• Title/Summary/Keyword: High elastic

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Evaluation of Deterioration of Concrete due to High Temperature through Harmonics (고조파 평가를 통한 콘크리트의 고온 열화 평가)

  • Hwang, Eui-Chul;Kim, Guy-Yong;Son, Min-Jae;Pyeon, Su-Jeong;Sasui, Sasui;Nam, Jeong-Soo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2021.11a
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    • pp.146-147
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    • 2021
  • In this study, the deterioration of concrete subjected to high temperature was evaluated using harmonics. When concrete is exposed to high temperatures, its mechanical properties deteriorate. In order to evaluate this deterioration, a method of analyzing the waveform of elastic waves was applied. As the heating temperature increased, the fundamental wave of the 50 kHz elastic wave passing through the concrete decreased. In addition, harmonics were generated at each temperature, and the higher the heating temperature, the greater the ratio of harmonics. The higher the compressive strength, the greater the amplitude of the fundamental wave, and this phenomenon is thought to be due to the internal structure of concrete.

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Elastic Modulus of Locally Stiffness-variant Polydimethylsiloxane Substrates for Stretchable Electronic Packaging Applications (신축성 전자패키징용 강성도 국부변환 polydimethylsiloxane 기판의 탄성계수)

  • Oh, Hyun-Ah;Park, Donghyeun;Han, Kee-Sun;Oh, Tae Sung
    • Journal of the Microelectronics and Packaging Society
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    • v.22 no.4
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    • pp.91-98
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    • 2015
  • In order to apply to stretchable electronics packaging, locally stiffness-variant stretchable substrates consisting of island structure were fabricated by combining two polydimethylsiloxane elastomers of different stiffnesses and their elastic moduli were characterized as a function of the width of the high-stiffness island. The low-stiffness substrate matrix and the embedded high-stiffness island of the stretchable substrate were formed by using Dragon Skin 10 of the elastic modulus of 0.09 MPa and Sylgard 184 of the elastic modulus of 2.15 MPa, respectively. A stretchable substrate was fabricated to be a configuration of 6.5-cm length, 0.4-cm thickness, and 2.5-cm width, in which a high-stiffness Sylgard 184 island, of 4-cm length, 0.2-cm thickness, and 0.5~1.5-cm width, was embedded. The elastic modulus of a stretchable substrate was increased from 0.09 MPa to 0.16 MPa by incorporating the Sylgard 184 island of 0.5-cm width to Dragon Skin 10 substrate matrix. The elastic modulus was further improved to 0.18 MPa and 0.2 MPa with increasing the Sylgard 184 island width to 1.0 cm and 1.5 cm, which were in good agreement with values estimated by combining the Voigt structure of isostrain and the Reuss structure of isostress.

A Characteristics of Crack Behavior on Graphite (그라파이트 재료의 고온 크랙특성 평가)

  • Koo, Song-Hoe;Lee, Young-Shin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.417-420
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    • 2009
  • The purpose of the present study is to evaluate high temperature fracture toughness through the experimental and analytical method. The analysis method is proposed to simulate the fracture toughness of high temperatures. Load-COD curves of compact test specimen acquired by finite element method analysis using hypo elastic model are simulated to determine the crack initiation load on high temperatures. The results of experimental work are in accord with analysis in thermal shock test.

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Experimental Study on the Long-Term Properties of High Strength Concrete (고강도 콘크리트의 장기거동 특성에 관한 실험적 연구)

  • Joung, Won-Seoup;Park, Dong-Su;Kwon, Ki-Joo;Lee, Wang-Hee;Kang, Min-Seok
    • Proceedings of the Korea Concrete Institute Conference
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    • 2009.05a
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    • pp.225-226
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    • 2009
  • Day by day, concrete buildings and structure became high-rising and magnificently vast scheduled, as contributed from the development of improved equipments that suitable to specific construction works and high qualitied Material, the durability of the concrete was highly improved. The temporary elastic reduction occur at vertical members such as walls and columns under vertical loads. Specially, inelastic reduction such as creep and shrinkage occur long termly with elastic one in case of reinforced concrete members. Generally, creep and shrinkage depend on time and this is affected by concrete strength, concrete type, member size, steel ratio, and relative humidity. And elastic reduction rely on time, too because concrete is loaded before revelation of perfect strength in terms of construction conditions. So, tests on mechanical properties of concrete certainly need in order to apply to construction by forecasting an amount of reduction caused by the complex factors. Therefore, in this study the tests on creep, shrinkage are carried out to offer basic data for predicting an amount of long-term Properties at the concrete columns of an object structure, and results of the tests are described.

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Structual Stability Analysis According to the Lumped Mass of High Speed Vehicles in Underwater (집중질량 변화에 따른 수중 고속 운동체의 구조 안정성 해석)

  • Oh, Kyung-Won;Sur, Joo-No;Cho, Byung-Gu;Ryu, Si-Ung;Kong, Gong-Duk
    • Journal of Ocean Engineering and Technology
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    • v.23 no.1
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    • pp.54-59
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    • 2009
  • In this paper, the effect of the position and size of a lumped mass on the structural stability of a high speed underwater vehicle is presented. For simplicity, a real vehicle was modeled as a follower force subjected beam that was resting on an elastic foundation, and the lumped mass effect was simplified as an elastic intermediate support. The stability of the simplified model was numerically analyzed based on the Finite element method (FEM). This numerical simulation revealed that flutter type instability or divergence type instability occurs, depending on the position and stiffness of the elastic intermediate support, which implies that the instability of the real model is affected by the position and size of the lumped mass.

Physical Properties Analysis of the High-Tech Fibers for Fishing Gear Materials - 2 . Creep Characteristics and Elastic Recovery of the High-tech Fibers - (어구재료용 신소재섬유의 물성분석 - 2 . 신소재섬유의 크리프특성 및 탄성회복도 -)

  • Kim, Tae-Ho;Ko, Kwan-Soh
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.29 no.3
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    • pp.191-199
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    • 1993
  • In order to analysis creep characteristics and elastic recovery of the high-tech fibers for fishing gear materials, creep and elasticity tests were carried out on netting twines made of nylon, kevlar 29 and techmilon respectively. After creep tests, the rupture surface of raw materials was observed by scanning electron microscope(SEM). The results obtained are as follows: 1. Netting twines were arranged in order of creep rupture time as follow: techmilon, kevlar 29, nylon. The creep progressive pace was the fastest in techmilon. 2. In order of the creep elongating, netting twines were arranged as follows: nylon, techmilon, kevlar 29. 3. The rupture time T sub(r) decreased almost linearly with the increase of applied load L on the log-log scaled graph. The empirical equations computed for kevlar 29 and techmilon are as follows: T sub(r kevlar 29)=1.9512$\times$1037L super(-15.773). T sub(r techmilon)=2.7146$\times$1016L super(-6.831). 4. It was observed by SEM that creep was progressed in all netting twines. The difference of rupture morphology was recognized clearly in tensile and creep tests. 5. In order of the elastic recovery, netting twines were arranged as follows: techmilon, kevlar 29, nylon.

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Analysis of vortex induced vibration frequency of super tall building based on wind tunnel tests of MDOF aero-elastic model

  • Wang, Lei;Liang, Shuguo;Song, Jie;Wang, Shuliang
    • Wind and Structures
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    • v.21 no.5
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    • pp.523-536
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    • 2015
  • To study the vibration frequency of super high-rise buildings in the process of vortex induced vibration (VIV), wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity ($V_r$), as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When $V_r$ is less than 8, the drift magnitude of the frequency is typically positive. When $V_r$ is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When $V_r$ is larger than12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Furthermore, the vibration frequency does not lock in the vortex shedding frequency completely, and it can even be significantly modified by the vortex shedding frequency when the reduced wind velocity is close to 10.5.

Development of Aluminum Matrix Composites Containing Nano-carbon Materials (나노탄소물질을 함유하는 알루미늄기지 복합소재 개발)

  • Kim, Jungjoon;Kim, Daeyoung;Choi, Hyunjoo
    • Journal of Powder Materials
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    • v.28 no.3
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    • pp.253-258
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    • 2021
  • There is increasing demand for the development of a new material with high strength, high stiffness, and good electrical conductivity that can be used for high-voltage direct current cables. In this study, we develop aluminum-based composites containing C60 fullerenes, carbon nanotubes, or graphene using a powder metallurgical route and evaluate their strength, stiffness, coefficient of thermal expansion, and electrical conductivity. By optimizing the process conditions, a material with a tensile strength of 800 MPa, an elastic modulus of 90 GPa, and an electrical conductivity of 40% IACS is obtained, which may replace iron-core cables. Furthermore, by designing the type and volume fraction of the reinforcement, a material with a tensile strength of 380 MPa, elastic modulus of 80 GPa, and electrical conductivity of 54% IACS is obtained, which may compete with AA 6201 aluminum alloys for use in all-aluminum conductor cables.

Comparative study between inelastic compressive buckling analysis and Eurocode 3 for rectangular steel columns under elevated temperatures

  • Seo, Jihye;Won, Deokhee;Kim, Seungjun
    • Steel and Composite Structures
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    • v.43 no.3
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    • pp.341-351
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    • 2022
  • This paper presents an inelastic buckling behavior analysis of rectangular hollow steel tubes with geometrical imperfections under elevated temperatures. The main variables are the temperature loads, slenderness ratios, and exposure conditions at high temperatures. The material and structural properties of steels at different temperatures are based on Eurocode (EN 1993-1-2, 2005). In the elastic buckling analysis, the buckling strength decreases linearly with the exposure conditions, whereas the inelastic buckling analysis shows that the buckling strength decreases in clusters based on the exposure conditions of strong and weak axes. The buckling shape of the rectangular steel column in the elastic buckling mode, which depicts geometrical imperfection, shows a shift in the position at which bending buckling occurs when the lower section of the member is exposed to high temperatures. Furthermore, lateral torsional buckling occurs owing to cross-section deformation when the strong axial plane of the model is exposed to high temperatures. The elastic buckling analysis indicates a conservative value when the model is exposed to a relatively low temperature, whereas the inelastic buckling analysis indicates a conservative value at a certain temperature or higher. The comparative results between the inelastic buckling analysis and Eurocode 3 show that a range exists in which the buckling strength in the design equation result is overestimated at elevated temperatures, and the shapes of the buckling curves are different.

Finite Element Analysis of 3-D Steady State Deformation of Rolls and Strip in 4 High Mill (4High Mill 열간 압연 공정의 3차원 정상상태 유한요소해석)

  • 류성룡;김태효;황상무
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1998.03a
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    • pp.130-133
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    • 1998
  • An integrated finite element computer simulator is presented for the prediction of three dimensional heat transfer and metal flow occurring in the strip, and heat transfer and thermo elastic phenomena occurring in the rolls in 4 high mill hot strip rolling. Basic finite element models are described, with emphasis on combining each model to deal rigorously with the coupled aspect of the thermo-mechanical behaviors of the rols and strip through an iterative solution procedure. A series of process simulation are carried out to investigate the effect of various parameters under the actual process conditions. The results are shown and discussed.

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