1,721,189 research outputs found
Prediction of wrinkling initiation in sheet metal forming processes
No full textThe initiation and growth of wrinkles are influenced by many factors such as stress ratios, the mechanical properties of the sheet material, the geometry of the workpiece, contact condition, etc. It is difficult to analyze wrinkling initiation and growth while considering ail the factors because the effects of the factors are very complex and studies of wrinkling behavior may show a wide scattering of data even for small deviations in factors. The finite element analyses of wrinkling initiation and growth in sheet metal forming process provide detailed information about the wrinkling behavior of sheet metal The direct analysis of wrinkling initiation and growth, however, brings about a little difficulty in complex industrial problems because it requires large memory size and long computation time. From the industrial viewpoint of tooling design, therefore, readily available information on the possibility and location of wrinkling is sometimes more preferable to detailed and time-consuming analysis results. In the present study, in order to give such readily available information on wrinkling initiation, the wrinkling factor, which shows the locations and relative possibility of wrinkling initiation, is proposed as a convenient tool of relative wrinkling estimation based on the energy criterion. The rehability of the wrinkling factor is verified through the buckling analyses of sheet strips. The location and relative possibility of wrinkling initiation are predicted by calculating the wrinkling factor in various sheet metal forming processes such as cylindrical cup deep drawing, spherical cup deep drawing, and elliptical cup deep drawing. Finally, the wrinkling factor proposed in the present study is also implemented in the prediction of wrinkling in the door inner stamping process. For verification of the calculated wrinkling factor, detailed zone analyses with fine meshes are carried out for the regions where wrinkling is predicted
Study on resistance welding of metallic sandwich panel
No full textInner structured and bonded ( ISB) panel, a type of metallic sandwich panel, consists of two thin skin plates bonded to a micropatterned inner structure. It has an overall thickness of 1-3 mm and attractive properties, such as ultralight weight, high efficiency in stiffness to weight and strength to weight ratios. In this paper, a new joining process using resistance welding is developed for joining ISB panels. Electrodes with curved surface are applied to join the two skin plates and micropatterned inner structure, while two stoppers are used to keep a gap between the electrodes during welding. Owing to this gap, the inner structure shape is maintained without damage. Current, welding time and electrode gap were selected as the process parameters. This process is simpler and more suitable for mass production than previous processes for joining the panel. Appropriate welding conditions were studied by measuring the tensile load with respect to variations in welding time and electrode gap
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation into hydromechanical reverse redrawing assisted by separate radial pressure - process development and theoretical verification
No full textHigh-quality cups with a deep drawing ratio of more than four cannot be simply drawn by conventional drawing and redrawing. A special technology is required to form cups of a high deep drawing ratio. In the present study, after the conventional mechanical deep drawing process, subsequent hydromechanical reverse redrawing with controlled radial pressure has been developed. In order to increase the deep drawing ratio by mon than four, the radial pressure is controlled independently of the chamber pressure and thus an optimum forming condition can be determined by varying the radial pressure. The process has been verified by a rigid-plastic finite element (FE) analysis considering all the external force boundary conditions induced by the hydrostatic pressure. The pressure distribution on the sheet is calculated numerically from the simplified Navier-Stokes equation. Through the experiment and the FE analysis, it has been shown that hydromechanical reverse redrawing assisted by separate radial pressure, developed in the present study, helps to increase the drawability of cylindrical cups, and thus it is useful when forming long cups
The effect of plastic anisotropy on compressive instability in sheet metal forming
No full textThe wrinkling behavior of a thin sheet with perfect geometry is associated with compressive instability. The compressive instability is influenced by many factors such as stress state, mechanical properties of the sheet material, geometry of the body, contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is difficult considering all the factors because the effects of the factors are very complex and the instability behavior may show a wide variation for a small deviation of the factors. In this study, the bifurcation theory is introduced for the finite element analysis of puckering initiation and growth of a thin sheet with perfect geometry. All the above mentioned factors are conveniently considered by the finite-element method. The instability limit is found by the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme proposed by Riks, The finite-element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite-element analysis is carried out using the continuum-based resultant shell elements considering the anisotropy of the sheet metal. In order to investigate the effect of plastic anisotropy on the compressive instability, a square plate that is subjected to compression in one direction and tension in the other direction is analyzed by the above-mentioned finite-element analysis. The critical stress ratios above which buckling does not take place are found for various plastic anisotropic modeling methods and discussed. Finally, the effect of plastic anisotropy on the puckering behavior in the spherical cup deep drawing process is investigated. From the results of the finite-element analysis, it is shown that puckering behavior of sheet metal is largely affected by plastic anisotropy. (C) 2000 Elsevier Science Ltd. All rights reserved
An analysis of springback with bifurcation behavior and its application to die design
No full textSpringback in sheet metal product makes difficulties in die design because small strain causes large displacement. Especially for the sheet metal product having small geometric constraints, springback displacement may become severe. After stamping of outer case of washing machine, a large amount of springback is observed with small geometric constraints. Also, a bifurcation takes place during the springback analysis. Figure 2 shows the springback shape of the outer case of washing machine. In order to reduce the springback displacement, the effect of tooling dimensions on bifurcation behaviour and springback displacement are investigated
Investigation into wrinkling behavior in the elliptical cup deep drawing process by finite element analysis using bifurcation theory
No full textThe initiation and growth of wrinkles in sheet metal forming processes are influenced by many factors such as the stress state, the mechanical properties of the sheet material, the geometry of the body, and the contact conditions. It is difficult to analyze wrinkling initiation and growth considering these factors, because the effects of the factors are very complex and the wrinkling behavior may show a wide variation for small deviation of the, factors. In this study, bifurcation theory: is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. The wrinkling initiation is determined by checking the determinant of the stiffness matrix at each iteration and the wrinkling behavior is analyzed by successive iteration with the perturbed guess along the eigenvector. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using continuum-based resultant shell elements. The initiation and growth of wrinkling in the elliptical cup deep drawing process are analyzed by the proposed algorithm. The effect of the aspect ratio of a punch on the wrinkling behavior in the elliptical cup deep drawing process is investigated. (C) 2001 Elsevier Science B.V. All rights reserved
Finite element analysis of the wrinkling behavior in the elliptical cup deep drawing process
No full textWrinkling is one of major defects in sheet metal forming processes. Wrinkling initiation and growth is influenced by many factors such as mechanical properties of the sheet material, geometry of the sheet and contact conditions. The analysis of wrinkling in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show wide variations even for small deviations of the factors. In this work, the bifurcation theory is introduced for the finite element analysis of the instability behavior of a thin sheet with initially sound geometry and property. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. The initiation and growth of wrinkling in the elliptical cup deep drawing process are analyzed by the proposed algorithm. Through the finite element analysis of flange wrinkling in the elliptical cup deep drawing process, the mechanism of wrinkling initiation is investigated and the effect of the tool and blank shape on wrinkling behavior is investigated
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