• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.92-96
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• 1996

최근 유용한 신소재로많은 광심을 보이고 있는 오스템퍼처리 구상흑연 주철(Austempered Ductile Cast Iron 이하 ADI라 한다) 은 기지조직이 베이나이트와 잔류 오스테나이트로 구성되어있기 때문에 같은 화학 조성을 갖는 일반 구상 흑연 주철에 비하여 연성 및 연성의 감소가 없이 2배 정도의 강도를 증가 시킬수 있기 때문에 자동차, 선박 부품 및 각종 기계부품에 적용시키기 위한 많은 연구가 진행되고 있다. 본 연구에서는 서로 재질의 성분이 다른 고속도강 드릴인 소경드릴을 이용하여 ADI재료를 보통(비관통)이송 및 단계이송 절삭가공시 발생되는 공구의 마멸량과 표면조도와의 관계, 절삭력의 변화에 따른 공구마멸과 공구수명과의 관계를 실험적으로 규명하여 ADI재료 의 보통 및 단계이송절삭시 공구수명에 미치는 제반 절삭특성의 영향에 관해 고찰 하고자 한다.

• Journal of the Korean GEO-environmental Society
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• v.12 no.12
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• pp.63-70
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• 2011

Expanded Polystyrene (EPS) is a type of geosynthetic material manufactured with various strengths, unit weights, and dimensions. Due to recent advances in research on EPS, the use of EPS has increased dramatically. This super light weight material has a unit weight of approximately $0.16{\sim}0.47kN/m^3$, equivalent to 6.3~15.7 of that of most natural soils with conditions of fill materials. In spite of this advantage, it is noted that no standard method of resilient modulus test on EPS geofoam was reported and no literature on resilient modulus test methods for EPS geofoam exist. The main object of this study was to investigate feasibility of the resilient modulus of EPS when it was applied for flexible pavement. The investigation of the feasibility was completed based on the results from triaxial tests.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.61-69
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• 2019

In this study, the flexural strength and curvature ductility factor of single and hybrid fiber reinforced ultra high strength concrete flexural members with conventional steel rebar were evaluated by experimental program with 3-UHSC beams. Test specimens were loaded by 4-pointed flexural loading. According to the test results, hybrid fiber reinforced UHPC test specimens had higher moment resisting capacity and ductility. For the safe design of hybrid fiber reinforced UHPC, test specimens were analyzed according to the sectional analysis method with material models suggested by K-UHPC design recommendation. Current K-UHPC design recommendation predict the moment resisting capacity of member conventionally and over-estimated the ductility.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.118-125
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• 2013

The synthetic fibers including Polyvinyl alcohol and Polyethylene fibers have been successfully used in the manufacture of high ductile fiber reinforced cementitious composites. Polypropylene (PP) fiber has also been used in composites, not for the purpose of achieving a high level of tensile ductility but to improve the fire resistance performance of concrete exposed to high temperatures. This paper discusses the method for enhancing the performance of composites supplemented with PP fiber. Five types of mixture proportions were designed with high volume fly ash for testing the performance of composites. Type I cement and fly ash F were used as binding materials. The water-to-binder ratio was 0.23~0.25, and the amount of PP fiber used was 2 vol%. Polystyrene bead were also used to increase the tensile ductility of composites. A series of experiments including slump, density, compression and uniaxial tension tests were performed to evaluate the performance of cementitious composites supplemented with PP fiber. From the test results, it was exhibited that the performance of composites supplemented with PP fiber can be enhanced by adopting the mechanics and statistics theory.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.4
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• pp.37-51
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• 2000

이 연구는 지진 시 철근콘크리트 교각의 비탄성 거동 및 연성능력을 해석적으로 파악하는데 그 목적이 있다. 재료적 비선형성에 대해서는 균열 콘크리트에 대한 인장, 압축, 전단모델과 콘크리트 속에 있는 철근 모델을 조합하여 고려하였다. 이에 대한 콘크리트의 균열 모델로서의 분산균열모델을 사용하였다. 두께가 서로 다른 부재간의 접합부에 단면강성이 급변하기 때문에 생기는 국소적인 불연속변형을 고려하기 위한 경계면 요소를 도입하였다. 또한, 축방향철근의 유무 및 그 양 등에 따른 구속효과를 적절히 표현할 수 있는 해석 모델을 개발하였다. 본 연구에서는 철근콘크리트 교각의 비탄성 거동 및 연성 능력의 파악을 위해 제안한 해석기법을 신뢰성 있는 연구자의 실험결과와 비교하여 그 타당성을 검증하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.87-94
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• 2014

In solid mechanics, the peridynamics theory has provided a suitable framework for material failure and damage propagation simulation. Peridynamics is computationally expensive since it is required to solve enormous nonlocal interactions based upon integro-differential equations. Thus, multiscale coupling methods with other local models are of interest for efficient and accurate implementations of peridynamics. In this study, peridynamic models are restricted to regions where discontinuities or stress concentrations are present. In the domains characterized by smooth displacements, classical local models can be employed. We introduce a recently developed blending scheme to concurrently couple bond-based peridynamic models and the Navier equation of classical elasticity. We demonstrate numerically that the proposed blended model is suitable for point loads and static fracture, suggesting an alternative framework for cases where peridynamic models are too expensive, while classical local models are not accurate enough.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.509-516
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• 2007

Mathematical modeling and vibration control of a tiltrotor aircraft composite wing-rotor system are investigated in this study. A wing-mounted rotor can be tilted from the vertical position to a horizontal one, and vice versa. Effect of vibration control of the wing-rotor system via piezoelectricity is studied as a function of tilt angle, ply angle of composite wing and rotor's spin speed. Composite wing is modeled as a thin-walled box beam having a circumferentially uniform stiffness configuration that produces elastic coupling between flap-lag and between extension-twist behavior. Numerical simulations are provided and pertinent conclusions are outlined.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.11
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• pp.919-926
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• 2014

In this paper, the effect of material properties on fracture behavior was studied using cohesive zone model and extended finite element method. The rectangular tensile specimen with a central inclined initial crack was modeled by plane stress elements. In the CZM modeling, cohesive elements were inserted between every bulk elements in the predicted crack propagation region before analysis, while in the XFEM the enrichment to the elements was added as needed during analysis. The crack propagation behavior was examined for brittle and ductile materials. For thin specimen configuration, wrinkle deformation was accounted for by geometrically nonlinear post-buckling analysis and the effect of wrinkling on the crack propagation was investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1192-1200
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• 2009

This paper deals with an analytical study on the aileron reversal characteristics of anisotropic composite aircraft wings modelled as thin-walled beam and having bending-torsion structural couplings caused by Circumferentially Asymmetric Stiffness layup scheme. For a study on the aileron reversal of CAS composite wings, it is essential to consider the following effects such as warping restraint, transverse shear flexibility, bending-twist structural coupling, wing aspect ratio, ratio of span-wise and chord-wise length of aileron to wing, and sweep angle, etc. The results on the aileron reversal could have a significant role in more efficient designs of thin-walled composite wing aircraft for which this aeroelastic instability is one of the most critical ones.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.56-64
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• 2002

Thermally induced vibration response of composite thin-walled beams is investigated in this paper. The flexible spacecraft appendages modeled as thin-walled beam incorporates a number of nonclassical effects of transverse shear, primary and secondary warping, rotary inertia and anisotropy of constitute materials. Thermally induced vibration responds characteristics of a composite thin walled beam exhibiting the circumferantially uniform system(CUS) configuration are exploited in connection with the structural flapwise bending lagwise bending coupling resulting from directioal properties of fiber reinforced composite materials and ply stacking sequence. A coupled thermal structure gradient is investigated.