• 항공우주시스템공학회지
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• 제17권2호
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• pp.45-55
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• 2023

본 연구에서는 V-22 Osprey 틸트로터의 25% 축소 모델인 TRAM에 대하여 회전익기 통합 해석 코드인 CAMRAD II를 이용하여 프롭로터의 Aeromechanics 모델링과 블레이드 및 피치 링크에 대한 구조 하중 해석을 수행한 후, DNW 풍동 시험 및 선행 해석 연구 결과와 상호 비교하였다. 본 연구에서는 저속 전진 비행 시 블레이드 플랩 굽힘 모멘트의 구조 하중 및 진동 하중 변화를 풍동 시험 결과에 대하여 비교적 잘 예측하였다. 리드-래그 굽힘 및 비틀림 모멘트의 구조 하중 및 진동 하중 해석은 풍동 시험과 다소 다르게 얻어졌으나, 평균값을 제거하였을 때 로터 회전 한 바퀴당 구조 하중 해석 결과가 풍동 시험 및 선행 해석 연구와 비교적 유사하였다. 피치 링크의 구조 하중 및 진동 하중 해석은 전반적으로 선행 연구의 시험 및 해석 결과와 유사하게 얻어졌다. 마지막으로 블레이드 구조 진동 하중의 조화 성분 해석 및 비교를 통하여 블레이드 리드-래그 굽힘 및 비틀림 모멘트의 오차 발생 원인을 분석하였다.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.123-137
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• 1998

The finite deformation with self contact problem of C. V. joint boots is analysed by using the implicit finite element code ABAQUS/Standard. It is shown that analysis results have a good agreement with experimental ones to the degree of maximum rotation angle. As an application of design modification, the effects of thickness change of the rounded part of boot model on the bending and the contact situation of deformed geometry are investigated. In this paper, the effect of the design modification in the end on the leakage is examined using 2-D finite element simulation. To solve the leakage problem of grease, the length of the small end is enlarged. From this study, it is confirmed that we can save the cost and time by applying FEM techniques to analyze and design the boot model.

• 대한기계학회논문집A
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• 제37권4호
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• pp.483-490
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• 2013

알루미늄 소재의 냉간 판재성형에서는 낮은 성형성과 성형 후 과도한 스프링백에 의한 치수정밀도가 저감되는 문제가 있다. 이에 본 연구에서는 기존 제조공법의 문제점을 개선하기 위해 새로운 제조공법인 Hot forming quenching(HFQ)을 제시하고자 한다. HFQ 은 용체화처리 온도로 가열된 알루미늄 판재를 열간성형하고, 다이 내에 설치된 냉각채널에 의해 ��칭하여 열간성형과 열처리를 동시에 함으로써 성형성 향상, 스프링백 저감 효과를 얻을 수 있다. 기존의 냉간성형 대비 HFQ 의 성형성 향상효과를 에릭슨 시험을 통해 평가하였다. 스프링백 특성을 파악하기 위해 V-beding 시험에 HFQ 를 적용하여 굽힘 성형된 제품의 치수정밀도를 기존의 냉간성형과 비교하였다. 또한 강도 및 경도를 측정하여 기존 냉간 성형에 의한 값들과 비교함으로써 알루미늄 제품 성형에 HFQ 을 적용하기 위한 타당성을 평가하였다.

• 콘크리트학회논문집
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• 제13권4호
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• pp.371-378
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• 2001

콘크리트의 파괴 특성을 평가하기 위한 매개변수, 모델, 그리고 시험방법 등이 현재 많이 제안되고 있으며, 이러한 발전으로 최근에는 콘크리트의 비선형 파괴와 준취성 파괴를 해석 가능하게 하고 있다. 이 논문에서는 파괴 매개변수에 대하여 간략히 소개하고 3점 휨시험을 시행하여 콘크리트의 파괴인성을 나타내는 J-적분값 ($J_{Ic}$ )과 다른 매개변수($K_{Ic}$ , $G_{F}$ )를 비교하였다. 콘크리트 보 시험체의 두께(width)와 노치 길이에 따라 파괴인성값이 어떻게 변화하는지를 실험적으로 고찰하였고 콘크리트 파괴 인성을 측정하기 위해서 응력-변위 곡선을 사용하였다. $G_{F}$ 와$ J_{Ic}$ 의 값은 노치 길이가 클수록 감소하는 경향을 보이며 $G_{F}$ 가 $J_{Ic}$ 보다 덜 민감한 반응을 보이는 것으로 나타났다. 따라서, 콘크리트 파괴 인성 매개변수로써 전자가 후자보다 더 유용한 것으로 나타났다. $G_{v}$ 와 $J_{Ic}$ 의 값은 콘크리트 시험체 두께가 75mm에서 150mm로 커질 때 증가한다. 따라서, 시험체 두께의 영향이 콘크리트 파괴 인성을 결정할 때 고려되어져야 한다.

• Structural Engineering and Mechanics
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• 제32권5호
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• pp.609-620
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• 2009

In this paper the results of a series of experimental tests upon three-point bending specimens made of polystyrene and containing re-entrant corners are firstly described. Tests involved different notch angles, different notch depths and finally different sizes of the samples. All the specimens broke at the defect, as expected because of the material brittleness and, hence, the generalized stress intensity factor was expected to be the governing failure parameter. Recorded failure loads are then compared with the predictions provided by a fracture criterion recently introduced in the framework of Finite Fracture Mechanics: fracture is assumed to propagate by finite steps, whose length is determined by the contemporaneous fulfilment of energy balance and stress requirements. This fracture criterion allows us to achieve the expression of the generalized fracture toughness as a function of the tensile strength, the fracture toughness and the notch opening angle. Comparison between theoretical predictions and experimental data turns out to be more than satisfactory.

• 한국기계가공학회지
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• 제8권2호
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• pp.60-68
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• 2009

The objective of this paper is to design stamping die of inner reinforcement panel with DL 950 advanced high strength steel as stamping materials through numerical analyses and experiments. The stamping process was designed as bending dominant process consisting of 1 step of notching and 4 steps of bending processes. In order to obtain a proper design of the stamping die, various three-dimensional elasto-plastic finite element analyses were performed using a commercial code AUTOFORM V4.2. Design parameter of stamping die was chosen as the corner radius of the stamping die for each step. From the results of the FE analysis, feasible corner radii of the stamping die, which can minimize the deviation of corner angle of the stamped part from design data, and forming load for each part were estimated. Stamping experiments were carried out using the manufactured stamping die according to the proposed die design. The results of experiments were shown that the stamping die can successfully manufacture the inner reinforcement panel with DL 950 advanced high strength steel as base stamping material.

• 한국의류학회지
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• 제26권10호
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• pp.1467-1477
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• 2002

This study was investigated physical properties of stretch fabrics by KES-FB system to show suitable basic data to making skirts of excellent capacity and develop more organized basic skirt pattern by fitness evaluation. 1. The results of T. H. V.(Total Hand Value) were as followa: In the kind of blending fiber, cotton/spandex was more excellent than nylon/spandex and polyester/spandex, in the direction of stretch, one-way(weft inserted polyurethan yarn) polyester/spandex and cotton/spandex were higher than two-way(warp and wet inserted polyurethan yarn) polyester/spandes and cotton/spandex, two-way nylon/spandex was higher than one-way nylon/spandex. 2. The results of calculating the variance between sample stretch fabrics and Japanese s/s women's suit fabrics after standardizing were as follows: Stretch fabrics has 2 range of tensile, bending, shearing, compression, surface, thickness and weight as compared with Jpanese s/s women's suit fabrics. In the tensile property, one-way stretch fabrics were almost the same with Japanese s/s women's suit fabrics, only two-way polyester/spandex had+1～+2 range. In the bending, shear property, there was no difference between sample fabrics and Japanese s/s women's suit fabrics 3. In the total fitness of the skirt, nylon/spandex is the best in the fabrics and one-way stretch fabric is better than two-way strethch fabric.

• International Journal of Safety
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• 제1권1호
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• pp.24-27
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• 2002

Recently the steel parts used in automobiles are required to be used under high stress more than ever before due to the need of keeping the weight down. To achieve this requirement of the high strength steel, it must be necessary to decrease inclusion contents and surface defects as like decarburization, surface roughness etc. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel (JISG408l-SUP7, SAE 9254 and DIN 50CrV4) are shaped. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotating bending fatigue test and it results from (1) decreasing the surface roughness (2) unchanging the surface hardness (3) increasing the compressive residual stress. Moreover, results also show fatigue failures originated at the inclusion near the surface, and this inclusion type is turned out to be an alumina of high hardness.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.618-618
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• 2013

Graphene is only one atom thick planar sheet of sp2-bonded carbon atoms arranged in a honeycomb crystal lattice, which has flexible and transparent characteristics with extremely high mobility. These noteworthy properties of graphene have given various applicable opportunities as electrode and/or channel for various flexible devices via suitable physical and chemical modifications. In this work, for the development of all-graphene devices, we performed to synthesize alternately patterned structure of mono- and multi-layer graphene by using the patterned Ni film on Cu foil, having much different carbon solid solubilities. Depending on the process temperature, Ni film thickness, introducing occasion of methane and gas ratio of CH4/H2, the thickness and width of the multi-layer graphene were considerably changed, while the formation of monolayer graphene on just Cu foil was not seriously influenced. Based on the alternately patterned structure of mono- and multi-layer graphene as a channel and electrode, respectively, the flexible TFT (thin film transistor) on SiO2/Si substrate was fabricated by simple transfer and O2 plasma etching process, and the I-V characteristics were measured. As comparing the change of resistance for bending radius and the stability for a various number of repeated bending, we could confirm that multi-layer graphene electrode is better than Au/Ti electrode for flexible applications.

• 열처리공학회지
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• 제3권4호
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• pp.10-22
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• 1990

A study has been investigated on the effect of mechanical properties (tension strength, rotary bending fatigue strength, wear resistance, hardness) according to the carbide particle size variation by the treatment of 1) quenching tempering, and 2) quenching, subzero treatment and tempering. The material used in this investigation was a typical bearing steel, high C high Cr, AISI E 52100. The result obtained in this study were as follows : (1) Finer the carbide particle size increasing the hardness and retained austenite in same quenching condition. (2) Finer the carbide particle size reduced the tension and rotary bending fatigue which were resulted from austenite grain growth and carbide precipitation on grain boundry that induced by carbide refine heat treatment. (3) Finer the carbide particel size increasing the wear resistance which were resulted by uniform distribution of carbide and increased hardness induced by microstructural uniform hardenability of matrix. (4) When the carbide particles were refinded, subzero treatment is effective only wear resistance and hardness.