• Title, Summary, Keyword: hardening

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Properties of Cementless Loess Mortar Using Eco-Friendly Hardening Agent (친환경 무기질 고화재를 사용한 무시멘트 황토모르타르의 특성)

  • Jung, Yong-Wook;Kim, Sung-Hyun;Lee, Dong-Gyu
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.3 no.4
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    • pp.355-365
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    • 2015
  • This study examined the fluidity and strength properties, water resistance, durability, and freeze-thaw of cementless loess mortar using an eco-friendly hardening agent. The experimental result indicates that 28 days compressive and flexural strength of the loess mortar was increased regardless of the weathered granite soil and loess mixture ratio as the replacement ratio of the hardening agent increases. The strengths were significantly increased until 14 days regardless of the hardening agent, while the effect on the strengths increasement was relatively low after 14 days. Thus, the strength development of loess mortar concrete was found to be faster than that of the normal concrete. In addition, when the hardening agent of 10% was used, the average flexural strength was 1.7MPa which is insufficient compared to the 28-day flexural strength of 4.5MPa for the paving concrete. However, the flexural strengths of the loess mortar concrete using the hardening agents of 20% and 30% were 4.0MPa and 5.3MPa, respectively. Thus, the hardening agent need to be at least 20% so that the loess mortar can be used for paving concrete. The experiment for water resistance shows that the repeated absorption and dry reduced mass regardless of the mixing ratio of the loess. The maximum length change also decreased with increasing the substitution rate loess mixture ratio and the hardening agent. The result of the freeze-thaw resistance test indicates that the relative dynamic modulus of elasticity at 300 cycle freeze-thaw with the hardening agents of 20% and 30% were 75% and 79%, relatively. Thus, the hardening agent of at least 20% is required to obtain the relative dynamic modulus of elasticity of 60% for the loess mortar.

A Modified Parallel Iwan Model for Cyclic Hardening Behavior of Sand(I) : Model Development (수정 IWAN 모델을 이용한 사질토의 반복경화거동에 대한 연구(I): 모델 개발)

  • 이진선;김동수
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.5
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    • pp.47-56
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    • 2003
  • In this paper, the cyclic soil behavior model. which can accommodate the cyclic hardening, was developed by modifying the original parallel IWAN model. In order to consider the irrecoverable plastic strain of soil. the cyclic threshold strain, above which the backbone curve deviates from the original curve, was defined and the accumulated strain was determined by summation of the strains above the cyclic threshold in the stress-strain curve with applying Masing rule on unloading and reloading curves. The isotropic hardening elements are attached to the original parallel IWAN model and the slip stresses in the isotropic hardening elements are shown to increase according to the hardening functions. The hardening functions have a single parameter to account for the cyclic hardening and are defined by the symmetric limit cyclic loading test in forms of accumulated shear strain. The model development procedures are included in this paper and the verifications of developed model are discussed in the companion paper.

Autofrettage Analysis of Compound Cylinder with Power Function Strain Hardening Model (멱함수 가공경화 모델을 이용한 복합실린더의 자긴가공해석)

  • Park, Jae-Hyun;Lee, Young-Shin;Shim, Woo-Sung;Kim, Jae-Hoon;Cha, Ki-Up;Hong, Suk-Kyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.6
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    • pp.488-495
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    • 2008
  • In order to achieve long fatigue lifetimes for cyclically pressurized thick cylinders, multi-layered compound cylinder has been proposed. Such compound cylinder involves a shrink-fit procedure incorporating a monobloc tube which has previously undergone autofrettage. The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage mo dels are based on different simplified material strain-hardening models, which is assumed that combination of linear strain-hardenig and power strain-hardening model. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material was proposed. The model was obtained using the von Mises yield criterion and plane strain condition. The tensile-compressive stress-strain curve was obtained by experiment. The parameters needed in the model were determined by fitting the actual tensile-compressive curve of the material. Finally, strain- hardening model was compared with elastic-perfectly plastic model.

Computer Simulation of Hemispherical Forming Process Texture-based Work hardening and Anisotropy (집합조직 기초 가공경화와 이방성에 의한 반구 성형공정의 전산 시뮬레이션)

  • Sim, J.K.;Keum, Y.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.199-202
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    • 2006
  • The hardening and anisotropy based on the crystal plasticity is considered in the numerical simulation of hemispherical sheet forming process to find more realistic simulation results For calculating the yield shear stresses of each crystal, Taylor's model of the crystalline aggregate is employed. The yield stress of crystalline aggregate is computed by averaging the yield stresses of the crystal. The hardening is evaluated by using the Taylor factor and the critical resolved shear stress of the crystal. In addition, by observing the crystallographic texture and slip system, the anisotropy of the sheet is traced during the forming process. The anisotropy and hardening behaviors of the sheet found by the crystal plasticity are described better than those of obtained from the Hill's quadratic criterion based on the continuum plasticity.

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A Study on the strain hardening of tube hydroforming according to process (튜브 액압성형품의 공정단계별 가공 경화 특성 연구)

  • Park, H.K.;Yim, H.S.;Yi, H.K.;Jeon, D.H.;Moon, Y.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.325-328
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    • 2008
  • In recent years, developments of light weight vehicle are one of the most important issues in automotive industry. It is important to know the variations of the mechanical properties in the hydro forming process for the safe and durable design purposes. Generally, tube hydroforming process consists of three main processes such as bending, preforming, and hydroforming. It means that the strain hardening histories of final products are nonlinear. In this study, strain hardening behavior during hydroforming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and strength were used as an index of strain hardening during respective processes. The correlationship between strength and hardness obtained from tensile test has been equivalently converted into correlation between hardness and measured strain.

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Estimation of Hardened Layer Dimensions Using Multi-Point Temperature Monitoring in Laser Surface Hardening Processes (레이저 표면 경화 공정에서 다점 온도 모니터링을 통한 경화층 크기 예측)

  • 우현구
    • Journal of Institute of Control, Robotics and Systems
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    • v.9 no.12
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    • pp.1048-1054
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    • 2003
  • In laser surface hardening processes, the geometrical parameters such as the depth and the width of a hardened layer can be utilized to assess the hardened layer quality. However, accurate monitoring of the geometrical parameters for on-line process control as well as for on-line quality evaluation is very difficult because the hardened layer is formed beneath a material surface and is not visible. Therefore, temperature monitoring of a point of specimen surface has most frequently been used as a process monitoring method. But, a hardened layer depends on the temperature distribution and the thermal history of a specimen during laser surface hardening processing. So, this paper describes the estimation results of the geometric parameters using multi-point surface temperature monitoring. A series of hardening experiments were performed to find the relationships between the geometric parameters and the measured temperature. Estimation results using a neural network show the enhanced effectiveness of multi-point surface temperature monitoring compared to one-point monitoring.

The influence of Jelly strength and Hardening agent on microcapsules by complex coacervation (복합상분리법에 의한 마이크로캡슐 제조 -젤리강도 및 경화제에 따른 특성변화-)

  • 김혜림;송화순
    • Journal of the Korean Society of Clothing and Textiles
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    • v.27 no.9_10
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    • pp.1172-1177
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    • 2003
  • Microcapsules were prepared by complex coacervation between gelatin and gum arabic. The object of this work is evaluation of the effect of jelly strength, hardening agent on the particle size distribution, surface morphology and DSC. It was found that the 300bloom jelly strength caused microcapsules' size larger. When the amount of hardening agent increased, the particle mean diameter was larger. The amount of hardening agent was determined to be 10m1 for getting suitable size to finish the fabric.

A Study on the High Temperature Properties of Self-hardening Sand Mold (High Temperature Properties of Self-Hardening Sand Mold using Calcium-Orthosilicate Powder) [I] (자경성 주형의 고온성질에 관한 연구 Calcium-Orthosilicate를 이용한 자경성 주형의 고온성질에 관하여 [I])

  • 강인찬;한윤희;문인탁
    • Journal of the Korean Ceramic Society
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    • v.13 no.1
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    • pp.20-24
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    • 1976
  • These are many kinds of self-hardening methods for sand mold using sodium silicate. When sodium silicate solution is mixed with calcium-orthosilicate powder hardening reaction occurs, which is based for self-hardening method at high temperature. The high temperature strength and resicual strength of mold are related to the mole ratio of sodium silicate and the contents of calcium-orthosilicate powder. The results obtained in this study were as follows: 1) The high temperature strength of mold was maximum at about $600^{\circ}C$, and at higher temperature showed lower value on the contrary. 2) The high temperature strength of mold was increased by increasing the amount of sodium silicate having lower mole ratio and high concentration. 3) The residual strength of mold was reduced by increasing the mole ratio of sodium silicate and increasing the concentration of calcium-orthosilicate.

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An Experimental Study on Optimal Mixture Ratio of Hardening Agent for Surface Soil Stabilization (연약지반 표층안정처리를 위한 고화재의 최적조합 산정에 관한 실험적 연구)

  • 천병식;김진춘;최현석
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.17-24
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    • 2000
  • Hardening agent has been the traditional material for surface soil stabilization of soft ground. This study aims at determining optimal mixture ratio of hardening agent in accordance with the required design specifications. Hardening agent is properly mixtured with Fly ash, Gypsum, Slag and Cement for the ettringite hydrates which is effective for early stabilization of unconsolidated soil. The treated soil is the clay which are widely found here and there in Korea. In this study, preliminary tests were performed to get optimal mixture ratio of stabilizer ingredient, and marine clay in Jin-Hae was used to get physical and chemical properties. Laboratory tests of 50 stabilized soil were peformed to get optimal mixture ratio for 16 stabilizer material of 6 type, and stabilizer mixing was determined.

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A Study on the Surface Soil Stabilization on Marine Clay by the Hardening Agent (고화재에 의한 해성점성토의 표층안정처리에 관한 연구)

  • 천병식;양진석
    • Journal of Ocean Engineering and Technology
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    • v.15 no.1
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    • pp.92-97
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    • 2001
  • Hardening agents have been the traditional material for surface soil stabilization of soft ground. This study aims at determining the optimal mixture ratio of the hardening agent in accordance with the required design specifications. Hardening agents which consists of fly ash, gypsum, slag and cement for the ettringite hydrates is effective for early stabilization of unconsolidated soil. The raw ground material is the clay that is widely found in Korea. In this study, preliminary tests were performed to get an optimal mixture ratio of the stabilizer ingredient and marine clay from Jinhae was used to get physical and chemical properties. Laboratory tests of 50 stabilized soils were performed to get an optimal mixture ratio for 16-stabilizer materials of 6 types, and a mixture ratio of the stabilizer ingredient and marine clay was determined.

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