• Smart Structures and Systems
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• 제14권5호
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• pp.869-881
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• 2014

This paper presents the materials analysis for combination of working modes of Magnetorheological (MR) damper. The materials were selected based on the optimum magnetic field strength at the effective areas in order to obtain a better design of MR damper. The design of electromagnetic circuit is one of the critical criteria in designing MR dampers besides the working mechanism and the types of MR damper. The increase in the magnetic field strength is an indication of the improvement in the damping performance of the MR damper. Eventually, the experimental test was performed under quasi-static loading to observe the performances of MR damper in shear mode, squeeze mode and mixed mode. The results showed that the increment of forces was obtained with the increased current due to higher magnetic flux density generated by electromagnetic coils. In general, it can be summarized that the combination of modes generates higher forces than single mode for the same experimental parameters throughout the study.

• Composites Research
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• 제23권4호
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• pp.21-27
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• 2010

대부분의 구조물 파괴는 피로에 의해서 발생한다. 따라서 지금까지 모드 혼합비가 피로 특성에 어떤 영향을 미치는지에 대한 수많은 연구가 수행되어 오고 있다. 하지만 대부분의 연구가 금속/금속 계면이나 복합재료 층간 분리에 관한 연구이다. 따라서 본 연구에서는 이종재료인 복합재료/금속 계면의 피로 특성에 대한 기초 자료를 얻고자 하였다. 이를 위하여 복합재료와 탄소강을 동시 경화법을 이용하여 접합한 SLB(single leg bending) 시편을 이용하여 피로 실험을 수행하였다. 특히, 피로 특성에 모드 혼합비$(G_{II}/G_T)$가 어떠한 영향을 미치는지에 대해 알아보고자 하였다. 전체적으로 모드 II 하중 성분 이 많을수록 균열진전속도가 빨라진다는 결과를 얻었다.

• Geomechanics and Engineering
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• 제29권5호
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• pp.567-582
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• 2022

In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

• 대한기계학회논문집
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• 제16권12호
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• pp.2226-2240
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• 1992

본 연구에서는 이방성체에 대한 구체적인 코스틱스 실험법을 확립하기 위하여 다음과 같은 연구를 수행 하였다. 첫째, 이방성체에 대한 코스틱스상 및 초기곡선의 사상방정식을 기하광학 및 Sih의 응력장을 이용하여 구하고, 이 식에 의한 이론상을 여러가지 경계조건하에서 컴퓨터 그래픽 하여 유도한 사상방정식의 타당성을 검토 하 였다.둘째, 본 논문에서 개발한 두 가지 종류의 직교이방성체를 사용하여 실험을 수행하고 실험에 의한 코스틱스상을 이론상과 비교, 검토 하였다.셋째, 이방성체의 코스틱스상으로부터 응력확대계수를 구하는 방법을 제시하고 이 방법을 실제 시편에 적용하여 신뢰 할수 있는 결과를 얻는 초기곡선의 범위를 결정 하였다. 그리고 이 범위에서 구한 응력확대 계수 값을 경계요소법을 이용한 변위외삽법에 의한 결과와 비 교함으로써 본 논문에서 제시하는 방법이 이방성체의 응력확대계수를 구하는 한 방법 으로 유효하게 사용될 수 있음을 밝혔다.

• 한국안전학회지
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• 제15권2호
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• pp.13-21
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• 2000

Under the mixed mode loading, it has been known that the influence of non-singular terms in the stress fields is serious, because the critical distance, ${\gamma}_o$ - the distance of nonlinear elastic region near the crack tip has no negligible value. In this paper, it has been studied on the influence of non-singular terms, T-stress, and the case of T=0, ${\sigma}cos^2{\beta}$, ${\sigma}cos(2{\beta})$ and $0.05{\sigma}cos(2{\beta})$, under uniaxial tension and compression. It has been seen that the T-stress of ${\sigma}cos(2{\beta})$ has better than others as comparing to the experimental data.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.212-217
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• 2000

The reliable determination of the stress intensity factors for cracks in bolted Joints is needed to evaluate the safety and fatigue life of them widely used in mechanical components. The weight function method is an efficient technique to calculate the stress intensity factors for various loading conditions using the stresses of an uncracked model. In this paper the mixed-mode stress intensity factors for cracks in bolted joints are obtained by weight function method, in which the coefficients of weight function are determined by finite element analyses far reference loadings. The effects of the magnitude of clearance and factional coefficient on the stress intensity factors are investigated.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.573-576
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• 2003

HTS superconducting tapes are now commercially available for practical applications such as magnets and cables. Since superconductors in such applications are subjected to high mechanical loads that can significantly degrade the superconducting properties, mechanical properties and the strain tolerance known as the strain effect on superconducting properties are needed to be estimated for developing superconducting devices. Influences of loading mode on the Ic degradation and the interaction on strain effect were discussed in this study.

• 한국안전학회지
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• 제29권6호
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• pp.9-14
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• 2014

Recently many efforts and researches have been done to cope with industrial facilities that require a low energy machines due to the gradual depletion of the natural resources. The fiber-reinforced composite materials in general have good properties and have the proper mechanical properties according to the change of the ply sequences and fiber distribution types. However, in the fiber-reinforced composite material, there are several problems, including fiber breaking, peeling, layer lamination, fiber cracking that can not be seen from the metallic material. Particularly, the fracture and delamination are likely to be affected by the thickness of the stacking laminates when the bi-material laminated structure is subjected to a load of the mixed mode. In this study, we investigated the effect of the thickness ratio of the difference in the CFRP/GFRP bi-material laminate composites by measuring the cracking behavior and the AE characteristics in a mixed mode loading, which may be generated in the actual structure. The results show that the thickness of the CFRP becomes more thick, the mode I energy release rate becomes a larger, and also the influence of mode I is greater than that of mode II. In addition, AE amplitude which shows the level of the damage in the structure was obtained the more damage in the CFRP with the thin thickness.

• 한국안전학회지
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• 제28권1호
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• 대한기계학회논문집
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• 제16권5호
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• pp.838-848
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• 1992

본 연구에서는 김성호등의 형상모델인 Fig.1(b)에서 전단하중이 작용하는 경 우에 대한, 복합재료의 탄성층 내부(레진층)에 존재하는 중앙균열의 응력확대계수 산 출을 위하여 균열부위를 제외하고는 섬유층과 레진층이 완전히 접착되었다고 가정한 모델을 다음과 같이 설정 하였다. 접착레진을 주로하는 탄성층(resin rich layer)을 중심으로 상하 각1개의 섬유층(fiber rich layer)과 균질한 특성을 갖는 복합재료의 층으로 단순화하였으며, 복합재료는 레진층이나 섬유층에 비하여 무한히 두꺼우므로 반무한체로 이상화 하였다. 선형탄 이론에 의한 혼합경계조건문제(mixed boundary value problem)로 부터 제2종 Fredholm 적분방정식(fredholm integral equation of a second kind)을 유도하였으며 수치해석적인 방법에 의하여 응력확대계수를 구하였다. 또한, 복합재료의 재료물성 및 균열길이, 섬유두께등이 기하학적 변수에 대하여 응력 확대계수를 산출하였다.