• Smart Structures and Systems
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• 제10권1호
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• pp.47-65
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• 2012

The presence of crack-like defects in mechanical and structural elements produces failures during their service life that in some cases can be catastrophic. So, the early detection of the fatigue cracks is particularly important because they grow rapidly, with a propagation velocity that increases exponentially, and may lead to long out-of-service periods, heavy damages of machines and severe economic consequences. In this work, a non-destructive method for the detection and identification of elliptical cracks in shafts based on stress wave propagation is proposed. The propagation of a stress wave in a cracked shaft has been numerically analyzed and numerical results have been used to detect and identify the crack through the genetic algorithm optimization method. The results obtained in this work allow the development of an on-line method for damage detection and identification for cracked shaft-like components using an easy and portable dynamic testing device.

• 의료ㆍ복지 건축 : 한국의료복지건축학회 논문집
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• 제18권3호
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• pp.51-59
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• 2012

Over a past century, the continuity in post-earthquake serviceability of medical facilities has been demonstrated to be essential for sustaining a society and/or a nation stable. However, not many countries including Korea have paid appropriate attention to such a lesson learned from the previous experiences of the countries located in high seismicity for various reasons, one of which may be the lack of social consensus in allocating a portion of the resources to the earthquake preparedness. As a result, an earthquake-related policy might have been pushed away out of the list of priority in the government agenda. Therefore, the present paper attempts to persuade the public general, experts and government officials together to seek a way to upgrade the seismic safety of the country a step forward by enhancing the seismic performance of medical facilities. For this the framework of seismic design codes and standards for medical facilities, and Californian experience in managing the seismic performance enhancement program and U.S.-Italian collaborative study to improve the seismic safety of Italian hospitals are reviewed. Finally, a list of further researches and practices to perform for seismic enhancement of medical facilities in Korea are suggested.

• Structural Engineering and Mechanics
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• 제62권2호
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• pp.247-258
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• 2017

Beam-like structures such as bridge, high building and tower, pipes, flexible connecting rods and some robotic manipulators are often excited by support motions. These structures are important in machines and structures. So, this study proposes an analytic method to accurately predict the dynamic behaviors of the structures during support motions or an earthquake. Using Timoshenko beam theory which is valid even for non-slender beams and for high-frequency responses, the analytic responses of fixed-fixed beams subjected to a real seismic motions at supports are illustrated to show the principled approach to the proposed method. The responses of a slender beam obtained by using Timoshenko beam theory are compared with the solutions based on Euler-Bernoulli beam theory to validate the correctness of the proposed method. The dynamic analysis for the fixed-fixed beam subjected to support motions gives useful information to develop an understanding of the structural behavior of the beam. The bending moment and the shear force of a slender beam are governed by dynamic components while those of a stocky beam are governed by static components. Especially, the maximal magnitudes of the bending moment and the shear force of the thick beam are proportional to the difference of support displacements and they are influenced by the seismic wave velocity.

• Structural Monitoring and Maintenance
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• 제11권1호
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• pp.57-70
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• 2024

Masonry arch bridges as a vital infrastructure were not designed for seismic loads. Given that masonry arch bridges are made up of various components, their contribution under the seismic actions can be very undetermined and each of these structural components can play a different role in energy dissipation. Iran is known as a high-risk area in terms of seismic excitations and according to the seismic hazard zoning classification of Iran, most of these railway infrastructures are placed in the high and very high seismicity zones or constructed near the major faults. Besides, these ageing structures are deteriorated and thus in recent years, some of these bridges using various retrofitting approaches, including sprayed concrete technique are strengthened. Therefore, investigating the behavior of these restored structures with new characteristics is very significant. The aim of this study is to investigate the cyclic in-plane performance of masonry arch bridges retrofitted by sprayed concrete technique through the finite element simulation. So, by considering the fill-arch interaction, the nonlinear behavior of a bridge has been investigated. Finally, by extracting the hysteresis and enveloping curves of the retrofitted and non-retrofitted bridge, the effect of strengthening on energy absorption and degradation of material has been investigated.

• 한국산업융합학회 논문집
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• 제24권5호
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• pp.597-608
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• 2021

The control head components used in small military vessels are designed to be domestically produced, prototypes, structural analysis, and casting methods are designed and cast. The control head assembly consists of a lever, an aluminum outside cover, Middle, front gear cover, back gear cover, and a zinc worm gear. In order to reverse the design of each component, 3D scanning device was used, 3D modeling was performed by CATIA, and prototype productions were carried out by 3D printer. In order to reduce the cost of components, gating system is used by gravity casting method. The SRG ratio of 1:0.9:0.6 was set by applying non-pressurized gating system to aluminum parts, 1:2.2:2.0 and pressurized gating system to zinc parts, and the shapes of sprue, runner and gate were designed. The results of porosity were also confirmed by casting analysis in order to determine whether the appropriate gating system can be designed. The results showed that all parts started solidification after filling completely. ANSYS was used for structural analysis, and the results confirmed that all five components had a safety factor of 15 more. All castings are free of defects in appearance, and CT results show only very small porosity. ZnDC1 zinc alloy worm gear has a tensile strength of 285 MPa and an elongation of 8%. The tensile strength of the four components of A356 aluminum alloy is about 137-162 MPa and the elongation is 4.8-6.5%.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.668-674
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• 2002

Structural integrity assessment is indispensable for preventing catastrophic failure of industrial structures/components/facilities. This diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive and complex procedure of specimen sampling. Especially, the mechanical properties at welded zone including weldment and heat affected zone could not be evaluated individually due to their size requirement problem. So, an advanced indentation technique has been developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. Also indentation technique can evaluate a residual stress based on the concept that indentation load-depth curves were shifted with the direction and the magnitude of residual stress applied to materials. In this study, we characterized the tensile properties and welding residual stress of various industrial facilities through the new techniques, and the results are introduced and discussed.

• Corrosion Science and Technology
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• 제2권6호
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• pp.266-271
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• 2003

Safety diagnosis of various structural components and facilities is indispensable for preventing catastrophic failure of material by time-dependent and environment accelerating degradation. Also, this diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive procedure and complex procedure of specimen sampling. So, a non-destructive and simple mechanical testing method using small specimen is needed. Therefore, an advanced indentation technique was developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. In this paper, we characterized the tensile properties including yield and tensile strengths of the V-modified Cr-Mo steels in petro-chemical and thermo-electrical plants. And also, the effects of hydrogen-assisted degradation of the V-modified Cr-Mo steels were analyzed in terms of work-hardening index and yield ratio.

• 한국식품과학회지
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• 제21권1호
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• pp.80-85
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• 1989

겉보리와 쌀보리의 전분 및 이들의 구성성분인 아밀로오스와 아밀로펙틴의 분자 구조적 성질을 비교 검토하였다. 쌀보리의 전분 및 아밀로오스와 아밀로펙틴의 ${\beta}-amylosis\;limit(%)$는 각각 56.3, 87 및 52% 이었고, 겉보리 58.6, 77.7 및 57.6%이었다. 쌀보리 아밀로펙틴의 outer chain length${\overline{OCL})$과 inner chain length ${\overline{ICL}}$을 각각 15.8 및 7.8 이었고 겉보리는 각각 17.0 및 7.8이었고, 두 chain 길이의 비는 각각 약 2.1:1 및 2.0:1이었다. 두 시료 전분 모두 pullulanase 로 debranching 한 후의 Sephadex G-75에 의한 용출곡선의 양상은 ${\overline{dp}}55$ 이상의 아밀로오스 성분을 나타내는 분획과 아밀로펙틴 성분으로 볼 수 있는 ${\overline{dp}}35-45$ 및 ${\overline{dp}}10-20$의 bimodal 분포를 갖는 분획 특징을 나타내었다. 또 debranching과 동시에 ${\beta}-amylase$로 처리한 경우는 가수분해 되지 않는 ${\overline{dp}}55$ 이상의 분획성분이 $0.3{\sim}1.5%$ 존재하였다. 아울러 ${\beta}-amylase$로만 가수분해한 경우도 시료차이 없이 ${\overline{dp}}\;55$ 이상의 ${\beta}-limit\;dextrin$ 성분과 ${\overline{dp}}\;10$ 이하의 과당성분으로 분획되는 비슷한 분획양상을 보였으나 분획성분의 분자량 분포사이에는 현저한 시료 차이를 나타내었다.

• Smart Structures and Systems
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• 제22권2호
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• pp.193-200
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• 2018

From the viewpoint of engineering applications, the prediction of the failure of bogies plays an important role in preventing the occurrence of fatigue. Fatigue is a complex phenomenon affected by many uncertainties (such as load, environment, geometrical and material properties, and so on). The key to predict fatigue damage accurately is how to quantify these uncertainties. A Bayesian model is used to account for the uncertainty of various sources when predicting fatigue damage of structural components. In spite of improvements in the design of fatigue-sensitive structures, periodic non-destructive inspections are required for components. With the help of modern nondestructive inspection techniques, the fatigue flaws can be detected for bogie structures, and fatigue reliability can be updated by using Bayesian theorem with inspection data. A practical fatigue analysis of welded bogies is utilized to testify the effectiveness of the proposed methods.

• International Journal of Computer Science & Network Security
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• 제21권11호
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• pp.328-332
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• 2021

The article considers general tendencies in world and education, and also both principles and methods of forming professional, communicative, intercultural competences and in the process of teaching foreign language for professional purposes in the conditions of engineering, economic and other non-linguistic specialties at technical university. The article views some essential issues of this competence including awareness of pedagogical values, the construction of the pedagogical process, pedagogical communication and behavior; pedagogical technology, its essence, structural components, understanding of innovative components of professional activity, requirements for the design and engineering of pedagogical technologies.