• Title/Summary/Keyword: work hardening rate

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Effects of Work-Hardening Exponent and Strain-Rate Hardening Exponent on the Determination of Friction Factor (가공경화지수 및 변형율속도 경화지수의 변화가 마찰상수 결정에 미치는 영향)

  • Park, C.Y.;Yang, D.Y.
    • Transactions of Materials Processing
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    • v.1 no.1
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    • pp.42-51
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    • 1992
  • The ring compression test has been widely employed as an experimental means to determine the friction factor. The calibration curves are obtained by the rigid-plastic finite element analysis for various work-hardening exponent and strain-rate hardening exponent. The effects of work-hardening exponent and strain-rate hardening exponent are thoroughly studied and discussed from the finite element computation. The change of friction factor during height reduction in ring compression is also discussed. Then, the method to estimate the change of friction factor during ring compression is proposed.

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Two Back Stress Hardening Models in Rate Independent Rigid Plasticity (변형률 독립 강소성 구성 방정식에서의 이중 후방 응력 경화 모델)

  • Yun S. J.
    • Transactions of Materials Processing
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    • v.14 no.4 s.76
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    • pp.327-337
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    • 2005
  • In the present work, the two back stress kinematic hardening models are proposed by combining Armstrong-Frederick, Phillips and Ziegler's hardening rules. Simple combination of hardening rules using simple rule of mixtures results in various evolutions of the kinematic hardening parameter. Using the combined hardening models the ultimate back stress fur the present models is also derived. The stress rate is co-rotated with respect to the spin of substructure due to the assumption of kinematic hardening rule in finite deformation regime. The work piece under consideration is assumed to consist of the elastic and the rigid plastic deformation zone. Then, the J2 deformation theory is facilitated to characterize the plastic deformation behavior under various loading conditions. The plastic deformation localization behaviors strongly depend on the constitutive description namely back stress evolution and its hardening parameters. Then, the analysis for Swift's effects under the fixed boundaries in axial directions is carried out using simple shear deformation.

INFLUENCE OF ALLOY COMPOSITION ON WORK HARDENING BEHAVIOR OF ZIRCONIUM-BASED ALLOYS

  • Kim, Hyun-Gil;Kim, Il-Hyun;Park, Jeong-Yong;Koo, Yang-Hyun
    • Nuclear Engineering and Technology
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    • v.45 no.4
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    • pp.505-512
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    • 2013
  • Three types of zirconium base alloy were evaluated to study how their work hardening behavior is affected by alloy composition. Repeated-tensile tests (5% elongation at each test) were performed at room temperature at a strain rate of $1.7{\times}10^{-3}s^{-1}$ for the alloys, which were initially controlled for their microstructure and texture. After considering the yield strength and work hardening exponent (n) variations, it was found that the work hardening behavior of the zirconium base alloys was affected more by the Nb content than the Sn content. The facture mode during the repeated tensile test was followed by the slip deformation of the zirconium structure from the texture and microstructural analysis.

Evaluation of Mechanical Properties of AZ31B for Sheet Metal Forming at Warm and High Temperature (온간, 열간 판재 성형을 위한 AZ31B의 기계적 성질 평가)

  • Choo D. K.;Kim W. Y.;Lee J. H.;Kang C. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.10a
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    • pp.256-259
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    • 2004
  • In the present study, AZ31B sheets has a bad formability in room temperature, but the formability is improved significantly as increasing the temperature because of rolled magnesium alloy sheet has a hexagonal closed packed structure (HCP) and a plastic anisotropy. In this paper, after tensile test in various temperatures, strain rate, show the tensile mechanical properties, yield and ultimate strength, K-value, work hardening exponent(n), strain rate sensitivity(m). As temperature increased, yield, ultimate strength and K-value, work hardening exponent(n) are decreased but strain rate sensitivity(m) is increased. As cross-head-speed increased, yield, ultimate strength and K-value, work hardening exponent(n) are increased. And according to the temperature, how change the plastic anisotropy factor R. In addition, we observed how temperatures and cross-head-speed effect on microstructure.

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Combined Two-Back Stress Models with Damage Mechanics Incorporated (파손역학이 조합된 이중 후방응력 이동경화 구성방정식 모델)

  • Yun, Su-Jin
    • Transactions of Materials Processing
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    • v.17 no.3
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    • pp.161-169
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    • 2008
  • In the present work, the two-back stress model is proposed and continuum damage mechanics (CDM) is incorporated into the plastic constitutive relation in order to describe the plastic deformation localization and the damage evolution in a deforming continuum body. Coupling between damage mechanics and isothermal rate independent plasticity is performed using the kinematic hardening rule, which in turn is formulated by combining the nonlinear Armstrong-Frederick rule and the Phillips rule. The numerical analyses are carried out within h deformation theory. It is noted that the damage evolution within a work piece accelerates the plastic deformation localization such that the material with lower hardening exponent results in a rapid shear band formation. Moreover, the results from the numerical analysis reflected closely with the micro-structures around the fractured regime. The effects of the various hardening parameters on deformation localization are also investigated. As the nonlinear strain rate description in the back stress evolution becomes dominant, the strain localization becomes intensified as well as the damage evolution.

The Analysis for Surface Hardening by Repeated Sliding Contact (반복 미끄럼 접촉에 의한 표면층의 경화에 대한 해석)

  • 박준목;김석삼
    • Tribology and Lubricants
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    • v.13 no.4
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    • pp.71-78
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    • 1997
  • Wear is affected by numerous factors-contact load, sliding velocity and distance, friction coefficient, material properties and environmental conditions. Among these wear factors, surface hardness is one of very important factors to determine wear. But surface hardness is varied by work hardening during repeated sliding contact. In this reason wear rate is increased or decreased with varying surface hardness, and transition of wear mechanism is happened. In this study, the surface hardening by accumulating residual stress was analyzed by considering the repeated sliding Hertzian contact model. The results showed that surface hardness was increased with increasing contact load, friction coefficient and contact number. And the depth of hardening layer, plastic layer and elastic layer depended upon contact load and number, but they didn't depend upon friction coefficient. The predicted surface hardness was about 1.5-1.8 times as hard as the material.

Dynamic plastic deformation behavior of Fe-X%Mn alloys (Fe-X%Mn 합금의 동적 소성변형거동)

  • Park, Hong Lae;Lee, Jeong Min;Sung, Wan;Kim, Won Baek;Choi, Chong Sool
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.4
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    • pp.266-278
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    • 1995
  • The high strain-rate dynamic plastic behavior of Fe-X%Mn alloys was investigated. The strain rate did not have an effect when tested under quasi-static strain rates($2{\times}10^{-3}/sec$ and $2{\times}10^{-1}/sec$). However, the true stress increased at all strain levels when the strain rate increased to $6{\times}10^3/sec$. Based on the experimental results, an constitution equation to calculate the dynamic strength for strain rates over $10^4/sec$ was determined. The Fe-5%Mn alloy containing athermal ${\alpha}^{\prime}$ martensite initially did not show work hardening. The work hardening increased with Mn content showing a maximum at 20% Mn. The high work hardening of Fe-20%Mn and Fe-30%Mn alloys appears to be closely related not only to the initial amounts of ${\varepsilon}$ martensite but to the strain induced transformation (${\gamma}{\rightarrow}{\varepsilon}$ and ${\varepsilon}{\rightarrow}{\alpha}^{\prime}$) occurring during each stages of deformation.

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Evaluation of Mechanical Properties for Magnesium Sheet Forming by Tension and Compression Tests (마그네슘 판재성형을 위한 인장 및 압축실험을 통한 기계적 물성 평가)

  • Oh, S. W.;Choo, D. K.;Lee, J. H.;Kang, C. G.
    • Transactions of Materials Processing
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    • v.14 no.7 s.79
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    • pp.635-641
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    • 2005
  • The crystal structure of magnesium was hexagonal close-packed (HCP), so its formability was poor at room temperature. But formability was improved in high temperature with increasing of the slip planes. Purpose of this paper was to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature was increased, yield·ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) were decreased. But strain rate sensitivity (m) was increased. As strain-rate increased, yield·ultimate strength, K-value, and work hardening exponent (n) were increased. Also, microstructures of grains fined away at high strain-rate. These results would be used in simulations and manufacturing factor fer warm and hot forming process.

Estimation of Mechanical Properties of Mg Alloy at High Temperature by Tension and Compression Tests (인장 및 압축실험을 통한 마그네슘 합금의 고온 물성 평가)

  • Oh S. W.;Choo D. K.;Lee J. H.;Kang C. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.05a
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    • pp.69-72
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    • 2005
  • The crystal structure of magnesium is hexagonal close-packed (HCP), so its formability is poor at room temperature. But formability is improved in high temperature with increasing of the slip planes. Purpose of this paper is to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature is increased, yield${\cdot}$ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) are decreased. But strain rate sensitivity (m) is increased. As strain-rate increased, yield${\cdot}$ultimate strength, K-value, and work hardening exponent (n) are increased. Also, microstructures of grains fine away at high strain-rate. These results will be used in simulations and manufacturing factor for warm and hot forming process.

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A Physically Based Dynamic Recrystallization Model for Predicting High Temperature Flow Stress (열간 유동응력 예측을 위한 물리식 기반 동적 재결정 모델)

  • Lee, H.W.;Kang, S.H.;Lee, Y.S.
    • Transactions of Materials Processing
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    • v.22 no.8
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    • pp.450-455
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    • 2013
  • In the current study, a new dynamic recrystallization model for predicting high temperature flow stress is developed based on a physical model and the mean field theory. In the model, the grain aggregate is assumed as a representative volume element to describe dynamic recrystallization. The flow stress and microstructure during dynamic recrystallization were calculated using three sub-models for work hardening, for nucleation and for growth. In the case of work hardening, a single parameter dislocation density model was used to calculate change of dislocation density and stress in the grains. For modeling nucleation, the nucleation criterion developed was based on the grain boundary bulge mechanism and a constant nucleation rate was assumed. Conventional rate theory was used for describing growth. The flow stress behavior of pure copper was investigated using the model and compared with experimental findings. Simulated results by cellular automata were used for validating the model.