• 한국기계가공학회지
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• 제20권3호
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• pp.24-32
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• 2021

The size of container ships is increasing to increase the cargo loading capacity. However, container ships are limited in terms of the hull longitudinal strength. To overcome this limitation, brittle crack arrest steel can be used. This study was aimed at examining the influence of the heat input on the welding procedures of flux cored arc welding and submerged arc welding. In the experiment, the crack tip opening displacement test, which pertains to a parameter of fracture mechanics, was performed, and a 3-point bending tester was adopted. Based on the results, the crack measurement method was presented, and the stress expansion coefficient value for the pre-fatigue crack length was derived according to the heat input after the pre-cracking length was measured. It was noted that the heat input affected the crack tip opening displacement of brittle crack arrest steel.

• 대한관절경학회지
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• 제16권1호
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• pp.9-16
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• 2012

목적: 경골 고평부 골절은 슬관절에 다양한 문제를 발생시킨다. 본 연구는 관절경하 경골 고평부 골절에서 반월상 연골 손상 양상을 확인하고자 한다. 대상 및 방법: 2007년 3월부터 2010년 3월까지 경골 고평부 골절을 진단 받은 39명의 환자 중 33명 환자를 대상으로 골절 고정 시내 관절경을 시행하였다. Schatzker 분류에 따르면 1명의 I형(3.3%), 19명의 II형(53.3%), 4명의 III형(13.3%), 2명의 IV형(6.6%), 2명의 V형(6.6%), 5명의 VI형(20%) 소견을 보였다. 결과: 25명의 환자(75.8%)에서 외측 반월상 연골 파열 소견을 보였다. Schatzker II형 환자 19명 중 18명의 환자(94.7%)가, Schatzker III형 환자 4명 중 3명의 환자(75%)가, Schatzker VI형 환자 5명 중 4명의 환자(80%)가 반월상 연골 파열 소견을 보였다. 반월상 연골 중 가장 많이 손상된 부분은 외측 연골의 전각부분이다(22/25). 25명의 반월상 연골 파열 환자 중, 한 명을 제외한 모든 환자에서 반월상 연골 변연부 수직 종파열 양상을 보였으며, 이는 대부분의 경우에 있어 관절경하 봉합술을 시도할 수 있었다. 결론: 경골 고평부 골절에 있어 관절경하 반월상 연골 손상에 대한 파악 및 치료에 유용하며, 경골 고평부 골절환자에서 관절경을 권한다.

• 콘크리트학회논문집
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• 제17권1호
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• pp.121-128
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• 2005

본 연구에서는 국내고속도로에서 많이 사용되고 있는 이주형 교각을 주하중방향에 따른 이축지진하중에서의 지진응답을 실험적으로 조사하였다. 실험체는 지름 400mm 높이 2,000mm인 이주형 원형 교각 6기 및 단주형 원형교각 1기를 제작하였으며, $0.1 f_{ck}A_g$ 크기의 축방향 하중작용하에서 횡방향 하중을 주하중방향을 교축방향과 교축방향으로 하여 이축으로 교번반복 재하하였다. 실험변수는 횡구속 철근비와 주하중방향으로 주하중이 교축방향인 실험체는 기존의 단주와 같이 하부에만 소성힌 지부가 발생하는 휨파괴 양상을 나타내었지만 주하중방향이 교축직각방향인 경우 교각의 하단부 뿐만 아니라 교각의 상부에서도 소성힌지가 발생하였으며, 주하중방향이 교축방향인 실험체보다 더 좋은 연성도를 나타내었다.

• Journal of the Korean Wood Science and Technology
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• 제48권6호
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• pp.820-831
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• 2020

참나무시들음병 고사목으로부터 피해확산을 막기위해 주로 훈증처리 방법을 이용한다. 훈증처리에 따른 신갈나무 피해목의 강도적 활용 가능성을 검증하기 위해 훈증처리목재의 압축성능과 휨성능평가를 수행하였다. 훈증처리목재는 약 9개월 간 네마섹트(Metam-sodium)로 훈증처리하였다. 참나무시들음병 훈증처리목재의 기건 종압축강도는 58.87 MPa, 압축탄성계수는 5.66 GPa로 측정되었으며 건전목과 비슷한 경향을 보였다. 혼증목의 성숙재부 강도성능은 미성숙재부보다 16% 더 높은 강도값을 보였다. 참나무 건전목의 압축파괴형상은 다양한 형상으로 나타나지만 훈증처리목재의 경우 대부분 전단형 파괴형상을 보였다. 훈증처리목재의 휨강도는 157.43 MPa로 건전재보다 8% 높게 측정되었고 휨 탄성계수는 16.38 GPa로 건전재보다 16% 낮게 측정되었다. 그러나 훈증처리목재의 휨강도성능치에 대한 변동계수는 건전목보다 낮은 것을 확인하였다.

• 한국결정성장학회지
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• 제31권4호
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• pp.159-165
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• 2021

본 연구에서는 CNT 첨가에 따른 유리섬유/에폭시의 강도 변화를 관찰하기 위해서 에폭시 기지 상에 CNT를 분산 시켜 유리섬유 표면에 도포하였다. 제작된 유리섬유/에폭시/CNT 복합재의 특성을 강도 측정기를 이용해 평가하고, 파괴 메커니즘을 분석하기 위해서, 원자힘현미경과 전자현미경을 활용하여 분석하였다. 원자힘현미경 이미지들을 기반으로 line trace 분석을 통해 CNT 소재의 굵기 및 길이를 분석한 결과, 대부분의 CNT는 약 10 ㎛ 이상의 길이와 평균적으로 47.72 ± 4.0 nm의 두께를 가진것으로 확인되었다. 3 wt%로 혼합한 유리섬유/에폭시/CNT 복합재의 경우 대조 시편인 유리섬유/에폭시와 비교 시, 740.17 ± 111.05 N/mm²에서 816.56 ± 200.26 N/mm²로 약 10 % 이상의 인장 강도 향상이 관측되었다. 전자 현미경을 이용한 파단면 분석 결과, 에폭시 기지 층에 분산된 CNT가 복합재의 길이 방향으로 배열되어 있음이 관찰되었으며, 유리섬유/에폭시/CNT에 하중 인가 시, 에폭시 층에서 생성된 크랙들의 성장을 에폭시 수지상에 분산된 CNT들이 넥킹 역할을 하면서, 복합재의 인장 강도 향상이 되었다고 판단된다.

• 한국작물학회지
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• 제43권2호
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• pp.77-82
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• 1998

Aerenchyma development in rice (Oryza sativa L.) roots is quite important for adaptation to waterlogged or reduced soil conditions. Anatomical observations were carried out to clarify the development of schizogenous and lysigenous aerenchyma in elongating crown roots of rice. The crown roots of 3rd and 4th phytomer were taken from rice plants of the 8th leaf stage grown by hydroponic culture. The schizogenous intercellular spaces in the cortex of crown root tip were observed using a light microscope with semi ultra-thin sections and the lysigenous aerenchyma in mature tissue of crown root were observed using a cryo scanning electron microscope (cryo-SEM) with freezing fracture method. The schizogenous intercellular spaces in the root tip exist obviously in the middle portion of cortical cell layers close to the root-root cap junction, but not in root cap, stele and outer cell layers of cortex. The air spaces were formed at the junction of four neighbouring cells of inner cortex in the transverse sections, and between longitudinal cell layer connected along the root axis. Although many of those spaces were filled with liquid, some spaces seem to exist as air spaces. The lysigenous aerenchyma in the cortex, which hardly filled with liquid, emerged at 3-4 cm segment from the root tip and increased toward the basal region of root axis. The developing process of lysigenous aerenchyma was primarily separation of a radial row of cells caused by the shrinking and collapsing of cortical cells and then formation of septa along the radial cell rows by the fusion of cell wall with each other. These results suggest that the schizogenous and lysigenous aerenchyma playa role as a passage for the movement of oxygen into the root tip region where oxygen is required for respiration.

• Smart Structures and Systems
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• 제3권1호
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• pp.51-68
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• 2007

High-strength concrete (HSC) is becoming increasingly attractive for various construction projects since it offers a multitude of benefits over normal-strength concrete (NSC). Unfortunately, current design provisions for shear capacity of RC slender beams are generally based on data developed for NSC members having a compressive strength of up to 50 MPa, with limited recommendations on the use of HSC. The failure of HSC beams is noticeably different than that of NSC beams since the transition zone between the cement paste and aggregates is much denser in HSC. Thus, unlike NSC beams in which micro-cracks propagate around aggregates, providing significant aggregate interlock, micro-cracks in HSC are trans-granular, resulting in relatively smoother fracture surfaces, thereby inhibiting aggregate interlock as a shear transfer mechanism and reducing the influence of compressive strength on the ultimate shear strength of HSC beams. In this study, a new approach based on genetic algorithms (GAs) was used to predict the shear capacity of both NSC and HSC slender beams without shear reinforcement. Shear capacity predictions of the GA model were compared to calculations of four other commonly used methods: the ACI method, CSA method, Eurocode-2, and Zsutty's equation. A parametric study was conducted to evaluate the ability of the GA model to capture the effect of basic shear design parameters on the behaviour of reinforced concrete (RC) beams under shear loading. The parameters investigated include compressivestrength, amount of longitudinal reinforcement, and beam's depth. It was found that the GA model provided more accurate evaluation of shear capacity compared to that of the other common methods and better captured the influence of the significant shear design parameters. Therefore, the GA model offers an attractive user-friendly alternative to conventional shear design methods.

• Journal of Biosystems Engineering
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• 제39권4호
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• pp.324-329
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• 2014

Purpose: The finite element method (FEM) is advantageous because it can save time and cost by reducing the number of samples and experiments in the effort to identify design factors. In computational problem-solving it is necessary that the exact material properties are input for achieving a reliable analysis. However, in the case of fiber boards, it is difficult to measure their cross-directional material properties because of their small thickness. In previous research studies, the Poisson's ratio was measured by analyzing ultrasonic wave velocities. Recently, the Poisson's ratio was measured using a high-speed digital camera. In this study, we measured the transverse strain of a fiber board and calculated its Poisson's ratio using a high-speed digital camera in order to apply these estimates to a FEM analysis of a fiber board, a corrugated board, and a corrugated box. Methods: Three different fiber board samples were used in a uniaxial tensile test. The longitudinal strain was measured using the Universal Testing Machine. The transverse strain was measured using an image processing method. To calculate the transverse strain, we acquired images of the fiber board before the test onset and before the fracture occurred. Acquired images were processed using the image processing program MATLAB. After the images were converted from color to binary, we calculated the width of the fiber board. Results: The calculated Poisson's ratio ranged between 0.2968-0.4425 (Machine direction, MD) and 0.1619-0.1751 (Cross machine direction, CD). Conclusions: This study demonstrates that measurement of the transverse properties of a fiber board is possible using image processing methods. Correspondingly, these processing methods could be used to measure material properties that are difficult to measure using conventional measuring methodologies that employ strain gauge extensometers.

• Steel and Composite Structures
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• 제20권5호
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• pp.1067-1085
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• 2016

Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for "standard" cogs as specified in concrete standards such as AS 3600 and ACI 318. Nevertheless, all of the tested specimens failed by bar fracture outside the steel tubes. A comprehensive 3D Finite Element model was developed to simulate the pull-out tests. The FE model took into account material nonlinearities, deformations in reinforcing bars and interactions between different surfaces. The FE results were found to be in good agreement with experimental results. This model was then used to conduct parametric studies to investigate the influence of the confinement provided by the steel tube on the infilled concrete.

• 한국안전학회지
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• 제24권2호
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• pp.17-22
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• 2009

Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop($\theta$) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-tenn service.