5,702 research outputs found
EXPERIMENTAL-VERIFICATION OF SUPERPLASTIC SHEET-METAL FORMING ANALYSIS BY THE FINITE-ELEMENT METHOD
No full textThe numerical result for superplastic sheet-forming simulation is compared with the experimental result to verify the validity of the finite-element code developed. The code calculates the optimum pressure cycle, the deformed shapes, and the distributions of the strain and strain-rate in the blow-forming processes. The calculation deals with the maximization of the strain-rate sensitivity, the protection of the localized deformation, the consistency of the desired strain-rate, and the control of the hour-glass mode and locking phenomenon. The comparison demonstrates the validity of the present algorithm and its results, especially in respect of the optimum pressure cycle, where there is only a slight difference between the two results
MODIFIED MEMBRANE FINITE-ELEMENT FORMULATION CONSIDERING BENDING EFFECTS IN SHEET-METAL FORMING ANALYSIS
No full textA modified membrane finite element formulation is derived to take the bending effect into account for sheet metal forming analysis. The algorithm developed is applied to a cylindrical and a square cup drawing problem to confirm its validity. The results show that the bending effect is appreciable in a class of deep drawing problems. It is also noted that the present algorithm enhances the convergence of a solution procedure and prevents numerical buckling
A tension split Hopkinson bar for investigating the dynamic behavior of sheet metals
No full textThe dynamic response of sheet metals at high strain rate is investigated with a tensile split Hopkinson bar test using plate type specimens. The tension split Hopkinson bar inevitably causes some errors in the strain at grips with the plate type specimens, since the grip and specimens disturb the one-dimensional wave propagation in bars. To validate the experiment, the level of error induced from the grips is estimated by comparing the waves acquired from experiments with the Pochhammer-Chree solution. The optimum geometry of the specimen is determined to minimize the loading equilibrium error. High strain rate tensile tests are then performed with auto-body sheet metals in order to construct their appropriate constitutive models for use in crash-worthiness evaluation
Formability of the steel sheet at the intermediate strain rate
No full textWhile the formability is important and indispensable for success in very complicated sheet metal forming, it seems that few studies has been carried out about the formability of sheet metal at the high strain rate. The present experimental results report that the elongation is dependent on the crosshead speed in tensile tests. In this paper, the tensile elongation has been obtained from various steel sheets for an auto-body at the. intermediate strain rate. The strain rate in the experiment is ranged, from 0.003/sec to 200/sec. The experimental result demonstrates that the tensile elongation does not decrease as the strain rate increases. This tendency has varieties depending on the microstructure and forming history of sheet metal. Some high strength steels have the tendency that the tensile elongation increases as,the strain rate increases, while others not. This phenomenon is very important not only in sheet metal forming but also in the crashworthiness evaluation to predict the fracture and tearing of sheet metal members
Modified Johnson-Cook model for vehicle body crashworthiness simulation
No full textDynamic response prediction of vehicle bodies is important for vehicle crashworthiness evaluation. The dynamic behaviour of vehicle body materials is dependent on material strain rates. One of the typical high strain rate tensile tests is the split Hopkinson bar test. In this paper, experiments have been conducted based on a new split Hopkinson bar apparatus specially designed for the dynamic tensile test of sheet metals. Results from both quasistatic and dynamic tests show that the strain rate hardening effect for sheet metals cannot be described by the original Johnson-Cook constitutive relation. This relation has been modified to include a higher-order term for the hardening effect. The modified constitutive relation represents a more accurate simulation than the original model for the dynamic behaviour of vehicle body structures
Optimum design of tailor welded blanks in sheet metal forming processes by inverse finite element analysis
No full textDesign of weld line in tailor welded blanks is indispensable for good manufacturing of stamped parts as assigned, since the initial weld line is distorted severely during the forming process. The initial weld line has to be determined such that desired weld line in a formed part can be obtained. The initial weld line can be predicted by inverse finite element analysis from the desired weld line in a formed part. in this paper, the multi-step inverse approach is employed to calculate more accurate initial blank shapes and initial weld line of tailor welded blanks for a cylindrical or square cup drawing. The applications demonstrates that the approach is useful for design of weld line in tailor welded blanks
RDLS-SS-DWT v. 0.9
No full textThis fileset contains the implementation of RDLS-DWT and SS-DWT in JPEG 2000 (RDLS-SS-DWT v. 0.9), which was used in a research described in: R. Starosolski, “Application of reversible denoising and lifting steps to DWT in lossless JPEG 2000 for improved bitrates,” Signal Processing: Image Communication, Vol. 39, Part A, pp. 249-63, DOI: 10.1016/j.image.2015.09.013, 2015 and R. Starosolski, “Skipping selected steps of DWT computation in lossless JPEG 2000 for improved bitrates,” submitted. This software is intended for research purposes only; it is provided "as is"; author makes no warranty of any kind, either express or implied, with respect to this software. <br
Finite element analysis of the hydro-mechanical punching process
No full textThis paper investigates the characteristics of a hydro-mechanical punching process. The hydro-mechanical punching process is divided into two stages: the first stage is the mechanical half piercing in which an upper punch goes down before the initial crack is occurred; the second stage is the hydro punching in which a lower punch goes up until the final fracture is occurred. Ductile fracture criteria such as the Cockcroft et al., Brozzo et al. and Oyane et al. are adopted to predict the fracture of a sheet material. The index value of ductile fracture criteria is calculated with a user material subroutine, VUMAT in the ABAQUS Explicit. The hydrostatic pressure retards the initiation of a crack in the upper region of the blank and induces another crack in the lower region of the blank during the punching process. The final fracture zone is placed at the middle surface of the blank to the thickness direction. The result demonstrates that the hydro-mechanical punching process makes a finer shearing surface than the conventional one as hydrostatic pressure increases
Crashworthiness assessment of side impact of an auto-body with 60trip steel for side members
No full textThis paper is concerned with the energy absorption efficiency of auto-body side Structures for the conventional steel and 60TRIP high strength steel. In order to evaluate the energy absorption efficiency, the dynamic crash analysis is carried out with the regulation of US-SINCAP. The analysis adopts the Johnson-Cook model for the dynamic material properties, which have been obtained from dynamic material tests. For the sake of the dynamic material properties, the analysis has been accurately performed for the crashworthiness assessment. The analysis result provides deformed shapes, amounts of penetration and accelerations at several important points during crash. The result confirms that 60TRIP greatly improves the crashworthiness of the side members without sacrificing the weight and thus can be used for the light-weight design of an auto-body
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