Papers by Keyword: Shear Strain

Abstract: Torsion tests allow to study the rheological properties of various materials, including properties in hot state, as well as they allow to conduct physical simulations of real material forming processes, including processes of intensive and alternating deformation. However, it is often a question what size the specimen should have to perform torsion test accurately. The article aims to study the influence of cylindrical specimen size on the distribution of deformation during torsion test. For this purpose, computer simulation of the torsion testing process was performed. The influence of the relative length of the specimen gauge on the deviation of the actual values of the effective strain from the calculated values was quantified. It is shown that the error in the calculation of the effective strain, based on the values of the twist angle and the specimen gauge size, is of 4%. In order to verify the results obtained by computer simulation, the physical simulation was performed. It is shown that the distribution of deformation along the length of the specimen gauge is also significantly influenced by the accuracy of specimen manufacture, as well as the specimen material. In some cases, the error in the calculation of the effective strain, based on the values of the twist angle and the specimen gauge size, can reach more than 80%.

Abstract: Severe plastic deformation (SPD) methods are based on obtaining materials with a grain size of about 100 nm by means of large strain. The SPD processes provide conditions for non-monotonic deformation of the billetsб due to the redistribution of metal macro-flows during shear or alternating strain. Numerous studies have proved the possibility of obtaining high total strain degree for a single SPD cycle. Traditional metal forming processes, such as rolling, implement monotonic deformation behaviorб due to one directional metal flow. In the process of longitudinal rolling, a banded coarse-grained structure with uneven distribution of properties in the volume of the processed metal is observed. The idea of ensuring the SPD in the process of longitudinal rolling of steel sheets is promising. The idea can be realized by the development of deformation tools and modes, which provide redistribution of metal macro-flows not only in the longitudinal but also in the transverse directions of the deformation zone.

Abstract: High-ratio differential speed rolling (HRDSR) is a process of severe plastic deformation (SPD) that can be used to improve the structure and properties of aluminum alloys. The mechanism of SPD during HRDSR comes from its large equivalent strain, which is composed of compressive strain and additional shear strain. Plastic strain control of aluminum alloys are of importance for improvement of sheet microstructure and properties. This paper presents the results of the finite element simulation of shear strain during high-ratio differential speed rolling of aluminum alloy 5083. Four deformation routes UD, TD, RD and ND were simulated. By the route UD the sheet was not rotated between two deformation steps, while by the other three cases it was rotated with 180° degrees. By the route RD the rotation axis was the rolling direction, by the route TD the transverse direction and by the route ND the normal direction. The effect of rolls velocity ratio, friction coefficient and deformation route on the shear strain and the effective strain of Al 5083 was found. The results of investigation can be used to optimize the high-ratio differential speed rolling process to improve microstructure and mechanical properties of aluminum sheets.

Abstract: The mechanism of a severe plastic deformation during asymmetric rolling comes from its large equivalent strain, which is composed of a compressive strain and additional shear strain. Physical simulation of shear strain, which is similar to that occurring in asymmetric rolling processes, is very important for design of technology of ultrafine grain material production. Shear testing is complicated because a state of large shear is not easily achievable in most specimen geometries. Application of the shear-compression testing and specimen geometry to physical simulation of asymmetric rolling is discussed in the paper. The results of the numerical simulation and comparison of the stress-strain state during shear-compression testing and asymmetric sheet rolling are presented. The results of the investigation can be used to optimize the physical simulation of asymmetric rolling processes and for the design of the technology for ultrafine grain material production by means of a severe plastic deformation.

Abstract: The electron spin properties of semiconductors are of immense interest for their potential in spin-driven applications. Silicon is a perfect material for spintronics due to a long spin lifetime. Understanding the peculiarities of the subband structure and details of spin propagation in thin silicon films in the presence of the spin-orbit interaction is under scrutiny. We have performed simulations to obtain the surface roughness limited, acoustic-and optical-phonon mediated spin relaxation time, when the film is under shear strain. The degeneracy between the non-equivalent valleys is lifted by strain, which in turn subdues the dominating inter-valley relaxation components and increases the spin lifetime. We also elaborate on the injection orientation sensitive spin relaxation model and predict that the spin relaxation time is maximum, when the spin is injected in-plane, relative to the (001) oriented silicon film.

Abstract: The paper gives a mathematical model of grain evolution and dislocation density during asymmetric cold rolling of aluminum alloy 7075 in an SPD mode. Correlations between the effect of equivalent and shear strain on Al 7075 structure are obtained. An agreement of simulation results with experimental data is shown.

Abstract: Materials with ultrafine grain structure and unique physical and mechanical properties can be obtained by methods of severe plastic deformation, which include asymmetric rolling processes. Asymmetric rolling is a very effective way to create ultrafine grain structures in metals and alloys. Since the asymmetric rolling is a continuous process, it has great potential for industrial production of ultrafine grain structure sheets. Basic principles of asymmetric rolling are described in detail in scientific literature. Focus in the well-known works is on the possibility to control the structure of metal sheets. However the systematic data on the influence of the process parameters (e.g., ratio of rolls velocity mismatch, reduction per pass, friction and diameter of rolls), and the shear strain rate required to achieve a significant grain refinement in asymmetric rolling are lacking. The influence of ratio of rolls velocity mismatch, reduction per pass, friction and the rolls diameter on the distribution of shear strain through the sheet thickness in asymmetric rolling has been studied in DEFORM 2D. The results of the study will be useful for the research of evolution of ultrafine grain structure in asymmetric rolling.

Abstract: Severe plastic deformation is now recognized the most efficient way of producing ultrafine grained metals and alloys. At the present time a lot of severe plastic deformation methods have been proposed and developed. They differ in the deformation schemes. Unlike such severe plastic deformation methods as high pressure torsion and equal-channel angular pressing, rolling with the velocity asymmetry is a continuous process. It helps to solve the problem of the limited length of manufactured bars with semi ultrafine structure. Rolling process with roll velocity asymmetry generates high shear strain necessary for obtaining ultrafine structures of the processed material. A new process of asymmetric rolling of profiles in multi-roll passes has been developed. This process can be used for production of high-strength profiles such as circles, hexagons, wire rods, etc. Compression of the bar in multi-roll passes can be done not only from two, as usual, but from three or four sides. In case of a multi-crimped bar, a uniform compression scheme with large hydrostatic pressure is created in the deformation zone. It enhances the ductility of the material and allows increasing the strain intensity. Simulation in DEFORM 3D^TM proved that the process of asymmetric rolling in multi-roll calibers allows to obtain higher values of shear strain and strain effective.

Abstract: With the constant increasing of traffic flow and axle load, the early failure of semi-rigid base asphalt pavement is increasingly serious in China. The bad durability and short service life of pavement have become main obstacles in road construction development. Based on the experience of successful application, the early failure of semi-rigid base asphalt pavement is solved, and the service life of pavement is increased by using of the composite asphalt pavement. To solve the design problem of the composite asphalt pavement , its mechanical properties influence results of are obtained by the factors, such as shear strain, shear stress, compression strain on top of subgrade, etc, by a lot of calculation using Shell pavement design software. These provide theoretical basis for durable asphalt pavement design based on rut-resistance property.

Abstract: For understanding the distribution of plastic deformation induced by asymmetric rolling (ASR), multi-pass ASR and symmetric rolling (SR) experiments combined with the finite element simulation were used for high-strength aluminum alloy in the present study. The influence of reduction per-pass on the shear / effective strain distributions were studied via different ASR processes. By measuring the shear angle (θ, the angle between the reference mark before and after rolling) of rolled sheets, redundant shear strain and equivalent strain were calculated. It is shown that with equal total thickness reduction for ASR and SR, ASR can induce much more shear deformation through the thickness. By calculating the evolution of redundant shear strain and total equivalent strain for different ASR routines, it indicates that small pass reduction could be much favorable to the strain accumulation than that of the large pass reduction under a same total reduction in ASR process. Also, the influence of shear stress on the strain distribution and the through-thickness strain distribution were studied and evaluated with FEM analyses.