The subject of the research is the process of helical rolling of balls with a diameter of 15 to 125 mm for grinding mills. Analytical estimates of the equivalent strain and the rate of equivalent ...strain averaged within the volume of the metal were obtained. A simple formal model of equivalent strain distribution within the ball in the direction of the rolling axis is also proposed. The proposed solutions predict that in the working ranges of the rolling parameters the value of the volume-averaged strain can vary from about 0.6 to 5, meanwhile in the jumper area the equivalent strain is two orders of magnitude higher than in the axial zone. It is shown that the principal influence on the magnitude of strain is caused by ovalization of the workpiece during rolling, which leads to multiple repeated deformation of the same volumes of metal when the workpiece rotates. As an example, the use of obtained estimates to calculate the strain, strain rate, flow stress, force and rolling torque under the conditions of the real experiment performed by other authors is shown. The proposed models allow solving engineering problems of certain classes (for example, calculation of energy-force parameters) without using FEM software packages and are recommended for optimization and real-time control of the helical rolling of balls.
Structural patterns found in living organisms have long been inspiring biomimetic materials design. Here, it is suggested that a rich palette of patterns occurring in inanimate Nature, and especially ...in the Earth's lithosphere, could be not less inspirational for design of novel architectured materials. This materials design paradigm is referred to as lithomimetics and it is demonstrated that some of the patterns found in the lithosphere can be emulated by established processes of severe plastic deformation. This opens up interesting avenues for materials design in which potentially promising structural patterns are borrowed from the lithosphere's repository. The key aim here is to promulgate the “lithomimetics” paradigm as a promising approach to developing novel architectured materials.
A novel lithomimetic approach is proposed, which entails mimicking structures and processes occurring in the Earth's lithosphere to produce man‐made advanced materials. Severe plastic deformation is considered as a viable vehicle for that.
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•Analytical model for bimodal harmonic-structure (HS) material rheology is built.•The model allows calculating back-stress hardening from a single uniaxial test.•Strain of ...coarse-grain phase is proportional to the strain of a whole specimen.•Strain of ultrafine-grain phase is proportional to the square of whole specimen strain.
Heterogenous bimodal harmonic-structure (HS) materials are interesting because of excellent structural efficiency. In this work, we present a simple yet powerful analytical model allowing to evaluate strain partitioning between coarse- and ultrafine- grain (CG and UFG, respectively) structure components in HS materials and to estimate the magnitude of back-stress forming at their interphases. The analysis of experimental results on pure nickel using this model shows that HS promotes a favourable strain partitioning between CG and UFG components and the build-up of back-stress in the vicinity of their interfaces allowing the material performance to exceed expectations from the rule of mixtures.
The article presents a theoretical study of the regimes of high-pressure torsion (HPT) for which slippage of the deforming material on the interfaces with anvils is possible. The approach taken is a ...generalisation of the currently accepted view of the HPT process. It enables a rational explanation of its salient features and the effects observed experimentally. These include a lag in the rotation angle of the specimen behind that of the anvils, an outflow of the material from the deformation zone, enhancement in gripping the specimen with anvils with increasing axial pressure, etc. A generalised condition for gripping the specimen with anvils, providing a basis for an analytical investigation of the HPT deformation at a qualitative level, is established. The results of the analytical modelling are supported by finite-element calculations. It is shown that for friction stress below the shear stress of the specimen material (i.e., for the friction factor m < 1), plastic deformation is furnished by non-shear flows, which expands the range of possible process regimes. The potential of these flow modes is impressive, which is reflected in the second meaning of the word “gripping” in the title of the article. Non-shear flows manifest themselves in the spreading of the material over the anvil surfaces whose cessation signifies the end of deformation and the beginning of slippage of the specimen as a whole. The model shows that for m < 1 such a finale is inevitable at any axial pressure. It predicts, however, that the highest achievable strain is increased when the axial pressure is raised in the course of the HPT process. Unlimited deformation of the specimen is only possible for m = 1, when slippage of the deforming material relative to the anvils is suppressed.
To verify the mathematical model of the water-jet cooling of steel plates developed by the authors, previously performed experimental studies of the temperature of the test plates in a ...roller-quenching machine (RQM) were used. The calculated temperature change in the metal as it moved in the RQM was compared with the readings of thermocouples installed at the center of the test plate and near its surface. The basis of the model is the dependence of the temperatures of the film, transition and nucleate boiling regimes on the thickness of the oxide scale layer on the cooled surface. It was found that the model correctly accounts for the oxide scale on the sheet surface, the flow rates and combinations of the RQM banks used, the water temperature, and other factors. For all tests, the calculated metal temperature corresponded well with the measured one. In the experiments with interrupted cooling, the calculated temperature plots repeated the characteristic changes in the experimental curves. The main uncertainty in the modeling of cooling over a wide temperature range can be attributed to the random nature of changes in the oxide scale thickness during water cooling. In this regard, the estimated thickness of the oxide scale layer should be considered the main parameter for adapting the sheet temperature-control process. The data obtained confirm the possibility of effective application of the model in the ACS of industrial TMCP (Thermo-Mechanical Controlled Process) systems.
•Mechanical mixing in the solid state, namely stirring by HPT, is considered.•HPT acts as a mixer enabling stirring of metals in the solid state.•A new stirring efficacy index based on the Gibbs ...parameter is introduced.•A useful tool for characterisation of the stirring efficiency is provided.
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A severe plastic deformation process of High-Pressure Torsion (HPT) is presented as a viable tool for mixing of metals in the solid state. At the billet or specimen scale, mixing occurs due to chaotic mass transfer (stirring) which sets in at a certain stage of HPT of layered assemblies of metals. To characterise this process quantitatively, a stirring efficacy index is introduced. It is based on a parameter that characterises the uniformity of the concentration of the constituents of a sample in the bulk in a quantitative way. The methodology is illustrated by considering the process of high-pressure torsion of assemblages of alternating Ni and Al layers. It is shown that up to a threshold shear strain of 120, only a distortion of the layers takes place, while no mechanical mixing occurs. Rupturing of the layers at larger shear strains leads to an increase in the degree of uniformity of the distribution of Al and Ni. Principal differences in stirring of solid metals and liquids are elucidated.
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