• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.2
• /
• pp.646-652
• /
• 2014

It is the primary aim of this paper to propose the empirical fatigue crack propagation model fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions. The empirical models estimated are Paris-Erdogan model, Walker model, Forman model, and modified-Forman model. The parameters of each model are estimated by maximum likelihood method. The statistical crack growth data needed for an estimation of empirical models are obtained by fatigue crack propagation tests under the three cases of specimen thickness. It is found that the good empirical models fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions are Paris-Erdogan model and Walker model. It is also verified that a fatigue crack growth rate exponent of a empirical model may be a material constant at the specimen thickness conditions of 4.75mm and 6.60mm.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.449-453
• /
• 2005

하천의 물리적 생태적 특성에 대한 연구는 하천유형분류의 기초 자료로서 큰 의미가 있다. 그러나 국내의 경우 이를 위한 하천의 조사는 매우 드물며, 국부적이었다. 더욱이 이러한 생태적 물리적 특성을 근거로 한 하천 유형적 특성을 연구한 사례는 없었다. 본 연구에서는 하천의 유형을 분류하는 것은 아니지만 하천을 더욱 효율적으로 계획하고 관리하는데 필요한 기초자료를 구축하고자 하였다. 그리하여 1차적 연구로 자연환경이 유사한 하천들을 일시에 선정하여 동일한 방법으로 각 하천의 물리적 생태적 특성을 조사하고 평가하여 대상 하천의 공통적 특성을 가려내고자 하였다. 이와 관련하여 본 연구에서는 하천의 물리적 구조조사법을 유럽공동체에서 사용하는 기준과 방법에 따라 시범적으로 실시하여 국내하천의 하천환경조사를 위한 적용성 여부도 진단하고자 하였다. 하천의 물리적 구조등급이란 하천의 공간적 환경과 저수로 하상재료의 물리적 차이를 의미하는 것으로 하천 자체는 물론 하천범람지에 영향을 주는 생태적 기능의 수리 특성, 하천의 물리 특성, 수생태 특성 등을 포괄하게 된다. 따라서 하천의 물리적 구조등급은 하천구조의 생태적 질과 하천구조로 나타나게 되는 동적 과정(dynamic process)의 질을 평가하는 척도가 될 수 있다. 본 연구에서는 남한강수계의 청미천, 양화천, 복하천을 대상으로 물리적 구조조사법과 식생조사를 병행하였으며 이로부터 하천의 물리적 구조등급이 수질등급과 정량적이지는 않지만 전반적인 하천의 생태성 또는 자연도를 가늠할 수 있는 하나의 지료로 활용할 수 있음을 알 수 있었다.양토를 기준으로 할 때 강우량과 침투수의 관계는 $I_{10}(mm)=0.44R(mm)+5.8(r^2=0.55)$이었다. y절이 발생한 이유는 이전 강우에 의해 침투되고 있는 물이 있음을 함축하며 기울기 0.40은 강우의 $40\%$가 지하로 침투하였음을 의미한다. 침투수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 1.12로 가장 컸고, 식양토 0.94, 식토 0.91로 평가되었다. 이는 토성간의 침투속도 및 투수속도의 경향이 반영된 것이다. 경사에 따라서는 경사도가 증가할수록 지수적으로 감소하였으며 $10\% 경사일 때를 기준으로 $I(mm)=I_{10}{\times}1.17{\times}e^{-0.0164s(\%)}$로 나타났다. 같은 조건에서 강우량과 유거수의 관계는 $Ro_{10}(mm)=5.32e^{0.11R(mm)}(r^2=0.69)$로 나타났다. 이는 토양의 투수특성에 따라 강우량 증가에 비례하여 점증하는 침투수와 구분되는 현상이었다. 경사와 토양이 같은 조건에서 나지의 경우 역시 $Ro_{B10}(mm)=20.3e^{0.08R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.3
• /
• pp.405-412
• /
• 2013

This paper reports the steady-state stresses within the heat affected zone (HAZ) of a welded straight pipe subject to creep. The creep constants and exponent are varied systematically to see the effect of various mismatches in creep properties on the steady-state creep stresses, via detailed two-dimensional finite element (FE) creep analyses. The weldments consist of the base metal and weld metal with the HAZ, which are characterized using the idealized power creep laws with the same creep exponent. The internal pressure and axial loading are considered to see the effect of the loading mode. To quantify the creep stresses, a creep mismatch factor is introduced as a function of the creep constants and exponent. It is concluded that the ratio of the section-averaged stresses for a mismatched case to those for an evenmatched case are linearly dependent on the mismatch factor. The results are compared with the FE results, including the Type IV region, as well as the R5 procedure.

• Proceedings of the Plant Resources Society of Korea Conference
• /
• 2019.10a
• /
• pp.60-60
• /
• 2019

개비자나무[Cephalotaxus harringtonia (Knight ex Forbes) K. Koch]와 비자나무[Torreya nucifera (L.) Siebold & Zucc.]의 3년생 실생묘를 유리온실에 재배하면서 실험재료로 사용하였다. 실내의 광량을 측정하여 10, 50, 100 및 200 PPFD (${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$)로 설정하였다. 광량을 제외한 광주기(12/12 h), 온도($25{\pm}1^{\circ}C$), 습도($55{\pm}3%$) 및 관수(1회/3일)주기를 일정하게 유지시킨 밀실에서 8주간 재배하였다. 유리온실에서 재배중인 식물과 광량별 처리구의 초장, 줄기직경, 엽수, 엽장, 엽폭, 엽록소함량(SPAD) 및 광화학반응을 평가하였다. 개비자나무의 생육결과, 모든 광량조건에서 줄기직경과 엽록소함량이 증가하는 경향을 보였으며, 초장, 엽폭의 경우 대조구와 유의한 차이가 없었다. 스트레스지수(Fm/Fo), 최대양자수율(Fv/Fm) 및 광계II 성능지수(Pi_Abs)는 대조구에 비해 모든 광량에서 증가하는 경향을 나타냈다. 10 PPFD의 광량을 제외한 처리구에서 재배된 비자나무의 초장, 줄기직경, 엽장, 엽폭은 대조구와 유사한 경향을 나타냈다. 한편, 엽수와 엽록소함량은 대조구에 비해 우수하였다. Fm/Fo, Fv/Fm, Pi_Abs 및 비광학적 에너지의 손실(DIo/RC)은 모든 광량처리구에서 대조구에 비해 유의적으로 높은 측정값을 나타냈다.

• Korean Journal of Construction Engineering and Management
• /
• v.17 no.2
• /
• pp.90-98
• /
• 2016

High-rise buildings construction project have various risk factors. Major risk factors are negative results such as time delay and increase of costs. Therefore, this study was analyzed risk factors in construction stages of high-rise buildings using by PROMETHEE technique. For this, this research were identified risk factors through experts Focus Group Interview(FGI). And, PROMETHEE was used to setup evaluation standard for analysis of high-rise building construction risks. Next, the standard of evaluation index calculation was composed by using the definition level in PDRI. Preference function and evaluation index were identified through questionnaires. Through these processes, this study has calculated the importance of high-rise building construction risks using by PROMETHEE technique. As a result, high degree risk factors were as following. These are 'Operation plan of material lifting', 'Outrigger & Belt Truss Construction', 'Foundation work plan of high-rise building' and 'Considering a Structure concept of high-rise building'.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.5
• /
• pp.397-401
• /
• 2000

The corrosion-fatigue characteristics of the 12Cr steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the Rayleigh surface wave. In this study, the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the aged specimens, and then compared to the corrosion-fatigue characteristics. The width of the backward radiation profile decreases as the increase of the aging temperature, which seems to result from the increase of the effective degrading layer thickness. This parameter also shows an inversely proportionality to the exponent, m, in the Paris law which predicts the crack size increasement due to fatigue. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion-fatigue characteristics of the aged materials.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.18 no.4 s.70
• /
• pp.427-434
• /
• 2005

In this study, to develop composite bridge deck of many advantages such as light weight, high strength, corrosion resistance and high durability, profile design, laminate design and finite element analysis were carried out. In the analysis, 5-girder single span bridge with composite deck was considered. Deflection serviceability, failure criteria and web buckling were evaluated. Composite deck of designed profile was fabricated with pultrusion process. The coupon tests were conducted for the fabricated deck and the results were described.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.12 no.5
• /
• pp.35-42
• /
• 2008

This study describes the tensile test results of AISI type 304 under room and elevated temperatures. The tensile tests for AISI type 304, which is widely used for airframe structural applications, are performed according to ASTM standard. Normal probability plot was used to evaluate A and B Basis value for tensile strengths. Ramberg-Osgood parameter assuming an exponential relationship between stress and small plastic strain was obtained by least square estimate for test data. After room and elevated temperature tensile tests the surface of fractured specimens was observed by SEM images and EDX.

• Electrical & Electronic Materials
• /
• v.10 no.6
• /
• pp.541-547
• /
• 1997

(Pb$_{1-x}$ La$_{x}$)Ti$_{1-x}$ $_4$O$_3$(x=0, 0.02, 0.04, 0.08) ceramic thin films were fabricated by Sol-Gel method. A stock solution of (Pb, La)TiO$_3$ with excess Pb 10 mol% was made and spin-coated on the Pt/Ti/SiO$_2$/Si substrate at 400rpm for 30 seconds. Coated specimens were dried on the hot-plate at 35$0^{\circ}C$ for 10 min and sintered at 500~75$0^{\circ}C$ for 1 hour. The dielectric constant, remanent polarization and coercive field of the PLT(6at.%) thin films sintered at $650^{\circ}C$ were 884, 13.95$\mu$C/$\textrm{cm}^2$ and 8.7kV/cm, respectively. Pyroelectric coefficient, figure of merit of pyroelectric current, voltage responsivity and detectivity of PLT(6at.%) thin films were 3.2$\times$10$^{-8}$ C/$\textrm{cm}^2$K, 1.02$\times$10$^{-8}$ C.cm/J, 2.9 $\times$10$^{-11}$ C.cm/J, 0.29$\times$10$^{-8}$ C.cm/J, respectively.ely.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.34 no.2
• /
• pp.89-96
• /
• 2018

Purpose: The aim of this study was to evaluate the effect of delayed time, surface treatment, and repair materials on repair of bis-acryl composite resin through comparison of shear bond strength and to evaluate the utility of bis-acryl composite resin repair using polymethyl methacrylate resin. Materials and Methods: A total of 90 bis-acryl composite resin specimens were fabricated and classified into 9 test groups, each of 10 pieces according to delayed time, surface treatment and repair material. The shear bond strength of each specimen was measured using a universal testing machine immediately after fabrication and analyzed using a statistical analysis program (IBM SPSS statistics 20). After the shear bond strength measurement, the fracture surface of the specimen was observed. Results: The highest shear bond strength ($17.54{\pm}3.14MPa$) was observed in the experimental group bonded immediately with a light-curing flowable composite resin using a bonding agent. Conclusion: When repairing bis-acryl composite resin, it is necessary to consider whether to remake according to the delayed time. For effective repair, it is desirable to consider appropriate materials and surface treatment methods according to the site or purpose of use.