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고온변형시 Alloy 718 의 동적 및 준동적 재결정 거동
나영상,김인수,박노광,손성만 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.10
Compression tests were carried out on Alloy 718 to investigate the microstructure development following dynamic recrystallization, meta-dynamic recrystallization and grain growth. Tests were performed in the temperature range of 927∼1066℃ and strain rate range of 5∼5×10^(-4)s^_(-1), with true strains up to 0.8. Dynamically recrystallized grain size decreases consistently with increasing Zener-Hollomon parameter (Z=ε exp(Q/RT)) which is function of strain rate and temperature. The extent of recrystallization increases with a decrease in Zener-Hollomon parameter due to an increase in the critical strain (ε_c) corresponding to the initiation of dynamic recrystallization. The fraction of meta-dynamically recrystallized grain, however, increases with increasing the strain rate from 0.01s^(-1) to 1s^(-1). This paper outlines the microstructural evolution of Alloy 718 during the high temperature deformation.
회주철의 진동감쇠능과 기계적 성질에 미치는 오스템퍼링처리의 영향
백승한,김정철,손용철,한동운 한국열처리공학회 1999 熱處理工學會誌 Vol.12 No.2
Gray cast iron with a high damping capacity has been used for controlling the vibration and noise in various mechanical structures. Nevertheless, its usage has been often restricted due to its poor tensile strength. Therefore, it is necessary to improve tensile strength at the expense of a loss in damping capacity. This study is aimed at finding the best combination of tensile strength and damping capacity by varying austempering time and temperature range from 320℃ to 380℃ after austenization at 900℃ for 1hr. The effect of austempering condition on hardness and the volume fraction of retained austenite is investigated as well. The results obtained are summarized as follows : (1) With an increase in austempering temperature, both tensile strength and hardness decrease while damping capacity improves. (2) Austempering at 350℃, resulting in a mixture of upper and lower bainite with partially retained austenite, exhibits the optimum combination of tensile strength and damping capacity.
Ewald 합 기법을 이용한 구형 도파관의 H-면에 위치한 타원 편파 오프셋 십자 슬롯에 대한 해석
김병문,조영기,윤리호,손현 경북대학교 전자기술연구소 2000 電子技術硏究誌 Vol.21 No.1
This paper presents the analysis of an offset cross slot in the broad wall of a rectangular waveguide. The problem is formulated in teens of integro-differential equation which is solved using the method of moments with triangular Roop-top basis. For the effective numerical intgral evaluation, the Ewald sum technique is applied to the Green's function of the rectangular waveguide, transforming them into the rapidly convergent form. We have shown that a pair of narrow slots crossed at arbitrary angles and located at the proper point in the broad wall of an ordinary rectangular waveguide will radiate a wave very nearly circularly polarized at the desired direction.
Zn-0.3wt.% Al 합금의 초소성 변형에 따른 미세조직의 변화
이원절,박찬경,하태권,손중락,장영원 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.9
The superplastic deformation of Zn-0.3wt.%Al alloys were investigated at room temperature under various strain rate. These alloys were highly elongated up to 1400% at the initial strain rate of 2×10^(-4)/s, revealing the rate sensitivity parameter of about 0.4. In order to investigate the microstructural change during superplastic deformation, the transmission electron microscopy(TEM) studies were performed on the specimen elongated up to the 100% tensile strain at various strain rate. The microstructure was composed of zinc rich matrix phase, with 1㎛ in grain size, and Al rich second phases precipitated generally at grain boundaries and/or triple point. In region III(5×10^(-2)/s), the high density of dislocations were observed within the grains and deformation twins were also formed within the grains. In region II(2^*10^(-4)/s), however, the dislocations were highly localized along the grain boundaries and deformation twins were not observed. Observation of severe deformation along the grain boundaries and grain boundary migration(GBM) suggest that grain boundary sliding(GBS) is a dominant mechanism of superplastic deformation in this alloy.
FDTD 방법을 이용한 원통형 유전체 봉 안테나의 해석
이철훈,조영기,손현,이동국 경북대학교 전자기술연구소 2000 電子技術硏究誌 Vol.21 No.1
The finite-difference time-domain (FDTD) method is used toanalyze circular dielectric rod antenna excited by conducting waveguide. Two dimensional cylindrical FDTD algorithm is applied for rotationally symmetric structure. UPML is used for the cylindrical structure. Radiation patterns and reflection coefficients of this structure am obtained and compared with those available in the literature. Antenna characteristics am also determined for different rod length, tapering angle, hole position, and diameter.
질소이온주입에 따른 생체안전성 티타늄 임플란트의 마모특성
변응선,최종운,손선희,정용수 한국산업안전학회 1999 한국안전학회지 Vol.14 No.4
In this study, plasma source ion implantation was used to improve the wear properties of biocompatible titanium implant. In order to observe the effect of ion energy and dose on wear property of titanium implant, pin-on-disk type wear tests in Hank's solution were carried out. The friction coefficient of ion implanted specimens were increased from 0.47 to 0.65 under high energy and ion dose conditions. As increasing ion energy and ion dose, the amount of wear was reduced.
김현수,윤한익,손종동 한국산업안전학회 1998 한국안전학회지 Vol.13 No.1
On the stability of the cantilever beam subjected to a follower force at the free end, the influences of the translational spring and the moment of inertia of a tip mass at the free end have been studied by numerical methods. The centroid of a tip mass is offset from the free end of a Beam and is located along its extended axis to vary the value of moment of inertia of a tip mass. It is proved that as the constants of a spring supporting the free end are augmented, the critical flutter loads of the above system decrease, whereas they increase without a tip mass.
손광락 한국재정학회 1993 재정논집 Vol.7 No.-
This paper develops and estimates a model of tax compliance in which the Internal Revenue Service uses its resources to maximize tax revenue. The model differs from previous models in two important respects. (i) It reflects the natural temporal sequence of decision making; i.e., a taxpayer first files a tax return and then the IRS decides whether or not to audit. (ii) The model does not restrict the basic variables to only two possible levels as several previous models have done. The theoretical analysis establishes that the probability of audit depends on many variables such as the taxpayer's reported income, the IRS's auditing costs, the tax rate, and the penalty rate. The IRS's budget is related to the probability of audit only when the IRS faces binding budget constraint. An increase in a taxpayer's risk aversion results in higher compliance and less auditing. The model shows that minimizing the variance of the IRS's estimate of a taxpayer's income does not always improve compliance. There is a unique variance for this estimation error which maximizes a taxpayer's compliance, and this optimal variance for the estimation error depends on the taxpayer's degree of risk aversion. Several authors have questioned whether it is useful for the IRS to keep secret the formula it uses to estimate taxpayer's incomes. We show that if the estimation errors are sufficiently small, the IRS would benefit from revealing the estimation formula and committing to audit any taxpayer with reported income less than the estimate.