• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.281-284
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• 2008

Performance evaluation exposing the performance of structure is affected by the material and structural characteristics. these should be necessary for the analysis about the effect of structure performance. Thus, to evaluate the structural performance affected the material properties and structural characteristics, firstly it is conducted the eigenvalues analysis and non-linear static analysis of the structure, secondly it is analyzed the performance influence factor of the structure. The performance influence factors affecting the performance of structure divided into five classes(strength of concrete, longitudinal and transverse reinforcement, aspect ratio, axial force). From the result of analysis about the change of performance influence factor, the more the strength of concrete is increasing, the more the maximum shear force is increasing and the yield displacement is not changed, the more longitudinal reinforce is increasing, the more yield displacement and the maximum basis shear force is increasing, the more the transverse reinforce is increasing, the change of maximum basis shear force is trivial. The yield displacement of structure is increasing and the maximum basis shear force is decreasing by increasing the aspect ratio, the more the axial force increases, the more yield displacement and maximum basis shear force decease.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.859-869
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• 2009

The sharp indenters such as Berkovich and conical indenters have a geometrical self-similarity in theory, but different materials have the same load-depth curve in case of single indentation. In this study, we analyze the load-depth curves of conical indenter with angles of indenter via finite element method. From FE analyses of dual-conical indentation test, we investigate the relationships between indentation parameters and load-deflection curves. With numerical regressions of obtained data, we finally propose indentation formulae for material properties evaluation. The proposed approach provides stress-strain curve and the values of elastic modulus, yield strength and strain-hardening exponent with an average error of less than 2%. It is also discussed that the method is valid for any elastically deforming indenters made of tungsten carbide and diamond for instance. The proposed indentation approach provides a substantial enhancement in accuracy compared with the prior methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.889-897
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• 2011

In this work, we investigated the theoretical forming limit models for Zircaloy-4 and Zirlo used for spacer grid of nuclear fuel rods. Tensile and anisotropy tests were performed to obtain stress-strain curves and anisotropic coefficients. The experimental forming limit diagrams (FLD) for two materials were obtained by dome stretching tests following NUMISHEET 96. Theoretical FLD depends on FL models and yield criteria. To obtain the right hand side (RHS) of FLD, we applied the FL models (Swift's diffuse necking, M-K theory, S-R vertex theory) to Zircaloy-4 and Zirlo sheets. Hill's local necking theory was adopted for the left hand side (LHS) of FLD. To consider the anisotropy of sheets, the yield criteria of Hill and Hosford were applied. Comparing the predicted curves with the experimental data, we found that the RHS of FLD for Zircaloy-4 can be described by the Swift model (with the Hill's criterion), while the LHS of the FLD can be explained by Hill model. The FLD for Zirlo can be explained by the S-R model and the Hosford's criterion (a = 8).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.127-128
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• 2007

고밀도 트렌치 게이트 전력소자 제조를 위해 HBr. He-$O_2$, $SiF_4$, $CF_4$ 등의 식각 가스를 이용하여 형성한, 트렌치 표면 거칠기 및 손상을 최소화 하여 고밀도 트렌치 게이트 전력소자를 제조하였다. 트렌치 형상 각도가 약 900일 경우 항복전압은 약 29 V인 반면, 트렌치 각도가 $88^{\circ}$일 경우 항복전압이 37V로 트렌치 형상에 따라 약 25%의 항복전압이 높아졌음을 알 수 있었다. n-채널 트렌치 게이트 전력소자의 전압-전류 측정 결과 트렌치 게이트 수가 45.000개일 때 게이트에 10 V를 인가했을 때 전류는 약 46 A로 측정되어 고밀도 트렌치 게이트 전력소자의 특성이 좋음을 알 수 있었다.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

• Transactions of Materials Processing
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• v.1 no.2
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• pp.7-13
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• 1992

분말의 압축과 소결책의 단조 공정에서 균일하고 강도 높은 제품을 얻기 위해서는 밀도 및 밀도 분포의 조절이 매우 중요하다. 이 연구에서는 재료의 밀도 변화 특성을 고려할 수 있고, 임계 밀도 이하에서도 적용시킬 수 있는 다공질 재료의 항복조건을 유한요소법에 적용시켜 업셋 단조, 3차원 압흔 공정을 해석하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.289-292
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• 2004

반도체 소자의 파괴 원인으로는 주로 열, 전압, 전류, 진동 및 압력 등이 있다. 이 중에서 전압과 열을 스트레스 인자로 적용하여 가속열화 시험을 진행하였다. 전압 및 열에 의한 소자의 열화정도를 파악하기 위해 현재 상용화되어 있는 Phase Control Thyristor 중 $V_{DRM}\;=\;1500V,\;V_{BRM}\;=\;1500V, \;T_{HS}\;=\;-40{\sim}125^{\circ}C$ 정도의 사양을 가지는 소자를 사용하였다. 열화에 의한 여러 가지 변동특성 중에서 소자의 순방향 및 역방향 항복특성의 변화와 누설전류의 변화에 대해 실험을 통해 알아보았다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.74-75
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• 2008

TIGBT has some merits which are lower on-state voltage drop and smaller cell pitch, but also has a defect which is relatively lower breakdown voltage in comparison with planar IGBT. This lower breakdown voltage is due to the electric field which is concentrated on beneath the vertical gate. Therefore in this paper, new trench IGBT structure is proposed to improve breakdown voltage In the new proposed structure, a narrow oxide beneath the trench gate edge where the electric field is concentrated is extended into rectangular shape to decrease the electric field. As a result, breakdown voltage is improved to 23%.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.2
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• pp.186-191
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• 2001

A crack with electrically impermeable surfaces in an electrostrictive material subjected to uniform electric loading is analysed. The effect of electric yielding on stress intensity factor is investigated by using a small scale yielding model and a strip yield zone model. Complete forms of electric fields and elastic fields are derived by using complex function theory. The electrical yield zone shapes for two models are different each other. The two models, however, predict similar yield zone sizes under the small scale yielding conditions. It is found that the influence of electric yielding on the stress intensity factor is insensitive to the modeling of the electrical yield zone shape.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.30-33
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• 1999

본 연구에서는 Pt/f4-SiC Schottky barrier diodes(SBDs)의 소자 성능향상과 미세구조와의 상관관계를 규명하였다. 다른 열처리 온도구간에 따른 금속/SiC 계면의 미세구조 평가는 X-ray scattering법을 사용하여 분석하였다. 소자의 역 방향 특성은 열처리 온도가 증가함에 따라 저하되었다. As-deposited와 $850^{\circ}C$ 온도에서 열처리된 소자의 최대 항복전압은 각각 1300 V와 626 V 이었다. 그러나, 소자의 순방향 특성은 열처리 온도가 증가함에 따라 향상되었다. X-ray scattering법으로 >$650^{\circ}C$ 이상의 열처리 온도에서는 Pt/SiC 계면에서 Pt-silicides가 형성되었고, 이러한 Silicides의 형성이 Pt/SiC 계면의 평활도를 증가시킨 원인이 됨을 보였다. SBDs의 순방향 특성은 열처리 과정동안 Pt/SiC 계면에서 형성된 silicides의 결정성에 강하게 의존함을 알 수 있었다.