• 소성∙가공
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• 제5권2호
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• pp.156-164
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• 1996

To investigate the behavior of plastic deformation in axisymmetric extrusion through square dies, experimental works with the plasticine as a model material are carried out at the room temperature. Some mechanical properties of the model material are determined by compression and ring compression tests. Visioplasticity method using expermental grid distortion in extrusion is introduced to analyze the plastic flow strain rate and strain distribution. In spite of severe deformation during the extrusion through square die the visioplasticity method shows good results for the distribution of effective strain rate and effective strain.

• 항공우주기술
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• 제6권1호
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• pp.1-6
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• 2007

본 연구에서는 상온에서 수작업으로 함침/경화시킨 일 방향 glass/epoxy 복합재료 적층판의 설계압축강도 값을 제시하고 있다. 총 39개의 시편으로부터 측정된 압축강도 값은 two-parameter Weibull 분포를 따른다고 가정하였다. MIL-HDBK-17F에 제시된 방법과 절차에 따라 동일형상의 복합재료 시편에 대해 구한 B-Basis 값과 A-Basis값은 각각 평균 압축강도의 82.6% 및 65.9%로 확인되었다. 항공기 주익의 스파 Cap에 동일 복합재료를 적용할 경우를 고려하여 B-base 값의 50%를 설계압축강도 값으로 산정하였다.

• 소성∙가공
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• 제30권5호
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• pp.226-235
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• 2021

The strain aging behavior of a low carbon dual phase steel was examined in two conditions: representing room temperature strain aging (100 ℃ × 1 hr after 7.5 % prestrain) and bake hardening process (170 ℃ × 20 min after 2 % prestrain), basing on carbon effective diffusion and dislocation distribution. The first principle calculations revealed that (Mn or Cr)-vacancy-C complexes exhibit the strongest attractive interaction compared to other complexes, therefore, act as strong trapping sites for carbon. For room temperature strain aging condition, the carbon effective diffusion distance is smaller than the dislocation distance in the high dislocation density region near ferrite/martensite interfaces as well as ferrite interior considering the carbon trapping effect of the (Mn or Cr)-vacancy-C complexes, implying ineffective Cottrell atmosphere formation. Under bake hardening condition, the carbon effective diffusion distance is larger compared to the dislocation distance in both regions. Therefore, formation of the Cottrell atmosphere is relatively easy resulting in to a relatively large increase in yield strength under bake hardening condition.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.162-167
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• 2000

The warm deep drawability in square cup drawing is investigated about a newly developed high-strength steel sheet with retained austenite which is transformed into martensite during forming. For this investigation, six steps of temperature ranges, from room temperature to $250^{\circ}C$, and five kinds of drawing ratio, from 2.2 to 2.6 were adopted. As a result the maximum drawing force and the maximum drawing depth were affected by the elevated temperatures, and the more stable thickness strain distribution was observed to the elevated temperatures. But blue shortness happened over $200^{\circ}C$. The FEM analysis using the LS-DYNA code is adopted to compare the experimental results with the analytical results for thickness strain distribution.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1988년도 추계학술대회 논문집
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• pp.1-4
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• 1988

The high frequency and quasi-state C-V curves were measured to determine the interface state density in MNOS devices. Berglund method was appropriate for determination of energy distribution of interface state density all over the energy gap. Applying Vg vs Øs relation by Berlund method to comparison-analysis method of the high-frequency and quasi-static C-V curves, we were able to determine the energy distribution by only measured C-V curves without theoretical C-V curves. The interface state density near the conduction band was high at lower temperature than room temperature.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.168-173
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• 2000

The limiting drawing ratio (LDR) under uniform heating of blanks was measured at the various temperature ranges between 25 and $250^{\circ}C$ by using two different blank shapes, square and circular blanks, and six different blank sizes with the drawing ratios(DR) of 2.4 to 2.9. The galvannealed steel sheet (SCP3CM 60/60) of 0.7mm thickness was used. The LDR at warm forming condition reached 1.2 times of that at room temperature, and the maximum drawing depth reached 1.9 times. The higher temperature was adopted, the more stable and uniform thickness strain distribution was observed.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.214-215
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• 2000

As silica based optical fibers and preforms are processed at a high temperature, residual stresses are bulit in the strucure when cooled down to the room temperature. The magnitude of the residual stress depends on the difference in the thermal expansion coefficients between core and cladding glass as well as on the temperature difference. Residual stress distribution determines the intrinsic strength and could affect the long term reliability of optical fibers. And furthermore, stress can introduces anisotropy into optical fibers by photoelastic effects. The analysis of thermal stress has been intensively studied for multimode fibers$^{(1)}$ and the authors and co-wokers recently reported the stress distribution in a depressed inner cladding structure$^{(2)}$ . The compositions of the glass in the previous studies, however, have been restricted to conventional glass formers, such as GeO2, B2O3, P2O5, Fluorine. (omitted)

• 소성∙가공
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• 제11권5호
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• pp.423-429
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• 2002

The limiting drawing ratio (LDR) under uniform heating of blanks was measured at the various temperature ranges between 25 and 25$0^{\circ}C$ by using two different blank shapes, square and circular blanks, and six different blank sizes with the drawing ratios(DR) of 2.4 to 2.9. The galvannealed steel sheet (SCP3CM 60/60) of 0.7mm thickness were used. The LDR at warm forming condition reached 1.2 times of that at room temperature, and the maximum drawing depth reached 1.9 times. The higher temperature was adopted, the more stable and uniform thickness strain distribution was observed. Some cases of the experimental results were compared with the analitical results using the commercial finite element method (FEM) code.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1992년도 춘계학술대회 논문집
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• pp.125-129
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• 1992

When relaxation time will be distributed, TSC observed in the experimental procedure was analysed by using a potential model having two equilibrium positions and equations of dielectric properties was derived. Calculation of distribution was made by matrix method and compared/confirmed values obtained by TSC and alternating current which have a correspondence with each other. In this measurement, distribution of activation energy and relaxation time was determined by TSC peak at around 147k/364 of which center is 10$\^$-4/ sec/10$\^$5/ sec respectively at room temperature and also obtained dielctric loss factor at the range of 10$\^$-7/-10$\^$5/Hz. It seems that low temperature peak is local dispersion and high temperature peak have a relation to dielectric transition of the material.

• 한국표면공학회지
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• 제29권6호
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• pp.884-890
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• 1996

We have investigated a structural change of Si(100)-($2 \times 1$)-Sb surface caused by atomic hydrogen adsorption at room temperature using time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS) and low energy electron diffraction (LEED). We found that when atomic hydrogen adsorbs on the Si(100)-($2 \times 1$)-Sb surface, (1) the partial desorption of Sb atoms from the Si(100) surface occurs even at room temperature, (2) the rest Sb atoms are displaced from their original positions and form an almost two-dimensional layer with dispersive distribution of Sb atoms, and (3) the structural transformation into the Si(100)-($1 \times 1$)-H periodicity is induced by the formation of the $1 \times 1$-H dihydride phase on the Si substrate.