• Computers and Concrete
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• 제3권5호
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• pp.285-299
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• 2006

The free vibration of stiffened and damaged coupled shear walls is investigated using the mixed finite element method. The anisotropic damage model is adopted to describe the damage extent of the reinforced concrete shear wall element. The internal energy of a locally damaged shear wall element is derived. Polynomial shape functions established by Kwan are used to present the component of displacements vector on each point within the wall element. The principle of virtual work is employed to deduce the stiffness matrix of a damaged shear wall element. The stiffened system is reinforced by an additional stiffening beam at some level of the structure. This induces additional axial forces, and thus reduces the bending moments in the walls and the lateral deflection, and increases the natural frequencies. The effects of the damage extent and the stiffening beam on the free vibration characteristics of the structure are studied. The optimal location of the stiffening beam for increasing as far as possible the first natural frequency of vibration is presented.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2004년도 ISMP Pb-free solders and the PCB technologies related to Pb-free solders
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• pp.257-261
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• 2004

Recently, Pb free solder technologies are developed, and start using for many packaging items. But this technology contains many problems. They are very high re-flow temperature and high cost than normal solder paste. Specially, high re-flow temperature effects heavy damage to packaging and occur many crack to packaging. We developed special ACI (anisotropic conductive ink) that becomes substitution of solder paste. This technology cans adhesive lower temperature such as $120\~150^{\circ}C$. Adhesion time is very short, too. This technology is suitable for mass production.

• Structural Engineering and Mechanics
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• 제33권1호
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• pp.31-46
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• 2009

An anisotropic damage mechanics approach is introduced which models the static and dynamic behavior of mass concrete in 3D space. The introduced numerical approach is able to model non-uniform cracking within the cracked element due to cracking in Gaussian points of elements. The validity of the proposed model is considered using available experimental and theoretical results under the static and dynamic loads. No instability and stress locking is observed in the conducted analyses. The Morrow Point dam is analyzed including dam-reservoir interaction effects to consider the nonlinear seismic behavior of the dam. It is found that the resulting crack profiles are in good agreement with those obtained from the smeared crack approach. It is concluded that the proposed model can be used in nonlinear static and dynamic analysis of concrete dams in 3D space and enables engineers to define the damage level of these infrastructures. The performance level of the considered system is used to assess the static and seismic safety using the defined performance based criteria.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.818-823
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• 2005

Creep damage is one of the mosl important characteristics for the stability of high temperature structures such as huge energy converting facilities. Creep failure of Type 316LN stainless steel is highly correlated to generation and growth of the voids. In this paper, in order to investigate the correlation of creep rupture time and ultrasonic parameters (group velocity, angular velocity), creep-damaged Type 316LN specimens and measurements for the ultrasonic parameters were made. However, bi-directional measurements were applied along the load direction and the perpendicular direction to the load line by means of the contact type probe of which the central frequencies are 10MHz, 15MHz and 20MHz. Analyzing the angular velocities of the ultrasonic signals obtained from the load direction, it was confirmed that the angular velocities were declined as the creep time passed when 15MHz and 20MHz probes were used. Also, the group velocities were declined for all three frequencies as the creep time increased. Thus, positive feasibility for the creep damage evaluation by means of the angular and group velocities was confirmed. Moreover, result of analysis for the ultrasonic signal which was obtained from the perpendicular direction upon the angular and group velocities indicated little variation for both of the angular and group velocities. Therefore, the creep damage is likely to represent anisotropic itself.

• 콘크리트학회지
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• 제7권5호
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• pp.172-178
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• 1995

콘크리트는 타설시부터 수많은 미세균열을 가지고 있으며, 이러한 미세균열등이 성장하고 전파되어 결국에는 콘크리트가 파괴된다. 이러한 일련의 과정을 손상이라 한다. 손상은 주로 2차 텐서로 표현되며 균열은 연속체적 현상으로 취급된다. 본 논문에서는 손상의 특성을 유효응력개념과 함께 등가탄성에너지법을 이용하여 나타내었으며, Helmholtz 자유에너지와 소산 포텐셜을 이용하여 손상모델의 손상전개와 구성방정식을 유도하였다. 구성방정식은 콘크리트의 탄성, 이방성 손상과 소성의 영향을 포함하도록 하였다. 두 가지 형태의 유효접선강성텐를 사용하였는데, 하나는 탄성-손상의 영향에 의한 것이며 다른 하나는 소성-손상의 영향에 의한 것이다. 모델을 검증하기 위하여 일축과 이축의 하중을 받는 콘크리트 요소에 대하여 유한요소해석을 하였으며 그 결과를 실험결과와 비교하였다.

• 한국공작기계학회논문집
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• 제15권5호
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• pp.97-103
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• 2006

A meso-scale analysis method using the natural element method, which is a kind of meshless method, is proposed for the analysis of material damage of brittle microcracking solids such as ceramic materials, concrete and rocks. The microcracking is assumed to occur along Voronoi edges in the Voronoi diagram generated using the nodal points as the generators. The mechanical effect of microcracks is considered by controlling the material constants in the neighborhood of the microcracks. The macro elastic moduli of anisotropic as well as isotropic solids containing a number of randomly distributed microcracks are calculated in order to demonstrate the validity of the proposed method.

• E2M - 전기 전자와 첨단 소재
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• 제8권1호
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• pp.90-94
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• 1995

Reactive Ion Etching(RIE) of Si$_{3}$N$_{4}$ in a CF$_{4}$/O$_{2}$ gas plasma exhibits such good anisotropic etching properties that it is widely employed in current VLSI technology. However, the RIE process can cause serious damage to the silicon surface under the Si$_{3}$N$_{4}$ layer. When an atmospheric pressure chemical vapor deposited(APCVD) SiO$_{2}$ layer is used as a etch-stop material for Si$_{3}$N$_{4}$, it seems inevitable to get a good etch selectivity of Si$_{3}$N$_{4}$ with respect to SiO$_{2}$. Therefore, we have undertaken thorough study of the dependence of the etch rate of Si$_{3}$N$_{4}$ plasmas on $O_{2}$ dilution, RF power, and chamber pressure. The etch selectivity of Si$_{3}$N$_{4}$ with respect to SiO$_{2}$ has been obtained its value of 2.13 at the RF power of 150 W and the pressure of 110 mTorr in CF$_{4}$ gas plasma diluted with 25% $O_{2}$ by flow rate.

• Composites Research
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• 제25권1호
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• pp.9-13
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• 2012

본 연구에서는 외부 충격에 의한 인체의 손상 정도를 수치적으로 예측하기 위한 인체의 근골격계 해석 모델을 제안하기에 앞서 골 조직이 가지는 기본적인 기계적 특성을 실험적으로 살펴보았다. 기계적 물성 시험의 결과, 골 조직의 위치에 따라 기계적 특성이 변화하는 비균질성을 확인하였다. 축 방향이 횡 방향에 비해 강도와 탄성계수가 2배 정도 높게 나타남을 통해 이방성 특성을 확인하였다. 점탄성 특성을 살펴보기 위해 시험 속도를 다르게 하여 시험을 수행한 결과 변형률 속도가 증가 할수록 강도 및 탄성계수가 높게 나타나는 결과를 확인하였다.

• Computers and Concrete
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• 제12권5호
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• pp.585-612
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• 2013

The paper presents quasi-static numerical simulations of the behaviour of short reinforced concrete beams without shear reinforcement under mixed shear-tension failure using the FEM and four various constitutive continuum models for concrete. First, an isotropic elasto-plastic model with a Drucker-Prager criterion defined in compression and with a Rankine criterion defined in tension was used. Next, an anisotropic smeared crack and isotropic damage model were applied. Finally, an elasto-plastic-damage model was used. To ensure mesh-independent FE results, to describe strain localization in concrete and to capture a deterministic size effect, all models were enhanced in a softening regime by a characteristic length of micro-structure by means of a non-local theory. Bond-slip between concrete and reinforcement was considered. The numerical results were directly compared with the corresponding laboratory tests performed by Walraven and Lehwalter (1994). The advantages and disadvantages of enhanced models to model the reinforced concrete behaviour were outlined.

• 한국지반공학회논문집
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• 제20권7호
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• pp.79-89
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• 2004

본 연구에서는 탄.소.점성 구성모델을 비교적 간단한 수학적 합성유도방식에 기초하여 제안하였다. 이를 위하여 비등방성 modified Cam-Clay model을 일반응력공간으로 확장시켰으며generalized viscous theory를 단순화하여 각각 소성 및 점성의 구성관계로 활용하였다. Damage 원리를 구성모델에 추가하였으며, 모든 식의 변형 및 개발은 모델정수의 수를 감소시키는 원칙에 입각하여 수행하였다. 개발된 구성모델을 활용하여 점성토의 크리프거동을 예측하였으며 이를 실험결과와 비교분석하였다. 예측된 결과는 크리프파괴의 경우를 포함한 실험결과와 비교적 양호하게 일치하는 결과를 보여주었다.