• Title/Summary/Keyword: Adiabatic shear bands

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Prediction of Serrated Chip Formation in High Speed Metal Cutting (고속 절삭공정 중 톱니형 칩 생성 예측)

  • 임성한;오수익
    • Transactions of Materials Processing
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    • v.12 no.4
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    • pp.358-363
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    • 2003
  • Adiabatic shear bands have been observed in the serrated chip during high strain rate metal cutting process of medium carbon steel and titanium alloy The recent microscopic observations have shown that dynamic recrystallization occurs in the narrow adiabatic shear bands. However the conventional flow stress models such as the Zerilli-Armstrong model and the Johnson-Cook model, in general, do not predict the occurrence of dynamic recrystallization (DRX) in the shear bands and the thermal softening effects accompanied by DRX. In the present study, a strain hardening and thermal softening model is proposed to predict the adiabatic shear localized chip formation. The finite element analysis (FEA) with this proposed flow stress model shows that the temperature of the shear band during cutting process rises above 0.5Τ$_{m}$. The simulation shows that temperature rises to initiate dynamic recrystallization, dynamic recrystallization lowers the flow stress, and that adiabatic shear localized band and the serrated chip are formed. FEA is also used to predict and compare chip formations of two flow stress models in orthogonal metal cutting with AISI 1045. The predictions of the FEA agreed well with the experimental measurements.s.

Prediction of Serrated Chip Formation due to Micro Shear Band in Metal (미소 전단 띠 형성에 의한 톱니형 칩 생성 예측)

  • 임성한;오수익
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.427-733
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    • 2003
  • Adiabatic shear bands have been observed in the serrated chip during high strain rate metal cutting process of medium carbon steel and titanium alloy. The recent microscopic observations have shown that dynamic recrystallization occurs in the narrow adiabatic shear bands. However the conventional flow stress models such as the Zerilli-Armstrong model and the Johnson-Cook model, in general, do not predict the occurrence of dynamic recrystallization (DRX) in the shear bands and the thermal softening effects accompanied by DRX. In the present study, a strain hardening and thermal softening model is proposed to predict the adiabatic shear localized chip formation. The finite element analysis (FEA) with this proposed flow stress model shows that the temperature of the shear band during cutting process rises above 0.5T$\sub$m/. The simulation shows that temperature rises to initiate dynamic recrystallization, dynamic recrystallization lowers the flow stress, and that adiabatic shear localized band and the serrated chip are formed. FEA is also used to predict and compare chip formations of two flow stress models in orthogonal metal cutting with AISI 1045. The predictions of the FEA agreed well with the experimental measurements.

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The Effect of Microstructure on the Static and Dynamic Deformation Behavior of Ti-6Al-4V Alloy (Ti-6Al-4V 합금의 미세조직에 따른 정적 및 동적 변형에 관한 연구)

  • Lee D. G.;Lee Y. H.;Lee S. H.;Hur S. M.;Lee C. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.10a
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    • pp.277-280
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    • 2001
  • The effects of a -phase morphology on the static and dynamic deformation behavior of a Ti-6Al-4V alloy was investigated in this study. Static tension test, static and dynamic tension test and hot compression test were conducted on three microstructures of Ti-6Al-4V alloy, i.e., equiaxed, widmanstatten and bimodal microstructures. Fracture surfaces of all three microstructures represented ductile fracture appearance, though the formation of adiabatic shear bands was noticed at dynamic torsion test. The susceptibility of forming adiabatic shear bands was greatest in the equiaxed microsoucture and lowest in the bimodal microstructure, which was evidenced by hot compression test.

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Toward Improving the Dynamic Deformation Properties of Metallic Materials via Role of Microstructure Factor (미세조직 인자의 영향을 고려한 금속 소재의 동적변형 특성 향상에 관한 연구)

  • Kim, Y.G.;Hwang, B.;Lee, D.G.;Ko, Y.G.;Lee, S.
    • Transactions of Materials Processing
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    • v.30 no.5
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    • pp.247-254
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    • 2021
  • This study reviews dynamic deformation behavior of ultra-fine-grained Al alloys, ultra-fine-grained conventional low carbon steel and dual phase steel and Zr-based amorphous alloys. Dynamic tests were conducted using a Kolsky bar then the test data was analyzed in relation to resultant microstructures, mechanical properties and propensity of adiabatic shear band. In addition, deformed microstructures and fracture surfaces were used to investigate the behavior of both the dynamic deformation and fracture, and adiabatic shear banding. As a result, increasing microstructural homogeneity, strain hardenability and forming multiple shear bands could be a better way to increase the fracture resistance under dynamic loading as the formation of adiabatic shear bands was reduced or prevented.

High Strain Rate Deformation Behavior of 5083 Aluminum Alloy Prepared via Equal Channel Angular Extrusion (ECAE 전단 가공된 5083 알루미늄 합금의 고변형률 변형거동)

  • Kim, Yang Gon;Ko, Young Gun;Shin, Dong Hyuk;Lee, Sunghak
    • Korean Journal of Metals and Materials
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    • v.47 no.7
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    • pp.397-405
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    • 2009
  • The high strain rate deformation behavior of ultra-fine grained 5083 aluminum alloys prepared via equal channel angular (ECA) extrusion was investigated in this study. The microstructure of ECA extruded specimens consisted of ultra-fine grains, and contained a considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. According to the dynamic torsion test results, the maximum shear stress and fracture shear strain of the route A (no rotation) specimen were lower than those of route C ($180^{\circ}$ rotation) specimen since that adiabatic shear bands of $100{\mu}m$ in width were formed in the route A specimen. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity associated with ECA operations.

A Study of Dynamic Deformation Behaviors of SCM415 steel with the Change of Ferritic Grain Size (SCM415강의 동적 변형거동에 미치는 페라이트 결정립크기 변화에 관한 연구)

  • Kim, Heon-Joo;Park, Moo-Yong
    • Journal of the Korean Society for Heat Treatment
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    • v.20 no.1
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    • pp.22-30
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    • 2007
  • Effects of ferrite grain size on static and dynamic deformation behaviors of SCM415 stels were investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Specimens with three different grain size of ferrite, $4.6{\mu}m$, $11{\mu}m$, $35.5{\mu}m$ were used. Dimple fracture mode of the dynamic test specimens showed adiabatic shear bands on the beneath of fracture surface. Increased uniform elongation and decreased non-uniform elongation appeared as grain size of ferrite decreased in dynamic torsional test. However, shear strength was independent on grain size of ferrite.

High-Strain Rate Deformation of Ultra-Fine Grained Al-Mg Alloys Fabricated by Equal-Channel Angular Pressing (ECAP으로 제조된 초미세림 Al-Mg 합금의 동적 변형거동)

  • Kim, Y.G.;Ko, Y.G.;Shin, D.H.;Lee, S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.05a
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    • pp.306-309
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    • 2009
  • The influence of equal-channel angular pressing (ECAP) route on dynamic deformation behavior of ultra-fine grained Al-4.4%Mg alloys was investigated in this study. The 8-pass ECAPed specimens consisted of ultra-fine grains of $0.5{\mu}m$ in size, and contained the considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. The result of dynamic torsional tests indicated that the maximum shear stress and fracture shear strain were lowest in the specimen deformed by ECAP via route A among the 8-pass ECAPed specimens. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

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A Study of Static and Dynamic Deformation Behaviors of SCM415 steel on the Change of Spherodization of Cementite (SCM415강의 정적 및 동적 변형거동에 미치는 탄화물 구상화율 변화에 관한 연구)

  • Kim, Heon-Joo;Lim, Jong-Min
    • Journal of the Korean Society for Heat Treatment
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    • v.17 no.6
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    • pp.327-335
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    • 2004
  • Effect of spherodization of cementite on static and dynamic deformation behaviors of SCM415 steels was investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Three type of specimens were used with different spherodization degree of cementite. Dynamic test results were analyzed comparing with static tensile results and microstructural changes. The obtained results are as follows; 1) All the specimens of static and dynamic tests showed a ductile fracture mode of dimple. Specimens of the dynamic test showed adiabatic shear bands on the beneath of fracture surface. 2) In static tensile test, decreased tensile strength and increased uniform and non-uniform elongations appeared as spherodization degree of cementite increased. 3) In dynamic torsional test, decreased shear strength and increased uniform elongation appeared as spherodization degree of cementite increased. 4) Due to the largest uniform elongation, superior cold forgeability at high speed is expected on high spherodization degree of cementite.

Dynamic Deformation Behavior of Ultra-Fine-Grained Pure Coppers Fabricated by Equal Channel Angular Pressing (ECAP으로 제조된 초미세립 순동의 동적 변형거동)

  • Kim, Yang Gon;Hwang, Byoungchul;Lee, Sunghak;Lee, Chul Won;Shin, Dong Hyuk
    • Korean Journal of Metals and Materials
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    • v.46 no.9
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    • pp.545-553
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    • 2008
  • Dynamic deformation behavior of ultra-fine-grained pure coppers fabricated by equal channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests were conducted on four copper specimens using a torsional Kolsky bar, and then the test data were analyzed by their microstructures and tensile properties. The 1-pass ECAP'ed specimen consisted of fine dislocation cell structures elongated along the ECAP direction, which were changed to very fine, equiaxed subgrains of 300~400 nm in size as the pass number increased. The dynamic torsional test results indicated that maximum shear stress increased with increasing ECAP pass number. Adiabatic shear bands were not found at the gage center of the dynamically deformed torsional specimen of the 1- or 4-pass ECAP'ed specimen, while some weak bands were observed in the 8-pass ECAP'ed specimen. These findings suggested that the grain refinement according to the ECAP was very effective in strengthening of pure coppers, and that ECAP'ed coppers could be used without serious reduction in fracture resistance under dynamic torsional loading as adiabatic shear bands were hardly formed.

Analysis of Adiabatic Shearbands via High Resolution Scheme (고분해능 스킴을 이용한 단열 전단띠 해석)

  • Cho, Young-Sam;Im, Se-Young
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.396-399
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    • 2001
  • Development of adiabatic shear bands in thermoviscoplastic materials is analyzed via high resolution scheme. Presented here are our initial results, which are for one dimensional elasto-viscoplastic materials. As the mesh-sizes are getting small, the convergence result of plastic strain rate is obtained using elasto-viscoplastic materials. The further study cases will be reported at the presentation in the framework of the one and the two dimensional shearbanding, respectively. They will be compared with finite element solutions, and the advantage of the scheme will be discussed.

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