• 콘크리트학회논문집
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• 제16권1호
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• pp.125-129
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• 2004

Hydrating concrete pavement is typically subjected to temperature-induced stresses that drive cracking mechanisms at early concrete ages. Undesired cracking plays a key role in the long-term performance of concrete pavement systems. The loss of support beneath the concrete pavement due to curling caused by temperature changes in the pavement may induce several significant distresses such as punch out pumping, and erosion. The effect of temperature on these distress mechanisms is both significant and intricate. Because thermal conductivity dominates temperature flow in hydrating concrete over time, this material property is back-calculated by transforming governing equation of heat transfer and test data measured in laboratory. Theoretically, the back- calculated thermal conductivity simulates the heat movements in concrete very accurately. Therefore, the back- calculated thermal conductivity can be used to calibrate concrete temperature predicted by models.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2008년도 추계 학술논문 발표대회
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• pp.17-20
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• 2008

This study investigated the fundamental properties and cracking shapes of mortar for the floor after Mock-up test with FRP as wastes of crafts. For the flowability of fresh mortar without FRP, it was favorable compared with fresh mortar using FRP, and the drop time at O-Lot was similar to the flowability. For the compressive strength of fresh mortar with FRP, it was increased about 10% compared with plain. The flexible strength was also increased on fresh mortar with FRP. On the cracking shape, there was many penetrated crack in all directions on plain. In the case that FRP was used, it seemed to have excellent resistance to the crack occurrence because there was no directive crack at a limited part.

• 비파괴검사학회지
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• 제25권6호
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• pp.451-458
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• 2005

The effects of fiber orientation on acoustic emission(AE) characteristics have been studied for various composite laminates. Reflection and transmission optical microscopy were used to investigate the damage zone of specimens. AE signals were classified through short time Fourier transform(STFT) as different types: AE signals with a high intensity and high frequency band were due to fiber fracture, while weak AE signals with a low frequency band were due to matrix cracking and/or interfacial cracking. Characteristic feature in the rate of hit-events having high amplitudes showed a procedure of fiber breakages, which expressed the characteristic fracture processes of notched fiber-reinforced plastics with different fiber orientations. As a consequence, the behavior of fracture in the continuous composite laminates could be monitored through nondestructive evaluation(NDE) using the AE technique.

• 한국화재소방학회논문지
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• 제2권1호
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• pp.3-10
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• 1988

Concrete is incombustible and has good fire resisting properties, i. e. when exposed to fire it continues to perform satisfactorily for a reasonable period of time. Nevertheless, with time and high temperature gradient, brought about the fire, causes cracking and spatting. Further deterioration and loss of strength are caused by gradual dehydration of concrete paste. This paper is aimed to make a proposal for the design and construction of reinforced concrete structures with more sufficent resistance to fire by the theoritical analysis, which is base4 on investigation of general damages by the fire and change of properties on concrete influenced by high temperature.

• 열처리공학회지
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• 제9권1호
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• pp.34-44
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• 1996

Austenite stainless steel was produced by arc welding with current 650A, voltage 50V and welding speed 10cm/min. It was post-welded and then heat treated at $1,050^{\circ}C$ for 120min. And then it was immersed in water or in air. The microstructural changes, ferrite contents, mechanical properties, and stress corrosion cracking(SCC) were investigated. The SCC was studied in 42wt% boiling $MgCl_2$($140^{\circ}C$) under the constant stress using SCC elongation curve. The results showed that; 1. The as-welded spedimen seemed to increase ${\delta}$-ferrite content largely, and revealed continuous network of lathy and vermicular type. The post-welded heat treatment changed the morphologies of ferrite from continuous type to island type. 2. The as-welded, air and water quenched specimens had the ${\delta}$-ferrite content 9.7%, 3.2% and 2.1% respectively. We also showed that ${\delta}$-ferrite was Cr-rich and Ni-poor by EPMA. 3. The time of failure on the SCC was measured and it was used for corrosion elongation curve. The condition of SCC was investigated under $35kgf/mm^2$ load and the results were as follows; 4. The intergranullar cracking by stress corrosion was most distinct in weld metal while the transgranular cracking occurred in the air cooled specimen.

• 한국전자통신학회논문지
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• 제4권3호
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• pp.217-223
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• 2009

최근, 다양한 네트워크의 발달은 심각한 사회문제를 발생시킨다. 그러므로 네트워크의 보안성을 통제할 수 있는 방법이 요구되어진다. 보안과 관련된 이러한 문제들은 해킹, 크래킹과 같은 비 보안분야에 직면해 있다. 새로운 암호알고리즘의 개발없이 해커나 크래커로부터 안전성을 보장받기 위한 방법은 확장된 키 길이를 통한 비 암호해석법을 유지시키는 것이다. 본 논문에서는 RSA 암호시스템에서 병목현상을 제거하기 위해서 가변길이 곱셈, 캐리 생성 부분을 하나의 어레이 방식을 사용하는 몽고메리 곱셈기 구조를 제안하였다. 그러므로 제안된 몽고메리 곱셈기는 크래킹으로부터 안전성을 제공하게 되며 실시간 처리가 가능해질 것이다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.158-159
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• 2014

In general, the shrinkage occurring in the floor mortar is large the influence by the dry shrinkage. In order to reduce the cracks occurring in the floor mortar, studies of physical methods are often performed, but these methods is difficult to prevent cracking of the floor mortar essentially. Therefore, in this study, the dry shrinkage properties of floor mortar of gypsum and red clay type using alpha-hemihydrate gypsum had been evaluated. The experimental variables were cement mortar(CM), gypsum mortar(GM), red-clay mortar(RM), the evaluation items was conducted experiment to evaluate the setting time, the compressive strength, drying shrinkage cracks, the dry shrinkage. As a result, it was confirmed that condensation time of GM is shorter that that of CM, and GM satisfied the compressive strength of the floor mortar standard. Also shrinkage deformation of GM reduced more than the CM.

• Structural Engineering and Mechanics
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• 제20권1호
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• pp.1-20
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• 2005

The present paper deals with the seismic response analysis and the evaluation of most likely failure modes for a water storage structure. For the stress analysis, a 3-D mathematical model has been adopted to represent the structure appropriately. The structure has been analyzed for both static and seismic loads. Seismic analysis has been carried out considering the hydrodynamic effects of the contained water. Based on the stress analyses results, the most likely failure modes viz. tensile cracking and compressive crushing of concrete for the various structural elements; caused by the seismic event have been investigated. Further an attempt has also been made to quantify the initial leakage rate and average emptying time for the structure during seismic event after evaluating the various crack parameters viz. crack-width and crack-spacing at the locations of interest. The results are presented with reference to peak ground acceleration (PGA) of the seismic event. It has been observed that, an increase in PGA would result in significant increase in stresses and crack width in the various structural members. Significant increase in initial leakage rate and decrease in average emptying time for the structure has also been observed with the increase in PGA.

• 한국컴퓨터정보학회논문지
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• 제6권3호
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• pp.84-90
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• 2001

네트워크의 발전은 통신망의 발전과 더불어 심각한 사회문제를 발생시킨다. 즉, 보안에 관련된 문제는 네트워크를 사용할 경우 해킹과 크래킹에 대하여 더욱 주의해야한다는 것이다. 이러한 해커나 크래커로부터 보안을 유지하기 위해서는 새로운 암호알고리즘을 개발하거나 키길이를 길게하여 정해진 시간안에 복호불가의 상태를 유지하는 방법이 일반적으로 사용되고 있다. 본 논문에서, RSA 암호시스템에서 제안된 몽고메리 승산기는 캐리부분만을 어레이 형태로 구성하였고 병목현상을 없애기 위하여 승산과정을 가변길이화로 구성하였다. 그러므로 제안된 몽고메리 승산기는 실시간 처리 및 외부의 크래킹을 막아낼 수 있는기능을 강화시켰다.

• Structural Engineering and Mechanics
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• 제69권1호
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• pp.33-42
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• 2019

Thermal cracks are cracks that commonly form at early ages in mass concrete. During the concrete pouring process, the elastic modulus changes continuously. This requires the time domain to be divided into several steps in order to solve for the temperature, stress, and displacement of the concrete. Numerical simulations of thermal crack propagation in concrete are more difficult at early ages. To solve this problem, this study divides crack propagation in concrete at early ages into two cases: the case in which cracks do not propagate but the elastic modulus of the concrete changes and the case in which cracks propagate at a certain time. This paper provides computational models for these two cases by integrating the characteristics of the extended finite element algorithm, compiles the corresponding computational programs, and verifies the accuracy of the proposed model using numerical comparisons. The model presented in this paper has the advantages of high computational accuracy and stable results in resolving thermal cracking and its propagation in concrete at early ages.