• Title, Summary, Keyword: Necking

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Prediction of Sheet Metal Necking with Anisotropic Hardening (이방성 가공경화를 고려한 냉간 압연강판의 넥킹 예측)

  • 인정제;김권희;함주희
    • Transactions of Materials Processing
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    • v.10 no.2
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    • pp.160-166
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    • 2001
  • Uniaxial necking is studied for steel sheets with initial anisotropy. The state of anisotropy is continuously altered by subsequent tensile deformation at angles to the rolling direction. The orientations of orthotropy axes are changed before the onset of necking. A simple hardening rule which incorporates the rotations of orthtropy axes is proposed and the necking strains are predicted at angles to the rolling direction. Predicted results show good agreement with the experiments.

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FE Analysis on Doming & Necking Process of Steel D&I Can (Steel D&I Can의 Doming 및 Necking 공정의 FEM 해석)

  • Jung, S.W.;Nam, J.B.;You, C.S.;Jin, Y.S.;Han, K.S.
    • Proceedings of the KSME Conference
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    • pp.452-457
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    • 2000
  • The object of this study is to develop a reliable FEM simulation technique for the analysis of can making process using PAM-STAMP software. The processes consist of doming and necking in addition to drawing, redrawing. After body making process, this study analyzed the stability for internal pressure by simulating buckling test. Through these technique, we estimated the dome reversal pressure of steel D&I Can for various can profile and process conditions. From this study, we found the cause and mechanism of wrinkling during necking process. This mechanism is largely affected by can wall thickness and the clearance between knock out punch and necking die. The dome reversal pressure improves with increasing dome depth. These results validate the usefulness of the developed simulation technique for the analysis of body making process and optimization of the dome profile.

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Two-dimensional Numerical Simulation of the Contact Angle and the Bubble Necking Using the Two Phase Lattice Boltzmann Method (2상 격자 볼츠만 방법을 이용한 접촉각과 Bubble Necking 2차원 수치 모사)

  • Ryu, Seung-Yeob;Kim, Jae-Yong;Ko, Sung-Ho
    • The KSFM Journal of Fluid Machinery
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    • v.14 no.3
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    • pp.10-17
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    • 2011
  • Free energy based lattice Boltzmann method (LBM) has been used to simulate the contact angle and the bubble necking with large density ratio. LBM with the proper contact angle model is able to reduce the spurious currents and eliminate the singularity in the contact lines. The numerical results of the contact angles are satisfied with the Youngs law. For bubble necking flows, simulations are executed for various viscosities and contact angles. The phenomena of the bubble necking are simulated successfully and the subsequent results are presented. The present method is also applicable to the nucleate boiling flows.

Enhancement of Hydroformability Through the Reduction of the Local Strain Concentration (국부적 변형 집중 저감을 통한 액압 성형성 개선연구)

  • Shin, S.G.R.;Joo, B.D.;Moon, Y.H.
    • Transactions of Materials Processing
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    • v.23 no.5
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    • pp.317-322
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    • 2014
  • Bursting during tube hydroforming is preceded by localized necking. The retardation of the initiation of necking is a means to enhance hydroformability. Since high strain gradients occur at the necking sites, a decrease in local strain gradients is an effective way to retard the initiation of necking. In the current study, the expansion at potential necking sites was intentionally restricted in order to reduce the strain gradient at potential necking sites. From the strain distribution obtained from FEM, it is possible to determine strain concentrated zones, which are the potential necking sites. Prior to the hydroforming of a trailing arm, an incompressible material(such as lead) is attached to the tube where the strain-concentrated zone would contact the die. Due to the incompressibility of lead, the tube expansion is locally restricted, and the resultant strain extends to adjacent regions of the tube during hydroforming. After the first stage of hydroforming, the lead is removed from the tube, and the hydroforming continues to the final targeted shape without any local restriction. This method was successfully used to fabricate a complex shaped automotive trailing arm that had previously failed during traditional hydroforming fabrication.

A Prediction of Bursting Failure in Tube Hydroforming Process Based on Plastic Instability (소성불안정성에 의한 관재 하이드로포밍 공정에서의 터짐 불량 예측)

  • Kim S. W.;Kim J.;Park H. J.;Kang B. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.210-213
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    • 2004
  • Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity fur anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy parameter, strain hardening exponent on bursting pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

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A Prediction of Bursting Failure in Tube Hydroforming Process Based on Necking Conditions (네킹발생조건에 의한 관재 액압성형 공정에서의 터짐 불량 예측)

  • 김상우;김정;박훈재;강범수
    • Transactions of Materials Processing
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    • v.13 no.7
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    • pp.629-634
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    • 2004
  • Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined infernal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity for anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy Parameter, strain hardening exponent and strength coefficient on bursting Pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

Prediction of Necking in Tensile Test using Crystal Plasticity Model and Damage Model (결정소성학 모델과 손상 모델을 이용한 박판소재의 네킹 예측)

  • Kim, Jong-Bong;Hong, Seung-Hyun;Yoon, Jeong-Whan
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.8
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    • pp.818-823
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    • 2012
  • In order to predict necking behaviour of aluminium sheets, a crystal plasticity model is introduced in the finite element analysis of tensile test. Due to the computational limits of time and memory, only a small part of tensile specimen is subjected to the analysis. Grains having different orientations are subjected to numerical tensile tests and each grain is discretized by many elements. In order to predict the sudden drop of load carrying capacity after necking, a well-known Cockcroft-Latham damage model is introduced. The mismatch of grain orientation causes stress concentration at several points and damage is evolved at these points. This phenomenon is similar to void nucleation. In the same way, void growth and void coalescence behaviours are well predicted in the analysis. For the comparison of prediction capability of necking, same model is subjected to finite element analysis using uniform material properties of polycrystal with and without damage. As a result, it is shown that the crystal plasticity model can be used in prediction of necking and fracture behavior of materials accurately.

Application of Electromagnetic Wave for Evaluating Necking Defects in Bored Piles (현장타설말뚝의 네킹 결함 평가를 위한 전자기파의 적용성 연구)

  • Lee, Jong-Sub;Song, Jung Wook;Yu, Jung-Doung
    • Journal of the Korean Geotechnical Society
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    • v.34 no.4
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    • pp.27-35
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    • 2018
  • The objective of this study is to demonstrate the suitability of electromagnetic waves for evaluating necking defects in bored piles using electromagnetic waves. Experiments are conducted with small-scaled defective model pile with diameter of 150 mm and length of 270 mm. Two necking defects are generated at the upper and lower positions on two different sides of the model pile, respectively. The other two necking defects are generated at the upper and lower positions on the same side of the model pile. Electrical wires are installed alongside the stainless steel wire of a steel cage to configure a two-conductor transmission line. A time-domain reflectometer is used to generate and defect electromagnetic waves. The experimental results show that electromagnetic waves are reflected at the necking defects and the end of the model pile. In addition, calculated defect locations are almost the same as actual defect locations. This study demonstrates that electromagnetic waves can be effective tool for evaluating necking defects in bored piles.

Laboratory Experiments for Evaluating Necking Defects in Bored Piles Embedded in Sandy Soils Using Electromagnetic Waves (전자기파를 이용한 모래 지반에 설치된 현장타설말뚝의 네킹 결함 평가를 위한 실내 모형실험)

  • Lee, Jong-Sub;Kim, Youngdae;Yu, Jung-Doung
    • Journal of the Korean Geotechnical Society
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    • v.36 no.5
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    • pp.25-34
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    • 2020
  • Studies on nondestructive evaluation methods using electromagnetic waves have been commonly conducted to evaluate necking defects in bored piles. However, the propagation of electromagnetic waves are affected by water contents of surrounding materials. This study aims to investigate a suitability of electromagnetic waves for evaluating necking defects in bored piles embedded in sandy soils through laboratory experiments. Laboratory experiments are performed with a model pile having a necking defect. The diameter and length of model pile are 600 mm and 1 m, respectively, and the model pile is embedded in sandy soils with different water contents of 10%, 20%, and 30%. For the propagation of electromagnetic waves, a transmission line is configured in reinforcement cage using an electrical wire. The generation and detection of electromagnetic waves are conducted using a time domain reflectometer. Experimental results show that the peak amplitude of electromagnetic waves reflected at the necking defect decreases with an increase in the water content in sandy soils. In addition, the velocity of electromagnetic waves reflected from the toe of the model pile decreases win an increase in the water content. However, estimated locations of the necking defects are almost the same to that of the actual location of the necking defect. This study demonstrates that electromagnetic waves may be an effective method for evaluating necking defects in bored piles embedded in sandy soils

The Effects of Thickness on the Plastic Instability under Uniaxial Tension in Sheet Metal (판재의 일축인장 소성불안정에 미치는 두께의 영향)

  • Han, K. T.;Kang, D. M.;Koo, Y.;Baek, N. J.
    • Journal of the Korean Society for Precision Engineering
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    • v.6 no.2
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    • pp.58-64
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    • 1989
  • Plastic instability in uniaxial tension of commercial purity Al has been studied with the emphasis of effects of thickness in cold worked specimens and recrystallized specimens. The thickness change gave rise to change in stress state and the amount of strain localization in specimen after diffuse necking. Therefore the thickness of speci- men could control modes of plastic instability. Regardless of recrystallized or cold worked state, the necking mode changed from diffuse necking to local necking, at about 1.5 .approx. 2 mm in thickness.

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