresee the potential use of the waste steel dust for the purpose of civil engineering applications. The significant findings from this study is evident that the waste steel dust ranges from 5% to 15% did not able to serve as soil stabilization agent. It can reduce the plastic behavior of the soil sample; however, it also caused the strength of the soil declined. In comparison with previous studies, the presence of activated agent could possibly enhance the performance of waste steel dust as an alternative treatment agent to soil improvement works. The use of activated agent is to serve as pozzolanic materials to create cementitious bonding in between the soil interparticles matrix.