• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.161-166
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• 2010

Elastomeric seals are widely used in dynamic seal applications, and it is well known that the sealing surfaces can be gradually worn out. Abrasive wear is known to be the most dominant factor; however, little research has been carried out on this problem until now. In this study, a new contact problem related to elastomeric seals-a small spherical particle and steel surface-was modeled and analyzed using MARC. Variations of von-Mises and residual stress distributions as well as deformed seal and steel surface shapes with seal materials and interferences are presented. The stress distribution and surface deformation are highly affected by the elastic properties of seal. For PTFE, the maximum von-Mises stress exceeds the yield strength, and plastic deformation occurs on the steel surface. Therefore, the sealing surface can also be worn down by sub-surface fatigue due to intervening hard particles in the sealing surfaces together with the well-known abrasion.

• Journal of the Korean Geotechnical Society
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• v.36 no.4
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• pp.5-15
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• 2020

This paper proposes a revised Modified Cam Clay type failure surface based on the critical state theory. In the plane of the mean effective and von Mises stresses, the original Modified Cam Clay model has an elliptic failure surface which leads the critical-state mean effective stress to be always half of the pre-consolidation mean effective stress without hardening and evolution rules. This feature does not agree with the real mechanical response of clay. In this study, the preconsolidation mean effective stress only reflects the consolidation history of the clay whereas the critical state mean effective stress only relies on the currenct void ratio of clay. Therefore, the proposed failure surface has a distorted elliptic shape without any fixed ratio between the preconsolidation and critical state mean effective stresses. Numerical simulations for various clays using failure surfaces as yield surface provide mechanical responses similar to the experimental data.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.197-198
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• 2006

본 연구에서 개발하는 성형렌즈는 그림1과 같이 한쪽 면이 비구면인 평볼록 형상이다. Glass렌즈의 고온압축성형을 위해서는 초정밀 가공기술로 제작된 성형Mold가 필요하며, Mold재질에 따른 성형기술의 확립이 필수적이다. 또한, 성형Mold의 표면과 융착반응이 없는 Glass소재가 요구된다. 본 실험을 위한 성형Mold는 코발트(Co) 함량 0.5 %의 초경합금(WC; 일본, Everloy社, 002K)을 초정밀 연삭가공하여 제작하였다. Glass소재는 전이점(Transformation Point; Tg) $572\;^{\circ}C$,항복점(Yielding Point; At) $630\;^{\circ}C$의 열적 특성을 갖는 K-BK7(일본, Sumita社)을 사용하였으며, d선에서 굴절률 및 아베수는 각각 1.51633, 64.1이다. 비구면 Glass렌즈 성형은 GMP(Glass Molding Press; 일본, Sumitomo社, Nano Press-S)장비를 사용하여 성형온도 $625\;^{\circ}C$, 서냉온도 $550\;^{\circ}C$로 고정하고 성형압력를 200-800 N 범위에서 변화시켰다. 표 1에 성형변수로 사용한 서냉속도와 서냉전환온도 조건을 나타낸다. 표1과 같이 각 서냉조건별로5장의 렌즈를 성형 후 특성값이 평균치에 가까운 3장을 선별하여 그 특성을 비교하였다. 각 조건에 따른 성형렌즈의 형상정도(일본, Panasonic社, UA3P, 자유곡면형상측정기), 두께(일본, Mitutoyo社, MDC-25M, 마이크로메터), 굴절률(일본, Shimatus社, KPR-200, 정밀굴절률측정기) 및 MTF[해상도](독일, Trioptics社, Image Master HR, MTF-Field)를 측정하여 각각의 광학적 특성을 비교 평가하였다. 비구면 Glass렌즈 성형장비와 형상측정기를 그림 2, 3에 각각 나타낸다.

• Journal of Korean Society of Steel Construction
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• v.17 no.5 s.78
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• pp.581-591
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• 2005

This paper proposes a design formulae that evaluates the design strength of T-joints made of cold-formed square hollow steel sections with longitudinal branch plate. The T-joints had a configuration that a branch member used to longitudinal plate to the main chord in the plane. This study focused on the branch plate T-joints governed by the main chord flange failure mode among the experimental results. Based on the test results of the longitudinal branch plate T-joint in the square hollow sections, the ultimate strength on the T-joints was defined as 1.5 times the load at 1% B the strength of joints that governed the serviceability in control for $16.7{\leq}2\gamma(B/T){\leq}31.3$ and $0.20{\leq}{\beta}(b1/B){\leq}0.75$. Existing yield line models for normal T-joints were investigated to be the main chord flange failure for the branch plate T-joint, and this proposal design formula was based on the theory of the yield line model. Finally, the value of the finite element method compared with the value of the test and theory for the T-joints verified the validity of the design formulae.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.81-92
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• 2011

The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S=0g/L and bilinear, Herschel-Bulkley and power-law for S=30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.223-232
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• 2003

In this study, a constitutive model called the disturbed state concept (DSC) was modified to be applied to the interface shear stress-displacement relationship between geosynthetics. The DSC model is comprised of two reference states, namely the relative intact (RI) and the fully adjusted (FA) state, and one function, namely the disturbance function. This model is a unified approach and can allow for various models as an RI state such as elastic-perfectly plastic model, hierarchical model, and so on. In addition, by using this model, the elastic and plastic displacements can be considered simultaneously. Comparisons between the measured data and predicted results through the parameters determined from four sets of large direct shear tests showed good agreements with each other, especially for the smooth geomembrane-involved interface. Although there are slight differences at peak shear strength for textured geomembrane-involved interface, this model can still be useful to predict the position of displacement at peak strength and the large displacement (or residual) shear strength.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.234-248
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• 1998

This paper presents a new constitutive model for numerical modeling the shear behaviour of rough rock joints. The model incorporates the dilatancy of joints on the basis of elasto-plastic theory. Barton's empirical shear strength formular are adopted in the formulation process. The mobilized JRC concept is evoked to address the shear strength hardening and sofrening phenomena. The mobilized JRC in the pre- and post-peak range is approximated by assuming that the variation of JRC is a function of tangential plastic work. Discrete finite joint element is used to implement the proposed constitutive model. The model is validated by the numerical direct shear test on a single joint which is subjected to different boundary conditions. The test results are in good agreement with the experimental observations reported by other authors. The numerical tests also exhibit that the proposed model can simulate the salient features envisaged in the behaviour of rough rock joints.

• Journal of Korean Society of Steel Construction
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• v.19 no.2
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• pp.223-231
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• 2007

Considering wind speed uncertainty, reliability analysis of the LNG unloading arm at Tongyoung Production Site was performed. Extreme distribution of wind speed was estimated from the data collected at the weather center and wind load was calculated using wind velocities and coefficients of wind pressure. The unloading arm was modeled with plate and solid elements. Contact elements were used to describe the interface between base of structure andground. Response surface for maximum effective stress was found for reliability analysis and then reliability functions was defined and used to determine exceeding probability of allowable and yield stresses. In addition, sensitivity analysis was also performed to estimate the effect of possible material deterioration in the future.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.2
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• pp.80-91
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• 1999

This paper presents the stress-strain , volumetric strain characteristics of the Pocheon weathered residual granite soil with variation of the initial water content under drained conditions. A series of consolidated drained triaxial compressiion tests and isotrpc compression tests with various initial water content on specimens were performed. All material parameters of Lade's double work hardening model were determined by using the results of tests. Most aspects of the soil behavior measured in the triaxial compression tests were reproduced with good accuracy by the constitutive model . Therefore double work hardening model has been shown to be applicable to weathered residual granite soil.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.2
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• pp.148-158
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• 1998

The aims of this study are to evaluate the application on the stress-strain behavior of granite Soil using Lade's double work hardening constitutive model based on the theories of elasticity and plasticity. From two different sites of construction work, two disturbed and compacted weathered granite samples which are different in partical size and degree of weathering respectively were obtained. The specimen employed were sampled at Iksan and Pochon in order to predict the constitutive model. Using the computer program based on the regression analysis, 11 soil parameters for the model were determined from the simple tests such as an isotropic compression-expansion test and a series of drained conventional triaxial tests. In conclusion, it is shown that Lade's double work hardening model gives the good applicability for processing of stress-strain, work-hardening, work-softening and soil dilatancy. Therefore, this model in its present form is applicable to the compacted decomposed granite soil.