• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.154-159
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• 2013

In this paper, the effect of bolt clamping force and form accuray of contact surface between mirror and mount on mirror surface was studied. Normally, mirror used in reflecting optical system was assembled with mount by bolts or adhesive. In this case, the tension caused by bolt clamping force or adhesive force may distort the mirror surface. Also, form accuracy error of the contact surface have a negative impact on wrenched mirror surface which assembled by bolts or adhesive. In this study, stress and distorted displacements on mirror surface were analyzed according to the different contact surface form accuracies and bolt clamping forces by using the finite element analysis method.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1137-1139
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• 1999

저가의 우수한 성능을 갖는 적외선 영상표시 소자 구현에 적합한 마이크로 볼로미터를 MEMS 기술을 사용하여 제작하였다. 작은 열질량을 갖는 마이크로미터 단위의 열적고립 구조(thermal isolation structure) 제작은 폴리이미드(PI2611)를 희생층으로 사용하여 최종적으로 ashing공정 단계에서 폴리이미드를 제거하여 마이크로 볼로미터 구조를 완성하였다. 이 때의 구조층으로는 PECVD 질화실리콘($SiN_x$) 박막, 감지층으로 산화바나듐($VO_x$) 박막을 사용하였다. 본 연구에서는 폴리이미드 패턴 형성시 건식식각 공정조건 변수에 따라서 패턴의 기울기를 조절하여 폴리이미드 측면에서 발생되는 불 균일한 박막 증착과 패터닝 문제를 개선하였다. 또한 저응력의 질화실리콘 박막을 사용하여 잔류응력에 의한 열적고립 구조의 뒤틀림 현상을 완화하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5A
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• pp.389-397
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• 2011

In this study, an experiment for the biaxial behavior of specimens was carried out to identify whether the isotropic flexure tensile stress of concrete in the BFT method is feasible. Another experiment for the improvement of the BFT method was conducted to ensure the isotropic flexure tensile stress of BFT specimens during the test. In addition, the biaxial flexure strength of concrete given by the improved BFT method was compared to the uniaxial flexure strength by the four-point bending test. Test results show that the isotropic flexure tensile stress of concrete using the BFT method was highly influenced by the surface conditions and warping of the specimens. Using improved BFT method, we could obtained the isotropic flexure tensile stress of concretes. The biaxial flexure strength of BFT was about 32% greater than the uniaxial flexure strength of the four-point bending test. In the experiment, with the smaller scatter, the improved BFT method gave a reliable biaxial flexure strength like the four-point bending test.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.5
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• pp.190-195
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• 2014

Because of the temperature gradient occurring during the growth of the ingot with directional solidification method, defects are generated and the residual stress is produced in the ingot. Changing the growth and cooling rate during the crystal growth process will be helpful for us to understand the defects and residual stress generation. The defects and residual stress can affect the properties of wafer. Generally, it was found that the size of grains and twin boundaries are smaller at the top area than at the bottom of the ingot regardless of growth and cooling condition. In addition to that, in the top area of silicon ingot, higher density of dislocation is observed to be present than in the bottom area of the silicon ingot. This observation implies that higher stress is imposed to the top area due to the faster cooling of silicon ingot after solidification process. In the ingot with slower growth rate, dislocation density was reduced and the TTV (Total Thickness Variation), saw mark, warp, and bow of wafer became lower. Therefore, optimum growth condition will help us to obtain high quality silicon ingot with low defect density and low residual stress.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.545-555
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• 2002

This paper presents a matrix analysis to get the torsional behavior of core structures with torsional reinforcements. Based on simplified assumptions, formulae for the forces and displacements of cote structures subjected to three typical load cases, i.e. uniformly distributed torque, triangularly distributed torque and a concentrated torque at the top of the structure, are derived analytically. The behavior of the cote according to the variation of reinforcement locations is investigated to estimate the optimum locations of reinforcements to minimize the core rotations and bimoments. The results by the program MIDAS-GEN have shown that this analysis can give quite satisfactory results for structural models with torsional reinforcements. Although three dimensional analysis by computer has come within reach as a normal structural design procedure, its use as an optimization tool may not be desirable in view of the expense and time required. Formulae that we presented here can be used to estimate the torsional rotations and forces of practical cote structures at the preliminary design stages.

• Journal of the Korean Institute of Gas
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• v.8 no.3 s.24
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• pp.8-15
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• 2004

This paper presents von Mises stress, deformation, and rotating distortion moment characteristics of inner tank bottom plate as a function of a cryogenic temperature difference along the radial distance from the center area to the corner one. The calculated results show that the filling level of LNG at the beginning of the cool-down process is very important for the design safety analysis of the inner tank. Obviously the thermal loading by a temperature difference between the LNG vapor gas of $-80^{\circ}C$ and a LNG temperature of $-162^{\circ}C$ affects to the thermal related characteristics of the bottom plates and annular one. From the computed results, the temperature difference by a vapor gas and liquid of LNG may lead to the thermal instability of the bottom plate. This phenomenon may cause the system failure of an inner tank.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.849-852
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• 2001

본 눈문에서는 뒤틀림, 응력, 압력[1], 토크, 가속도 등의 물리적인 동적 현상을 측정하여 수집된 데이터를 처리하기 위한 신호처리(Signal Processins) 기능이 결합되어 넓은 용도로 활용할 수 있는 센서 신호 수집 시스템을 구현하였다. 구현된 시스템은 data acquisition board 의 하드웨어와 소프트웨어로 나누어 볼 수 있다. 하드웨어의 구성은 아날로그부, 디지털부, 그리고 시스템 인터페이스 처리부로 되어 있다. 아날로그부에서는 센서신호를 받아서, PGA (Programmable Gain Amplifier)[2]와 Op-Amp를 사용하여 signal conditioning 처리하여 8차 Lowpass Filter 로 보낸다. Filtering 된 신호는 ADC (Analog to Digital Converter) 가 내장되어 있는 PIC(3) microcontroller로 보내져 AD변환과 디지털 신호 처리를 한다. 처리된 신호는 RS232 인터페이스를 통해 호스트 컴퓨터로 보내 사용자가 분석할 수 있도록 한다. 또한 LCD display 실시간으로 확인, 분석할 수 있으며 동시에analog output에서 센서신호의 특징을 분석 할 수 있도록 한다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.38-38
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• 2003

PTO/PZO 초격자 박막은 박막 계면에 응력이 발생하여 기존의 박막처럼 size effect가 적용되지 않고 두께가 감소해도 높은 유전상수를 갖는다. Antiferroelectric PbZrO$_3$(PZO)와 ferroelectric PbTiO$_3$(PTO)를 적층 성장시킨 초격자는 400도에서 성장한 (100) Pt/SiO$_2$기판 위에 rf magnetron sputtering으로 증착하였다. PTO/PZO의 증착 주기는 30(PTO $_{4unti cells}$/PZO $_{4unti cells}$) 에서 1(PTO $_{125unti cells}$/PZO $_{125unti cells}$)까지 두께의 변화를 주어 준비했고 초격자 박막의 전체두께는 100nm로 고정시켰다. XRD결과, PTO/PZO는 주기에 따라 초격자의 특성인 main peak과 satellite peak을 관찰 할 수 있었다. 초격자의 주기가 감소함에 따라 2$\theta$값이 증가하고 평균 d 값이 감소되면서 PTO층에 뒤틀림이 증가하였다. PTO층의 뒤틀림 증가로 인해 superlattice의 주기가 증가함에 따라 초격자의 유전율이 증가하였고 강유전성이 향상되었다.향상되었다.

• Polymer(Korea)
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• v.36 no.2
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• pp.131-136
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• 2012

Residual stress is developed in the injection molded articles during the molding process due to temperature variation and shear stress. The residual stress causes the deformation and warpage in the injection molded parts shortly within several days or after several years. Therefore, the injection molding conditions should be optimized to reduce the residual stress. And residual stress in the part should be also relaxed after molding process to maintain its shape. According to the annealing conditions, such as relative humidity, temperature and time, this study investigates the relaxation of residual stress generated in the transparent injection molded specimens. Through the experimental results, it was realized that the residual stress was relaxed at a relative humidity higher than 50%. Utilizing photoelasticity equipment, it was found that the residual stress was rapidly relaxed near glass transition temperature. Additionally, we recognized that the specimen shrunk along the flow direction but expanded to the perpendicular direction of the flow during the annealing processes, which resulted in the warpage of the specimen.

• Journal of Korean Society of Steel Construction
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• v.25 no.2
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• pp.115-130
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• 2013

In this study, lateral-torsional buckling (LTB) strength of high-strength H-beams built up from 800MPa tensile-strength steel was experimentally and analytically evaluated according to current lateral stability provisions (KBC 2009, AISC-LRFD 2010). The motivation was to evaluate whether or not current LTB provisions, which were originally developed for ordinary steel with different stress-strain characteristics, are still applicable to high-strength steel. Two sets of compact-section specimens with relatively low (Set A) or high (Set B) warping stiffness were prepared and tested under uniform moment loading. Laterally unbraced lengths of the test specimens were controlled such that inelastic LTB could be induced. All specimens exhibited LTB strength exceeding the minimum limit required by current provisions by a sufficient margin. Moreover, some specimen in Set A reached a rotation capacity required for plastic design, although its laterally unbraced length belonged to the inelastic LTB range. All the test results indicated that extrapolation of current provisions to high-strength steel is conservative. In order to further analyze the test results, the relationship between inelastic moment and laterally unbraced length was also derived in explicit form for both ordinary- and high-strength steel based on the effective tangent modulus of inelastic section. The analytical relationship derived again showed that extrapolation of current laterally unbraced length limit leads to a conservative design in the case of high-strength steel and that the laterally unbraced length to control the inelastic LTB behavior of high-strength steel beam should be specified by including its unique post-yield strain-hardening characteristics.