• 제목, 요약, 키워드: 압축변형율

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Thermally-Expandable Molding Process for Thermoset and Thermoplastic Composite Materials (열팽창 고무치공구를 이용한 열경화성 및 열가소성 복합재료의 성형공정 연구)

  • 금성우;이준호;안영선;남재도;임인철;이창희;김이경
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.116-119
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    • 2000
  • 본 연구에서는 온도의 상승에 의하여 부피가 팽창하는 열팽창 고무 치공구의 팽창 특성을 이용하여 열경화성 복합재료를 경화하고 압축하는 과정을 실험과 모델링을 통하여 해석하였으며, 열가소성 복합재료의 함침공정을 연구하였다. 열팽창 고무치공구가 사용되는 닫힌계와 열린계에서 예상되는 압력을 이론적으로 유도하였고, 경화가 수반되는 과정에 있어서는 실험을 통하여 열팽창치공구와 프리프레그가 나타내는 압력을 측정하였다. 온도가 상승하고 경화가 수반되는 경우에 등속도 압축실험에 의하여 얻어지는 응력-변형율 곡선은 비선형점탄성 특성을 보여주었는데, 본 연구에서는 Maxwell모델을 KWW(Kohlrausch-Williame-Watts)식으로 변형시킨 모델식을 이용하여 이를 매우 정확하게 표현할 수 있었다. 또한 고무치공구를 이용하여 열가소성 수지의 복합재료 성형공정을 실험하였고, 중성자 레디오그래피 촬영을 통하여 기공의 분포를 관찰하였다.

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A Study on the Sensitivity of Reinforced Concrete Element Design Factors (변형율속도변화에 대한 철근콘크리트부재 설계인자의 민감성 연구)

  • Sim, Jong Sung
    • Journal of The Korean Society of Civil Engineers
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    • v.9 no.4
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    • pp.9-14
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    • 1989
  • A strain rate-dependent element model was used to study the loading rate-sensitivity of R/C beams and columns with different design factors. Conclusions were derived regarding the differences between the element axial/flexural performance under impulsive and quasi-static loads. Practical design formalas for predicting the loading rate-dependent axial and flexural strengths of R/C elements were also suggested.

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Characterization of Cemented Sand for Building of Levee (하천제방축조재료로서 시멘트혼합토의 특성)

  • Jeong, Woo-Seob;Kim, Yung-Su
    • Journal of Korean Society of Hazard Mitigation
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    • v.6 no.4
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    • pp.29-36
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    • 2006
  • There are loss of lives and properties in many areas of the basin of the Nak-Dong river by the unusual weather and the localized heavy rain recently, and many difficulties of levee construction for prevention of disasters by acquisition of material and expensive transportation. In this research, The factors and causes which affect the strength through laboratory tests about the cemented sand that is mixed a few portland cement and sand of Nak-Dong river bed was researched closely. For providing the fundamental data which is needed in design and analysis of levee material, the compaction test and the standard triaxial compression test etc was conducted., analyzed compression strength and characteristic of stress-strain behavior in which the influence of cement content.

Ductility of Circular Hollow Reinforced Concrete Piers Internally Confined by a Steel Tube (내부 강관 보강 원형 R.C 기둥의 연성 거동 특성)

  • Han, Taek-Hee;Han, Sang-Yun;Han, Keum-Ho;Kang, Young-Jong
    • Journal of Korean Society of Hazard Mitigation
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    • v.3 no.2
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    • pp.127-137
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    • 2003
  • In locations where the cost of concrete is relatively high, or in situations where the weight of concrete members is to be kept to a minimum, it may be economical to use hollow R.C. members. The ductility of circular hollow R.C. columns with one layer of longitudinal and spiral reinforcement placed near the outside face of the section and the steel tube placed on the inside face of the section is investigated. Such hollow sections are confined through the wall thickness since the steel tube is placed. In this study, moment-curvature analyses are conducted with Mander's confined concrete stress-strain relationship. The variables influenced on the ultimate strain is the ratio and yield strength of confining reinforcement and the compression strength for confined concrete. From this ultimate strain - the transverse reinforcement ratio relationship, the transverse reinforcement ratio for circular hollow reinforced columns with confinement is proposed. The proposed transverse reinforcement ratio is confirmed by experimental results.

Study on the Consolidation Characteristics of Marine Clay by CRS and Conventional Tests (일정변헝률 및 표준압밀시험을 이용한 해성점토의 압밀특성 연구)

  • Lee, U-Jin;Im, Hyeong-Deok;Lee, Won-Je
    • Geotechnical Engineering
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    • v.14 no.4
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    • pp.47-60
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    • 1998
  • A series of conventional tests and CRS consolidation tests with different rates of strain were performed to investigate the consolidation characteristics of marine clay. Preconsolidation pressures were evaluated by applying previously proposed methods for both the conventional tests and CRS tests results in order to check the legitimacy of those methods. The effects of strain rate on effective consolidation stress strain relationship, porewater pressure, and preconsolidation pressure were also discussed It was found that the effective stress strain relationship and the preconsolidation pressure are a function of strain rate imposed during consolidation test, but compression index isn't. The preconsolidation pressure ratio ($a_2=\sigma'_{pCRS}/\sigma'_{pConv}$)of marine clay appears proportional to the logarithm of strain rate, with average values ranging from 1.11 to 1.30 for strain rates between $1\timesx10^{-4} %/sec\; and\; 4\times10 %/sec$. The porewater pressure ratio during CRS teats does not exceed 6.0% except when the strain rate is $6.67\times10^{-4} %/sec$. Coefficient of consolidation or coefficient of permeability at normally consolidated range was not affected by the type of consolidation tests and the strain rate. Typical values of compression index (C.), coefficient of consolidation(c.), and coefficient of permeability (k.) at normally consolidated range were 0.56-0.95, $0.56\times10^{-4}~3.0\times10^{-4}cm2/sec,\; and\; 2.0\times10^{-8}~7.0\time10^{-4}cm/sec,$ respectively.

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REMOTELY SENSEDC IMAGE COMPRESSION BASED ON WAVELET TRANSFORM (Wavelet 변화을 이용한 우리별 수신영상 압축기법)

  • 이흥규;김성환;김경숙;최순달
    • Journal of Astronomy and Space Sciences
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    • v.13 no.2
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    • pp.198-209
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    • 1996
  • In this paper, we present an image compression algorithm that is capable of significantly reducing the vast mount of information contained in multispectral images. The developed algorithm exploits the spectral and spatial correlations found in multispectral images. The scheme encodes the difference between images after contrast/brightness equalization to remove the spectral redundancy, and utilizes a two-dimensional wavelet trans-form to remove the spatial redundancy. The transformed images are than encoded by hilbert-curve scanning and run-length-encoding, followed by huffman coding. We also present the performance of the proposed algorithm with KITSAT-1 image as well as the LANDSAT MultiSpectral Scanner data. The loss of information is evaluated by peak signal to noise ratio (PSNR) and classification capability.

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Evaluation of Properties of 80, 130, 180 MPa High Strength Concrete at High Temperature with Heating and Loading (고온가열 및 하중재하에 따른 80, 130, 180 MPa 초고강도콘크리트의 역학적특성평가)

  • Choe, Gyeong-Cheol;Yoon, Min-Ho;Lee, Tae-Gyu;Lee, Seong-Hun;Kim, Gyu-Yong
    • Journal of the Korea Concrete Institute
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    • v.25 no.6
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    • pp.613-620
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    • 2013
  • Concrete has been recognized as a material which is resistant to high temperatures, but chemicophysical property of concrete is changed by the high temperature. So, mechanical properties of concrete may be reduced. Because of this, standards and researches on the degradation of the mechanical properties of concrete at high temperatures have been presented. However, research data about the state that considering the loading condition and high-strength concrete is not much. Therefore, this study evaluated the high-temperature properties of high-strength concrete by loading condition and elevated temperature. The stress-strain, strain at peak stress, compressive strength, elastic modulus, thermal strain and the transient creep are evaluated under the non-loading and $0.25f_{cu}$ loading conditions on high strength concrete of W/B 12.5%, 14.5% and 20%. Result of the experiment, decrease in compressive strength due to high temperature becomes larger as the compressive strength increases, and residual rate of elastic modulus and compressive strength is high by the shrinkage caused by loading and thermal expansion due to high temperature are offset from each other, at a temperature above $500^{\circ}C$.

A Proposal for Damage Index of Steel Members under Cyclic Loading (반복하중하에서의 강부재에 대한 손상지수 제안)

  • Park, Yeon Soo;Kang, Dae Hung;Oh, Jung Tae;Choi, Dong Ho;Oh, Back Man
    • Journal of Korean Society of Steel Construction
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    • v.14 no.5
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    • pp.613-625
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    • 2002
  • This paper aimed to investigate the damage process of steel parts experiencing failure under strong repeated loading. Likewise, a damage index using various factors related to the damage was proposed. An analysis method for evaluating the damage state was also developed. The damage assessment method focused on the local strain history at the cross-section of the heaviest concentration of deformation. Cantilever-type steel parts were analyzed under uniaxial load combined with a constant axial load, considering horizontal displacement history, Loading patterns and steel types were considered as the main parameters in analyzing the models. The effects of the parameters on the failure modes, deformation capacity, and damage process as seen from the analysis results were also discussed. Each failure process was compared as steel types. In addition, the failure of steel parts under strong repeated loading was determined according to loading. Results revealed that the state of the failure is closely related to the local plastic strain.

Thermally-Expandable Molding Process for Thermoset Composite Materials (열팽창 치공구를 이용한 열경화성 복합재료의 성형연구)

  • 이준호;금성우;장원영;남재도
    • Polymer Korea
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    • v.24 no.5
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    • pp.690-700
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    • 2000
  • In this study, an elastomer-assistered compression molding process was investigated by experiments as well as modeling for the long-fiber reinforced thermoset composites. The consolidation pressure generated by fixed-volume and variable-volume conditions was thermodynamically derived for both elastomer and curing prepregs, and was compared with the pressure measured during curing of epoxy matrix. Exhibiting non-linear viscoelastic characteristics in the compressive stress-strain tests, the measured stress was well compared with a modifed KWW (Kohlrausch-Williame-Watts) equation, which is based on the Maxwell viscoelastic model. Using the developed model equations, the consolidation pressure generated by the elastomer was successfully predicted for the compression molding process of thermoset composite materials in tile closed mold system.

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Study on Characteristics of Shock Sensitivities of Pressable Plastic-Bonded Explosives(PBXs) Applying Multimodal Particle System (다성분 입자계를 적용한 압축형 복합화약의 ?감도특성 연구)

  • Park, Haneul
    • Journal of the Korean Society of Propulsion Engineers
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    • v.21 no.4
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    • pp.96-106
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    • 2017
  • In pressable polymer bonded explosives (PBXs), densification occurs due to rearrangement and deformation of explosive particles during pressing. If brittle explosives are compressed till particle fraction become higher than theoretical random close packing fraction (RCPF), bigger particles should be fractured to fill the void. In this study, multi-modal particle system was introduced for the decrease in possibility of particle fracture during compression expecting decrease in shock sensitivity of highly filled pressable PBX. The experimental results showed the trimodal particle system had low sensitivity with high density, compared to bimodal particle system.