|عنوان فارسی مقاله:||یک تکنیک جدید تغییر شکل پلاستیک شدید بر اساس برش مطلق (خالص)|
|عنوان انگلیسی مقاله:||A new severe plastic deformation technique based on pure shear|
|رشته های مرتبط:||مهندسی مواد، شکل دادن فلزات، متالوژی صنعتی، مهندسی پلیمر و مهندسی مواد مرکب|
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|توضیحات||ترجمه این مقاله تا صفحه 16 انجام شده است.|
|نشریه||الزویر – Elsevier|
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Pure shear extrusion (PSE) is introduced as a new severe plastic deformation (SPD) technique. The new SPD process provides the possibility of severely deform metals and alloys in a combined mode of pure and simple shear with the opportunity of changing the ratio of pure to simple shear. The process is fundamentally based on what in the literature known as pure shear, in which, a square deforms to a rhombic alongside its diagonals. The deformation zone in PSE process is composed of two sections, i.e., upper and lower deformation zones. In the upper deformation zone, an initial square cross section of a sample gradually changes shape to a rhombic while keeping a constant cross sectional area. The constancy of the cross sectional area certifies no velocity change and therefore, no strain in the direction perpendicular to the cross section of the sample leading to a plane-strain deformation. In the lower deformation zone, the sample gradually gains its initial geometry back by an inverse deformation regarding the upper zone. The constancy of cross section of the sample provides the possibility of repeating the deformation process which makes the PSE as a new candidate for SPD processing of metals and alloys. Effective strain is estimated using a geometrical approach. AA1050 aluminum alloy is deformed up to two passes using PSE in order to verify the feasibility of SPD processing by PSE.
1 Introduction In recent years, nanostructured metals and alloys have gained significant interest in academic research due to their unique physical and mechanical properties [1-5]. Among every production technique of bulk nanostructured materials (BNM), severe plastic deformation has shown remarkable capacities for in different metals and alloys [6-9]. SPD techniques, e.g., equal channel angular extrusion (ECAE) [10-12], high pressure torsion (HPT) [12-14], twist extrusion (TE)  accumulative roll bonding (ARB) , repetitive corrugation and straightening (RCS) , multi-directional forging (MDF) , cyclic expansion extrusion (CEE)  and recently developed simple shear extrusion (SSE) [20, 21] have been developed towards producing BNM  in different metals and alloys [6-9]. Despite of having different technological characteristics, these processes are normally used for similar purposes to produce BNM, however, the deformation modes rang from pure shear to simple shear and as well, from monotonic loading to cyclic and cross loading. It has been shown by Segal  that the deformation state, i.e., simple or pure shear, causes significant differences in the response of the material towards grain refinement. It is found  that application of simple shear provides a short stage of continuous evolution, early localization and cross loading resulting in a considerable grain refinement while pure shear may not play a similar role. However, it should be mentioned that the process which was used for applying pure shear in that study  was rolling which obviously does not provide the capacity of keeping the cross section of the material constant. Therefore, it is not surprising if a long stage of continuous evolution, planar high angle grain boundaries and monotonic loading with effective reduction of material cross section are among the findings. One may add that rolling is associated with redundant work which results in an inhomogeneous deformation in addition to not maintaining a constant cross section and therefore, may not be a most suitable process for SPD. The lack of the presence of a SPD process providing the possibility of applying homogeneous pure shear deformation and returning the initial shape of the sample has made it quite difficult for investigating the effect of deformation mode, i.e., simple and pure shear, on microstructural evolution. The deformation mode in most of the wellknown SPD processes, e.g., ECAE, HPT, TE and SSE, is simple shear or most significantly governed by simple shear . The rest of SPD processes, e.g., ARB, RCS, MDF and CEE which act totally or partly in pure shear, are based on traditional metal forming processes such as rolling, extrusion and forging [16-19]. These processes are inherently involved with redundant work  which causes an inhomogeneous deformation and consequently a nonhomogeneous microstructure and mechanical properties throughout the processed sample. To the knowledge of the author, no SPD technique exists for applying strain in non-simple shear or in pure shear deformation state without redundant work.Recently, pure shear extrusion (PSE) is introduced as a new SPD technique . In this article, the process is thoroughly investigated. The process defines the possibility of applying combined deformation state of pure and simple shear without redundant work and strain inhomogeneity. It is claimed that PSE is a single SPD process by which it is possible to apply a homogeneous combined pure and simple shear deformation on materials. The process introduced in this study provides the possibility of a fair comparison between the efficiency in grain refinement by applying simple and pure shear which may be the subject of study in future research activities. The possibility of severe deformation of materials with different ratios of pure and simple shear may result in unique applications for this process.