• 한국지반공학회논문집
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• 제25권12호
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• pp.57-67
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• 2009

최근 시공기술이 발전함에 따라 댐 축조재료로 사용되는 조립재료의 최대입경은 수cm에서 1m이상에 달하고 있다. 실제 현장 원입도 시료에 대한 시험을 실시하는 것은 비용적으로 고가일 뿐만 아니라 기술적으로도 많은 문제가 존재하므로 일반적으로 상사입도 시료에 대하여 실내시험을 실시하고 그 결과를 실제 지반구조물의 설계 및 해석에 적용한다. 지반구조물에 대한 보다 정확한 거동특성을 예측하기 위해서는 입자크기에 따른 전단거동 특성의 변화를 파악하는 것이 필수적이라고 할 수 있다. 이에 본 연구에서는 국내 B댐 현장 댐 축조시료인 하상 사력재에 대하여 최대입경을 서로 달리하여 재구성한 상사입도시료를 대상으로 같은 상대밀도로 공시체를 제작하여 대형삼축시험을 실시하였으며, 최대입경의 변화에 따른 상사입도시료의 응력-변형특성, 전단강도특성을 비교.분석하였다. 시험결과 조립재료는 전단과정에서 응력연화 및 체적팽창 거동을 나타내고, 상사입도 시료의 최대입경이 증가할수록 그 현상이 더욱 뚜렷한 것으로 나타났다. 내부마찰각, 전단강도는 상사입도 시료의 최대입경이 증가함에 따라 증가하는 것으로 나타났다.

• 한국세라믹학회지
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• 제43권2호
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• pp.69-73
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• 2006

A full retention of the tetragonal phase with coarse grains $(50\~60\;{\mu}m)$ was possible with the specimen $ZrO_2-1.9\;mol\%\;Y_2O_3$. In these coarse grains, $\{101\}_t$ annealing twins were frequently observed, although they do not exist in the usual fine grained specimens. The morphology and growth rate of the isothermally formed individual products are studied at an optical microscopic level. The habit planes of both products are also identified by performing two-surface trace analysis on the grains whose orientations are determined by the Electron Back Scattering Pattern (EBSP) method. The morphologies of isothermal martensite were well-defined thin plates and lenticular types. The growth rate in their longitudinal directions was quite slow and temperature-dependent. A two-surface trace analysis, incorporated with the EBSP method, identified the habit planes near $\{013\}_c$, in agreement with previous reports obtained from TEM works.

• 한국재료학회지
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• 제27권1호
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• pp.53-61
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• 2017

Magnesium alloys are of emerging interest in the automotive, aerospace and electronic industries due to their light weight, high specific strength, damping capacity, etc. However, practical applications are limited because magnesium alloys have poor formability at room temperature due to the lack of slip systems and the formation of basal texture, both of which characteristics are attributed to the hcp crystal structure. Fortunately, many magnesium alloys, even commercialized AZ or ZK series alloys, exhibit superplastic behavior and show very large tensile ductility, which means that these materials have potential application to superplastic forming (SPF) of magnesium alloy sheets. The SPF technique offers many advantages such as near net shaping, design flexibility, simple process and low die cost. Superplasticity occurs in materials having very small grain sizes of less than $10{\mu}m$ and these small grains in magnesium alloys can be achieved by thermomechanical treatment in conventional rolling or extrusion processes. Moreover, some coarse-grained magnesium alloys are reported to have superplasticity when grain refinement occurs through recrystallization during deformation in the initial stage. This report reviews the characteristics of superplastic magnesium alloys with high-strain rate and coarse grains. Finally, some examples of SPF application are suggested.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.25-26
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• 2007

At the time when nanostructured materials (NSMs) are becoming a major focus of materials research, the attention of researchers is turning more to their mechanical performance. In contrast with conventional coarse grained materials, which are either strong or ductile, but rarely both at the same time, it is expected that with NSMs both high strength and ductility can be achieved and confirmed by several experimental studies. In spite of the significant interest and efforts in the mechanical properties of NSMs, deformation mechanisms during plastic deformation as well as elastic deformation are not well established yet. In this talk, the deformation mechanisms of NSMs under various grain sizes, temperatures and strain rates were investigated. It is based on recent modelling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NSMs. Based on the theoretical model that provides an adequate description of the grain size dependence of elasticity and plasticity covering all grain size range from coarse down to the nanoscale, the tensile deformation response of NSMs, especially focusing on the deformation mechanisms was investigated.

• 암석학회지
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• 제15권3호
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• pp.139-153
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• 2006

서울특별시 종로구 훈정동에 위치한 종묘는 세계문화유산으로 등록되어 있다. 이 연구에서는 종묘의 어도에 깔려 있는 약 2,361개의 박석에 대해 규격과 재질특성을 규명하고자 하였다. 박석에서는 암종, 암색, 입도, 광물조성, 화학조성, 대자율, 박석의 크기, 표면상태, 파손상태 등이 조사를 실시하여 박석의 특성을 해석하고, 박석의 규격조건을 설정하였다 박석은 4종의 화강암류, 즉, 담회색 세중립질 각섬석흑운모화강암, 담회색 세중립질 흑운모화강암, 담홍색 중립질 내지 중조립질 흑운모화강암, 홍색 중립질 내지 중조립질 흑운모화강암과 페그마타이트, 편암류로 구성된다. 이들 중 화강암이 99.8%이다. 박석의 평균크기는 $65{\times}46cm$(표준편차 $12{\times}7cm$)이며, 박석의 표면상태는 양호 34.7%, 보통 41.4%, 보통 이하 23.8%이다. 종묘 삼도박석에서 2조각 이상으로 깨져 있는 박석은 약 720장 30.5%이다. 담홍색과 홍색을 띄는 흑운모화강암, 화강암 이외의 암석과 표면상태가 보통이하인 박석은 원래의 박석부재는 아니었을 것으로 생각되며 후세에 보수 과정에서 교체된 것으로 보인다. 이러한 박석의 수는 약 560여장이다. 박석의 주요 부재로 사용할 수 있는 화강암의 규격은 담회색 흑운모화강암(미량의 각섬석 허용)으로 입도는 세중립질$(0.5{\sim}3mm)$이며, 구성광물은 석영, 사장석, 미사장석, 퍼다이트, 흑운모 등으로 된 IUGS 분류상의 화강암 영역에 속해야 할 것으로 판단된다. 또한 $SiO_2$ 성분은 70wt.% 이상, 대자율은 $0.1{\tims}10^{-3}\;SI$ 내외(최대 $2{\times}10^{-3}\;SI$ 내외 허용)의 암석이 가장 적절 할 것으로 생각된다.

• 자원환경지질
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• 제23권3호
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• pp.343-352
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• 1990

The Cretaceous granites are widely distributed in the studied area, Mungyeong-Sangju, which belongs to the southwestern part of the Ogcheon Folded Belt. The granites are characterized by medium-coarse grained, spotted miaroles, partly flow textures of biotite, aplitic dykes and pegmatitic pockets with druse. From the major compositions, the granites indicate peraluminous, calc-alkaline, salic and late stage products of differentiation. In the view of normative compositions of Qz-Ab-Or and perthitic alkali feldspar, they were formed under 1-4kb and $426^{\circ}-456^{\circ}C$ in acqueous conditions. The K/ Ar biotite age shows $72{\pm}1$ Ma for this grante, corresponding to the igneous activity of the Bulgugsa Disturbance periods in the area. The above results represent that these granite bodies are differentiated from a single magma.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1020-1028
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• 2012

This work compares various models for geminate reversible diffusion influenced reactions. The commonly utilized contact reactivity model (an extension of the Collins-Kimball radiation boundary condition) is augmented here by a volume reactivity model, which extends the celebrated Feynman-Kac equation for irreversible depletion within a reaction sphere. We obtain the exact analytic solution in Laplace space for an initially bound pair, which can dissociate, diffuse or undergo "sticky" recombination. We show that the same expression for the binding probability holds also for "mixed" reaction products. Two different derivations are pursued, yielding seemingly different expressions, which nevertheless coincide numerically. These binding probabilities and their Laplace transforms are compared graphically with those from the contact reactivity model and a previously suggested coarse grained approximation. Mathematically, all these Laplace transforms conform to a single generic equation, in which different reactionless Green's functions, g(s), are incorporated. In most of parameter space the sensitivity to g(s) is not large, so that the binding probabilities for the volume and contact reactivity models are rather similar.

• Journal of Welding and Joining
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• 제5권2호
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• pp.9-16
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• 1987

Post weld heat treatment (PWHT) is carried out to increase the fracture toughness in heat affected zone(HAZ) and remove the residual stress. There occur some problems such as toughness decreement and stress relief cracking(SRC) in the coarse grained HAZ subjected to the effect of tempering treatment. Especially, embitterment of structure directly relates to the mode of fracture and is appeared as the difference of fracture surface, that is, grain boundary failure. Therefore, in this paper, PWHT was carried out under the stress of 0, 10, 20 and $30kg/cm^2$ to simulate residual stress in HAZ welded by heat input of 10, 30 and 40KJ/cm. Applied stress in weld HAZ during PWHT assisted precipitin of over saturated alloying element in the structure, and grain boundary failure according to welding heat input didn't almost appear at the heat input of 10 KJ/cm, but it appeared from being the applied stress of $30kg/cm^2$ at $30KJ/cm and 20kg/mm^2$ at 40KJ/cm.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.668-669
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• 2008

In this paper, we introduce various coarse-grained elastic network modeling (ENM) techniques as a novel computational method for simulating atomic scale dynamics in macromolecules including DNA, RNA, protein, and polymer. In ENM, a system is modeled as a spring network among representative atoms in which each linear elastic spring is well designed to replace both bonded and nonbonded interactions among atoms in the sense of quantum mechanics. Based on this simplified system, a harmonic Hookean potential is defined and used for not only calculating intrinsic vibration modes of a given system, but also predicting its anharmonic conformational change, both of which are strongly related with its functional features. Various nano and bio applications of ENM such as fracture mechanics of nanocomposite and protein dynamics show that ENM is one of promising tools for simulating atomic scale dynamics in a more effective and efficient way comparing to the traditional molecular dynamics simulation.

• Journal of Welding and Joining
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• 제4권2호
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• pp.40-46
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• 1986

This investigation is concerned with the toughness and microstructure of manneristically simulated HAZ in 12% Cr steel. Unnotched specimens were subjected to weld thermal cycles a weld simulator. The parameters-peak temperatures, cooling rate, influence of PWHT and plastic deformation were considered. After weld simulation, the specimens were heat-treated, V-notched and impact tested. An optical metallographic examination was performed to correlate the HAZ toughness with microstructure. Also a fractographic examination was done to obtain information on the fracture mode. The toughness of the coarse grained zone and the part of HAZ subjected to a peak temperature range 700-800.deg. C are lower than the other parts. However, they are still high enough. The double PWHT cycle could not improve the HAZ toughness in present study. However, if the first PWHT is conducted before the work piece is cooled below $M_f$, it is expected that the double PWHA may be beneficial to the toughness of the HAZ. It is also expected that martensitic welding can be used on production welds.