• Title, Summary, Keyword: hardening

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Multiscale Modeling of Radiation Damage: Radiation Hardening of Pressure Vessel Steel

  • Kwon Junhyun;Kwon Sang Chul;Hong Jun-Hwa
    • Nuclear Engineering and Technology
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    • v.36 no.3
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    • pp.229-236
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    • 2004
  • Radiation hardening is a multiscale phenomenon involving various processes over a wide range of time and length. We present a multiscale model for estimating the amount of radiation hardening in pressure vessel steel in the environment of a light water reactor. The model comprises two main parts: molecular dynamics (MD) simulation and a point defect cluster (PDC) model. The MD simulation was used to investigate the primary damage caused by displacement cascades. The PDC model mathematically formulates interactions between point defects and their clusters, which explains the evolution of microstructures. We then used a dislocation barrier model to calculate the hardening due to the PDCs. The key input for this multiscale model is a neutron spectrum at the inner surface of reactor pressure vessel steel of the Younggwang Nuclear Power Plant No.5. A combined calculation from the MD simulation and the PDC model provides a convenient tool for estimating the amount of radiation hardening.

Modeling the Plastic Deformation of Crystals with Thin Precipitates (석출 강화된 단결정의 소성변형에 관한 모델링)

  • Kim J. H.;Han C. S.;Kang T. J.;Chung K.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.155-158
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    • 2005
  • Precipitates, present in most commercial alloys, can have a strong influence on strength and hardening behavior of a single crystal. The effect of thin precipitates on the anisotropy of initial slip resistance and hardening behavior of crystals is modeled in this article. For the convenience of the computational derivation and implementation, the material formulation is given in the unrelated intermediate configuration mapped by the plastic part of the deformation gradient. Material descriptions for the considered two phased aggregates consisting in lattice hardening as well as isotropic hardening and kinematic hardening are suggested. Numerical simulations of various loading cases are presented to discuss and assess the performance of the suggested model.

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Interfacial Crack-tip Constraints and J-integrals in Plastically Hardening Bimaterials under Full Yielding (완전소성하 변형경화 이종접합재의 계면균열선단 구속상태 및 J-적분)

  • Lee, Hyung-Yil;Kim, Yong-Bom
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.7
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    • pp.1159-1169
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    • 2003
  • This paper investigates the effects of T-stress and plastic hardening mismatch on the interfacial crack-tip stress field via finite element analyses. Plane strain elastic-plastic crack-tip fields are modeled with both MBL formulation and a full SEC specimen under pure bending. Modified Prandtl slip line fields illustrate the effects of T-stress on crack-tip constraint in homogeneous material. Compressive T-stress substantially reduces the interfacial crack-tip constraint, but increases the J-contribution by lower hardening material, J$\_$L/. For bimaterials with two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint in the lower hardening material and J$\_$L/. The fracture toughness for bimaterial joints would consequently be much lower than that of lower hardening homogeneous material. The implication of unbalanced J-integral in bimaterials is also discussed.

A Study on the Optimal Mixture Ratio for Stabilization of Surface Layer on Ultra-soft Marine Clay (초연약 해성점토의 표층고화처리를 위한 최적배합에 관한 연구)

  • 천병식;고경환;김진춘;한유찬;문성우
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.731-738
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    • 2002
  • Recently, as large constructions on the coast are performed frequently, surface layer stabilization method which Is one of the improvement methods for dredged soft clay has been applied. However, there have been few studies about the surface layer stabilization method. The purpose of this study is to clarify characteristics of ultra-soft marine clay and hardening agent. Also, optimal mixture ratio of hardening agent was verified through the laboratory tests such as statistical analysis and pilot tests. Laboratory tests were performed with proper hardening agent and test soil and standard mixing tables of hardening agent were determined according to ground conditions through statistical analysis. Also, applicability of surface layer stabilization method to field was verified by pilot tests. From the results of the tests, it was found that hardening agent materials such as cement, slag, fly-ash, inorganic salts, arwin, gypsum etc. affect on the appearing compressive strength. It was defined optimal mixture ratio which satisfies the required compressive strength from the statistical analysis. Also, It was compared the effect of ground improvement by cements and hardening agents through the pilot tests. This study will serve as data for design or construction criteria of stabilization of surface layer on ultra-soft marine clay.

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Derivation of work-hardening exponent through indentation contact detph analysis (압입접촉깊이 분석을 통한 가공경화지수의 유도)

  • Jeon, Eun-Chae;Ahn, Jeong-Hoon;Choi, Yeol;Kwon, Dong-Il
    • Proceedings of the KSME Conference
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    • pp.523-528
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    • 2001
  • In this study we tried to determine the work-hardening exponent using continuous indentation test. Work-hardening exponent, which was determined by Hollomon equation, in tensile test, is an important parameter to determine plastic deformation and brittle/ductile property of materials. For using Hollomon equation, true stress and true strain were defined by indentation depth and indentation load. Using them the new equation, which is constituted by indentation depth, indentation load and work-hardening exponent, was induced. Indentation depth was calibrated because of elastic deflection and pile-up/sink-in phenomena. Work-hardening exponents of various steels derived by it showed good agreement to the results of tensile tests. In addition to experiments, FEM simulation was accomplished to investigate changes of real contact depth with materials properties changes. Through this simulation it is concluded that the real contact depth is changed by Y/E value which affect the early stage of indentation, and work-hardening exponent which the latter stage.

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An Anisotropic Elasto-Plastic Constitutive Model Based on the Generalized Isotropic Hardening Rule for Clays (일반 등방경화규칙에 의거한 점토의 비등방 탄소성 구성모델)

  • 이승래;오세붕
    • Geotechnical Engineering
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    • v.10 no.3
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    • pp.17-32
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    • 1994
  • To model the anisotropic behavior of soils in the case of reverse loading, an anisotropic hardening description is proposed on the basis of generalized isotropic hardening(GIH) rule. There is a core of the GIH rule in the allowance of the concept that the center of homology of isotropic hardening can be any proper stress states inside a yield surface. The plastic deformations could be represented for the condition of reverse loading, and an explicit constitutive relationship was formulated by utilizing a simple hardening function. The proposed hardening description has been compared with other anisotropic hardening models. For verification three sets of triaxial test results have been predicted for the drained and undrained behavior of overconsolidated clays and Ko consolidated clays.

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Kernel Hardening by Recovering Kernel Stack Frame in Linux Operating System (리눅스 운영체제에서 커널 스택의 복구를 통한 커널 하드닝)

  • Jang Seung-Ju
    • The KIPS Transactions:PartA
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    • v.13A no.3
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    • pp.199-204
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    • 2006
  • The kernel hardening function is necessary in terms of kernel stability to reduce the system error or panic due to the kernel code error that is made by program developer. But, the traditional kernel hardening method is difficult to implement and consuming high cost. The suggested kernel hardening function that makes high availability system by changing the panic() function of inside kernel code guarantees normal system operation by recovering the incorrect address of the kernel stack frame. We experimented the kernel hardening function at the network module of the Linux by forcing panic code and confirmed the proposed design mechanism of kernel hardening is working well by this experiment.

A Study on Mechanical Properties and Microstructure of Local-Hardening Heat-Treated Automotive Panel (국부 경화 열처리된 차체 부품의 기계적 성질과 미세조직에 관한 연구)

  • Lee, Jae Ho;Jeong, Woo Chang
    • Journal of the Korean Society for Heat Treatment
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    • v.23 no.6
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    • pp.301-308
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    • 2010
  • A steel with chemical composition, 0.22% C, 0.25% Si, 1.26% Mn, 0.22% Cr, 0.04% Ti, 0.0042% B, and a microstructure of ferrite and spheroidized cementite has been press-formed to automotive center pillar followed by local-hardening heat-treatment. Hardness, tensile properties, fractography, microstructure and surface roughness of local-hardening heat-treated automotive center pillar have been examined. The directly heated and quenched area had fully martensitic structure with Vickers hardenss in the range of 500 to 510. The heat affected area close to the directly heated area showed dual-phase structure of ferrite and martensite. The width of the heat-treated and heat-affected areas after the local-hardening heat treatment was ranging from 32 mm to 50 mm. The surface of the local-hardening heat-treated center pillar revealed some temper color as a consequence of the oxidation during the heat treatment, but the surface roughness was not affected by the local-hardening heat treatment.

Characteristics of 14K white gold by age-hardening treatment

  • Yun, Don-Gyu;Seo, Jin-Gyo;Sin, So-Ra;Park, Jong-Wan
    • Proceedings of the Materials Research Society of Korea Conference
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    • pp.107.1-107.1
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    • 2012
  • Because of beautiful glossy and color, the value of gold leverage is very high in Europe. For improve the quality of white gold, we performed heat treatment on 14K white gold alloys at various age-hardening conditions. Age-hardening behavior and the related phase transformation changes were studied to elucidate the hardening mechanism of 14K white gold alloys. For solid solution treatment [ST], casted 14K white gold alloy specimens were treated at high temperature ($750^{\circ}C$) during 30 minute, and the specimens dropped to water for quenching immediately. For Age-hardening treatment [AT], the specimens were treated at various temperatures ($250^{\circ}C{\sim}300^{\circ}C$). After the heat treatment, we observed increased hardness from 144 Hv to 214 Hv by Vicker's hardness tester. Variation of the grain size measured by optical microscopy (OM) and scanning electron microscopy (SEM) images. By electron probe micro-analysis (EPMA) mapping analysis, we investigated that irregular particles were changed uniformly. After heat treatment, 14K white gold alloys showed improved hardness and became uniformity of grain size by age-hardening treatment.

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Microscopic Investigation of the Strain Rate Hardening for Polycrystalline Metals (철강재료 변형률속도 경화의 미시적 관찰)

  • Yoon, J.H.;Park, C.G.;Kang, J.S.;Suh, J.H.;Huh, M.Y.;Kang, H.G.;Huh, H.
    • Transactions of Materials Processing
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    • v.17 no.1
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    • pp.46-51
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    • 2008
  • Polycrystalline materials such as steels(BCC) and aluminum alloys(FCC) show the strain hardening and the strain rate hardening during the plastic deformation. The strain hardening is induced by deformation resistance of dislocation glide on some crystallographic systems and increase of the dislocation density on grain boundaries or inner grain. However, the phenomenon of the strain rate hardening is not demonstrated distinctly in the rage of $10^{-2}$ to $10^2/sec$ strain rate. In this paper, tensile tests for various strain rates are performed in the rage of $10^{-2}$ to $10^2/sec$ then, specimens are extracted on the same strain position to investigate the microscopic behavior of deformed materials. The extracted specimens are investigated by using the electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) results which show the effect of texture orientation, grain size and dislocation behavior on the strain rate hardening.