• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.08a
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• pp.35-40
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• 2003

In order to develope springback control technology for high-strength steel sheets, some studies have been conducted: dome stretching test, stepped s-rail forming and springback measurement, and optimally shaped initial blank design. First, to find out the formability of TRIP60, dome stretching test was performed. Next the stepped s-rail die, which was designed to form a channel type panel with large twist and wall curl, was manufactured and used to know the effect of controlling forming variables, such as blank holding force and flange amount on the springback. Furthermore, new measurement method of the springback was introduced to define wall curl and twist in geometrically complex panels. Finally, the optimally shaped initial blank was employed to verify one of the best ways to control the springback in channel type, high strength sheet panels.

• Korean Journal of Computational Design and Engineering
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• v.17 no.3
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• pp.188-197
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• 2012

Recently, aluminum ships are constructed more than ever because of the environmental pollution generated by FRP (Fiber Reinforced Plastic) ships. In particular, FRP ships have been replaced by the Aluminum ships. The forming process of the curved aluminum plate has been performed only by labor works without systematic technique. Therefore, it is difficult to construct the aluminum ship that the design satisfies both required propulsion performance and hull design. Present study introduces a MPSF (Multi Point Stretching Forming) that is a flexible manufacturing technique to form large sheet panels of doubly curvature. The hull pieces are stretch-formed over the MPSD (multi-point stretching die) generated by the punch element matrix. In this study, MPSF is applied to deform the doubly curved surfaces of aluminum ship. The forming system including FEA (finite element analysis) of the processes for stretching the plate were carried out by static implicit analysis is suggested. Residual deformation of the surface is modeled by an elasto-plastic contact phenomena while the forming process is simulated by FEA. Finally, the proposed system is also validated, comparing the deformed shape by MPSF with that of object surfaces.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.39 no.1 s.119
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• pp.16-24
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• 2007

This study was performed to investigate the reaction between alkylketene dimer(AKD) and cellulose molecules in AKD-sized paper sheet. AKD was added to highly beaten($80{\pm}3^{\circ}SR$) SwBKP(ca. 0.8% on pulp) in order to have much AKD retention in the paper sheet. This AKD-sized paper sheet was aged at different temperatures, $60^{\circ}C,\;80^{\circ}C,\;105^{\circ}C\;and\;125^{\circ}C$. Changes in FT-IR spectra of AKD in paper sheet during the ageing were measured. In addition, sizing degrees of the AKD-sized paper sheet pretreated for 30 sec. at $105^{\circ}C$ were measured by HST size tester during the storage at different temperature. IR spectra of AKD-sized paper sheet preheated at $105^{\circ}C$ for 30 sec. showed unchanged spectra two absorption bands at $1849cm^{-1}\;and\;1722cm^{-1}$ which refer to the typical AKD IR bands. However, these typical AKD bands were gradually reduced with increasing ageing, completely disappeared after 6 hrs. and formed new absorption band at $1706cm^{-1}$, which refers to carbonyl stretching vibration of dialkylktone. Eventually the AKD molecule was hydrolyzed to diakylketone without formation of ${\beta}$-ketoester with cellulose in paper sheet. After 6 days ageing, a little amount of ${\beta}$-ketoester bands was identified in 6 or 7 days ageing, because of the absence of water due to long-term heating. The same tendency was observed at different ageing conditions. At the practical papermaking process, AKD reacts prevailing with water, and mostly seems to be hydrolyzed to dialkylketene. Concerned to the sizing development, AKD-sized paper sheet was shown no sizing development at the initial stage of ageing at $60^{\circ}C$ after heating treatment at $105^{\circ}C$ for 30 sec., and gradually increased the sizing degree with increasing ageing, such as Hercules Sizing Tester (HST) 130 see for 12 hr, HST 300 sec. for 3 days and HST 400 sec. for 5 days. It was concluded that hydrolyzed AKD could contributed to the sizing development of the paper sheet.

• Transactions of Materials Processing
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• v.12 no.8
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• pp.710-717
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• 2003

The implicit, finite element analysis program for analyzing the springback in the warm forming process of aluminum alloy sheets was developed. For the description of planar anisotropy in warm forming temperatures, Barlat's yield function is employed, and the power law type constitutive equation is used in terms of working temperatures for the depiction of work hardening in high temperatures. Also, Jetture's 4-node shell elements are introduced for reflecting the mechanical behavior of aluminum alloy sheet and the non-steady heat balance equations are solved for considering heat gain and loss during the forming process. For the springback evaluation, Newton-Raphson iteration method is introduced for overcoming the geometric nonlinearlity problem. In order to verify the validity of the FEM program developed, the stretching bending and springback processes are simulated. Though springback analysis results are slightly bigger than experimental ones, they have the same trend of the decreasing springback as the forming temperature increases.

• Transactions of Materials Processing
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• v.23 no.4
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• pp.199-205
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• 2014

The current study examines the effect of the analytical parameter values on the theoretical forming limit diagram (FLD) based on the Marciniak-Kuczynski model (M-K model). Tensile tests were performed to obtain stress-strain curves and determine the anisotropic properties in the rolling, transverse and diagonal direction of SPCC sheet materials. The experimental forming limit curve for SPCC sheet material was obtained by limiting dome stretching tests. To predict the theoretical FLD based on the M-K model, the Hosford 79 yield function was employed. The effects of three analytical parameters - the exponent of the yield function, the initial imperfection parameter and the fracture criterion parameter - on the M-K model, were examined and the results of the theoretical FLD were compared to the experimentally measured FLD. It was found that the various analytical parameters should be carefully considered to reasonably predict the theoretical FLD. The comparison of the acceptable forming limit area between the theoretical and experimental FLD is used to compare the two diagrams.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.08a
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• pp.13-20
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• 2003

The implicit, finite element analysis program for analyzing the springback in the warm forming process of aluminum alloy sheets was developed. For the description of planar anisotropy in warm forming temperatures, Barlat's yield function is employed, and the power law type constitutive equation is used in terms of working temperatures fur the depiction of work hardening in high temperatures. Also, Jetture's 4-node shell elements are introduced for reflecting the mechanical behavior of aluminum alloy sheet and the non-steady heat balance equations are solved for considering heat gain and loss during the forming process. For the springback evaluation, Newton-Raphson iteration method is introduced for overcoming the geometric nonlinearlity problem. In order to verify the validity of the FEM program developed, the stretching bending and springback processes are simulated. Though springback analysis results are slightly bigger than experimental ones, they have the same trend of the decreasing springback as the forming temperature increases.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.293-296
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• 2009

In roll forming process, a sheet metal is continuously progressively formed into a product with required cross-section and longitudinal shape, such as a circular tube with required diameter, wall-thickness and straightness, by passing through a series of forming rolls in arranged in tandem. In recent years, that process is often applied to the bumper rail in the automotive industries. In this study, a optimal front side member manufacturing technology, model deign and proper roll-pass sequences can be suggested by forming number of roll-pass and bending angle. And also effects of the process parameters on the final shape formed by roll forming defects were evaluated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.14-17
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• 1999

The finite element formulation is developed for predicting strain distributions and weld line movements in the forming processes of laser welded blank. The welded zone(WZ) is modelled with several narrow finite elements whose material characteristics are analytically obtained from those of base metals based on the tensile tests. In order to show the reliability and effectiveness of weld element the forming process of hemispherical dome stretching and auto-body door inner panel stamping are simulated FEM predictions show good agreements with experimental observations.

• Nuclear Engineering and Technology
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• v.49 no.8
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• pp.1636-1644
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• 2017

The main purpose of this article is to describe the magnetohydrodynamic stagnation point flow of Walter-B nanofluid over a stretching sheet. The phenomena of heat and mass transfer are based on the involvement of thermal radiation and chemical reaction. Characteristics of Newtonian heating are given special attention. The Brownian motion and thermophoresis models are introduced in the temperature and concentration expressions. Appropriate variables are implemented for the transformation of partial differential frameworks into sets of ordinary differential equations. Plots for velocity, temperature, and nanoparticle concentration are displayed and analyzed for governing parameters. The skin friction coefficient and local Nusselt and Sherwood numbers are studied using numerical values. The temperature and heat transfer rate are enhanced within the frame of the thermal conjugate parameter.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.195-198
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• 2009

In this study, in order to get the forming limit of AHSS sheet in the negative minor strain region, the shapes of die corner and drawbead are redesigned by employing the Taguchi's design of experiment method and the FEM forming simulation. With the redesigned FLD tool, the forming limit tests of automotive multi-phase(Dual Phase and Complex Phase) steel sheets which induce the normal fractures on the blank are performed.